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University of Toronto St. George
Earth Sciences

GLG 103: Geology and Public Issues  The entire course content for this course is contained in the Power Point lectures(posted on the website as pdf files) and these lecture notes, which are designed to accompany them. Each week’s lecture is indicated by the week number and date, and the notes are keyed by slide number to the number of the illustration in the relevant lecture. You are encouraged to printoutthese notes and each week’s lecture pdf file, and bring them with you to class as a basis for taking notes. You will not need to purchase a separate textbook for this course.  Important note: In this and all subsequent lecture notes, important terms that you should know about are underlined. Week 1 (September 10, 12) Lecture 01-A: General Introduction What is this class all about? It is about how the earth affects our lives, on a daily basis as individuals, and on a longer term it affects societies, the economy, the history of cultures and nations. Earth sciences is often ignored during our daily life, and its implications poorly understood. An example from the winter of 1998-9: an avalanche in northern Quebec that buried many people in a school gymnasium: to my knowledge, no illustration of the mountain behind the school from which the snow slid down was ever shown on television or in the print media. Nobody in the media thought to stand back and take an overview perspective of the land and its influence. Nobody got up there in a helicopter to do this. Other examples: the terrible damage of the hurricanes in central America in late 1998. Many of the deaths were due to mudslides and debris flows from volcanoes covered in loose ash.There was no appreciation of the dangers of deforestation on this ash. And very few pictures in the media of the path of the mudslides from the mountain sides to the nearby villages. The heavy rains in Venezuela in early 2000 resulted in similar catastrophic debris-flow damage. The effects of a major hurricane on the city of New Orleans had been predicted many times, and the damage that resulted from Hurricane Katrina in August 2005 was almost exac tly what had been predicted, but nobody at the federal, state or local level would take the predictions seriously and set aside the necessary funds for flood protection. The potential for a major damaging earthquake in Vancouver is well known, but littlehas been done to prepare for it. People build huge homes and resort developments on floodplains and barrier islands, totally ignoring the dangers inherent in such activity. Building codes can protect property from all but the most serious of earthquakes,but frequently are ignored or are (in many third-world countries) non-existence. This is the main reason why the damage and loss of life in the Haiti earthquake of January 2010 was so severe. GLG 103: Weekly lecture notes There is absence of the sense of “place” in modern society, especially in modern urban settings. We take our earth for granted. It can be a dangerous place. SOME EXAMPLES OF HOW WE ARE AFFECTED BY OUR PLACE ON EARTH —Much early exploration was carried out in order to trade ingeological commodities: e.g., the Phoenicians of the Mediterranean sailed to Cornwall in SW England to trade fortin ore. —Martin Frobisher, a British explorer, sailed to Baffin Island in the sixteenth century to mine what he thought was gold, but turned out to be pyrite. —One of the reasons for the early predominance of Britain as an industrial nation was the ready availability of coal and iron with which to begin the industrial revolution in the late eighteenth century. —And of course, the Spanish conquest of central America in the sixteenthcentury had everything to do with the search for commodities, primarilygold and silver. —And why are modern Saudi Arabia and Kuwait so rich? And why is Iraq so important internationally? It has a lot to do withoil. Lecture 01B-Earth Slide 4: Earth systems. The four reservoirs of energy and matter that are dynamically interconnected and inter-dependent: lithosphere, hydrosphere, atmosphere and biosphere. Three kinds of system: isolated – cannot receive or emit energy or materials;closed: can receive input but cannot emit energy or can receive and emit energy and matter. The Earth receives energy and occasional astronomical objects. It emits reflected energy.It is therefore an open system. Slides 5, 6: Earth’s components —crust, mantle and core —differentiation of earth’s layers according to composition and density of earth materials. The core consists of an iron-nickel mixture. it has aliquid outer half and a solid inner half The mantle consists of a mixture of iron and magnesium alumino-silicates and functions like a stiff plastic or warm tar. It flows very slowly under pressure(centimeters per year). The crust consists of the lightest of earth materials which have, over the geological past, tended to “float” to the surface of the Earth, to create the continents. Note the dimension of these layers on the slide. Also shown are the velocities of seismic waves through these materials. Velocities increase with the density of the rocks. Slide 7: Two types of crust on the earth’s surface. The crust “floats” on the mantle. because oceanic crust is more dense (heavier), it floats lower (like a heavily loaded boat), which is why it is always below sea level. How do we know about earth’s interior? 1) seismic analysis (P and S waves) (Slides 8-12) P waves: primary or “push-pull” waves. 2 GLG 103: Weekly lecture notes S waves: secondary or “shake” waves. P waves are faster and arrive first after an earthquake. S waves cannot be transmitted through fluid, and that is why we know that the earth’s core is partly liquid (Slide 12: S-wave shadow) 2) xenoliths are fragments of rock from the mantle, carried to the surface by igneous intrusionand by volcanic eruption. (Slide 13) 3) assumption that meteorites are from similar planets(Slide 14) Two types of meteorite: “stony” (thought to be from the mantle of an earth-like planet) iron-nickel (similar to an earth-type core) Slide 15: The difference between a mineral and a rock minerals as indicators of environmental conditions (temperature, pressure, chemical environment) definition of rocks as mineral aggregates differentiation by mineral composition and texture. Slide 16: The rock cycle: earth materials are recycled through the crust and mantleover geologic time. Slides 17-19: Three types of rocks: —igneous rocks formed from a molten melt or magma —metamorphic rocks formed by the alteration of a previously existing rock by the effects of heat and/or pressure —sedimentary rocks formed from fragments or dissolved remains or previously existing rocks by surface processes. Igneous rocks are generate at sea-floor spreading centresand within subduction zones. They may be uplifted and eroded to form sedimentary rocks, or altered by heat and/or pressure to form metamorphic rocks. Crustal materials are returned to the mantle in subduction zones, thereby completing the rock cycle. Slide 20: —relative elemental abundances Note the great importance of oxygen, iron and silicon The differences between the crust and the rest of the earth were brought about by the process of differentiation (see slide for explanation) Week 2 (September 17, 19) Earth systems and cycles Lecture 02A: Plate Tectonics Slide 1: 3 GLG 103: Weekly lecture notes A plate-tectonic interpretation of the Middle East, using a photograph taken from a satellite. The Arabian continent is moving northward relative to Africa. This has opened up the Red Sea, and created a major fault zone along the course of the Jordan river and the Dead Sea, the basin at its southern termination. Displacement along the Dead Sea rift is about 105 km. Slide 2: The main principles of plate tectonics were developed in the 1960s. Before that time, some geologists had speculated about “continental drift”. The distribution of fossil plants and animals and the evidence of past climates from the rock record wasmuch better explained if the continents had occupied different positions in the geologic past. Amongst the most persuasive support for the former existence of Pangea is the evidence for the so-called “Gondwana glaciation”.Gondwana is the name given to all the southern continents. During the Carboniferous and Permian periods, about 300 million years ago, Gondwana lay across the south pole, and underwent a major glacial episode lasting about 90 million years. The Gondwana continents are now dispersed, including South America, Africa, and Australia, which remained in the southern hemisphere, India, which drifted northward and is now in the northern hemisphere, and Antarctica, which still lies over the south pole. The distribution of Gondwana glacial rocks makes no sense based on present-day continental distributions. This slide shows a reconstruction of “Pangea”, a “supercontinent” that we now know existed from Carboniferous time (about 300 million years ago) until about 200 million years ago. Plate tectonics: how it works: Slide 3: Mantle overturn is driven driven by convection (heat) currents, just like a boiling pot of water (only slower!). The source of the heat is the widespread presence of radioactive materials (uranium, thorium, radium, etc) widelydispersed in the mantle. Continental plates forming of pieces of the Earth’s crust are rafted on the mantle, are carried away fromsea-floor spreading centres, and periodically collide with each other, creating mountain belts. Slide 4: Generation of oceanic crust at sea-floor spreading centres. —Lateral movement of oceanic crust away from spreading centres at rates of about 2-4cm/yr, rarely as fast as 10 cm/yr. Slide 5: Sea-floor spreading is approximately the same rate as the growth of finger nails. Slide 6: Motion may be tracked by chains of volcanoes above hot spots (e.g., Hawaiian chain). Note how the volcanic islands get older as you track them westward, away from the big island of Hawaii, which is the only place where volcanism is now taking place in the Hawaiian island chain. Slide 4, 7, 8: —Divergent margins .. The continental breakup process starts withrift faulting, along which blocks of crust drop down to create rift valleys. Basaltic volcanoes often form along the rift. The 4 GLG 103: Weekly lecture notes continental crust is also stretch and thinned. As the divergent margin is moved away from the spreading centre by sea-floor spreading, it is moved away from the source of mantle heat close to the surface, and begins slowly to cool and contract. As a result, the continental margin slowly sinks, allowing a wide continental shelf to form across its trailing edge. This explains the wide shelf regions bordering oceans such as the Atlantic, e.g., the continental shelf west of Britain, and