Midterm 2 GO125

What is elastic rebound theory?

After earthquake, all stress on the fault has been removed

What is the windows of opportunity theory?

If a fault only lasts long enough for half of the energy to be released, then the other half is stored.

What is a thrust fault?

Type of reverse fault that has a dip of 45 degrees or less.

What is a blind thrust fault?

thrust faults that do not reach the surface and are difficult to detect

What are normal fault earthquakes?

A dip slip fault in which the block above the fault has moved downward relative to the block below.

What are examples of normal fault earthquakes?

Pacific Northwest: Oregon, Washington, British Columbia.

What happened in Puget Sound in Washington in 1949 and 1965?

Earthquake near epicenter of 1949 earthquake, with a magnitude of 6.8.

what determines the size of the earthquake

Amount of offset

How can prehistoric earthquakes be dated?

Using radioactive carbon.

What are the different types of earthquake forecasts?

Quasi-periodic timing

Clustered movements

random movements

What is quasi-periodic timing?

Detectable with paleoseismology

What are clustered movements?

Can estimate when the next one might come.

What are random movements?

Inherently unpredictable

What are human triggered earthquakes?

Earthquakes triggered by human events

What are examples of human triggered earthquakes?

Disposal wells (Denver, Colorado and Ashtabula Township, Ohio)

Increases in oil and natural gas production

Dam earthquakes

Bomb blasts (Nevada)

Where do 3.5+ earthquakes mostly happen?

Alaska, California, Hawaii, Nevada.

Where are the western North America plate boundary zone earthquakes?

Owens Valley,

Pull apart region

Hebgen Lake,

Borah Peak

New Mexico,

What are examples of Intraplate earthquakes?

New Madrid MO

New England earthquakes

St. Lawrence river valley

Charleston, SC

What is the difference in wave propagation in eastern vs. western North America?

Young tectonically fractured rock of west coast impede wave propagation and cause wave energy to die out faster in older, more homogeneous rocks of central US.

What will soft sediments do in earthquakes?

It will amplify ground shaking

What is the Reelfoot Rift?

Ancient rift valley in Missouri, Arkansas, Tennessee, Kentucky, Illinois.

What is the connection between earthquakes and volcanos in Hawaii?

Movement of magma can cause earthquakes

What are harmonic tremors?

Earthquakes caused by the movement of magma in volcanos.

What two cities were buried by eruption of Mt. Vesuvius?

Pompeii and Herculaneum

Are people fearful of future volcanic events?

No

What determines what will make a volcano peaceful or explosive?

Variations in magma’s chemical composition, ability to flow, gas content, and volume.

__ percent of volcanism is associated with plate boundaries.

90

__ percent of volcanism is associated at spreading centers

80

__ percent of volcanism is association at subduction zones

10

The remaining __ percent of volcanism occurs above hot spots

10

What lowers the melting temperature of rock?

Water

are transform faults and continent continent collisions associated with volcanoes?

No.

Are oceanic volcanoes peaceful?

yes.

What is the behavior of subduction zone volcanoes?

Explosive and dangerous

Of the 92 elements, which two are the most abundant?

Oxygen and silicon

What are plutonic rocks?

Magma cools slowly and solidifies beneath the surface

What are volcanic rocks?

Magma erupts and cools quickly at the surface

What are the properties of magma with low viscosity?

High temps, less silicon and oxygen, less mineral crystals, low volatiles, less pressure.

What are the properties of magma with high viscosity?

Low temps, more silicon and oxygen, more mineral crystals, high volatile, high pressure

What is basaltic magma and where is it dominant?

Has highest temps and lowest silicon content so the lowest fluid flow. Most dominant at spreading centers

What is andesitic magma and where is it dominant?

Melted mantle at subduction zone rises through continental crust before reaching the surface incorporating continental high silicon rock as it rises.

What is rhyolitic magma and where is it dominant?

Lowest temps and highest silicon content so highest viscosity does not flow. most common when overriding lithosphere is continental rather than oceanic.

What is the most abundant dissolved gas in magmas?

Water

What magmas cause peaceful safe eruptions?

Basaltic magma.

What magmas cause violent dangerous eruptions?

rhyolitic magma

What are the types of eruptions at spreading centers?

Peaceful and abundant volcanism

What are the types of eruptions at subduction zones?

Violent eruptions

What are the three things causing rocks to melt?

Lowering pressure

Rising temperature

Increasing water content

What is the most common way to melt rock?

Lowering pressure

What are all five eruption styles?

Icelandic type: Low water content

Hawaiian type: Low viscosity

Strombolian: Moderate water content

Vulcanian: Moderate to high water content

Plinian: High water content

What is the difference b/w lava flows and pyroclastic debris?

Lava flows are molten rock from a volcano eruption. Pyroclastic flows are high-speed avalanches of ash, pumice, and rock from a volcano.

What is Pahoehoe?

Smooth ropy rock from highly liquid lava

What is Aa

Rough blocky rock from more viscous lava

What is pyroclastic debris

High water content, high viscosity magma

What is obsidian?

Volcanic glass forms when magma cools very fast

What is Pumice?

porous rock from cooled froth of magma and bubbles

What is a volcanic bomb?

