Exam 2 Study Guide
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EAPS 106, Geosciences in the Cinema
Exam 2 Study Guide
Know the following:
Unit 4 - Tsunamis
1. Why it is not sufficient to be a good swimmer to survive a tsunami.
Being a good swimmer will not help if you are crushed by a house
2. The process associated with subduction zone earthquakes that causes a tsunami to be generated.
A tsunami is a wave caused by the displacement of a large volume of water, most often by subduction zone earthquakes
3. The direction an island above a subducting plate moves between earthquakes.
An island above a subduction zone subsides (sinks) as the overriding plate is drawn down by the locked plate interface. During an earthquake, the overriding plate experiences elastic rebound, causing the island and water above to suddenly rise.
4. The magnitude a subduction zone earthquake has to be to generate a large tsunami.
Earthquake generated tsunami are generally associated with a M9 or larger earthquake that ruptures 100s of miles of a fault, leading to big tsunami waves hitting 100s of miles of coastline.
5. That tsunami waves traveling through the deep ocean are influenced by seafloor topography.
Because a subduction zone tsunami is initiated on the seafloor, it involves the full depth of the ocean. Thus, tsunami waves are influenced by seafloor topography (called bathymetry), which complicates wave propagation.
6. That slip on an underwater strike-slip faults cannot cause a significant tsunami.
Strike-slip faults will not cause a change in the height of the seafloor; thus, they do not displace water and will not generate a tsunami.
7. How tsunami waves differ from large wind-blown waves.
Tsunami waves can have similar heights to large wind-blown waves, but carry a much larger volume of water, have a much longer wavelength (distance from crest to crest), and travel much further inland.
8. What happens to a tsunami wave speed and height as it approaches the shore.
In deep water tsunami waves have long wavelengths, low wave heights. As waves approach the
shore they slow down, which causes the back of the waves to catch up to the front, reducing
wavelength, but increasing wave height.
9. What happens to the distance between tsunami wave crests as they approach the shore.
The distance between tsunami wave crests decreases as they approach the shore. This is because
the wavelength of a tsunami decreases as the water depth decreases.
10. What “tsunami” translates to in Japanese.
Harbor wave
11. What happens to a boat in the middle of the ocean when a tsunami wave passes underneath.
A boat in the middle of the ocean would rise less than a meter over a period of 10s of minutes
and thus not even know that a large tsunami passed underneath.
12. When a wave moving toward shore typically breaks.
Tsunami waves (like wind blown waves) break when the wave height is about equal to the water depth.
13. Why inlets (natural harbors) are particularly dangerous places when a tsunami hits.
Inlets (natural harbors) are particularly dangerous places when a tsunami hits because the incoming
water becomes trapped and piles up.
14. That an earthquake on the San Andreas Fault cannot cause a tsunami.
The San Andreas is a strike-slip fault and thus cannot generate a significant tsunami.
15. That tsunami waves can be extremely deadly even many miles inland from the shore.
True
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16. The approximate number of people killed by tsunamis in the past 1000 years.
Several hundred thousand people have been killed by tsunamis — but today this is potentially one of the most avoidable natural hazards
17. That the 2011 Japan tsunami was not unprecedented in Japan’s history.
True
18. What a Japanese tsunami l is.
Dozens of Tsunami Stones along the coast of Japan warn residents not to build below them.
19. How we know that the northwest coast of the U.S. has experienced large tsunamis.
Buried sand deposits along the coast of the Pacific northwest reveal a history of large tsunamis
20. The time it takes from earthquake to a tsunami reaching the nearest coastline.
Significant seismic shaking near the shore: 20-40 minutes before a tsunami hits Head to high ground.
21. Why sea level drops dramatically before a tsunami arrives.
Tsunami waves are often preceded by coastal waters being dragged out when the trough arrives before the crest.
22. Why it is dangerous to return to the beach after a tsunami wave first arrives.
Tsunami consist of 3-10 waves, and often the 2nd or 3rd wave is the largest — don’t go back to
the shore until given the all clear or at least many hours have passed.