east of the United States. The faulted margins of continents are left behind as new ocean crust is generated in front of them.The Atlantic Ocean formed this way, startingabout 200 million years ago. The East African rift system has been formed by this process. The rift extends northwards through Ethiopia into the Red Sea, a new “ocean.” Slides 4, 7, 9: —Subduction of oceanic crust at convergent margins. The Pacific Ocean is mostly encircled by convergent margins (“ring of fire”: see Volcanoes, weeks 4-5).Here, ocean crust and its covering blanket of marine sediments, all saturated with seawater, are carried down into the Earth’s interior at a subduction zone. At a depth of around 100 km it begins to melt, and the hot material, called magma, begins to rise back to the surface. —Magmatic arcs (or volcanic arcs) are the regions above subducting plates that are characterized by plutonic intrusions and chains of volcanoes(Slide 9)(Magma is the term for molten rock. This is called lava when it is extruded at the earth’s surface). Arcs are called this because they are typically curved (“arc-shaped”), consisting ofchains of volcanoes and trenches; e.g., Aleutian Chain, Alaska; Japan arcs and trenches. Slide 10, 11: —Rafting of continents on the plates.Rafting of a continent on a plate as the plate is consumed at a subduction zone leads tocollision of continents formingsuture zones. —Orogeny=mountain building. The collision of India with Asia is the classic example (Slide 10). Subduction of arcs and small continents off the coast of BritishColumbia led to the development of the Rocky Mountains. The front ranges consist of a series of “stacked thrust sheets”. The Front Ranges are formed of slabs of hard Paleozoic limestone and dolomite pushed up along the faults Slide 11 shows the structure of the Rocky Mountains, andSlide 12 is a close-up of the McConnell Thrust, where Cambrian limestones rest on Cretaceous shales and sandstone. Many of the intervening valleys, such as the Canmore valley (Slide 13), were formed by the erosion of softer sedimentary rocks, in this case Triassic-Cretaceous sands and shales with coal. Slide 14: A comparison of two collisional orogens. Top: the structure of the Himalayan Mountains, formed by the crumpling and elevation of the southern margin of Asia by the subduc tion of the Indian continent. Bottom: cross-section of the Grenville rocks of Muskoka. This represents an ancient collision zone one billion years old, which raised a mountain belt of the scale and elevation of the Himalayas. Now it has been eroded to itsroots. At least 20 km of rock were stripped off by erosion before the beginning of the Phanerozoic era 550 million years ago. The white dashed line in the top section shows the depth of erosion that would have to take place on the Himalayas to reach the same level. Slide 15: —Transform faults and transform plate margins,where the plates are sliding sideways past each other. E.g., California continental margin: San Andreas fault system, Dead Sea rift system. 5 GLG 103: Weekly lecture notes Slides 16, 17, 18, 19: The present-day arrangement of Earth’s plates (Slide 16) and how this pattern developed as Pangea broke up and the continents were dispersed by sea-floor spreading ( Slide 17). The gradual development of sea floor is illustrated inSlide 17, which shows by a colour code the age of the oceanic crust, ranging from Late Jurassic (blue) to present-day (purple). There is no oceanic crust older than Jurassic preserved anywhere on Earth, except as fragments caught up in suture zones. All oceanic crust older than this has been subducted. The rate and direction of movement of the major plates is shown inSlide 18, and Slide 19 is a summary of the breakup of Pangea. Slide 20: Some tectonically active areas today, showing the relative movements of major plates. Slides 21, 22: The types of fault found in the rocks indicate the type of displacement that the crust has undergone locally, including extension, contraction (compression), and sideways displacement. Lecture 02B: Earth Systems and Cycles Earth systems: Earth cycles Slide 2: The energy cycle: solar energy 17.3 x 10 watts per year, geothermal energy 32.3 x 10 12watts tidal energy 2.7 x 10 watts Slide 3: The energy budget Distribution and usage of solar energy Slide 4: Energy transfer: wind and oceanic currents are driven primarily by heat transfer from the equator to the poles. One of the major results of this is violent weather events (Slide 5) The Coriolis effect is caused by differences in angular speed between objects moving near the equator and those at higher latitudes. Slides 6, 7: The constancy of energy transfer patterns has set up permanent air circulation cells, which result in a latitudinal zonation of climate belts and wind patterns across Earth.Trade winds, belts of deserts, equatorial rain forests, etc., are all located in accordance with this pattern. Slides 8, 9, 10: Oceanic currents are also driven by wind pressures and energy transfers. The great pattern of oceanic circulation is shown inSlide 10. It would take a single molecule of water about 1000 years to circle the earth completely along this oceanic pathway. 6 GLG 103: Weekly lecture notes The great oceanic conveyor system(Slide 10) comprises warm surface currents (shown in pink) and cold ocean-bottom currents (shown in blue). The transition from warm to cold occurs in high latitudes (e.g., in the North Atlantic Ocean) as surface currents cool and become more dense, causing the water masses to sink. Slides 11, 12, 13: The hydrologic cycle: reservoirs and pathways. 97.5% of all earth water is in the oceans 2.5% is fresh water, of which 74% is in ice caps and 25% is groundwater. Less than 1% is in surface rivers and lakes Slides 14, 15: The carbon cycle: carbon sinks and storage Note the relatively small amount of carbon that is present as atmospheric CO2. Slides 16, 17: Concepts of geologic time. The logarithmic time scale and standard geologic time subdivisions. Early concepts of the age of the earth were flawed in the absence of information about radioactivity. Lord Kelvin in the 19 century estimated that the earth was 40 million years old (time taken to cool from a molten body) Slide 18: Significant time markers(you should memorize these) Age of Earth 4.5 Ga (Ga=billions of years ago) Archean-Proterozoic boundary (appearance of widespread continents) 2.5 Ga Proterozoic-Phanerozoic boundary (appearance of abundant organisms with fossilizable hard parts) 600 Ma (Ma=millions of years ago) End Cretaceous and end of the Mesozoic (extinction of dinosaurs) 65Ma Appearance of humans on earth ~ 5 Ma Recorded history (China, Egypt) 4000-5000 ka (ka=thousands of years ago) Week 3 (September 24, 26): Lecture 03A-Earthquakes Slides 2, 3: Earthquakes indicate rock deformation. Bending (folds) and fracturing (faults) This deformation occurs because rocks are understress and suddenly give way, generating shock waves that travel through the Earth. Stress is caused by the lateral movement of the Earth’s plates. Most quakes are at plate boundaries. Subduction earthquakes tend to be the most severe. But quakescan occur in the middle of stable plates, e.g., mild quakesoccur every year or so in the Ottawa-St. Lawrence valley. Larger “mid-plate” quakes include the great earthquakes of New Madrid, 1811-1812,in the Mississippi Valley, with forces up to 8.8. These quakes occur along old fault lines. Definition of earthquakefocus (this is where the earthquake actually occurs) andepicentre (the point on the earth’s surface above the epicentre 7 GLG 103: Weekly lecture notes Principle of the seismograph (see week 01B) Location of epicentre by trigonometry(see week 01B) Extensional () and contractional () stress Rocks have a certain elasticity that permitsductile deformation(bending, like a soft plastic)and the formation of folds. Beyond a certain point they will fracture, formingfaults. Elastic rebound or “snap-back” especially in the area of subduction zones. This is when the ground returns to an unstressed configuration after the stress has been released by the break that was recorded as the earthquake. Types of fault: normal, reversed, thrust, strike-slip Earthquakes occur when build-up of stress leadsto sudden release of energy. Subsidence (>2 m) and uplift (>6 m)were associated with the Alaska Earthquake of 1964(see lecture 03B) Slide 4: Types of seismic wave —Primary (P) compressional, or “push-pull” waves —Secondary (S) shear, or “shake waves”. Do not travel through liquids (which is how we know the Earth’s core is liquid: see alsoLecture 01B) Slide 5: Richter and Mercalli scales of earthquake magnitude Logarithmic intensity scale(each increment of one in the scale means an increase of the earthquake magnitude by a factor or ten). World’s largest earthquakes:Magnitude of quake is proportional to the length of the fault. May never exceed about9 to 9.5 because of limits to rock strength and limits to size of Earth’s plates. Slides 6, 7, 8: Typical daily occurrence of earthquakes. These maps are generated automatically by the U.S. Geological Survey. The pattern is very similar from one day to the next, consisting of many small quakes, mostly along plate boundaries, and most of which are not felt at the surface or result in very minor shaking. Only large-magnitude quakes in populated areas that result in significant damage and/or loss of life, tend to be “noticed”’ by the media (Slide 10: large, damaging quakes in recent history). Slide 9: Earthquake frequency: note large number of small quakes. Slide 11: The “10.5” earthquake of the recent NBC miniseries is a ludicrous distortion of actual science. Horizontal and vertical ground motion. Importance of good building foundations Slides 12, 13: 8 GLG 103: Weekly lecture notes Secondary damage: is damage caused by shaking which can rupture utility lines(broken gas and electricity lines), leading to fires, landslides, liquefaction of clays,changes in ground level (flooding by the sea or drying out of harbours), tsunamis, etc. Damage to water mains may prevent fire crews from putting out the fires (this is what happened in San Francisco in 1906) Slides 14, 15: Note that most quakes occur near plate boundaries. Some major recent earthquakes around the world: Slides 16, 17, 18: The great Sumatra earthquake and tsunami of Boxing Day, 2004 Oneof the largest ever recorded. This was a classic “subduction” earthquake. The tsunami was probably triggered by a gian t submarine landslide set off by the quake(see week 5). Other major recent earthquakes: Japan (Slide 19), Pakistan (Slide 20), Haiti (Slide 21) Also, Izmit, Turkey (strike-slip fault, August 1999); Taiwan (subduction earthquake, September 1999); El Salvador (subduction earthquake, January 2001). Slide 22: Earthquakes in North America. Most occur along the “convergent” western