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EAPS 106 > Midterm 2 > Flashcards

Midterm 2 Flashcards

1
Q

Why is it not sufficient to be a good swimmer to survive a tsunami?

A

Debris and the power of the current would make swimming near impossible

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2
Q

How do subduction zone earthquake cause tsunamis?

A

the elastic rebound from the overriding plate breaking free of the subducting plate causes an uplift in the seafloor causing a wave of water as water first rises and then falls

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3
Q

What direction does an island above a subducting plate move between earthquakes

A

The island subsides (sinks) as the overriding plate is drawn down by the locked plate interface

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4
Q

What is the magnitude of subduction zone earthquakes that cause tsunamis?

A

M9 or larger; normally ruptures 100s of miles of a fault

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5
Q

How are tsunami waves traveling through the deep ocean influenced by seafloor topography?

A

A subduction tsunami is initiated on the seafloor; thus, it involves the full depth of the ocean

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6
Q

How do tsunami waves differ from large wind-blown waves?

A

Tsunami waves carry a larger volume of water, have a much larger wavelength, and travel further inland

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7
Q

Can a slip on an underwater strike-slip fault cause a tsunami?

A

No, as strike-slip faults will not cause a change in the height of the seafloor

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8
Q

What happens to a tsunami wave’s speed and height as it approaches shore?

A

The wave slows down which reduces wavelength, causing an increase in height

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9
Q

What happens to the distance between tsunami wave crests as they approach the shore?

A

The distance between the crests become shorter

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10
Q

What does “tsunami” translate to?

A

Harbor wave; this is because sometimes fishermen would encounter no unusual waves out at sea, then find their harbor destroyed by a huge wave

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11
Q

What happens to a boat in the middle of the ocean when a tsunami wave passes underneath?

A

A boat would rise less than a meter over a period of 10s of minutes and not be aware that a tsunami passed underneath

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12
Q

When does a wave moving toward the shore typically break?

A

Tsunami waves break when wave height is about equal to the water depth

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13
Q

Why are inlets (natural harbors) a dangerous place to be when a tsunami hits?

A

Because the incoming water gets trapped and piles up

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14
Q

Can an earthquake on the San Andreas Fault cause a tsunami?

A

No, the San Andreas Fault is a strike-slip fault and mostly on land

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15
Q

Can tsunami waves be deadly even miles inland from shore?

A

Yes

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16
Q

What is the approximate number of people killed by tsunamis in the past 1000 years?

A

Several hundred thousand

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17
Q

Was the 2011 Japan tsunami an unprecedented event in Japan’s history?

A

No, Japan has a history of tsunamis going back centuries

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18
Q

What is a Japanese tsunami stone?

A

Stones along the coast of Japan warning residents to not build below them

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19
Q

How do we know that the northwest coast of the U.S. has experienced large tsunamis?

A

Buried sand deposits along the coast of the Pacific northwest

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20
Q

How long does it take for a tsunami to reach the coastline?

A

About 5-10 minutes

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21
Q

Why does the sea level dramatically drop before a tsunami hits?

A

The oscillating wave brings water from the shoreline into it as the amplitude gains in height

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22
Q

Why is it dangerous to return to the beach after a tsunami wave first arrives?

A

Tsunamis typically consist of multiple waves that hit the shore over the span of several hours

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23
Q

What is a tsunami seawall?

A

A concrete barrier built near the shoreline to stop tsunamis from reaching inland

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24
Q

How long does it take for a tsunami wave to cross the Pacific?

A

Almost 24 hours

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25
Q

Why was there a high death toll in the Indonesian tsunami of 2004?

A

Lack of education about tsunamis and a system to notify the public if a tsunami is suspected

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26
Q

How does the DART tsunami early warning system work?

A

The DART system detects water pressure changes on the seafloor

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27
Q

What process causes the largest tsunamis?

A

Asteroid impact, though an asteroid induced tsunami has never been observed

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28
Q

What process caused the largest tsunami run-up recorded in the past 100 years?

A

A landslide

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29
Q

How long does it take for a tsunami to travel from the Åkerneset cliffs to Geiranger?

A

About 10 minutes

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30
Q

What generally causes tsunamis at the Hawaiian Islands?

A

Underwater landslides on the largest island, the only current volcanically active one

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31
Q

What is most likely to cause a tsunami to hit the U.S. east coast?