A combination of earthquake rupture complexity, rebound off the near shore, and the effects of seafloor bathymetry cause multiple tsunami waves.
23. What a tsunami seawall is.
Japan has built seawalls near the shoreline to keep tsunami waters from reaching inland.
24. The length of time it takes a tsunami wave to cross the Pacific Ocean.
7 hours.
25. Why there was a high death toll in the Indonesian tsunami of 2004 around the Indian Ocean.
These people could have been saved through education about tsunamis and a system to notify
the public if a tsunami is suspected – all doable
26. How the DART tsunami early warning system works.
Pressure sensor on the seafloor.
27. The process that can cause the largest tsunamis.
Any process that displaces a large volume of water.
28. The process that caused the largest tsunami run-up recorded in the past 100 years.
Landslide
29. The time it takes for a tsunami to travel from the Åkerneset cliffs to Geiranger.
10 minutes.
30. What generally causes tsunamis generated at the Hawaiian Islands.
Underwater landslides
31. The mostly likely cause of a tsunami to hit the U.S. east coast.
the Americas are vulnerable to tsunamis generated by underwater landslides on the flanks of volcanoes
like the Canary Islands, which have very steep underwater cliff faces
32. The cause of the tsunami that killed 36,000 people in Indonesia in 1883.
The 1883 the volcanic eruption of Krakatoa caused a tsunami that killed 36,000 people in Indonesia as
the volcano is surrounded by a lot of shoreline. Original size of Krakatoa prior to the eruption.
33. The vulnerabilities of Florida if a 10-km-diameter asteroid hit the Gulf of Mexico.
You would not survive.
Unit 5 - Volcanoes
34. The difference between magma and lava.
Magma is transported to the surface where it flows out as lava or explodes as ash and pyroclastic flows.
35. That there is no ocean of magma beneath the lithosphere.
Tectonic plates do not float over an ocean of molten rock.
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36. The temperature of the mantle compared to its melting temperature.
Most of the mantle is below its melting temperature. Magma (melted rock) only occurs in very
specific places and comprises only a very small percentage of the mantle.
37. The processes which will promote the melting of hot rocks.
1. Increase temperature: While this could work to melt rocks, there are few processes in the crust
that will cause rocks to heat up, so this is not a common way to induce volcanism.
2. Decrease pressure (called depressurized melting): This reduces the melting temperature of rocks, which experience a decrease in pressure if they rise closer to the surface, thus enabling already hot rocks to melt.
3. Add water to the mineralogy (called hydration-induced melting). This breaks up long silica chains, which reduces the rock’s melting temperature and thus can cause already hot rocks to melt.
38. The type of volcanism found far from plate boundaries.
Hotspot volcanism.
39. The process that causes hot rocks to melt at subduction zones.
Hydration induced melting
40. What the Ring of Fire refers to.
Subduction zone volcanism occurs everywhere plates are subducted, causing a “Ring of Fire” around the Pacific Ocean.
41. Why there are fewer active volcanoes in the southwestern US.
Because there is no active subduction zone in the southwestern US, there are fewer active volcanoes compared to the northwestern US.
42. The process that causes hot rocks to melt at hot spots.
Decompression Melting
Hot spot volcanism begins when the base of the mantle is heated by the outer core, causing a hot (but still solid), buoyant plume of mantle to rise. When the hot spot plume head reaches the base of the lithosphere, it begins to melt by depressurized melting, causing massive volcanism.
43. Where the rising plume originates from at hot spots.
Base of mantle is heated by outer core.
44. Where a hot spot plume melts.
When it reaches the base of the lithosphere.
45. Why hot spots lead to a line of volcanoes.
As hotspot is stationary but as a tectonic plate moves over it, the volcano that is created at the hotspot is carried with the plate.
46. Where hot spot tracks found.
Hotspot tracks are found all over the world.
47. The process that causes hot rocks to melt at mid-ocean ridges.
Depressurized melting.