continental margin, where the Pacific plate is plunging beneath the American plate. Other major clusters occur in eastern Canada and the Canadian Arctic. The eastern Canada quakes are associated with movement on ancient faults. Many of those in the Arctic may be related to rebounding (uplift) of the crust, following removal of the great weight of the ice sheets, which began about 12,000 years ago. This is called isostatic rebound. Slides 22-32 By far the most hazardous area for earthquakes in North America, as far as the human population is concerned, is the San Andreas system of California. This passes right through San Francisco (slides 23, 24, 25) Slides 26, 27, 28: Daily activity in California: most quakes are NOT on the San Andreas fault itself, but on subsidiary faults, indicating that the stress is widely distributed across rocks that are not completely rigid, but can bend and fail just about anywhere that stress builds to a breaking point. Slides 29, 30, 31 The San Andreas fault itself, and remaining evidence of the great quake of 1906, which resulted in most of San Francisco being destroyed by secondary damage (fire). The epicentre of this quake was at Point Reyes, some miles north of the city(see slide 26). Slide 32 Recent movement on the Hayward Fault, across the bay from San Francisco. Displacement is indicated by the offset in the curb stones. Note that the displacement is “right lateral”. Lecture 03B-Earthquakes 9 GLG 103: Weekly lecture notes Other areas where major earthquakes can occur: Slides 2-6: Palestine and Israel lie on the Dead Sea Rift, which is actually a majortransform plate boundary between Africa and Arabia. Many quakes have occurred during historical times, and are interpreted in the Bible as God‘s punishment for man’s sinfulness. “Armageddon”, a word meaning a catastrophic disaster, actually comes from the name of a small Palestinian village, “Haar Meggido”, which lies on a strand of the fault, and has experience many quakes in the historic past. Slide 6: Fault planes exposed along the west side of the Dead Sea Rift showing where the ground dropped down along the fault surfaces. Slides 6, 7, 8: Intraplate earthquakesresult from stresses transmitted across plates from plate boundaries. The “ridge-push” effect , which is the lateral pressure resulting from the movement of plates away from sea-floor spreading centres, is a major source of stress in continental interiors.Slide 8 shows what is a very common result of the minor but pervasive stress that is present in most continental interiors: patterns of regularjoints, or fractures, in the crust. Earthquakes in Canada Slides 9, 10: Earthquake frequency and earthquakehazard in Canada. Areas of greater and lesser potential hazard in Canada. Slides 11, 12: By far the most earthquake-prone area is the west coast, around Vancouver and Vancouver Island. This diagram explains the mechanism ofsubduction earthquakes, and shows the location of some major ones in the recent past. The areas affected by two of these are shown inSlide 12. The only reason that these did not result in severe damage is that the epicentres werelocated away from the major population centres. Slides 13, 14: What happens during a subduction earthquake. A major bend in the earth’s crustcaused by locking of the crust in the subduction zone, is released, resulting in sudden uplift of the area immediately above the subduction zone, and subsidence of the area behind it. In the case of the major quake of 28 March 1964in Alaska, vertical displacement of the crust locally exceeded 6 m. Slide 15 Not all west-coast earthquakes are “subduction” quakes. A series of modest earthquakes in August 2008 occurred along the spreading centre off Vancouver Island, probably related to magma movement. Slides 16, 17: Earthquakes in eastern Canada occur mainly along faults generated when North America first split from Europe/Africa with the breakup of Pangea, beginning in the Triassic. The Ottawa-St. Lawrence rift system is the name given to the major faultsystem shown in this map area. Slides 18, 19, 20 10 GLG 103: Weekly lecture notes In the Toronto area there are very ancient faults in the Precambrian basement that may be places where stored intraplate stress is released as occasional modest earthquakes. Slides 21, 22, 23: These quakes may be related to intraplate stress, but another significant process ispost-glacial rebound – the slow uplift of the crust following the removal of the weight of ice after the end of the Ice Age (similar to what happens to a block of wood floating on the water. If you push on it, it will sink - comparable to the weight of ice on the continent– if you remove your finger, analogous to the removal of the ice, the block will rise back to its original position on the water.). Slide 24: Rates of post-glacial rebound in Canada. Slides 25, 26: Possible danger to Pickering nuclear power station. This hazard was not assessed at the time the station was constructed, but the danger is thought to be very small. Nonetheless, largely as a result of the concerns expressed by University of Toronto professors, the city of Pickering has developed some emergency procedures. Slide 27: A major earthquake occurred in eastern Canada in 1929, probably as a result of failure on a deep- seated fault. It triggered a major underwater slump and tsunami (seeweek 5). Week 4 (October 1, 3): Volcanoes Lecture 04A Slide 2: Volcanoes are the most visible product of the process of melting in the Earth’s interior. This map shows the location of the world’s major volcanoes. They occur in three main settings: 1) Along subduction zones 2) At mid-oceanic spreading centres 3) Above mantle plumes (e.g., Hawaiian volcanoes) Slide 3: terminology: Heating of the mantle generates moltenmagma (see plate-tectonics section: Week 02A). This may be injected to formplutonic intrusions at great depths, or dykes and sills at shallower depth or is extruded at the surface from volcanoes). Volcanic products include moltenlava, which may be extruded quietly and form flows, or may be extruded violently in the form of molten clots and blebs orlava fountains, which may cool in the air to form ash (tephra) and volcanic bombs —collectively termedpyroclastic material. Lava extruded under water forms pillow lava (see below). Slide 4: The main features of a subduction zone. Slide 5: Illustrates examples of the plutonic rocks (granite) that form the roots of most subduction zones. Slide 6: 11 GLG 103: Weekly lecture notes Minor types of igneous intrusion(see inset in Slide 4 for explanation of terms) Slide 7: Main types of volcano Types of magma and origins of magma types —basalt, 50% silica, low viscosity, formsgabbro plutonic intrusions at depth. Formed by melting of the mantle at spreading centres and in mantle plumes that rise from great depths. Forms oceanic crust. Rocks are rich in the minerals of iron and magnesium, which gives the rocks a very dark, commonly almost black colour. —andesite, 60% silica, intermediate viscosity, formsdiorite intrusions. Formed by melting of oceanic crust and sedimentary cover in subduction zones. Rocks are a lighter grey in colour, owing to the presence of some quartz and feldspar. —rhyolite, 70% silica, high viscosity, formsgranite intrusions. Formed by partial melting of continental crust in subduction zones.Rocks are pale in colour, often pink or red, owing to the presence of pink feldspar. Clear, glass-like quartz, is abundant. Types of eruption, types of volcano and type of magma: —basaltic magmas are of low viscosity and have low gas content. This leads to relatively quiet (non-explosive) eruptionswith freely flowing lava. They form so-called “shield volcanoes”, named on account of their shield-like blanketing of the Earth.Not to be confused with the Canadian Shield. Example: Hawaii (Mauna Kea, in Hawaii, is 4205 m high and rests on ocean several km deep, making it the tallest mountain on earth).Shield volcanoes also occur at sea-floor spreading centres, e.g., Iceland, East Africa Rift System (e.g., Goma eruption, Congo, January 2002). —rhyolitic and andesitic magmas are of high viscosity because of their higher silica content. Dissolved gases can only escape slowly, and tend to be released explosively upon eruption, leading to violent eruptions and steep, conical volcanoes. e.g., Mt. St. Helens, Etna, Vesuvius, Krakatoa, Mt. Pinatubo: Other terms, to be illustrated later: —“Ring of Fire” (see lecture 04B) name given to ring of andesitic and rhyolitic volcanoes that encircles the Pacific Ocean. Actually a misleading term because there is no fire involved in lava eruption itself (burning of trees and buildings may, of course, be asecondary effect). Intermediate types of volcanoare formed of mixture of viscous lava and tephra,and are called stratovolcanoes, e.g., Mt. Fuji, in Japan. The Cascade Range is the chain of andesitic volcanoes extending from British Columbia to northern California. This is part of the Ring of Fire. it includes Mount St. Helens, which erupted violently in 1980. Eruptions occurred in Mt. Meager, British Columbia (near Whistler) only about 2400 years ago (see lecture 04B). Calderas are large basins formedby crater collapse following emptying of the magma chamber by eruption. This may happen catastrophically; e.g., Crater Lake, Oregon, Long Valley, California Geysers (e.g., Old Faithful, Yellowstone),fumaroles (e.g., Solfatara, near Naples), formed by gas emission. Hot springs (e.g., Banff, Yellowstone), caused by heating of descending groundwater. 