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University of Waterloo
SCI 250
Carol Ptacek

Chapter 1: An Overview of Our Planetary Environment o About five billion years ago evolved our solar system from a mass of gas and dust o Environmental geology explores the many and varied interactions between humans and that geologic environment o Stars formed from the debris of the Big Bang o The early Earth lacked oceans, the atmosphere, and the surface closely resembled the barren cratered surface of the moon. o Earth was formed by accretion, as gravity collected together the solid bits that had condensed from the solar nebula o Modern geoscientists draw on the principles of chemistry to interpret the compositions of geologic materials, apply the laws of physics to explain these materials’ physical properties and behavior, use the biological sciences to develop an understanding of ancient life-forms, and rely on engineering principles to design safe structures in the presence of geologic hazards. o The emphasis on the “why,” rather than just the “what,” has increased. o Exponential growth: Even when the population growth rate is constant, the number of individuals added per unit of time increases over time. o Doubling time: the length of time required for a population to double in size. Doubling time ( D ) in years may be estimated from growth rate ( G ), expressed in percent per year, using the simple relationship D = 70 / G o The higher the growth rate, the shorter the doubling time of the population o Carrying capacity: its ability to sustain its population at a basic, healthy, moderately comfortable standard of living o Natural systems tend toward a balance or equilibrium among opposing factors or forces. When one factor changes, compensating changes occur in response. Chapter 2: Rocks and Minerals o An atom is the smallest particle into which an element can be divided while still retaining the chemical characteristics of that element o The nucleus contains protons and neutrons o Electrons circle the nucleus with a negative charge o The number of protons determine the atomic number of the element o The sum number of protons and neutrons is the atom’s atomic mass number o A compound is a chemical combination of two or more chemical elements, bonded together in particular proportions, that has a distinct set of physical properties Minerals o A mineral is a naturally occurring, inorganic, solid element or compound with a definite chemical composition and a regular internal crystal structure o Crystalline materials are solids in which the atoms or ions are arranged in regular, repeating patterns o The two fundamental characteristics of a mineral that together distinguish it from all other minerals are its chemical composition and its crystal structure o Hardness, the ability to resist scratching, is another easily measured physical property that can help to identify a mineral, although it usually does not uniquely identify the mineral. o Cleavage , a distinctive way some minerals may break up when struck. o Luster describes the appearance of the surfaces—glassy, metallic, pearly, etc o Silicate group, all of which are compounds containing silicon and oxygen o The basic building block of all silicates is a tetrahedral arrangement of four oxygen atoms (anions) around the much smaller silicon cation o May be linked in chains, sheets of 3D frameworks by the sharing of the oxygen atoms o E.g. quartz o Feldspars: most abundant in the crust o Olivine: ferromagnesium mineral, abundant in the mantle o Mica: sheet silicates that can easily be broken apart o Clays are also sheets that can easily slide past each other, can absorb or lose water o The carbonates all contain carbon and oxygen combined in the proportions of one atom of carbon to three atoms of oxygen (written CO3). o Most abundant is calcite, which is calcium carbonate o The sulfates all contain sulfur and oxygen in the ratio of 1:4 (SO4) o When sulfur is present without oxygen, the resultant minerals are called sulfides. A common and well-known sulfide mineral is the iron sulfide pyrite o Native elements are minerals that consist of a single chemical element Rocks o A rock is a solid, cohesive aggregate of one or more minerals, or mineral materials o Magma is the name given to naturally occurring hot, molten rock material o An igneous rock is a rock formed by the solidification and crystallization of a cooling magma o When magma cools slowly below the surface plutonic igneous rock forms o Granite is probably the most widely known example of a plutonic rock o A magma that flows out on the earth’s surface while still wholly or partly molten is called lava o Volcanic is given to an igneous rock formed at or close to the earth’s surface o At the lower end of the spectrum of rock-formation temperatures are the sedimentary rocks. o Sediments are loose, unconsolidated accumulations of mineral or rock particles that have been transported by wind, water, or ice, or shifted under the influence of gravity, and redeposited  When sediments are compacted or cemented together into a solid, cohesive mass, they become sedimentary rocks  The set of processes by which sediments are transformed into rock is collectively described as lithification (rock is more compact and dense) o Clastic sedimentary rocks: are formed from the products of the mechanical breakup of other rocks (sandstone, conglomerate, shale) o Chemical sedimentary rocks form not from mechanical breakup and transport of fragments, but from crystals formed by precipitation or growth from solution (limestone, rock salt)  A sequence of sedimentary rocks may include layers of organic sediments, carbon- rich remains of living organisms; coalis an example o A metamorphic rock is one that has formed from another, preexisting rock that was subjected to heat and/or pressure.  