EESA05 - Environmental Hazards - Lec 5 - near verbatim.docx

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Environmental Science
Mandy Meriano

EESA05 Lecture 5: Volcanoes and Mass Wasting PY Date: Oct 16, 2012 Question Time: Consider a dangerous volcano such as Vesuvius, near Napoli, or Mt. Shasta in California. What are likely to be the main difficulties in evacuating ppl from a large eruption? Slide 2: Volcanic Forms – Caldera  The most famous caldera in N. America is Yellowstone o Allowed the mapping of the eruptions in geological history  This truly massive volcano is a hot spot volcano that erupts about every 600,000 yrs o Last eruption was very large and if it erupts again it could put out around 1000 cubic meters of volcanic ash, pyroclastic material etc;  Its history is recorded in extensive ash deposits which cover over half of the US  One of the main impacts of such a large volcanic event = volcanic ash deposit = near the site will be around 100 m thick and will be around 1m thick even if you move 100 km away from source o Significant in terms of pop’n, infrastructure, agriculture – devastating event when it happens  Resurgent calderas – they haven’t erupted in a long time but we know that deep in the reservoir there’s magma residing there and the caldera at the Earth’s surface is kind of bulging up with the pressure and the heat of the magma that’s in there o They’re not extinct; still alive and working Slide 3: Magma Rises Animation  Mantle = orange part – continental crust residing on top  Magma starting to come up thru mantle – lower density magma that rises up  Mafic magma rises thru denser mantle – highly basaltic composition magma with low silica content – would expect non-explosive eruption with this type of magma – it’s mafic and basaltic and doesn’t have a lot of silica – runnier magma, less viscosity – expect it to rise to surface and be extrusive  High gas content and high water vapor content, really hot, really runny – find weakness in rock, fractures and finds its way up  Magma rises b/c it’s density is lesser than the mantle density will come out of rock  Shield volcano  Ex) higher silica content makes the magma more viscous o Higher viscosity = harder for it to flow o Felsic magma composition – it rises through continental crust but b/c of its viscosity, it’s going to have hard to reaching surface, will find reservoir and stay there – if there’s no heat around it, it’ll cool very slowly and we end up with larger minerals (lower melting point it’ll come out when the magma is cooling; the last thing that usually comes out is quartz- end of magma cooling) o If for instance some felsic magma does happen to find it’s way up to the surface – stratovolcano (composite volcano) 1 EESA05 Lecture 5: Volcanoes and Mass Wasting PY Date: Oct 16, 2012 Slide 4: Volcanic Hazards – Outline  Hazards o Lava flows o Ash falls o Famine o Tsunami o Gas emission  Benefits o Soil fertility o Hot springs and geothermal power  Mitigation and Prediction of Volcanic Hazards Slide 6: Volcanic Hazards – Lava flows  People in Hawaii have to deal with troublesome lava flows, but the flow is seldom life- threatening  Lava flows destroy whatever they overrun  2 diff types of lava: o Pahoehoe  Has ropy, smooth surface lava = cools and hardens – becomes like shell over hot lava  This flows faster than Aa lava; but not quite fast o Aa  Really choppy and blocky – not smooth  Can’t go very fast o What is the difference btn the 2 lava types?  They’re both basaltic compositions, why is one runny and the other isn’t?  Temperature of the lava  Pahoehoe is hotter than Aa? And has higher gas (water vapor) content?  The composition of magma is impt in terms of what we see on the surface but so is the temp and so is the water content  The greater the water content of magma, the hotter it will be  Can bury or burn things as its flowing Slide 7: Volcanic Hazards – Lava flows  One of the most celebrated volcanic eruptions was the fissure eruption on Heimaey in 1973 o Island off the south coast of Iceland – 4000 ppl o Harbor town so a lot of the economy depends on the harbor o When the lava started to flow, wanted to protect the harbor  Destroyed homes and as the lava was getting closer to the harbor, they were alarmed b/c didn’t want the lava to destroy the harbor also – so they started 2 EESA05 Lecture 5: Volcanoes and Mass Wasting PY Date: Oct 16, 2012 pumping seawater and sprayed the flow and actually managed to deflect the flow of lava away from the harbor  When you have basaltic composition that’s not very explosive, that’s just moving along with the slope – this is one way to manage any hazards if there’s access to a lot of water  The eruption was `peaceful`but released 230 million m3 of lava, which flowed partially into the town of Vestmannaeyja, threatening to fill in the harbour Slide 8: Volcanic Hazards – Lava Flows  The residents fought the lava