12 GLG 103: Weekly lecture notes Slides 8-14: Shield volcanoes in Hawaii Slides 8, 9: Views of the major volcanoes in Maui and the big island (Hawaii). Note the characteristic gently - sloping cone shape. In one way, Mauna Kea is the highest mountain in the world, rising more than 10 km from the floor of the Pacific Ocean (Mt. Everest rises 8848 m from sea level). Slides 10, 11: Kilauea, the main crater, andHalemaumau, the active inner crater. Active crater on the big island. Last erupted in 1968. The ridges around the sides mark the highest point reached by a lava lake which once filled the crater, reaching its highest level in 1968. The lake collapsed in 1971 following a series of eruptions. The lava on the floor now dates from 1976. Steam and carbon dioxide are emitted from cracks in the sides, because the molten magma reservoir is not far below the surface. Slide 12: Active flow entering the sea on the south coast of Hawaii (1987). Steamis rising where the hot lava encounters sea water. There has been almost continuous volcanic activity on Hawaii for several decades. Slide 13; Characteristic “ropy” lava texture of fresh lava (this view is of a flow only a few weeks old). The texture is formed when the surface crust cools and rumples up like a table cloth as the molten lava below continues to flow. Slides 14, 15: When a lava flow enters the sea if forms characteristic “pillow lava” texture. This pair of slides shows a modern and an ancient pillow lava field. Slides 16, 17: Modern lava flows. The heat sets all surface vegetation and human constructions alight. This is the “fire” of the Ring of Fire, a secondary effect of volcanic eruptions. Lava flows, including lava fountains, are not “on fire”. They are red because they are hot, not because burning is taking place. Slide 18: Spatter cone (top) and black-sand beach (bottom). Local erosion of fresh lava flows in Hawaii creates beaches composed of lava fragments, and fragments of the minerals of which the lava is composed. In places the main beach material is black basalt fragments, as shown here. In other places beaches are composed of the green mineral olivine. Slide 19: The effects of the eruption in Iceland in April 2010: unusual amounts of ash shut down trans-Atlantic air travel for weeks. Lecture 04B Andesitic volcanoes. These are the main types of volcano that form in magmatic arcs, above subduction zones. They characterize the Ring of Fire around the Pacific Ocean (Slide 2). In North America, the Cascade 13 GLG 103: Weekly lecture notes Range is the collective name given to a chain of volcanoes extending from west-central British Columbia to northern California (Slide 3). Slide 4: Eruption activity along the Cascade Range. All of the volcanoes are considered to be“dormant”, that is, currently inactive but not extinct. They will probably erupt again. Mount St. Helens surprised everyone in 1980 with a major catastrophic eruption, but it should not havebeen a surprise. Slides 5: Mount Baker is close to Vancouver! Slides 6, 7: Mount St. Helens. Current view and setting. Slides 7, 8, 9: The great eruption of 1980. th After weeks of activity, thenorth side of the mountain blew outon 18 May, 1980. This had not been anticipated. A cloud of hot volcanicash, a debris avalanche and a pyroclastic flow swept northward from the crater.The flow overran an observation site set up at the foot of the volcano occupied at that time only by USGS volcanologist David A. Johnston. He was killed instantly. The current Johnston Ridge Volcanic Observatory, nearby, was built after the eruption and named after him. Slides 7 and 10 show how the area in the immediate vicinity of the crater was completely transformed by the eruption. Slide 11 shows what a pyroclastic flow looks like and the deposit it leaves behind. A pyroclastic flow consists of a cloud of incandescent gas and molten ash. It may reach temperatures of 1000ºC and may travel at speeds of up to700 km/hr. Slides 12, 13: Ash may be carried for hundreds ofkilometers, and can form blankets many centimeters thick. An ancient (Cretaceous) example is illustrated. Larger volcanic fragments, calledbombs (Slide 12), are only carried a few hundred metres.These may be up to metres across, and can cause severe damage. Slides 14-17: Post-1980 the volcano was intermittently active for several years. Occasional swarms of minor earthquakes (Slide 14) indicated the movement of magma below the surface, were thought tobe the precursor to another major eruption, but the volcano has now gone dormant and activity there is currently minimal. Slide 16: There is a webcam permanently set up at the Johnston Observatory. it can be accessed at Slides 18-20: Volcanoes in Alaska. The Aleutian Islands constitute a volcanic arc. The chain of volcanoes extends onshore into southern Alaska. Mount Spurr is visible from Anchorage. Many of the 14 GLG 103: Weekly lecture notes Aleutian volcanoes are intermittently active, and some seismic and other activity has been recorded in recent years from Mount Spurr and vicinity. Slides 21, 22: The build-up of a volcanic cone over a magma chamber may eventually lead to instability. Draining of the magma chamber can lead to collapse of the cone, explosiveeruption, forming a caldera, and eventually the formation of a lake over the former site of the crater. Shown here is Crater Lake in Oregon. Mazama Ash, the ash cloud released during this event, is extremely widespread in western North America. Much larger calderas occur in other parts of the world (see below). Slides 14 - 33: Other arc volcanoes, showing the characteristic steep-side cone shape, may be seen in northern California (Mount Shasta), Japan (Fuji, near Tokyo), Italy (Vesuvius, near Naples) and Mt. Aso, on the southern island of Kyushu in Japan.The last major eruption of Vesuvius was in 1944 (Slide 25). Fuji has not erupted since 1708. Mt. Aso (Slides 26, 27) is intermittently active. It is a favourite tourist site, despite the dangers of explosive activity. Nearby is the town of Beppu (Slide 27), built over a series of rifts marked by numerous hot springs and bubbling mud pools. These provide the source for traditional hot baths, making Beppu a favourite holiday resort.Slide 28: Krakatoa, the site of the world’s loudest explosion. The current crater has grown from within the caldera formed by the explosion and destruction of the original volcano. Slides 29-33: Volcanoes in New Zealand. The North Island is situated over a major magmatic arc that is undergoing crustal extension. There are many active volcanoes here, and many rifts with geothermal activity. The most famous geothermal area is Rotorua. Slide 30: Within 20 km of the centre of Auckland, there are the remains of 49 separate volcanoes . The last one erupted 600 years ago. Lake Taupo (Slide 32) is one of the largest calderas in the world. It is 193 km across and up to 186 m deep. It was formed initially during a gigantic explosion about 26,500 years ago,when an estimated 1170 cubic kmof material was ejected, and there have been eruptionssome 28 times since then. The most recent eruption was in 180 AD. Ash blown into the upper atmosphere at this time caused red skies that were observed in Rome and in China. There was no human population in NZ at the time (Maori settlement did not start for another couple of hundred years). Slide 34: Rocks formed in volcanic arcs:Shown here are some ancient (Paleozoic) lavas in Nova Scotia. On the left, a rhyolite, a very viscous lava, in which the traces of flow-banding can be seen, plus the fragmentation (intobreccia) that takes place as theflow “freezes” while still moving. On the right is a lithified ash deposit containing many small bombs. These have all been squashed together during geological burial. Slide 35: Remnant volcanic landforms. The central lava-filled vent(or “plug”) of a volcano is often the most resistant to erosion, and may be all that is left after the cone of ash and other materials have been eroded away. Here are two examples. On the right is also seen a prominent dike extending out from the vent. 15 GLG 103: Weekly lecture notes Slides 36-38: Geothermal activity. In active or recent volcanic areas the rocks below the surface are extremely hot. Groundwater seeping downwards may be heated to the boiling pointand re-emerge as steam. In some places, notably the Rotorua area of New Zealand, this heat source is enough to supply hot water for geothermal power plants. The Wairakei power plant,north of Lake Taupo, part of which is shown in Slide 38, produces 1550 GWH of electricity per annum, which is enough to supply Taupo, Rotorua, Napier and Hamilton. It produces 4.3% of NZ's electricity production Slide 39: Summary of volcanic hazards lava flows: set fire to everything and bury it. Hawaiian lava flows can travel at up to 64 km/hr pyroclastic flows (flows of hot ash mobilized by gases): violent, hot, fast-moving (up to 700 km/hr). e.g., destruction of Mt. Pelee in Martinique in 1902, killed 29,000 people and destroyed entire city. Explosive eruptions: blasts travel at speed of sound (700 km/hr), e.g., Mt. St. Helens in 1980 Ash falls: e.g., burial of Pompeii in AD 79, blanketing of Clark Air base and surrounding villages flanking Mt. Pinatuboin 1991. Mt Mazama 6600 years ago (eruption formed Crater Lake, Oregon. Ash covered most of Washington, Oregon and much of Idaho and Montana.Recent ash emitted by Mt. St. Helens . mud flows (lahars) and debris flows: loose ash set in motion by water (rain or melting of ice cap). Catastrophic burial of land below, commonlywith much loss of life. May be long after eruption (e.g., in Guatemala and Nicaragua following recent hurricanes) poisonous gas emission: water vapour (steam) isthe main emission, but carbon monoxide, carbon dioxide, hydrochloric acid, hydrofluoric acidand sulphuric acid may also be present. E.g., Cameroon, 1984, 1700 peoplewere killed by release of carbon dioxide, which is heavier than air, and simply flowed silently down the side of the volcano, suffocating people and animals in the village below. tsunamis triggered by collapseof the side of volcanoes into the sea:see Week 5. Slides 40, 41: Prediction of eruptions Volcano monitoringcan help to predict an eruption: —natural seismic activity (indicates magma movement) —studies of magnetic field (magnetism lost when rocks heated to critical point) —ground deformation caused by magma movement (swelling, detected by tiltmeters, detailed surveying) —change in temperature of crater lake water, springs (these are not likely to be catastrophically sudden, as in the movie Dante’s Peak, in which a young couple is boiled to deathin a hot spring) —change in gaseous composition of fumaroles Slide 41: It looked as if Mount Spurr would erupt in 2004, but it did not. Slide 42: volcanoes that have not erupted in historic times and are deeply eroded are said to beextinct. 