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Virginia Tech - GEOS 1034 - Class Notes - Week 7

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Virginia Tech - GEOS 1034 - Class Notes - Week 7

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background image Super volcanoes World's biggest and most deadly volcanic eruptions VEI: volcanic explosivity index Small- 0-1 Moderate- 2-3 Large 4-5 Mt. St. Helens § Very large- 6-7 Super - 8 Pompeii is studied tremendously Mt. Vesuvius- 79 AD (stratovolcano formed by a subduction zone) Most active volcanoes in the world § 2000 people were killed § Has erupted more than 6 times in the last 25000 years § A description of the eruption was written down by Pliny the Younger Pompeii was buried under 20ft of ash and lost from history for 1500 years,  but was preserved by ash and dug out Ash preserved the forms of the dead Rediscovered in 1599 and over past 250 years the ash has been removed to  reveal ancient society On second day of eruption, super hot toxic clouds of gas and debris blasted  down the slopes of Vesuvius and overwhelmed Pompeii, killing everyone 
who had not left yet
Gas clouds didn't burn bodies § Bodies buried in time-hardened ash eventually decayed, leaving  hollow spaces § When found, these spaces were filled with plaster to form casts of  the victims at the moment of their death § Inspired many artists and writers Volcanic bombs Pyroclastic flow Plinian eruptions Named after Pliny the younger who wrote down the account of the  eruption of Mt. Vesuvius and the destruction of Pompeii Yellowstone: a hidden super volcano 3 extremely large eruptions in the past 2.1 million years, 280-2500x bigger  than 1980 Mt. St. Helens eruption Super eruptions are not the only global volcanic danger: giant flood basalts may  have been responsible for mass extinctions Lave flows with volumes 1000s of times those of ordinary eruptions May have resulted from plume heads reaching the surface Hotspot Volcanism Hot, buoyant mantle plumes rise from the core/mantle boundary Plumes melt when they get near the surface (decompression/depressurized  melting) The motion of the plates over the stationary hotspots leads to a chain of  volcanoes Ex. Hawaiian islands Yellowstone Hotspot Track Hawaiian hotspot track- age progressive, age of rocks increase as they get further  away from Hawaii Mantle plume model- plume carries the volcanoes away from the hotspot Most hotspot tracks are in the oceans Yellowstone & snake-river plain volcanism is an age progressive track of  volcanism The model only works if NA plate has been moving southward over a  mantle, unlikely Seismic tomography: x-ray of Earth's interior Can reveal structures in the mantle African super plume- major plume structure in Earth's mantle beneath  Africa (1/2 super plumes) Magma chamber has been imaged by measuring the change in speed of  seismic waves as they pass under the park Slow down- less dense hotter material § Speed up- more dense, cooler material § Plume is not evident in seismic tomography beneath Yellowstone Hot material at 410 depth but it's not a plume bc at the bottom there is a  depressed lower mantle transition zone Reversed subduction and the Yellowstone hotpot track, hot material rises  through 410 discontinuity Yellowstone geysers and hot spots Fueled by heat from an enormous reservoir of magma beneath Features Sinking cold water § Rising hot water § Hot spring nearby- if rises in linear fashion § Geyser- pressure builds up from nonlinear path § 3 calderas, indicating 3 large eruptions in the past 2.1 million years ago Hard to distinguish because of erosion and their size Very vast ashfall GPS measures surface displacement at Yellowstone Shows uplift  Calderas Large circular depression formed when a surface collapses into an emptied  magma chamber Much bigger than an eruption crater Crater lake in Oregon is a caldera that formed after Mt. Mazama (VEI 7) Calderas are evidence that major eruption has taken place, usually VEI 7 or 8 26,000 yrs ago in New Zealand from super eruption produced Lake Taupo Mantle transition zone: the transition between the upper and lower mantle Between the depths of 410km and 660 km Mantle transition zone is poorly resolved with seismic tomography Large discrepancies among seismic velocity models in the transition zone Hot, weak material in the mantle transition zone makes the top of the mantle  transition zone to depress and the bottom of the transition zone to rise Cold, strong material in the mantle transition zone makes the top of the mantle  transition zone rise and the bottom of the transition zone to depress Effects of Volcanoes Explosive eruptions emit large amounts of ash and SO2 SO2 reacts with oxygen and water vapor to create sulfuric acid droplets Sulfuric acid droplets following large explosive volcanic eruptions can cause  loner sustained global cooling than volcanic ash Pyroclastic flows and ash fallout cause starvation and disease Influences artists Toba Caldera supereruption in Sumatra 74,000 years ago, lead to global cooling  that almost wiped out humanity Observations from ice cores suggest ash caused a 6-10 yr