flows by bulldozing diversions out of pyroclastic debris  They saved the harbour by spraying seawater on the advancing lava flow, to cool it and stop it Slide 9: Volcanic Hazards – Ash Falls  Ash falls can cover vast areas of landscape o Ex) Mt. St. Helens  The ash is like very fine powder. It is known to choke aircraft engines and is a hazard for generating lahars  Ash falls can interfere with a lot of things o Health o Vegetation covered by ash o Aircraft engines will be stopped if there’s significant o Not an immediate danger, may happen later down the road – if enough deposit of ash and there’s rainfall – can get lahar o Immediate and long-term effects of hazards are also present  Volcanic material: o 1) Ash  Less than 2mm in diameter o 2) Lapilli  2-64mm o 3) Block/Bombs  >64  Can hit the ground when soft – ‘cow dung’  Makes cool shapes like teardrops  Pretty dense, not porous o There’s a difference in size of the volcanic material o Scoria/cinder  Can be compared to lapilli but in this case, the magma was a lot more frothy = more holes/vesicular – can end up with something very light = pumice  Scoria/cinder has air holes whereas lapilli doesn’t; if there’s a lot of holes = get pumice  This porosity is pretty diff; when put pumice in water = floats 3 EESA05 Lecture 5: Volcanoes and Mass Wasting PY Date: Oct 16, 2012  When take ash (which has much lower density than pumice), the ash will sink in water but pumice won’t sink  Ash also has pores but these pores are connected so when you put in water, water goes into pores and it sinks  Pumice has pores but these pores are NOT connected and filled with air- so when put in water they float; if the pores were connected, they would fill with water and sink  This is how you can have something with lower density (ash) sink while having something of higher density (pumice) float  Mt. Pinatubo ash Slide 10: Volcanic Hazards – Famine  In 1259, a volcanic eruption spread ash over the Earth. Ice cores in both Greenland and Antarctica recorded this blast as a peak in sulfuric acid, the source of which is known to have been between 10 and 20 degrees North of the equator o Ash and high amounts of sulfuric acid – so cold the following year – frost in June – ppl famine – looked for food in diff areas o Major challenge around the world in terms of agri and food  The volcano is believed to be El Chichon, which appears to have erupted around the year 900 AD and again around 1250  At about 900 A.D., the Maya civilization began a sudden and mysterious decline. Mayan artifacts have been discovered buried by ash from El Chichon and it is possible that the volcano may have led to the decline of Mayan civilization. o Change in global climate affected agri output  A very large eruption would have brought on a drier climate, which may have combined with the ash fall to have a disastrous impact on agriculture  Famines are the largest indirect hazards whereas ashfalls, burning etc; are direct hazards Slide 11: Volcanic Hazards – Famine  Massive volcanic eruptions can cause climate change – not only locally, but on a global scale  The eruption of Tambora in Indonesia in 1815 resulted in poor weather throughout 1816 `the year without a summer` - 80,000 ppl died  Snow fell in every month in New England, and harvests were so poor that a mass migration started over the Appalachians into the Mdiwast  Poor harvests and increased disease occurred in many parts of the world o Disease after changing climate so much; pests to thrive and cause more damage Slide 12: Volcanic Hazards – Tsunami  The eruption of Krakatau volcano in 1883 generated a large tsunami  This tsunami devastated much of the coastline around the Indian Ocean (just as the Boxing Day EQ off Sumatra – this was the last tsunami prior to the event of 2004) 4 EESA05 Lecture 5: Volcanoes and Mass Wasting PY Date: Oct 16, 2012 o Compared to 2004 tsunami in terms of devastation  Tsunami waves were also felt in the Pacific Ocean as far away as the west coast of North America, and were even detected in England  These volcanic tsunamis generated by landslides – create wave o Ex) have submarine volcano – major landslide – can create major wave o Ex) can have landslide on land that falls into the water really quickly – cause tsunami  These deep water waves can travel really fast – up to 800km/hr – travel really far – when it hits the coast, the height is enormous  Mitigation of tsunami hazards is pretty hard unless you have really good warning system – the waves travel real fast and very little time to warn ppl – esp danger for coast pop’n Slide 13: Volcanic Hazards – Gas Emissions  Gases emitted during volcanic eruptions may be toxic and or corrosive  The most common gas is H2O and the most common hazardous gas is CO2 which is neither toxic or corrosive, but which can cause suffocation by driving away O2 o CO2 heavier than air and if there’s high *CO2+ then can hug the ground