A

Underwater landslides on the flanks of volcanoes like the Canary Islands, which have very steep underwater cliff faces

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32
Q

What was the cause of the tsunami the killed 36,000 people in Indonesia in 1883?

A

The volcanic eruption of Krakatoa

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33
Q

What are the vulnerabilities of Florida if a 10-km-diameter asteroid hit the Gulf of Mexico?

A

Everything as the impact would cause megatsunamis over 100m tall

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34
Q

What is the difference between the magma and lava?

A

Magma is melted rock beneath the surface of the earth, lava is melted rock extruded onto the surface of the earth

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35
Q

Is there an ocean of magma beneath the lithosphere?

A

No, most of the mantle is below its melting point

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36
Q

What is the temperature of the mantle compared to its melting temperature?

A

The temperature of the mantle is on a curve, most of which is lower than the melting point of rock

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37
Q

What processes promote the melting of hot rocks?

A
  1. An increase in temperature
  2. A decrease in pressure (depressurized melting)
  3. An addition of water to the mineralogy (hydration-induced melting)
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38
Q

What is the type of volcanism found far from plate boundaries?

A

Hot spots

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39
Q

What is the process that causes hot rocks to melt at subduction zones?

A

Hydration induced melting

40
Q

What does the ring of fire refer to?

A

Subduction zone volcanism that occurs where plates are subducted, causing a “Ring of Fire” around the Pacific Ocean

41
Q

Why are there fewer active volcanoes in the southwest U.S.?

A

There are no active subduction zones in the southwestern U.S.

42
Q

What process causes hot rocks to melt at hot spots?

A

Depressurized melting

43
Q

Where does the rising plume originate from at hot spots?

A

The base of the mantle

44
Q

Where does a hot spot plume melt

A

The base of the lithosphere

45
Q

Why do hot spots lead to a line of volcanoes?

A

When a tectonic plate moves over a hot spot, volcanoes initiate over the hot spot then go extinct as the volcano moves away from it, and a new volcano develops

46
Q

Where are hot spot tracks found?

A

All over the world

47
Q

What process causes hot rocks to melt at mid-ocean ridges?

A

Depressurised melting

48
Q

What is viscosity a measure of

A

Resistance of a fluid to flow

49
Q

What kind of volcano is produced by low viscosity lava?

A

Broad, shallow, sloped volcanoes

50
Q

Is the big island of Hawaii the tallest mountain on Earth?

A

Yes, Mauna Kea is the tallest mountain on Earth as measured from its base to its top

51
Q

How does a stratovolcano form?

A

Alternating layers of pyroclastic flows and high viscosity effusive lava flows

52
Q

What kind of volcano forms when tephra is thrown out of a volcanic vent?

A

Cinder cone volcanoes

53
Q

What is an effusive volcanic eruption?

A

Magma flowing up to the surface through a vent or crack without building up high pressure

54
Q

Why does pressure in magma build up as it rises toward the surface?

A

Magma contains dissolved gas in solution form. As magma moves up to the surface the pressure on it from overlying rocks decreases, this causes dissolved gas to expand to form gas bubbles

55
Q

What is volcanic ash?

A

Tiny grains of volcanic glass from magma sprayed into the air by gas pressure

56
Q

What is the combination of magma viscosity and gas content that leads to effusive eruptions?

A

Low viscosity, low pressure, and hotter temperatures

57
Q

What is the most powerful type of explosive eruption?

A

Plinian eruptions

58
Q

How many volcano-related deaths have occurred in the past 500 years?

A

More than 250,000

59
Q

What volcanic hazard leads to the least number of deaths?

A

Lava

60
Q

What volcanic hazard leads to the greatest number of deaths?

A

Pyroclastic flows

61
Q

Can volcanic flows be stopped by spraying water on them?

A

Sometimes

62
Q

Can volcanic flows be redirected?

A

Sometimes

63
Q

What are the characteristics of volcanic ash?

A

Hard, abrasive, corrosive, electrical conducting, and does not dissolve in water

64
Q

What are the characteristics of pumice?

A

More air bubbles than scoria
Less dense; floats on water
Light coloured
Used as scouring agent

65
Q

What is a pyroclastic flow?

A

A dense, destructive mass of very hot ash, lava fragments, and gases ejected explosively from a volcano and typically flowing downslope at up to 200 mph

66
Q

Can pyroclastic flows be redirected?

A

Sometimes

67
Q

Why are lahars dangerous?