cooling of 3-5  degrees, which may have triggered  Questions Why can't this be what Mt. Vesuvius looked like in the days leading up to the 79  AD explosive eruption Volcanoes only have craters after they erupt a. The lava outpouring is releasing pressure, so no pressure is building up b. The crater is too deep for lava to reach the surface c. The fire should be blue because of the intense heat of the lava d. 1. How do we know Yellowstone is not a hotspot volcano? From the size of its past eruptions a. Because it's located above an ancient subducted slab and not a hot spot b. Because it lies at the end of a trail of extinct volcanoes c. All of the above d. 2. Why might have giant flood basalts caused mass extinctions? Large amounts of ash blocked by the sun caused global warming a. Large amounts of greenhouse gases led to global warming and acid rain b. Lava flows were large enough to cover entire ecosystems c. All of the above d. 3. Review
Tsunamis
The most common means of generating a tsunami is elastic rebound during an  earthquake Tsunami waves can have similar wave height to large wind blown waves but  carry a much larger volume of water and travel much further inland Tsunami wave mechanics- close to land the troph arrives first which creates the  tsunami Tsunami waves (like all water waves) break when the wave height is equal to the  water depth Strike-slip fault doesn't generate tsunamis because there is NO vertical  movement What you should do Significant seismic shaking near the shore: 20-40 minutes before a tsunami hits: head to high ground § 1. Tide appears to go out very fast and far 5-10 mins before tsunami hits: get to high ground faster § 2. Massive white water heading toward you Seconds before tsunami hits: RUN and maybe get to higher floor  (choose building wisely) § 3. Tsunami consists of 3-10 waves and often after the 2nd or 3rd wave is the  largest, don't go back to shore until you know for sure another wave isn't 
coming
4. How many were available to assist those in danger of Sumatra tsunami in 2004?  Not many What would cause a tsunami on East Coast of US? Landslides What is runup? Runup is a measurement of the height of the water onshore observed above  a reference sea level. Largest tsunami run-up is from a landslide Volcanoes Less than 1% of crust is magma Melting can be caused by: Add water Raise temperature Decrease pressure Most volcanoes found near subduction zones at convergent plate boundaries Week 7 (10/1, 10/3, 10/5) Monday, October 1, 2018 12:20 PM
background image Super volcanoes World's biggest and most deadly volcanic eruptions VEI: volcanic explosivity index Small- 0-1 Moderate- 2-3 Large 4-5 Mt. St. Helens § Very large- 6-7 Super - 8 Pompeii is studied tremendously Mt. Vesuvius- 79 AD (stratovolcano formed by a subduction zone) Most active volcanoes in the world § 2000 people were killed § Has erupted more than 6 times in the last 25000 years § A description of the eruption was written down by Pliny the Younger Pompeii was buried under 20ft of ash and lost from history for 1500 years,  but was preserved by ash and dug out Ash preserved the forms of the dead Rediscovered in 1599 and over past 250 years the ash has been removed to  reveal ancient society On second day of eruption, super hot toxic clouds of gas and debris blasted  down the slopes of Vesuvius and overwhelmed Pompeii, killing everyone 
who had not left yet
Gas clouds didn't burn bodies § Bodies buried in time-hardened ash eventually decayed, leaving  hollow spaces § When found, these spaces were filled with plaster to form casts of  the victims at the moment of their death § Inspired many artists and writers Volcanic bombs Pyroclastic flow Plinian eruptions Named after Pliny the younger who wrote down the account of the  eruption of Mt. Vesuvius and the destruction of Pompeii Yellowstone: a hidden super volcano 3 extremely large eruptions in the past 2.1 million years, 280-2500x bigger  than 1980 Mt. St. Helens eruption Super eruptions are not the only global volcanic danger: giant flood basalts may  have been responsible for mass extinctions Lave flows with volumes 1000s of times those of ordinary eruptions May have resulted from plume heads reaching the surface Hotspot Volcanism Hot, buoyant mantle plumes rise from the core/mantle boundary Plumes melt when they get near the surface (decompression/depressurized  melting) The motion of the plates over the stationary hotspots leads to a chain of  volcanoes Ex. Hawaiian islands Yellowstone Hotspot Track Hawaiian hotspot track- age progressive, age of rocks increase as they get further  away from Hawaii Mantle plume model- plume carries the volcanoes away from the hotspot Most hotspot tracks are in the oceans Yellowstone & snake-river plain volcanism is an age progressive track of  volcanism The model only works if NA plate has been moving southward over a  mantle, unlikely Seismic tomography: x-ray of Earth's interior Can reveal structures in the mantle African super plume- major plume structure in Earth's mantle beneath  Africa (1/2 super plumes) Magma chamber has been imaged by measuring the change in speed of  seismic waves as