16 GLG 103: Weekly lecture notes volcanoes that show no signs of current activity but are not deeply eroded are classified as dormant. Mt. St. Helens had been dormant for 123 years before 1980 eruption, Mt. Pinatubo for 400 years before 1991 eruption. Slides 43-44: Volcanic hazards in the lower mainland of BC. Mount Baker is regarded as dormant, NOT extinct. Fortunately for Vancouver residents (but perhaps not for those in Hope or Princeton!) the prevailing wind is from the west. Week 7 (October 10 ): th Lecture 07-Tsunami Slides 2, 3: definitions and terms Definition of tsunami: a long ocean wave generated by sudden displacement of the sea floor Also termed seismic sea waves. Incorrectly termed tidal waves, but theyhave nothing to do with tides. Generated by sudden vertical movement of the sea floor, mainly by movement on normal or reversed faults, or by volcanic eruption orby submarine landslides(which may be triggered by an earthquake) Tsunami are quite unlike normal coastal wind-driven waves, which have short wavelengths relative to their amplitude (Slide 4). Tsunami have amplitudes of <1 m and wavelengths of 200 km in open ocean. They travel at 950 km/hr in the open ocean (Slide 5). Commonly undetectable in open oceans They are so dangerous because the waves slow down and pile up when they reach the shore(Slide 5) —amplitude may reach 40 m. —may take up to an hour for successive waves to all reach shore —catastrophic destruction of coastal communities. Tsunami are particularly common in coastal areas around the Pacific Ocean. Japan and Hawaii are commonly seriously affected(Slide 6). Slides 7-12: The great tsunami in the Indian Ocean following the Boxing Day 2004 earthquake off northern Sumatra. The earthquake was one ofthe greatest ever recorded and the tsunami by far the most damaging ever in history. The wave was up to 20 m high when it hit Sumatra. This wave encircled the earth and was detected by sensitive tidal measurements on the Maritime coast of Canada severaldays later. There was little or no warning given about this tsunami. Nobody was prepared for it. Huge loss of life (several hundred thousands of people), including many tourists in beach resorts of Thailand, Sri 17 GLG 103: Weekly lecture notes Lanka, etc. A warning system similar to that in the Pacific Ocean, has now been installed in the Indian Ocean. Tsunamis hitting Hawaii(Slide 13) have originated all around Pacific margin and have taken up to 15 hours to hit (Slide 6). Tsunami have also affected the west coast of Vancouver Islandand coastal Alaska (Slides 14-15). Geological evidence from near Port Alberni on the Pacific coast of Vancouver Island (including carbon-14 dating) demonstrates that there was a major tsunami in the th year 1770. Historical records in Japan correlate with this, and suggest a precise date of 26 January in that year (Slide 17). A computer simulation shows the tsunami wave traveling out across the Pacific Ocean (Slide 18). Automatic warning systems for the Pacific rim and are paid particular attention toin vulnerable areas such as Japan and Hawaii (See below). Slide 19: There was a devastating tsunami on the south coast of Newfoundland, following the earthquake in the Laurentian Channel on 18 November, 1929. Slides 20, 21: There is potential for tsunamis in the Atlantic Ocean as a result of collapse of large volcanic islands, such as the Canaries.Many large landslides have been known to have occurred there. Major detachment faults have been mapped, and a possible collapse could occur. The danger is very difficult to estimate, but is not thought to be imminent.Slide 21 shows a computer simulation of a tsunami crossing the Atlantic, which could, according to this model, be over 20 m hg i h when it hits the coast of Florida. Slide 22: A very graphic simulation of a tsunami in the movie “The day after tomorrow.” In this case the tsunami was supposed to have been caused by flash freezing of the north Atlantic (absolute nonsense), but the simulated wave is frighteningly real. Slide 23: Tsunami warning systemshave been in place in the Pacific region since 1946,and have now been installed in the Indian Ocean since the 2004 disaster. However, useful warning cannot be issued for tsunamis that originate close to shore. A tsunami hit the northern Japanese of Hokkad i o in 1993, only 3-5 minutes after the earthquake, and more than 200 people lost their lives. Slide 24: Another tsunami in Indonesia. After having been out of mind for decades, tsunamis are now very much on the minds of residents of Indian Ocean-rim countries. Week-6 (October 15 ): Erosion, landslides and mass wasting Slide 2: Example of problems that can be caused by rockfalls and landslides.The Sea-to-Sky Highway was a critical part of the infrastructure servicing the Whistler-Blackcomb area during the 2010Winter Olympics. Slide 3: 18 GLG 103: Weekly lecture notes Surface weathering processesand soil formation —rock weakening by temperature changes —organic processes —frost heave, freeze-thaw, joint widening in limestones. Slide 4: Types of mass wasting process: slope failures (slumps, rockfalls) and flows including: 1) debris flows, e.g., Venezuela, winter 2000(see below) —sand, gravel and boulders in muddy or sandy matrix, flow at up to 1 km/hr 2) mudflows: highly fluid watery mud, but may pick up coarser material on the way. —flow at up to 100 km/hr. origin of flows: —they occur when large masses of loose materialare mobilized by water. —source of loose mass: volcanic ash buildups or soil loosened by deforestation —may be loosened by catastrophic rainfall, may be triggered by earthquake or rainfall. —debris flows and mudflows can also occur in places where they have never been known to occur before in human memory, as a result of unusually strong rainfall descending on a steep slope with a thin soil cover and with much loose detritus, plant material, etc. Slow movement: —solifluction (creep): slow downhill movement of water saturated soil andregolith (the weathered top surface of the bedrock) —downhill creep, slow granular movement under gravity (leads to curved tree trunks, tlited fence posts, etc) —frost heaving: expansion of water-saturated soil upon freezing and shrinkage upon thawing. This makes for very unstable ground conditions. It is because of frost heaving that buildings in cold climates need deep foundations that penetrate below the frost line. Troublesome earth material —liquefaction of muds (“quick clays”). When saturated, such muds loose all mechanical strength. Severe shaking of wet mud can bring this about (this is one possible form of secondary earthquake damage, as discussed in Week 3). Formation of natural arches as a result of water sapping(see below) Slide 5: Erosion can be surprisingly rapid. In this case, it has been accelerated by human foot passage. Slides 6, 7: Soil formation. Root penetration andtemperature change help to break up the rock intosubsoil. Organic acids break down the rocks, and decayed organic material adds carbon compounds to the mixture. Slide 8: Buildings composed of natural stone and more than a few decades old commonly show ev idence of surface weathering. Sedimentary rocks, in particular, tend to be more porousthan, say, granite, 19 GLG 103: Weekly lecture notes and may contain clays or salt particles that expand and contract with changes in wetness.This can weaken the surface, causing layers to flake off. Slide 9: Downslope creep of soil under gravity may distort human constructions. Slides 10, 11 and 12: Erosion and surface formation under different climatic conditions: Slide 10: In the Arctic there is a surfaceactive layer a few tens of centimeters thick, which freezes in winter and thaws during the summer.Stone polygons are caused by thermal sorting of the surface materials. These may be dragged out intostone stripes on a sloping surface. In arid climates (Slide 11) surface temperature changes weaken the rocks and occasional cloudbursts carry fine material away. Sudden heavy rains, characteristic of many desert regions, where there is no vegetation cover,can be powerfully erosive(Slide 12). Slides 13, 14, 15 In cool-temperate regions, such as inmuch of Canada, frost-heaving is a very important mechanism. Small cracks in the rock are widened each winter by water expanding as it turns into ice. Each year the cracks get wider, and soil and debris fall into them to keep them from closing up. Eventually, large blocks may be separated from the rock face and move outwards. In the case of the Blue Mountain escarpment, near Collingwood, the top layer of hard limestone rests on a softer shale, which has allowed these large blocks to slide away from the scarp face. Slides 16, 17, 18: Water seeping through limestonecan undercut and sap away at rock faces where the water emerges at the surface. Limestone is soluble in rainwater, which is naturally slightly acidicbecause of dissolved CO 2 This forms a characteristic surface of erosional rills, called karst (Slide 16) and allows water to penetrate into the subsurface. It may emerge as springs, to feed vegetation growth on steep cliff faces, as at Niagara Falls (Slide 17). Water can also seep down through porous sandstone (Slide 18). Where it emerges at the base, there may be a spring, and softer rocks underneath can be sapped away. Slide 19: On a large scale, frost-shattering may lead to the build-up of largedebris cones. These may or not be sorted by running water to form alluvial fans. Exotic landforms: Slide 20: Hoodoos, formed where mixtures of boulders, sand and clay are subject to rainfall. Hard objects or layers serve as protective caps. Slides 21, 22: natural arches in the US southwest. Formed by water sapping along joint surfaces. Slides 23, 24: In arid regions, rivers can cut downwards very rapidly, formingincised meanders, and slot canyons. Pebbles and boulders violently circulating in turbulent floodwaters can erode out circular potholes. 20 GLG 103: Weekly lecture notes Week 7A (October 22 ) Too much Water 1: Landslides and mass wasting Slide 2: Origins of rock falls and landslides —weak materials underlying slope. —materials rendered weaker by water saturation —presence of joints or fractures, may be widened by repeated freeze-thaw(frost-heave process) —triggering event, such as earthquake, or build-up of weathered soil released by sudden rainfall. Slide 3: Types of landslide and rockfall. Slide 4: A simple example of slope failure. These are very common in soft muds and shales. Slide 5: Landslides can be very devastating. As we shall see, examples like this could be avoided. Slide 6: The ravine leading down to Bluffers Park collapsed in 1991. Many of the Ravines in Toronto were used for garbage disposal in the early part of thetwentieth century. This is a very bad idea. It blocks drainage, leads to groundwater pollution, and also yields a very unstable landscape. Slides 7, 8: Landslide near Fort St. John’s and collapse of highway. The road was carved into the hillside, and this set up an unstable condition (an over-steepened slope). The temporary solution has been to carve even deeper into the hillside. Slide 9: Frank Slide, a major natural disaster. Caused by failure of crevices at the top of the mountain. The debris was carried hundreds of metres away from the foot of the mountain on an “air cushion” How human activitymakes slope failure worse: —Deforestation can be a major cause of slope failure, landslides and mudflows because the loss of vegetation and root systems leavesslopes very vulnerable to heavy rains(Slide 10). —Activity of all-terrain vehicles (ATVs: Slides 11, 12) can cause severe gully erosion, damage to plant roots, release of sediment into waterways, which then damages fish habitats, damages local ecosystems—building on steep or weak slopes (e.g., much housing in urban California; Fraser Valley near Vancouver) —undercutting, and steepening of slopes, e.g., for highway and railroad construction(Slides 13,14) Slide 15: Types of mass wasting: 21 GLG 103: Weekly lecture notes Slide 16: Examples in the Rocky Mountains of British Columbia.The west flank of Kicking Horse Pass, where the