EAPS 106 Exam 2

What is the process that makes subduction zone earthquakes cause tsunamis?

Uplift of the seafloor from elastic rebound during a large subduction zone

How tsunami and wind-blown waves differ

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.

How does a tsunami wave in deep water change when it hits shallow water?

In deep water, long wavelengths, low wave height, and great speed (jet)
Approaching shore, they slow which causes the back of the wave to catch up. Reduces wavelength, but increases wave height.

When do water waves typically break?

When the wave height is equal to water depth
Wave Height = Water Depth

What type of earthquakes will cause a tsunami?

strike-slip fault earthquakes

What type of earthquakes will NOT cause a tsunami?

earthquakes between the magnitude of 6.5-7.5

How many people have been killed by tsunamis in the past 1,000 years?

Several Hundred Thousands

What might it mean if you feel shaking near the shore?

Tsunami 20-40 min away

why does the sea level drop before a tsunami?

the ocean is being dragged out when the trough arrives before the crest.

Why is it dangerous to return to the shore after a tsunami wave?

Consists of 3-10 waves and 2nd or 3rd wave is largest

Why did so many people die around the Indian ocean during 2004 tsunami?

1961 Chilean earthquake made tsunamis all over

How does the DART tsunami early warning system work?

1. Pressure sensor on ocean floor measure water pressure
2. Measurements are sent by acoustic signal to a buoy on the surface
3.Buoy sends signal to satellite
4. Signal sent to early-warning stations on land
-can send 15 min after earthquake, including path and size

Which process has the potential to cause the largest tsunamis?

asteroid and volcanoes

How do the Hawaiian Islands generate tsunamis?

Underwater landslides

What will most likely cause a tsunami in the Atlantic ocean?

Underwater landslides

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

1958 Alaska tsunami, generated by an avalanche into Lituya Bay

What are the tectonic settings where the different types of volcanism are found?

1. Mid-ocean ridges
2. Subduction zones
3. Hot spots

Is the mantle a subsurface ocean of magma?

No

What process will cause already hot, but not yet melted rocks, to melt?

1. Increase temperature
2. Decrease pressure as rock rises
3. Add water to decrease melting temp

What causes hot rocks to melt at each of the tectonic settings where volcanoes are found?

- In subduction zone settings,
water pushed out from subduction plate lowers the melting temp of hot mantle above causing it to melt. (Hydration-induced melting)
- In mid-ocean ridge and hotspot settings,
hot unmelted mantle rises due to convection.
Once near the surface it melts due to lower pressure. (Decompression melting)

Why does hotspot volcanism lead to a chain of volcanoes?

1. Base of mantle is heated by outer core, causing hot/solid plume of mantle to rise
2. When plume head reaches shallow, it melts by depressurizing, causing volcanism
3. As plate moves across plume, volcanoes go extinct and new ones arise, creating a chain

What is viscosity a measure of?

measure of how easily a fluid flows

How do stratovolcanoes form?

Alternating layers of pyroclastic flows (explosive) and lava flows (effusive)

Which combinations of magma viscosity and gas content leads to effusive and explosive eruptions?

effusive: low gas and low viscosity
Explosive: high gas and high viscosity

What happens to dissolved gas when it rises near the surface?

The gas expands to form a vapor phase (bubbles) and stream

What are the four main types of eruptions and their relative explosiveness?

1. Hawaiian 6,500 ft
2. Strombolian
3. Vulcanian
4. Plinian 180,400

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

250,000

What are the basic characteristics of the various volcanic hazards and which one causes the most and least fatalities near and far from a volcano?

Least: lava, lightning, flood
Most fatal: Pyroclastic flow, indirect, and tsunamis

What are some basics of volcanic ash?

1. Volcanic glass from gas bubbles
2. Smaller than sand
3. Hard electrical conducting
4. Wet ash can destroy roof
5. 5 cm can kill crops

What is a pyroclastic flow?

A fast-moving avalanche of hot rock, ash and glass fragments

What is a lahar?

Mudflow avalanche of ash, soil, rock, and water. Can occur days or months later

Can volcanic eruptions be predicted?

yes, but never straightforward

What are harmonic tremors?

A continuous release of seismic energy typically associated with the underground movement of magma (long duration)

Why is Pompeii so interesting?

-2,00 people died
-buried under 30 ft of ash and lost from history for 1500 years
-ash preserved the dead

What was Pliny the Younger famous for?

-Description of Pompeii written by Pliny the Younger
-Plinian eruptions were named after him

What can a volcano look like before an eruption? What can it not look like?

-Pressure cannot build with lava at surface

What is the Volcano Explosivity Index (VEI) a measure of?

The volume of ash and other rock ejected

What is the relative size difference in size of eruptions at different VEI levels?

small 0-1, moderate 2-3, large 4-5, VERY large 6-7, SUPER 8

Why do geysers erupt but hot springs do not?

Geysers erupt because the water is trapped and becomes superheated until finally the pressure builds enough for it to break the seal.

How do we know Yellowstone is a hotspot?

By the trail of extinct volcanoes that lead up to it

How do calderas form?

Calderas form when the summit of a volcano collapses.

Have many large explosive eruptions occurred at Yellowstone in the last 2.1 million years?

3

How much of the US was covered by ash from Yellowstone's supereruptions?

Most of the West (stops at midwest) (missouri) 5,790 square miles with ash

How is the current size of the magma chamber under Yellowstone measured?

Seismic network

How do we monitor pressure changes in a magma chamber?

GPS on ground measure uplift (ground elevation)

What are the global consequences of large explosive volcanic eruptions?

-Global cooling
-SO2 reacts with oxygen and water vapor to create sulfuric acid droplets
-The ash and acid block the sun

What is the connection between the Tambora eruption and monsters?

1816 cold summer in Switzerland
Mary Shelley Frankenstein
John Polidori came up with the Vampyre, Stoker used to make Dracula

Why was the Toba eruption an important event in our species history?

Toba is a super-eruption lead to global cooling and almost wiped out humanity.

What are the global consequences of giant flood basalts?

-Might cause mass extinctions.
-Large amounts of greenhouse gases led to global warming and acid rain