A large mass of partically molten rock that cools when it leaves the volcano, coming down to hit the surface as a solid form

What are the three V’s of Volcanology?

Viscosity

Volatile

Volume

What are the properties of the three volcanologies?

Viscosity: May be Low or high due to temp variation

Volatile: Abundance may be low, meds, high due to water content

Volume: may be small, med, large.

What are the six volcanic landforms?

Shield volcanoes

Flood basalts

Scoria cones

Stratovolcanoes

Lava domes

Calderas

What type of eruptions are contributed with each of the six volcanic landforms?

Shield: Basaltic lava w/ low viscosity

Flood: Low viscosity/ large volume

scoria: med viscosity/med volatile/small volume

strato: High viscosity/high volatile/large volume

Domes: High viscosity/low volatile/small volume

Calderas: High viscosity/high volatiles/very large volume

What is the curtain of fire?

fissure vent on the east rift of Kilauea. Low cone with high fountains of magma

What is a flood basalt?

Very large volume and is the largest volcanic event on earth. may cause mass extinction

What was the cause of Vesuvius?

Caused by subduction, characterized with Vulcanian-type eruption, followed by plinian-type eruption

What is Lahar?

steam blown up into atmosphere during eruption can cool/condense/fall as rain that picks up loose volcanic ash then flows downslope.

What is the difference between a crater and a caldera?

Craters are formed by outward explosion of rocks and calderas are formed by inward collapse of volcano.

What is Crater Lake, Oregon?

Large volume of magma erupted to leave void beneath surface in which water filled into crater.

How does a caldera form?

Large volcanic depressions formed by downward roof collapse into partially emptied magma reservoirs.

What are the different settings of Calderas?

Summit of Shield volcanoes (Mauna Loa)

Summit of stratovolcanoes (Crater Lake)

Giant continental caldera (Yellowstone)

What are the characteristics of volcanism at spreading centers?

Basaltic lava, ocean spreading centers. Mostly peaceful fissure eruptions.

What is an example of a spreading center volcano?

Iceland

What are the characteristics of volcanism at subduction zones?

Where largest earthquakes occur, also where big eruptions occur. Usually heavily populated.

What is the cause of the cascade range?

Subduction of Juan De Fuca plate under Pacific Northwest

What are examples of a cascade range?

Mt St. Helen’s, Mt. Shasta

What are the issues in Mt. Shasta, CA?

It’s an active volcano with 11 eruptions in 3400 years.

What are the top five volcanic causes of death?

Pyroclastic flow

Tsunami

Lahar

Indirect (famine)

Gas

What are four ways of generating pyroclastic flows?

Dome collapse

Overspilling crater rim

Direct blast

Eruption column. Collapse

What are the causes of dome collapse?

steady magma supply and unstable topography makes chunks of lava dome frequently break off creating pyroclastic flow

An over spilling crater is filled with what?

Hot water or magma

What is a tsunami as it relates to volcanos?

Tsunami generated by a volcano, usually when a caldera collapses

What are Lahars as it relates to volcanoes?

Primary events during volcanic eruptions or occur later due to addition of water such as from heavy rain or melting glacial ice.

What are examples of Lahars relating to volcanoes?

Nevado Del Ruiz, Colombia 1985

What is a concern in Mt. rainier, WA?

It has great height

Extensive glacial cap

Frequent earthquakes

Active hot water spring systems

What was the cause of famine in Laki, Iceland Fissure eruption of 1783?

Haze of SO2 and fluorine killed Icelandic livestock and this caused 20% of the human population died of famine

What was Death at Ashfall, Nebraska?

Eruption at Yellowstone blanketed Nebraska with a thick layer of volcanic ash killing animals and people because of the particles inhaled

What happened at Lake Nyos in Cameroon, Africa?

there was a gigantic plume of carbon dioxide that killed animals but not plants

What is VEI?

Semi quantitative estimate of magnitude of volcanic eruption using volume erupted and eruption-column height

Does energy of eruption correlate to number of fatalities?

No

What did the Toba eruption almost do?

Drive humans in extinction

What is the volcano warning success story in Mr. Pinatubo Philippines, 1991?

There was an intense monitoring program done by the US and Philippines saved nearly one million people in the danger zone of the largest eruption in the 20th century

What are the signs of impending eruption?

seismic waves

Ground deformation

Gas measurements

What are the four US states with the most powerful eruptions?

Alaska, California, Hawaii, Washington

What are the top five volcano observations in the US?

Alaska, cascades (Washington-Oregon), Hawaiian, California, Nebraska

What was the Indian Ocean Tsunami?

Caused by the third largest earthquake, on subduction zone of Indian-Australian plate under Asian plate. Estimated 245 thousand deaths.

What is a tsunami?

very rapidly rising tide rushing inland

What does the Japanese word tsunami mean?

Harbor waves

What happens to a tsunami when they ever harbor or other narrow space?

They can reach a greater height

Why is Tidal wave not an appropriate term for tsunami?

Because they have nothing to do with the tides

Tsunamis are most often created by what?

earthquakes, usually vertical fault motions at subduction zones.

Where do earthquake caused tsunamis usually happen?

Pacific ocean