GLG Test 3

The eruption that occurred on Mount St. Helens was triggered by:

- A huge landslide caused a lateral blast that knocked down trees and buildings. -A landslide removed rocks and released pressure on the magma.

What is NOT a way a volcano's history indicates the level of hazard it poses to nearby population centers?

- Age of the oldest volcanic layer present

relationship between stream velocity and sediment load?

- As velocity increases, so does the streams capacity to carry a larger load

Ash layers from the three most recent caldera-forming eruptions at Yellowstone stretch -

- Canada to Mexico

What are ways a volcano's history indicates the level of hazard it poses to nearby population centers?

- Length of time since last eruption -Avg time between eruptions -Abundance of felsic pyroclastic materials in its deposits

Which of the following are ways that viscosity affects gases in magma?

- Viscous magma prevents gas from escaping easily

A delta forms when

- a river slows and deposits sediment as it enters a lake or sea

What factor indicates a high risk for volcanic mudflows or lahars?

- a volcano w/ a thick covering of snow or ice

The most common volcanic rock found in lava flows on composite volcanoes is:

- andesite

Which signs of volcanic activity has recently occurred at Yellowstone?

- ground inflation -hydrothermal activity in the form of geysers / mud pots -earthquakes

Which of the following are NOT associated with a hurricane?

- high atmospheric pressure

What is properly called a flood?

- if water spreads out over the floodplain

What happens to water velocity downstream? It generally:

- increases

volcanic hazards made worse by being located along a river valley directly downhill from a volcano?

- lava flows -small pyroclastic flows -mudflows

Which of the following typically decreases downstream in a river?

- maximum sediment grain size

a Plinian eruption with an eruption column 9 kilometers high. What is the overall climatic effect of that ash cloud?

- regional warming

Which sign of volcanic activity has not recently occurred at Yellowstone?

- small ash eruptions

What does the Volcanic Explosivity Index (VEI) describe?

- the amount of material ejected and height of eruption column

What happens to a river as it flows through a delta and encounters the sea?

- the total sediment load carried by the river decreases

How does ash from Plinian eruptions affect the entire globe?

-Ash in the stratosphere reflects sunlight and causes global cooling.

Why are volcanic mudflows (lahars) common on composite volcanoes

-Because large amounts of rain and snowmelt mix w/ loose ash on steep slopes

Storm surge is at its highest height underneath of what part of a hurricane?

-Eye

What reaction commonly precede a volcanic eruption?

-Increased gas flow from a volcano -Steam eruptions from the volcanic crater -Increased heat flow from the volcano

What does it mean when the amount of SO2 emitted from the vent of a composite cone or caldera quickly decreases?

-The volcano has stopped degassing because of an obstruction at the vent -i.e. the gas is trapped in the magma

hazards associated with ash clouds and ash fall

-Volcanic weather -Jet engine failure -roof collapse -contamination of surface water

What is associated with a hurricane?

-a relatively calm area in the center of the storm -strong winds and heavy rain -mound of water pushed ahead of the storm

What typically happens when tributaries join the main river?

-channel size increases -water velocity increases -the amount of discharge increases -total sediment load increases

Eruptions on the islands of Santorini in Greece and Krakatau in Indonesia resulted in

-collapse of a huge caldera that caused part of an island to disappear beneath the sea -a huge ash column and pyroclastic flows -destructive waves that traveled across the sea

What happens to the erosive power of a stream as velocity increases?

-erosion increases

What types of rocks would be common in a composite volcano?

-felsic and intermediate lava flows -pyroclastic rocks from an eruption column -pyroclastic rocks from pyroclastic flows -rocks with fragments formed by landslides and mudflows

What is commonly associated with tributaries?

-rapids when the tributary joins the main river -delivery of sediment to the main river -an increase in the discharge in the main river

What is urbanization

-replacing farms or natural land with buildings

Which of the following accompanies urbanization

-runoff occurs more quickly and produces a higher peak flow

Which of the following is NOT a hazard associated with ash clouds and ash fall?

-structures catching on fire

Some scientists think that Yellowstone could cause a future disaster because (4)

-the area is part of a caldera -magma is still present at depth -past eruptions from Yellowstone carried ash over a huge area of western North America -land near Yellowstone is uplifting in some places and subsiding in others

Which of the following influences whether a flood occurs?

-the height of levees -the amount of discharge -urbanization -the width of the channel

What is a drainage divide?

A ridge or strip of high ground separating one drainage basin from another

Huge circular depressions from which volcanoes erupt are called:

Calderas

discharge

The amount of water flowing through a channel over a given amount of time

describe how flooding is caused by storm surge

The ocean rises up under the low pressure system and wind pushes the water on shore as the hurricane moves

f bubbles cannot escape easily from a magma, the resulting eruption is likely to:

be explosive

a volcanic hazard NOT made worse by being located along a river valley directly downhill from a volcano?

burial by falling ash

relatively large, symmetrical volcano contains interlayered lava flow, pyroclastic deposits, and volcanic mudflows. What kind of volcano is it?

composite

The force behind a river's flow is

gravity

4 ways to monitor volcanoes?

measuring: -seismic activity with seismic instruments -sulfur dioxide gas emissions -changes in heat flow from satellites -tilting on the flanks of a volcano

tectonic setting is interpreted to be the cause of volcanism at Yellowstone?

movement of North America over a mantle plume

volume of water flowing through a river per unit time is calculated by:

velocity x cross-sectional area of the river