A

Lahars are avalanches of ash, soil, rock, and water that can occur several days to months after an eruption. The flows can extend 10s of km and can reach 10m high

68
Q

What is the time frame for volcanic gases to make lakes very acidic?

A

Weeks to months

69
Q

What killed almost 2000 people in Cameroon in 1996?

A

A carbon dioxide gas cloud that descended from the volcanic lake Nyos

70
Q

What is a harmonic tremor?

A

A small, “rhythmic” earthquake that lasts for many minutes that occurs when magma moves underground

71
Q

Can volcanic eruptions be predicted a few days before they occur?

A

Sometimes as explosive volcanic eruptions are generally preceded by precursors associated with a build up of pressure;
-Gas release increases
-Rapid ground deformation
-Earthquake frequency increases
-Harmonic tremors

72
Q

Why is the destruction of Pompeii in 79 AD historically remarkable?

A

-16,000 people were killed
-An amazing description of the eruption was written by Pliny the Younger
-Pompeii was preserved by 80ft ash and dugout, including bodies

73
Q

What kind of volcano is Mount Vesuvius?

A

A stratovolcano formed by a subduction zone along the coast of Italy

74
Q

What volcanic process created Mount Vesuvius?

A

Subduction and hydration-induced melting

75
Q

How was Pompeii preserved for 2000 years?

A

How was Pompeii preserved for 2000 years?

76
Q

Of the bodies of Pompeii, what was preserved?

A

Only the volume and the bones

77
Q

Who was Pliny the Younger?

A

A roman lawyer, author, and magistrate. He wrote an account of the eruption of Mount Vesuvius and the destruction of Pompeii

78
Q

Who was Pliny the Elder?

A

Pliny the Younger’s uncle, a naturalist and commander of the Roman Navy in the Bay of Naples; died trying to rescue victims of the Vesuvius eruption

79
Q

Why is Yellowstone considered a hidden supervolcano?

A

Because there is no recognizable sources

80
Q

Why do geysers erupt but hot springs do not?

A

Hot springs are continuously replenished due to straight plumbing. Geysers erupt due to bends in plumbing that require a threshold pressure to be achieved before they erupt

81
Q

How do we know Yellowstone is a hot spot volcano?

A

Because it lies at the end of a trail of extinct volcanoes

82
Q

What is the Volcano Explosivity Index (VEI) rating based on?

A

The volume of ash and other rock ejected

83
Q

How do different VEI ratings compare to each other?

A

The ratings are on a logarithmic scale (VEI 7 is 10 times larger than VEI 6 and 100 times larger than VEI 5)

84
Q

What percentage of the U.S. was covered by ash from past Yellowstone supereruptions?

A

At least 50%

85
Q

How does a caldera form?

A

A large circular depression that forms when the surface collapses into an emptying magma chamber

86
Q

How many large eruptions has Yellowstone experienced in the past 2.1 million years?

A

3

87
Q

What is the evidence for Yellowstone’s very large eruptions?

A

Three calderas along with the measured ash fallout and the size of its pyroclastic flows

88
Q

How do volcanologists monitor Yellowstone?

A

Using a large seismic network to monitor seismic activity, using GPS to monitor ground deformation, and measuring changes in ground temperature

89
Q

How do we know the size of the current magma chamber under Yellowstone?

A

Yellowstone’s seismic network and robust seismicity; seismic imaging is used to infer Yellowstone’s substructure

90
Q

how do we monitor changes in pressure of a magma chamber?

A

Uplift of the ground, measured by GPS

91
Q

How do large explosive volcanic eruptions influence climate?

A

Explosive eruptions emit large amounts of sulfur dioxide which react with oxygen and water vapor in the atmosphere to create sulfuric acid droplets. These droplets block sunlight causing global cooling

92
Q

What volcanic eruption influenced Mary Shelley to come up with Frankenstein?

A

The 1816 eruption of Mount Tambora

93
Q

Why is the Toba supereruption 74,000 years ago considered an important event?

A

The Toba supereruption caused 10 years cooling of 4°C, which may have triggered a 1000-year ice age

94
Q

What are giant flood basalts?

A

Very large volcanic flows that occur over a geologically short time (10s of thousands of years)

95
Q

What do giant flood basalts originate from?

A

Mantle plume heads when they first reach the surface then undergo depressurized melting

96
Q

How have giant flood basalts caused extinction events?

A

Large amounts of greenhouse gases led to global warming and acid rain

EAPS 106 (3 decks)

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