TransCanada Highway and the Canadian Pacific Railway meet major landscape challenges. Slide 17: The debris flow chute and avalanche tunnel built over theCPR track, west of Field, B.C. Slides 18, 19: Mass wasting leading to debris flows is particularly common on the slopes of volcanoes, where there are great quantities of loose ash. Effects on human environmentof landslides and mass-flow processes: —destruction of roads and bridges —burial of villages —commonly much loss of life because flows occur without warning. —all these effects may lead to much destruction and loss of life Severe debris flow disasters occurredin central America following hurricanes in late 1998, and in coastal Venezuela following heavy rains inJanuary 2000 (Slides 20-22). Note the extremely large boulders carried by these floods. Other effects of slope failure, soil creep and debris flows on human structures, and their mitigation: Should housing be built in areas subject to debris flow events? Slide 23 shows two views looking upstream and downstream from a bridge along a potential debris-flow channel – a cobble-lined creek flowing into the Canmore valley, near Banff Alberta. Debris flows have been known to occur along this creek, and one event about a decade ago overtopped the bridge which carries the Trans-Canada Highway across the creek (in the far distance of the right-hand picture). The solution adopted here is to make the creek-bed abnormally deep by dredging out much of the gravel along the base. Slide 24: The deepening of the creek bed did not work: damage caused by spring runoff in 2012: the undercutting of asphalt pathways along gthe creek bank. Slides 25-26: A debris flow on the ski slope: Blue Mountains, Ontario(Arrowhead, Alpine Ski Club). Heavy rains in April 2012 triggered a failure that had been many years in the making.Saturated muds covered by a build-up of fallen tree and other plant debris failed suddenly and threatened housing downstream. Slide 27: The effects of human activity on unstable slopes. Housing has been built up the sides of many steep-sided valleys in places like the Fraser Valley in British Columbia, around Los Angeles , etc. Often this is done because of a shortage of land for housing, but often it is done because people like to live high up, in a place with a view. But there can be consequences! Burial and/or destruction of housing in North Vancouver, at the foot of the mountains, is a regular event. People continue to build in places like this and invariably claim that they knew nothing about the dangers, nobody warned them, etc., etc. So at least you (the students in GLG 103) have now been warned! Slide 29: Mitigation: —regrading slopes to reduce angle —improved drainage —rock bolts 22 GLG 103: Weekly lecture notes —spray exposed surfaces with concrete —diversion walls —limit ATV access to undeveloped areas Slides 30-31: examples of mitigation —Road cuts, covered with concrete (common in Japan) or with mesh nets, or stabilized with rock bolts —Slopes graded back and vegetated. —Slopes developed into a series of terraces. very common in southeast Asia. —Construction of check dams and debris traps along creeks. Common in Japan. Slide 32: Do they ever learn? - No Repeat, in 2005, of a landslide in almost exactly the same place as a landslide in 1995. Potential disaster is usually something property owners don’t want to know about. When disaster strikes it is always someone else’s fault, and they always expect to be saved from their bad choices by government bail-out. In this case, the willful blindness is quite obvious. Week 7B (October 24 ) Too Much Water 2 Floods, Coastal Processes, Hurricanes Floods Slide 2: River valleys consist of channels bordered by levees (raised banks) and floodplains —floodplains are constructed by deposition of fine-grained sediment during occasional over-bank flow. Most of the sediment is deposited close to the river bank, forming the levees. —silt and mud carried onto floodplains contain valuable nutrients (natural fertilizers) e.g., the name “Huang He” or “Yellow River” (China) derives from brown silt content. —Ancient Egyptian civilization was possible because of the fertility of the Nile floodplain-15 cm of silt and mud were deposited every 100 years before Aswan Dam was constructed) —human settlement, agriculture and urban development typically takes place on the floodplain because of water supply, ease of accessibility water transport (St. Louis, New Orleans) The natural levees of the Mississippi, where it runs through New Orleans, are amongst the more elevated portions of the city (e.g., French Quarter), and were therefore above the worst flood damage during Hurricane Katrina(discussed below). Runoff is the amount of water flowing through the river, typically measured in cubic feet or cubic metres per second. Runoff = precipitation-infiltration-interception-evaporation (infiltration is what seeps into the ground. Interception is what is diverted, e.g., into irrigation canals. Dense vegetation or impermeable soil will also inhibit infiltration). Covering open land with concrete housing subdivisions will dramatically reduce infiltration and increase runoff. Runoff in rives shows a logarithmic patternas a result of the natural variability in rainfall frequency and intensity 23 GLG 103: Weekly lecture notes Slide 3: The recurrence interval of floods of a given magnitude is statistically predictable. The frequency of floods corresponds to what is called a logarithmic distribution. —Geographers, planners, etc., refer to a concept called thehundred-year flood. This is the largest event that can typically be predicted to occur once every hundred years (but this is a statistical average, and could occur twice in a decade and then not again for hundreds of years) . Its size is predicted from historical runoff patterns. The scale of this imagined event is often used to plan for flood protection dams and canals. —But most human experience relates to last 50-100 years. —The “hundred-year flood” may not yet have been experienced. Or there could be two “hundred- year” floods within a few years of each other– and then nothing much for decades. It’s all a matter of probabilities. —flash floods in occur in arid areas because there is no vegetation or soil to cause “interception” they may trigger mudflows/debris flows (see Venezuela floods,:Week 7A) —Apparent safety of floodplain flatlands near a river may, therefore, be an illusion Examples of floods: Slide 4: The great floods of 1994 in the Mississippi valley Slide 5: Frequent floods in the Danube River of eastern Europe. These pictures were taken a few km upstream from Vienna. Slides 6-9: Red River valley floods of North Dakota and southern Manitobain 1997 Winnipeg is protected by the “Red River Floodway” which was constructed between 1962 and 1968. An enlargement was started in 2005 andwas planned for completion in 2010(Slide 9). Slides 10-11: Hurricane Hazel, which hit Toronto in 1954. This very rare event resulted in catastrophic flooding of Toronto’s ravines and some loss of life. As a result of the flood, legislation prohibited further development of housing, etc., in the ravines, andgave Toronto some major parks. Slide 12: Force exerted by moving flood waters is enormous —movement of large concrete blocks, rail and bridge girders distances of hundreds of metres —blankets of silt and mud may be tens of cm deep. The slide shows the destruction of a bridge over Finch Avenue in 2005, over a period of an hour or so. —see also floods and debris flows in Venezuela (SeeWeek 7A) Slides 13: Beach processes Water and sediment movement beneath breaking waves: Most waves hit the beach at an angle. This sets up a circulation patterns on the beach, which carries sand by a circular route slowly along shore. This process is calledlongshore drift. 24 GLG 103: Weekly lecture notes Tides generate currents moving in and out of inlets. The rising (flood) tide moves water on to the tidal flats behind the barrier island (grey areas in Slide 13). The falling (ebb) tide drains the tidal flats and moves sediment out of the inlet, where it may form anebb-tide delta. Note also the movement of sand by longshore drift (at right, in Slide 13) toform a spit. In most areas, tides are said to besemidiurnal. That is, they have a period or cycle of approximately one-half of a tidal day. The predominant type of tide throughout the world is semidiurnal, with two high waters and two low waters each tidal day. For example, tides along the East Coast of Florida are semidiurnal. Slide 14: Waves Generation of waves depends onwind shear and fetch. Fetch is the distance available in a particular direction for winds to exert shear on the water surface to build wave size.The longer the fetch, the larger the waves. As waves “touch bottom” they become asymmetric, as forward speed of the upper portion of the circulatory motion continues unchecked, while the bottom (return) portion is slowed by friction against the sea floor. Waves become unbalanced, and this explains why they eventually break close to shore. Slides 15-19: Beaches and coastal protection A groin is an artificial barrier constructed across a beach perpendicular to the shoreline, designed to trap sediment and slow down longshore drift. Construction is usually carried out to stabilize beaches, but this leads to down-current sediment-starvation and erosion. Sediment may build up on the upcurrent side of a protected inlet but be eroded from the far side (see Slide 15) leading to severe erosion at the downcurrent location (Slide 16). Hard sea walls are a bad idea. Typicallythey are undercut by storm waves and collapse(see example illustrated below). Sloping sea walls absorb and diffuse the wave energy and are therefore more effective. Slides 17-19: formation of barrier islands, spits Sediment is moved along shore by longshore drift,forming spits. Much sediment may be added to a beach in some areas, and removed in others. Over the long term (decades) coastlines may therefore advance or retreat by tens to hundreds of metres. Slide 19: The folly of beach land ownership: —barriers and beaches are dynamic systems in constant adjustment to changing weather and long-term changes in climate and sea level. —barrier destruction and retreat by wave actionis almost continuous, particularly during storms (see below) Slides 20-24: Cliffs Waves undercut the cliff, leading to instability and collapse. 