48. What viscosity is a measure of.
A measure of how easily a fluid flows.
49. The kind of volcanos produced by low viscosity lava.
Broad shallow sloped volcanoes. High viscosity lave = narrow high sloped volcanoes.
50. That the big island of Hawaii is the tallest mountain on Earth.
Mauna kea. Is the tallest mountain on earth.
51. How a stratovolcano forms.
Stratovolcanoes are midsized volcanoes that form due to alternating layers of pyroclastic flows (debris from explosive eruptions) and high viscosity effusive lava flows.
52. The kind of volcano that forms when tephra is thrown out of a volcanic vent.
Very high viscosities lead to cinder cone volcanoes, small volcanoes built when tephra (air cooled lava fragments) are thrown out of a volcanic vent.
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53. What an effusive volcanic eruption is.
If magma can flow to the surface through a vent or crack without building up
high pressure, the result is an effusive lava flow.
54. Why pressure in magma builds up as it rises toward the surface.
At depth, magma contains dissolved gas (e.g., SO2) in solution form. As magma moves
up to the surface the pressure on it from overlying rocks decreases, which causes this
dissolved gas to expand to form gas bubbles.
Gas bubble take up a lot more volume than dissolved gas, causing pressure to build within
the magma.
55. What volcanic ash is.
Ash are the shards of the volcanic bubbles – broken glass!
56. The combination of magma viscosity and gas content that leads to effusive eruptions.
Low gas content, and low viscosity.
57. The most powerful type of explosive eruption.
Plinian eruption.
58. About how many volcano-related deaths have occurred in the past 500 years.
more than 250,000.
59. The hazard near a volcano that leads to the least number of deaths.
Lava.
60. The hazard near a volcano that leads to the greatest number of deaths.
Pyroclastic flows.
61. That volcanic flows can sometimes be stopped by spraying water on them.
sometimes
62. That volcanic flows can sometime be redirected.
sometimes
63. Characteristics of volcanic ash.
Shards of volcanic glass left over from magma gas bubbles.
• Smaller than sand grains
• Hard, abrasive, corrosive, electrical conducting, and does not dissolve in water
• Not fluffy like ash from wood or your BBQ
• 15 cm of wet ash can collapse a roof
• 5 cm can kill crops
• 1 mm will close an airpor
64. Characteristics of pumice.
Explosive eruptions can throw out pumice, a volcanic rock with so many trapped gas bubbles that it floats.
65. What a pyroclastic flow is.
Pyroclastic flows are the heavier parts of an explosive eruption that run down the flank of a volcano at up to 200 mph, powered by expanding hot gases at over 1000 °C.
66. That pyroclastic flows can sometimes be directed away from inhabited areas.
Japan built channels to direct pyrotechnic flows away.
67. Why lahars are dangerous.
Lahars (mudflows) are avalanches of ash, soil, rock, and water that can occur days or even months after an eruption
68. The time frame for volcanic gases to make lakes very acidic.
Volcanoes can create lakes dense with sulfuric acid (from mixing sulfur, oxygen, and water), but the process takes many years to build up a strong acid content.
69. What killed almost 2000 people in Cameroon in 1986.
In 1986, a carbon dioxide gas cloud descended from the Cameroon volcanic Lake Nyos, suffocating 1,746 people and 3,500 livestock in the surrounding region.
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70. What a harmonic tremor is.
A small earthquake in terms of shaking that last a very long time (many minutes). It happens when magma moves underground.
13 minutes
71. That some volcanic eruptions can be predicted a few days before they occur.
Explosive volcanic eruptions are generally preceded by several precursors associated with a build up of pressure beneath the surface that enables eruptions to sometimes be predicted to within a few days:
• Gas release increases
• Rapid ground deformation (uplift or tilt)
• Earthquake frequency increases
• Harmonic Tremors
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Unit 6 – Volcano Catastrophes
72. Why the destruction of Pompeii in 79 AD is historically remarkable.
-16,000 people were killed (a lot, but not a record).