and move really fast along the slopes – can suffocate animals and ppl in it’s path  Trees may be killed by the excess CO2 o This area is the site of an ancient caldera  Magma lies close to the surface and up to 150 t per day of CO2 has caused numerous tree kills – Cameroon (west Africa)  Gases that come out of solution – can replace the air that’s around them Slide 14: Volcanic Hazards – Gas Emissions  Lake Nyos sits atop a volcano in Cameroon. CO2 gas leaks from the volcano but the waters at the bottom of the lake store it all in solution  In 1986, the stored CO2 flooded out of the lake  About 100 million cubic meters of gas flowed down the hillside suffocating 1700 ppl and innumerable cattle in low-lying areas Slide 15: Volcanic Hazards – Gas Emissions  A lot of gas can dissolve in the water and won’t go anywhere – it’s not until it reaches that high pressure that it becomes like coke bottle and the gas comes out o If have lake sitting on top of caldera – it holds the gases down but once the pressure reaches threshold, then it comes out o Try to manage this by releasing these gases with other management systems – put vertical pipes to allow the gases that are accumulating deep within the lake to come out once in a while o If done in managed way, then the concentration of the gases won’t reach an unsafe amt  Mitigation of this hazard is being carried out by reducing the CO2 content of the lakes  A suspended pipe draws CO2 saturated water from the depths of the lake 5 EESA05 Lecture 5: Volcanoes and Mass Wasting PY Date: Oct 16, 2012 o The fountain is caused by the expansion of CO2 gas as the pressure drops Slide 16: Volcanic Hazards – Gas Emission  Kivu Lake, at the boundary of Rwanda and the Democratic Republic of Congo, is rich in dissolved methane o Hashed line = boundaries between plates – margins; red triangles = convergent; arrows = divergent boundaries o Red sea, river Jordan, region of the rift  Red sea will one day become an ocean b/c opening  Rift continues down eastern Africa and Lake Kivu is sitting at the boundary of the rift  What’s nice about the rift is that you can see little lakes and rivers that follow the rift  Have volcanoes along the rift and will have some volcanic activity below lakes o Methane = released and is dissolved in lake water o X-axis = [] of dissolved CO2 and methane – concentration increases deeper in lake  Several (possibly active) volcanoes lie on the lake floor, creating an explosive hazard  Again, have same hazard associated with this; if not managed, can accumulate and once it reaches certain capacity = comes out  Lake full of methane – natural gas – can get the gas out and sell to other African countries – what Congo wants to do – can improve the economy of the country Slide 17: Volcanic Hazards – Gas Emissions  Photo shows volcano just north of the lake – erupted in 2002 o May have directly threatened the lake and any source of activity in lake  Recent fissure eruptions (January 2002) at Nyiragongo directly threaten the lake and suggest possible activity within the lake o The rivers are going along the fissure o Divergent movement along the divergent boundary o Eventually E.Africa will come off  The eruption occurred due to tectonic separation (rifting) of the East African plate away from the African plate  The amount of methane dissolves in Kivu Lake is approximately 65 km3 - resource Slide 18: Benefits of Volcanoes – Soil Fertility  Fresh volcanic soils are rich in minerals, making them both exceptionally fertile and providing additional health benefits in the foods grown on the soils – lush, crops  The combo of soil fertility and the additional health benefits have always attracted ppl to live near volcanoes Slide 19: Benefits of Volcanoes – Hot Springs 6 EESA05 Lecture 5: Volcanoes and Mass Wasting PY Date: Oct 16, 2012  Get hot springs anywhere there’s some sort of geothermal activity – don’t necessarily have to have hot springs everywhere there are volcanoes – have to have some geothermal heat, have to have geothermal heat to heat up the water as it moves thru the rocks o In some places where there aren’t volcanoes can still have hot springs b/c there’s enough geothermal heat to heat up the water  Near-surface magma means heat o Groundwater in the vicinity of an active magma chamber will be heated, occasionally to steam and driven off  a hot spring is a body of water that is at least 5C warmer than the average annual air temp in its area  a geyser is a hot spring that discharges water intermittently as the result of the water being heated to steam o old faithful in Yellowstone occurs after certain period of time – water and steam  hot springs in terms of volcanoes  diagram: o how geyser works o there’s a channel and there’ water which heats up o the magma here is hot and can build really steep temperature gradient as the water gets heated as it gets closer and closer to the source of heat o at