When hot magma formed at depth rises to shallower levels in the crust, it heats the adjacent, cooler rocks, and they may be metamorphosed; this is contact metamorphism  Metamorphism can also result from the stresses and heating to which rocks are subject during mountainbuilding or plate-tectonic movement.  Such metamorphism on a large scale, not localized around a magma body, is regional metamorphism Rock Cycle Chapter 3: Plate Tectonics o Continental drift: a single super continent had split apart and drifted apart to their present position o Tectonics is the study of large scale movement and deformation of the earth’s outer layers. o Plate tectonics relates such deformation to the existence and movement of rigid “plates” over a weaker, more plastic layer in the earth’s upper mantle. o An object is under stress when force is being applied to it. o The stress may be compressive, tending to squeeze or compress the object o Tensile: tending to pull the object apart o Shearing stress: tends to cause the different parts of the object to move in different directions across a plane or slide past one another o Strain: the deformation resulting from stress o Elastic deformation: the amount of deformation is proportional to the stress applied o Plastic deformation: relatively small added stress yield large strains and are permanent \ o Confining pressure is that uniform pressure which surrounds a rock at depth o Lithosphere: the earth’s crust and upper most mantle (elastic) o Asthenosphere: layer below the lithosphere. (plastic) o Curie temperature: the temperature below which it remains magnetic, above which it loses its magnetic properties o Seafloor spreading: the moving apart of lithospheric plates at the ocean ridges Types of Plate Boundaries o Diverging plate boundary: lithospheric plates move apart. A great deal of volcanic activity occurs because the release of pressure causing melting in the asthenosphere. o Converging plate boundary: plates move toward each other. One plate of oceanic lithosphere may be pushed under the other plate and descend into the asthenosphere. (subduction zone) o Subduction zones are very active places. Ocean-ocean convergence result a line of volcanic islands. o Transform fault: the opposite sides of a transform fault belong to two different plates, and these are moving in opposite directions. As the plates scrap past each other, earthquakes occur along these faults. o Hot spots: isolated areas of volcanic activity usually not associated with plate boundaries o One possible driving force for plate tectonics is slow convection in the asthenosphere; another is gravity pulling cold, dense lithosphere down into the asthenosphere, dragging the asthenosphere along. o They play an integral part in the rock cycle—building continents to weather into sediments, carrying rock and sediment into the warm mantle to be melted into magma that rises to create new igneous rock and metamorphoses the lithosphere through which it rises, subjecting rocks to the stress of collision— assisting in the making of new rocks from old. Chapter 4: Earthquakes o Earthquakes, in general, represent a release of built-up stress in the lithosphere o They occur along faults: planar breaks in rock along which there is displacement of one side relative to the other o Creep: when movement along faults occurs gradually and relatively smoothly (fault displacement without earthquake activity) o Earthquake: When the stress at last exceeds the rupture strength of the rock, a sudden movement occurs to release the stress o Elastic rebound: the rocks snap back elastically to their previous dimensions o Focus: the point on a fault at which the first movement break occurs during an earthquake o Epicenter: the point on the earth’s surface directly above the focus o A strike-slip fault , then, is one along which the displacement is parallel to the strike (horizontal) o A dip-slip fault is one in which the displacement is vertical, up or down in the direction of dip. o thrust faults , which are just reverse faults with relatively shallowly dipping fault planes o The deep-focus earthquakes are concentrated in subduction zones, where elastic lithosphere is pushed deep into the mantle. o When an earthquake occurs, it releases the stored-up energy in seismic waves that travel away from the focus o Body waves (P waves and S waves) travel through the interior of the earth o P waves: compressional waves o S waves: shear waves, involving a side-to-side motion of molecules o Surface waves: they cause rocks and soil to be displaced in such a way that the ground surface ripples or undulates o Waves travel faster through rocks than do S waves o Intensity is a measure of the earthquake’s effects on humans and on surface features o Liquefaction: When wet soil is shaken by an earthquake, the soil particle may be jarred apart, allowing water to seep in between them, greatly reducing the friction between soil particles that gives the soil strength, and causing the ground to become somewhat like quicksand. o dormant, sections of otherwise-active fault zones are called seismic gaps o earthquake cycle that would occur along a (non-creeping) fault segment: a period of stress buildup, sudden fault rupture in a major earthquake, followed by a brief interval of aftershocks reflecting minor lithospheric adjustments, then another extended period of stress buildup o fluid injection might be used along locked sections of major faults to allow the release of built-up stress Chapter 5: Volcanoes o Magma are typically generated in one of three plate-tectonic settings: 1. at divergent plate bound-aries, both ocean ridges and continental rift zones 2. over subduc-tion zones 3. at “hot spots,” isolated areas of volcanic activity that are not associated with current plate boundaries. o The major compositional variables among magmas are the proportions of silica (SiO2), iron, and magnesium o The silica-poor mafic lavas are characteristically “thin,” or low in viscosity, so they flow very