-An amazing description of the eruption was written down by Pliny the Younger.
-Pompeii was preserved by up to 80 ft ash and dugout, including preserved forms of the dead
73. The kind of volcano that Mount Vesuvius is.
Mount Vesuvius is a stratovolcano formed by a subduction zone along the coast of Italy
74. The volcanic process that created Mount Vesuvius.
Magma is generated by hydration induced melting.
75. How Pompeii was preserved for 2000 years.
-The 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 deaths.
76. That it was only the volume of the bodies (and bones) of the Pompeii that were preserved.
False
77. Who Pliny the Younger was.
Pliny the Younger was a lawyer, author, and magistrate of ancient Rome.
78. Who Pliny the Elder was.
He was raised by his uncle, Pliny the Elder, who was a naturalist and commander of the Roman Navy in the Bay of Naples, who died trying to rescue victims of the Mt. Vesuvius eruption.
79. Why Yellowstone is considered a hidden supervolcano.
Yellowstone National Park is considered a hidden supervolcano as there are no recognizable volcano.
80. Why geysers erupt while hot spring do not.
Hot springs are continuously replenished due to straight plumbing.
Geysers erupt periodically due to bends in the plumbing that require a threshold pressure to be achieved before the water/steam can erupt.
81. How we know Yellowstone is a hot spot volcano.
It lies at the end of a trail of extinct volcanoes.
82. What the Volcano Explosivity Index (VEI) rating is based on.
volume of ash and other rock ejected.
83. How different VEI ratings compare to each other. Small (0-1), moderate (2-3) 0.001-0.01, large (4-5) 0.1-1, very large (6-7)10-100, super (8) 1000.
84. The percent of the U.S. that was covered by ash from Yellowstone’s supereruptions.
50%
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85. How a caldera forms.
A caldera is a large circular depression formed when the surface collapses into an emptying magma chamber
86. How many very large eruptions has Yellowstone experienced in the past 2.1 million years.
3 87. The evidence for very large explosive eruptions at Yellowstone in the past.
One way that we know that Yellowstone has had two supereruptions in its past if from the estimated volume ofash expended by its last three eruptions
88. How volcanologists monitor Yellowstone.
Volcanologist monitor earthquake activity, ground deformation, and ground temperature in
Yellowstone so as to not be surprised by a sudden eruption
89. How we know the size of the current magma chamber under Yellowstone.
Yellowstone’s current magma chamber has been imaged by measuring the change in speed of seismic waves as they pass under the park
90. How we monitor changes in pressure of a magma chamber.
Measured by GPS station at yellowstone
91. How large explosive volcanic eruption influence climate.
Explosive eruptions also emit large amounts of sulfur dioxide (SO2) which reacts with oxygen and water vapor in the atmosphere to create sulfuric acid droplets.
The ash and sulfuric acid droplets block sunlight causing global cooling — the sulfuric acid droplets stay aloft longer than the ash and can thus be more detrimental to climate.
92. The volcanic eruption that influenced Mary Shelley to come up with Frankenstein.
1816 eruption of Mt. Tambora
93. Why the Toba supereruption 74,000 years ago is considered such an important event.
Global cooling due to the Toba supereruption has led to two theories regarding human evolution:
The first is that it potentially explains a bottleneck detected in human DNA that indicates that our population may have been reduced to under 10,000 mating pairs and maybe as few as 1000.
Cooling due to the supereruption might not have been distributed evenly but may have been concentrated in the northern Hemisphere; leading to the theory that this caused the decline of Neanderthals in Europe and the rise of humans from Africa.
94. What giant flood basalts are.
Giant flood basalts are incredibly large volcanic flows that occur over geologically short time-
periods (10s of thousand of years)
95. What giant flood basalts originate from.
Giant flood basalts result when mantle plume heads first reach the surface then melt due to depressurized melting.
96. How giant flood basalts caused extinction events.
Large amounts of greenhouse gases led to global warming and acid rain.
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