the same time, towards the surface, the little passages are narrower – water is heating up and near the top there’s surface and ground water there as well  heat convection doesn’t work really well b/c of these narrow passageways; can get down thru hole and cool everything down  have greater density water that’s colder stops the water in the channels AND the water closer to the heat is getting hotter and hotter  when it becomes super heated, it’s above boiling but it’s still liquid not gas  pressure is building up b/c the water is blocking it at the top of the channel  eventually, the pressure can’t be held in anymore and as the pressure moves up from the high pressure to low pressure area – it pushes out the water or whatever was blocking it – water and steam come out  If see only steam coming out (NO water)  fumerols  Geysers = water AND steam come out  b/c the water that comes out is high in minerals – precipitated mineral material around opening = mound  fumerols look like little chimneys with steam coming out Slide 20: Benefits of Volcanoes – Geysers  For a geyser to form, there must be a source of water, a source of heat, and the underground `plumbing system` must ordinarily restrict water flow from the surface  The restriction allows pressure to rise so that the water remains liquid until the pressure is sufficient to overcome the overlying pressure 7 EESA05 Lecture 5: Volcanoes and Mass Wasting PY Date: Oct 16, 2012 Slide 21: Hot water and Geothermal Power  Another benefit of volcano b/c so much heat associated – capture that heat and use it to make energy o Use heat to move turbine which will generate electrical NRG  Geothermal heat – in Canada  A naturally occurring system of heating water is more than just a geological curiosity – it can be used to generate power  The source of water is usually rain. This water can seep thru fractures towards the active magma chamber  After being heated, the water returns to the surface as steam or hot water  Once the water rises to the surface, it may be used to generate power by driving a turbine  Geothermal heat = renewable resource? o The way to actually get the heat is by injecting water. What if you take so much heat out that it actually gets cold? Would it still be renewable? o Inject water into a well, the other well takes the steam up and the steam is what turns the turbine – NRG o If you remove heat faster than how fast the heat can produce a change in temperature, then it will cool off – useless for NRG production o Geothermal heat is not entirely renewable like hydro/wind; can actually run out of it if not managed properly o Iceland uses geothermal heat with strict rules for how the heat is taken out and how much taken o It can be renewable if managed properly Slide 22: Hot water and Geothermal Power  Depending on conditions, the power plant may use steam emanating from the gound to turn the turbine, or if the water is still liquid and under pressure, it can be `flashed` to steam by employing a low-pressure flash tank  Some units employ heat-exchange units which convert water to steam by transferring the heat to cooler surface water, especially where the heated water is heavily contaminated with metals  Injection well and extraction well diagram: o Capture steam to make NRG  Sometimes, when you start injecting a lot of water in regions of geothermal heat – can actually cause EQs o Sometimes inject recycled unclean water – which isn’t good Slide 23: Benefits of Volcanoes – Beauty  The old caldera at Yellowstone National Park is responsible for the attractions at the Park, including prismatic springs  Colors: o Made by organisms that have been fried in harsh enviro – algae, chemotrophs etc; 8 EESA05 Lecture 5: Volcanoes and Mass Wasting PY Date: Oct 16, 2012  Another benefit of volcano – minerals, diamonds (found in kimberlites – S.Africa, Russia, Canada – large diamonds) o Old volcanos = diamonds  Volcanic Ash – toothpaste may contain this; mixed in cement b/c doesn’t react well with water (falls apart); mix cement with lime rock, resistant to water erosion – volcanic ash improves this slurry cement – get strength  Volcanic rocks break up – stones for buildings Slide 24: Other Uses for Volcanoes  The volcanic cone is being used as a reservoir  Cinder/scoria that’s being used as reservoir in photo and the city below it uses this water Slide 25: Mitigation and Prediction of Volcanic Hazards  Most volcanic hazards can`t be mitigated after the eruption has begun (the only exception being lava flows)  Mitigation before an eruption can be done by assessing a region for its potential volcanic hazards and creating a hazard-zone map, which indicates the type and degree of risk in particular areas  Such maps are useful for urban planning Slide 26: Prediction of Volcanic Hazards The main precursor that signal and impending volcanic eruption are:
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