easily o The more felsic (silica-rich) lavas are more viscous, thicker and stiffer, and flow very sluggishly o Rhyolite: the volcanic equivalent of granite o Andesite: intermediate in composition between the mafic basalt and felsic rhyolite o fissure eruption ,the eruption of magma out of a crack in the lithosphere, rather than from a single pipe or vent o Shield volcano: is very fl at and low in relation to its diameter and large in areal extent o The bits of violently erupted volcanic material are described collectively as pyroclastics o The cinders may pile up into a very symmetric cone-shaped heap known as a cinder cone o Volcanoes built up in this layer-cake fashion are called stratovolcanoes ,or, alternatively, composite volcanoes ,because they are built up of layers of more than one kind of material o Volcanic ash and water can combine to create a fast-moving volcanic mudflow called a lahar o a deadly, denser-than-air mixture of hot gases and fine ash that forms a hot pyroclastic flow (hot and can rush down the slope of the volcano) o volcanoes emit a variety of gases: carbon dioxide, carbon monoxide, sulfur gases, and HCl. o phreatic eruption: large quantities of seawater may seep down into the rock, come close to the hot magma below, turn to steam, and blow up the volcano like an overheated steam boiler o A volcano is generally considered active if it has erupted within recent history. o When the volcano has not erupted recently but is fresh-looking and not too eroded or worn down, it is regarded as dormant : inactive for the present but with the potential to become active again. o Historically, a volcano that has no recent eruptive history and appears very much eroded has been considered extinct , or very unlikely to erupt again. o Volcanic Explosivity Index(VEI) has been developed as a way to characterize the relative sizes of explosive eruptions o A calderais an enlarged volcanic crater, which may be formed either by an explosion enlarging an existing crater or by collapse of a volcano after a magma chamber within has emptied Chapter 6: Streams and Flooding o The hydrosphere includes all the water at and near the surface of the earth o The main processes of the hydrologic cycle involve evaporation into and precipitation out of the atmosphere. Precipitaion onto land can reevaporate (directly from the ground surface or indirectly through plants by evapotranspiration), infiltrate into the ground, or run off over the ground surface. o A stream is any body of flowing water confined within a channel o The region from which a stream draws water is its drainage basin o Discharge: the volume of water fl owing past a given point (or, more precisely, through a given cross section) in a specified length of time. Discharge is the product of channel cross section (area) times average stream velocity o Material of intermediate size may be carried in short hops along the stream bed by a process called saltation o The suspended load consists of material that is light or fine enough to be moved along suspended in the stream, supported by the fl owing water o some substances may be completely dissolved in the water, to make up the stream’s dissolved load. o Load: The total quantity of material that a stream transports o Stream capacity is a measure of the total load of material a stream can move o The steepness of the stream channel is called its gradient .  It is calculated as the difference in elevation between two points along a stream, divided by the horizontal distance between the along the stream channel (the water’s fl ow path) o base level: the lowest elevation to which the stream can erode downward o If velocity decreases along the length of the stream profile, then so will the coarseness of sediments deposited o Once a meander forms, it tends to enlarge and also to shift downstream.  It is eroded on the outside and downstream side ofthe meander, the cut bank , where the water flows somewhat faster  point bars , consisting of sediment deposited on the insides of meanders, build out the banks in those parts of the channel  braided stream may develop a complex pattern of many channels that divide and rejoin, shifting across a broad expanse of sediment o floodplain: the area into which the stream spills over during floods o The cutoff meanders are called oxbows o When rain falls or snow melts, some of the water sinks into the ground ( infiltration ) o The steeper the terrain, the more readily water runs off over the surface and the less it tends to sink into the soil o A stream is at flood stage when stream stage exceeds bank height  The stream is said to crest when the maximum stage is reached  Floods that affect only small, localized areas (or streams draining small basins) are sometimes called upstream floods  Flash floods are a variety of upstream fl ood, characterized by especially rapid rise of stream stage. They can occur anywhere that surface runoff is rapid, large in volume, and funneled into a relatively restricted area o Floods that affect large stream systems and large drainage basins are called downstream floods o Fluctuations in stream stage or discharge over time can be plotted on a hydrograph o Retention ponds: These ponds are large basins that trap some of the surface runoff, keeping it from fl owing immediately into the stream o Levees: raised banks along a stream channel  However, confining the water to the channel, rather than allowing it to flow out into the fl oodplain, effectively shunts the water downstream faster during high-discharge events, thereby increasing fl ood risks downstream. o Excess water is held behind a dam in the reservoir formed upstream and may then be released at a controlled rate that does not overwhelm the capacity of the channel beyond Chapter 7: Coastal Zones and Processes o One factor that influences the geometry of a coastline is plate tectonics
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