they pass under the park Slow down- less dense hotter material § Speed up- more dense, cooler material § Plume is not evident in seismic tomography beneath Yellowstone Hot material at 410 depth but it's not a plume bc at the bottom there is a  depressed lower mantle transition zone Reversed subduction and the Yellowstone hotpot track, hot material rises  through 410 discontinuity Yellowstone geysers and hot spots Fueled by heat from an enormous reservoir of magma beneath Features Sinking cold water § Rising hot water § Hot spring nearby- if rises in linear fashion § Geyser- pressure builds up from nonlinear path § 3 calderas, indicating 3 large eruptions in the past 2.1 million years ago Hard to distinguish because of erosion and their size Very vast ashfall GPS measures surface displacement at Yellowstone Shows uplift  Calderas Large circular depression formed when a surface collapses into an emptied  magma chamber Much bigger than an eruption crater Crater lake in Oregon is a caldera that formed after Mt. Mazama (VEI 7) Calderas are evidence that major eruption has taken place, usually VEI 7 or 8 26,000 yrs ago in New Zealand from super eruption produced Lake Taupo Mantle transition zone: the transition between the upper and lower mantle Between the depths of 410km and 660 km Mantle transition zone is poorly resolved with seismic tomography Large discrepancies among seismic velocity models in the transition zone Hot, weak material in the mantle transition zone makes the top of the mantle  transition zone to depress and the bottom of the transition zone to rise Cold, strong material in the mantle transition zone makes the top of the mantle  transition zone rise and the bottom of the transition zone to depress Effects of Volcanoes Explosive eruptions emit large amounts of ash and SO2 SO2 reacts with oxygen and water vapor to create sulfuric acid droplets Sulfuric acid droplets following large explosive volcanic eruptions can cause  loner sustained global cooling than volcanic ash Pyroclastic flows and ash fallout cause starvation and disease Influences artists Toba Caldera supereruption in Sumatra 74,000 years ago, lead to global cooling  that almost wiped out humanity Observations from ice cores suggest ash caused a 6-10 yr cooling of 3-5  degrees, which may have triggered  Questions Why can't this be what Mt. Vesuvius looked like in the days leading up to the 79  AD explosive eruption Volcanoes only have craters after they erupt a. The lava outpouring is releasing pressure, so no pressure is building up b. The crater is too deep for lava to reach the surface c. The fire should be blue because of the intense heat of the lava d. 1. How do we know Yellowstone is not a hotspot volcano? From the size of its past eruptions a. Because it's located above an ancient subducted slab and not a hot spot b. Because it lies at the end of a trail of extinct volcanoes c. All of the above d. 2. Why might have giant flood basalts caused mass extinctions? Large amounts of ash blocked by the sun caused global warming a. Large amounts of greenhouse gases led to global warming and acid rain b. Lava flows were large enough to cover entire ecosystems c. All of the above d. 3. Review
Tsunamis
The most common means of generating a tsunami is elastic rebound during an  earthquake Tsunami waves can have similar wave height to large wind blown waves but  carry a much larger volume of water and travel much further inland Tsunami wave mechanics- close to land the troph arrives first which creates the  tsunami Tsunami waves (like all water waves) break when the wave height is equal to the  water depth Strike-slip fault doesn't generate tsunamis because there is NO vertical  movement What you should do Significant seismic shaking near the shore: 20-40 minutes before a tsunami hits: head to high ground § 1. Tide appears to go out very fast and far 5-10 mins before tsunami hits: get to high ground faster § 2. Massive white water heading toward you Seconds before tsunami hits: RUN and maybe get to higher floor  (choose building wisely) § 3. Tsunami consists of 3-10 waves and often after the 2nd or 3rd wave is the  largest, don't go back to shore until you know for sure another wave isn't 
coming
4. How many were available to assist those in danger of Sumatra tsunami in 2004?  Not many What would cause a tsunami on East Coast of US? Landslides What is runup? Runup is a measurement of the height of the water onshore observed above  a reference sea level. Largest tsunami run-up is from a landslide Volcanoes Less than 1% of crust is magma Melting can be caused by: Add water Raise temperature Decrease pressure Most volcanoes found near subduction zones at convergent plate boundaries Week 7 (10/1, 10/3, 10/5) Monday, October 1, 2018 12:20 PM

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School: Virginia Polytechnic Institute and State University
Department: Geoscience
Course: Geoscience
Professor: Ying Zhou
Term: Fall 2018
Tags:
Name: Week 7 Notes
Description: These notes cover super volcanoes and hotspots
Uploaded: 10/09/2018
5 Pages 57 Views 45 Unlocks
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