25 GLG 103: Weekly lecture notes Also, joints form by water seepage and temperature change, and this leads to failure of slabs and blocks, which collapse onto the beach. This material is then removed by waves, which exposes the base of the cliff to further erosional attack. Sea stacks (Slides 21-23) form and collapse as a result of wave erosion undercutting and removing rock material. London Bridge (Slide 22) is the name given to a series of arches formed by wave undercutting on the south coast of Australia. Continued undercutting led to the collapse of one of the arches in the early 1900s. Slide 24: Coastal landslides are not at all uncommon, and have often led to the destruction of housing. The Scarborough Bluffs are now a protected area, and no housing is being built close to the cliff edge. Slides 25-45: Hurricanes! Hurricanes (Slides 25, 26, 27) are initiated as “tropospheric waves,” generated by temperature differences between the hot African landmass anda cooler ocean. The hurricane season in the North Atlantic region officially lasts from 1 June to 30 November. The terms "hurricane" and "typhoon" are regionally specific names for a strong "tropical cyclone". A tropical cyclone is the generic term for a “non-frontal synoptic scale low-pressure system over tropical or sub-tropical waters with organized convection (i.e. thunderstorm acitvity) and definite cyclonic surface wind circulation”. If winds reach 33 m/s (74 mph), then the storm iscalled: - a "hurricane" This type of weather system is also called a "typhoon," “tropical cyclone," “cyclonic storm," or "tropical cyclone“ in different parts of the world. In the North Atlantic, hurricane tracks (Slide 28) are determined mainly by the size and strength of a high-pressure system that usually occupies the central Atlantic area (Slide 29). Slide 30: Classification of storm strength and hurricane type. Storm surge (Slide 31) is simply water that is pushed toward the shore by the force of the winds swirling around the storm. This advancing surge combines with the normal tides to create the hurricane storm tide, which can increase the mean water level 4.5 m (15 feet) or more. In addition, wind driven waves are superimposed on the storm tide. This rise in water level can cause severe flooding in coastal areas, particularly when the storm tide coincides with the normal high tides. Because much of the United States' densely populated Atlantic and Gulf Coast coastlines lie less than 10 feet above mean sea level, the danger from storm tides is tremendous. Slides 32-40: Coastal flooding and wind damage in US due to hurricanes Slide 32: The Galveston Island disaster Hurricane in September 1900 is still regarded as the greatest natural disaster to hit the US, because of the loss of life. Nowadays, radar and satellite weather observations provide continuous 26 GLG 103: Weekly lecture notes updates of weather patterns, and civil authorities are very active in getting out warnings and moving people out of the way. Slide 33: Before and after maps of Galveston Island, showing the effects of Hurricane Carla in 1961. The inlets that opened up during the storm were formed by wavesbreaking over the barrier. These are filled in by “normal” sedimentation between storms, and are crossed by bridges, causeways or ramps constructed to carry roads along the axis of the barrier. These structures are amongst the first things to be destroyedduring a major storm, thereby preventing residents who stay behind from changing their minds and trying to make an exit during the storm. Be warned! Slide 34: Note the destruction of “hard” sea-wall defences by Hurricane Jeanne, 2004. Slides 35-40: Hurricane Katrina, August 2005 The severe flooding in New Orleans followingHurricane Katrina was caused by the storm surge into Lake Pontchartrain, north of the city, which then broke through the artificial flood walls protecting the city. The damage was, ofcourse, made much worse by the fact that much of New Orleans is below sea-level. Slides 36: the vulnerable coastline The storm surge raised water levels on lake Pontchartrain, and breached barriers (levees) that had not been built or maintained to withstand such pressures (warnings had been expressed about the vulnerability, but nobody had done anything about it). Slides 37-38: Flooding of downtown New Orleans:Flooding virtually destroyed low-lying areas of the city that had subsided because of compaction and settling (Slides 37, 38). Levees close to the river, composed of sand, had not subsided as much and were largely spared flooding (Slide 39). This is where the old “French Quarter” is mainly located) Wetlands along the coast and around the delta (Slide 36), that should have been able to absorb the force of the wind and waves have been removed, filled in, built over or channeled to provide marinas and other forms of access. The city government of New Orleans, the State of Louisiana, and the federal government, were all unprepared for a disaster of this scale. Slide 40: Before and after views of the Chandaleur Islands (location shown in Slide 36) Slides 41-43 Hurricane Stan, October 2005. A different type of disaster. It hit mountainous areas and triggered major mudslides that buried villages. Slide 44: There is no evidence that hurricane frequency has changed as a result of global warming. There is a natural cycle of changing frequency, reflecting oscillations in regional Atlantic climates. The dramatic increase in hurricane damage in the US in recent years simply reflects the greater density of development (especially resort homes) along vulnerable shorelines. 27 GLG 103: Weekly lecture notes There is some evidence that hurricaneintensity has increased in recent years, and some authorities attribute that to higher ocean water temperatures as a result of global warming. These higher temperatures lead to greater evaporation, and therefore more moisture to “fuel” the hurricane. Slide 45: The problem with coastal storm and tidal damage is simply that too many people are building in inappropriate areas and refusing to face the fact that coastlines are very vulnerable to natural forces (letter to the Toronto Star by Prof. Miall). th st Week 8 (October 29 , 31 ) Water: Lecture 8A: Global distribution of water, principles of groundwater, problems of drought and overuse of water Slide 2: Where is the world’s water? There is not nearly as much fresh water as most people think, and Canada does NOT have an excessive supply of fresh water. Water use for domestic needs, agriculture, industry, etc., depends on two sources: —surface waters in rivers and lakes —groundwater 2.5% of the world’s water is fresh water, of which 74% is in ice caps and 25%is groundwater. Less than 1% is in surface rivers and lakes (These are rounded numbers for convenience. For more precise figures see Slide 12 of lecture 02B) Surface waters are very unevenly distributed. —Some countries have abundance of surface waters (e.g., Canada, New Zealand, Iceland) —Some areas have limited resources, e.g., California, Israel. Urban areas in California rely on major water diversions from inland California and Nevada. —Desalination of sea water used in Israel, Saudi Arabia and otherarid countries, but is energy- intensive. Slides 3, 4: As we shall see, drought is an increasing problem worldwide, exacerbated by over use of surface and groundwater supplies. Slides 5-10: Principles of Groundwater Slide 5: Water is present down to great depths but most useful water supplies are within 750 m of earth’s surface. The earth’ surface layers are typically under-saturated or even dry (vadose zone) Below this is the saturated zone (phreatic zone). The top of which is called thewater table —The water table follows the rise and fall of the land surface, sloping towards areas of surface water. 28 GLG 103: Weekly lecture notes —Streams and lakes occur where the water table intersects the surface. Slide 6: The amount of groundwater in a particular rock body depends on porosity and permeability. —porosity: the amount of empty space in rocks that can be occupied by water (or oil and gas), typically up to 20% of rock volume in clean (mud-free) sands, may be 70% in soft mud —permeability: the measure of the linkage between pores thatallows fluid to flow through. Typically high in soft sand and limestone, but is reduced by deposition of cements between grains and is very low in clay because of tight contacts between clay particles There may also be significant porosity in fractures (Slide 7), but this can be very unpredictable. Slide 8: Rain water that falls on the surface infiltrates the surface soil and descends under gravity to the water table. This is calledrecharge. Groundwater percolates through the saturated zone towards pointsof discharge. —discharge adds water to lakes or rivers —or occurs as springs. Slides 9, 10: Aquifers and aquitards Percolation is along curved flow paths, which may be diverted along more porous units —an aquifer is a porous rock unit that may be tappedfor water supply by wells. —an aquitard or aquiclude is an impermeable rock which may form the base of a zone of water flow (e.g., underlies a spring). —water may also be held in fracture systems —withdrawal of water by a well may create acone of depression around the well. unconfined aquifer: one whose upper surface is the water table, and is therefore in direct contact with the surface. confined aquifer is one bounded by aquicludes. artesian systems are those where recharge is great enough and at an elevation such that the aquifer is under increased hydrostatic pressure. —pressure may cause fountains to rise as much as 60 m above ground level, but most artesian systems have now been depleted by wells Slides 11,12: Problems with groundwater use —Excessive use of groundwater leads to water aquiferdepletion, lowering of water table, and possibly subsidence. There may be a cone of depression around a water well, if withdrawal is too rapid. —Salt-water intrusion may occur in coastal areas, and pollution from human, agricultural or industrial wastes may also occur. Slides 13-20 Problems associated with irrigation: 29 GLG 103: Weekly lecture notes —Replenishment by natural means is slow(Slide 13). Note that deep groundwater takes thousands of years to recharge, meaning that existing reserves are essentially irreplaceable “fossil water” —Traditional irrigation methods are wasteful (Slide 14) and some groundwater sources are currently being used at a rate that it is unlikely to ever be replaced,e.g., High Plains Aquifer of US Plains states (Slide 15), which is much used for agricultural irrigation(Slide 14). —Numerous new golf coursesare being developed everywhere. Those around Las Vegas (see below) are particularly problematic. —other areas in North America also are undergoing severe drought, which is probably part of a long-term climatic cycle (Slide 16). —groundwater over-use is responsible for subsidence, whether it be for agriculture (Slide 17: the agricultural valleys of California [Imperial Valley, San Joaquin Valley], the problem of“aquifer mining”) or by cities (Slide 18), much of it is irreversible because of natural compaction and porosity loss. —Water misuse in the US (especially in the arid west) is exacerbated by huge federal subsidies , especially to agribusiness, and thisdiscourages efficient use of water. —urbanization can prevent efficient recharge; e.g., potential problem of development of the Oak Ridges Moraine, north of Toronto. Slides 19-23: Diversion of water for urban use or agriculturemay cause serious problems. The Colorado River Basin in the SW United States(Slides 19, 20) is a particularly acute problem. —very little water from the Colorado River now enters the Gulf of California, most has been diverted into Californiaalong the All American and Alamo Canals (Slide 20). Water levels are now approaching an all-time low in the Colorado Riverand behind the major hydro dams (Slides 21, 22). This is partly becauseof over-use (e.g., for urban water supplies and to serve golf courses: Slide 22), but is partly a reflection of a cycle of natural drought that has recently become steadily worse. Slide 24 Areas undergoing drought are much more susceptible to wild-fires. Slides 25-30: Drought is a serious issue in many parts of world.Disputes about water are a major cause of international conflict, e.g., the division of the headwaters of the Euphrates River, which flows from Turkey through Syria and Iraq. Slides 26, 27: —Aral Sea was once the world’s fourth largest lake.It has now almost disappeared because of agricultural diversion of feeder rivers, leading to amajor increase in regional aridity,with salts from the lake bottom blown inland,complete disappearance of a flourishing fishery, and so on. Recently, attempts to replenish the sea by allowing the some of therivers to return to their original course, are having some success. Slide 28: The Jordan River, the only source of water for the Dead Sea, on the Israe- lJordan border, is heavily polluted and over-used for agriculture. Much of the water is diverted intoirrigation canals at the Sea of Galilee, so that the river, where it enters the Dead Sea, is little more than a muddy ditch. 30 GLG 103: Weekly lecture notes The water level in the Dead Sea is now dropping at a rate of about 1 m per year, largely because of this diversion of Jordan Riverwaters (Slide 29). Better irrigation technology and water recycling, including artificial recharge, are helping in some areas. Instead of spray irrigation (Slide 14), a more water-efficient irrigation method is called drip- irrigation. This is a technique developed in Israel (Slide 30). Slides 31-34: Could the Great Lakes become the next major water problem? Lake levels are down(Slide 33), but not yet to record low levels. This is partly a cyclic climatic problem, but is undoubtedly made worse by water withdrawals. There has been a long-standing fear that the dry US states would look north and put pressure on the US government to extract water from the Great Lakes and send it south. Only about 1% of Great Lakes water is circulated each year, so any addito i nal withdrawal would lead to permanent loss. However, the US states bordering the lakes are themselves aware of this problem, and opposed to any major diversions. A new international water agreement completed by the International Joint Commission (the body formally responsible for the Great Lakes water) seems to have taken care of the problem for the time being(Slide 34). As of August 2008 this agreement was undergoing final approval in the US Congress, having being ratified by the Canadian provinces andthe US states. It has now been approved. Lecture 8B Groundwater pollution Slide 2: Increasing recognition of the problems of water shortage and pollution Slide 3, 4: Landfills and their possible effect on groundwater —groundwater percolation generatesleachate, which is water contaminated with soluble materials, including metals such as cadmium, zinc, copper. arsenic, manganese, at levels far above safe limits —location of landfills in dry areas with low infiltration rates, or on aquitards, is preferable. —leachate may accumulate at the base of the landfill (bathtub effect) —modern landfills use liners and pipes to carry off waste gases, and may even burn the methane on site to generate power. Slide 5: Toxic spills, agricultural and other waste point sources: confined sources, such as individual landfills, or leaking chemical dumps nonpoint sources: e.g., fertilizer from agricultural sources —sewage pollution is rendered harmless by passage through sand. Within ~30 m harmful bacteria trapped or oxidized. Toxic materials may be: —light nonaqueous phase liquid(LNAPL) —dense nonaqueous phase liquid (DNAPL) 31 GLG 103: Weekly lecture notes LNAPL: e.g., petroleum (less dense than water), will move across the top of the water table DNAPL: e.g., trichloroethylene and other industrial chemicals. Will sink down through saturated zone and spread with groundwater flow. Very difficult to monitor and clean up. Slide 6: Many projects to redevelop urban lands have been stalled because of serious pollution problems. The term brownfields is applied to land polluted by industrial chemicals and other wastes. These th th wastes accumulated during earlier industrial phases (late 19 to early 20 century) before the nature of the problem was fully appreciated. Slide 7: Polluting substances may diminish because of absorption onto soil particle, bydispersion and dilution, or by bioremediation (the use of bacteria and other biological agents to “eat” the pollutants.) remediation of polluted soil and groundwater can be extremely expensive (USSuperfund). —Bioremediation may be enhanced by adding appropriate organic materials —toxic chemical pools may be pumped out —neutralizing chemicals can be added —polluted soils may be physically removed by surface mining. Slides 8-13: Problems of urbanization Pressure for suburban development of greenfield lands (hitherto undisturbed agricultural land) around the edges of the city of Toronto have become almost unstoppable. There is continuing demand for less-expensive housing, especially from new immigrants to Toronto, and the development industry is only too happy to provide it. The Oak Ridges Moraine exemplifies the problem. Environmental activists are concerned about the unique ecology of the area (Slide 8), the surface geology of which was formed during the last ice age (Slide 9). There are unique assemblages of plants and animals here, which are threatened by development, which has largely succeeded in fragmenting the moraine into small pieces. The effects of urbanization are to reduce groundwaterinfiltration and recharge. Covering large areas with concrete directs runoff into storm drains, resulting in rapid runoff instead of slow seepage (Slide 10). More recently, concern and controversy have focused on the “Big Pipe”, a major new trunk sewerage pipe to carry waste down to the Ashbridge’s bay treatment plant in Scarborough (Slide 13). Completion of the pipe encourages more suburban sprawl. Slides 14, 15: The Walkerton tragedy May 2000: 2300 cases of gastrointestinal illness and 7 deaths caused by the bacteriumE. coli. Agricultural wastes had been seeping into the groundwater close to the municipal water wells. Water testing procedures failed to detect the problem owing to local incompetence and cutbacks by the Government of Ontario. Slides 16-18: 32 GLG 103: Weekly lecture notes Bottled water: One of the biggest con-jobs ever perpetrated on an unsuspecting public by clever corporate promoters. Consumers have been persuaded to pay up to 3000 times the usual value of a common and universally available commodity.Slide 18 lists ten reasons why the purchase and use of bottled water is a really, really bad idea.Discarded water bottles are now the single largest type of waste found in parks, on beaches, and other places where people congregate Slide 19: Things the individual can do. th th Week 9 (November 5 , 7 ): Mineral resources and Mining Slide 1: Gossan: This is the brown stain on the weathered surface of rocks that contain iron-and magnesium-bearing minerals. It is the first sign of possible mineralization, searched for by prospectors. Slide 2: terminology A mineral resource is any element, compound, mineral, rock or aggregate that can be extracted from the ground and has potential economic value. An ore is an aggregate from which a substance may be extracted profitably because of its concentration. It typically consists of a body of rock, most of which has no value, but within which a valuable mineral is present in greater than normal concentrations. An ore deposit is therefore the body of rock containing a valuable concentration of a valuable mineral. Gangue is the non-valuable rock in which the ore minerals occur.Typically this is discarded after ore extraction and/or concentration as a pile oftailings left behind at the mine site. Ore grade is the concentration (typically expressed in pounds or grams of mineral concentrate per tonne of ore). How valuable the ore is (theeconomic cutoff), which leads to the establishment of the minimum mineable grade,depend on such factors as ore accessibility (remoteness from transport, depth), the complexity and expense of chemical extraction process, etc. Slides 3, 4, 5: Many naturally occurring substances have economic value. In fact, life as we know it would be impossible without the availability of a vast array of natural mineral resources. These slides indicate the location and value of some mineral deposits in North America generally, and Canada, specifically. Look around you. Everything of which a room (including the lecture room) is constructed, and most of the clothes we wear, are made from non-renewable natural resources obtained from he Earth. Slide 6: Most economically valuable minerals, especially metals, depend on specific set of geologic processes for their formation and accumulation, particularly the process of plate tectonics. This slide illustrates some of the major ore-forming processes, in relation to the basic structure of a typical subduction zone (not the only place where ore deposits form, but one which illustrates a lot of the basic principles). Many valuable deposits are theresult of the circulation of hotfluids (hydrothermal fluids), which carry dissolved mineral material, or “scavenge”such material from host strata. This dissolved material is deposited somewhere else along the pathway followed by the 33 GLG 103: Weekly lecture notes water, when physical and chemical conditions change. Often this results in a locally increased concentration of the material in question, to form the ore body. It is the job of the geologist to locate these concentrations and to understand how they come about. Slides 7-22: Six major processes of ore formation: Most involve the enrichment or concentration of previously dispersed material —hydrothermal deposits: enrichment by circulation of hot fluids —concentration by metamorphic recrystallization —crystallization from a magm
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