question

Why are most active volcanoes associated with plate tectonic boundaries?

answer

spreading or sinking plates interact at plate boundaries with other materials to produce magma

question

Viscosity of a magma is controlled by

answer

temperature and silicon content of the magma

question

The shape of shield volcanoes is a function of

answer

lava viscosity

question

Why do composite volcanoes consist of alternating lava and pyroclastic layers?

answer

composite cones are created by a mixture of explosive activity and lava flows

question

Mid-ocean ridge volcanism produces what type of volcanic rock?

answer

basalt

question

Composite cones typically are associated with what type of plate tectonic feature?

answer

subduction zone

question

What is the principal difference between craters and calderas?

answer

calderas are much larger depressions created by collapse of the upper portions of the volcano

question

Why were the citizens of Heimaey, Iceland, successful in stopping the lava flow that threatened their harbor?

answer

they had a ready supply of water with which to chill the lava

question

What is one reason that ash fall is such a significant hazard?

answer

the weight of the ash can cause structural damage to buildings

question

A lahar is produced when

answer

ash and other pyroclastic ejecta become saturated with water

question

Hundreds of residents near a dormant volcano at Lake Nyos died when

answer

a dense cloud of volcanic gas was released

question

The number of fatalities from the Mt. Pinatubo eruption was relatively low because

answer

the eruption was predicted successfully, and the area was evacuated

question

Seismic activity under serves as a tool of volcanic forecasting because

answer

moving magma causes earthquakes

question

Why is the geologic history of a volcano important in hazard prediction?

answer

the geologic history reveals the frequency and style of eruptions

question

Why is topographic monitoring sometimes useful in forecasting a volcanic eruption?

answer

a volcano sometimes swells as lava moves into the edifice

question

Viscosity is a primary control on the nature of volcanic activity

answer

True

question

Composite volcanoes are typically associated with subduction zones.

answer

True

question

Lahars are usually produced by saturation of thick volcanic ash.

answer

True

question

A shield volcano is typically andesitic in composition.

answer

False

question

Composite volcanoes consist almost completely of lava flows.

answer

False

question

Volcanic domes form on oceanic plates above hotspots.

answer

False

question

Caldera eruptions are very common features of subduction zones.

answer

False

question

Lava flows are the most dangerous of the primary volcanic hazards.

answer

False

question

The 1980 eruption of Mt. St. Helens produced large lava flows that filled the nearby river valleys.

answer

False

question

Volcanic gas emissions are important because they tell geologists how flammable the gases in the magma are likely to be.

answer

False

question

The eruption of Mt. __________ in 1991 killed several tens of people with pyroclastic flows.

answer

Unzen

question

Shield volcanoes typically consist of the rock type ____________.

answer

basalt

question

Volcanic domes typically consist of the rock type _____________.

answer

rhyolite

question

___________ __________ are small volcanoes formed from tephra accumulation near a volcanic vent.

answer

cinder cones

question

The Hawaiian islands were formed volcanism associated with a _______ ___________.

answer

hot spot

question

_____________ eruptions are among the most violent and largest known.

answer

Caldera

question

_____________ ___________ are dangerous, hot masses of ash and gas that travel down the flanks of a volcano.

answer

Ash flows

question

_____________ ___________ is a volcanic gas associated with acid rain and vog.

answer

Sulfur dioxide

question

The May 18, 1980 eruption of Mt. St. Helens began with a massive ___________.

answer

landslide

question

________________ is the primary human adjustment to volcanic activity.

answer

Evacuation

question

Why did extensive flooding occur upstream of St. Louis during the 1993 Mississippi River flood?

answer

floodwalls protecting St. Louis caused a bottleneck in the river's flow

question

The portion of rainfall that flows off the land and directly into a river is called

answer

runoff

question

What is river base level?

answer

the lowest level to which a river may erode

question

The suspended load of most rivers consists mostly of

answer

silt and clay

question

If a stream channel is of constant width and depth, how must increased discharge be accommodated?

answer

increased velocity

question

The Ventura Beach RV Resort was flooded because

answer

it was constructed in an unrecognized distributary channel that became active

question

The total load of sediment that a river carries in a given period of time is called

answer

capacity

question

Why might logging of a drainage basin change the slope of the river?

answer

increased sediment load causes the river to steepen its gradient to transport more sediment

question

What type of river channel is characterized by multiple channels and gravel bars?

answer

braided

question

How do point bars and cut banks differ from one another in a stream system?

answer

cut banks are sites of erosion, while point bars are sites of deposition

question

Which type of flood is typically caused by intense rainfall of short duration?

answer

upstream flood

question

What is the best description of the "10-year flood"?

answer

a flood that has a 10% chance of occurring each year

question

The degree of urbanization consists of

answer

percentage of impervious cover and the percentage of area served by storm sewers

question

In what way can structural control of floods actually increase flood damage?

answer

by encouraging development on the floodplain

question

Why is flood hazard mapping considered an important step in floodplain management?

answer

flood hazard mapping guides appropriate development in the floodplain

question

The floodplain is usually considered as a distinct system with respect to the river system.

answer

False

question

The bed load is the dominant portion of the total load for most rivers.

answer

False

question

Braided channels are typically characterized by fine-grained bed load.

answer

False

question

The 100-year flood is the flood that occurred exactly 100 years ago.

answer

False

question

Urbanization generally increases the lag time between the peak of rainfall and the peak of the resulting flood.

answer

False

question

The base level of a stream is typically sea level.

answer

True

question

For the same amount of discharge, a narrow, shallow channel will have a higher water velocity than will a wide, deep channel.

answer

True

question

A faster-moving stream has greater competence than a slow-moving stream.

answer

True

question

Downstream floods typically cover larger areas than do upstream floods.

answer

True

question

The principal objective of channelization is to control floods.

answer

True

question

The region drained by a single river or river system is the ____________ _____________.

answer

drainage basin

question

The total load of a river is dominated by the ________________ load.

answer

suspended

question

The continuity equation pertains to the accommodation of ____________ by a stream channel.

answer

discharge

question

Streams generally maintain a _______________ _________________ between the sediment transported and the sediment delivered to the stream.

answer

dynamic equilibrium

question

______________ are shallow portions of a meandering stream, in which the water is typically fast-moving at low flows.

answer

Riffles

question

The _________________ __________________ is the period of time in which a flood of given magnitude is expected.

answer

recurrence interval

question

__________________ changes many characteristics of floods in smaller streams.

answer

Urbanization

question

Protection of banks by planting trees and other vegetation is a form of ______________ _____________.

answer

channel restoration

question

The objective of __________ ____________ is to maximize beneficial use of the floodplain while minimizing flood damage and the cost of flood protection.

answer

floodplain regulation

question

Following Hurricane Floyd in 1999, residents in one part of the state of _____________ ____________ were relocated from a badly impacted floodplain.

answer

North Carolina

question

A comprehensive term for any type of downslope movement of Earth materials is

answer

mass wasting

question

What strategy stabilized the Portuguese Bend landslide?

answer

water drainage

question

In Yosemite National Park, strong bedrock influences the formation of what types of hillslopes?

answer

free face and talus

question

How do slumps and translational slides differ?

answer

slumps are rotational, while translational slides are planar

question

The safety factor for landslides is

answer

the ratio of resisting to driving forces

question

Why are landslides more common on steep slopes?

answer

slope angle determines the relative magnitude of driving forces

question

Vegetation influences landslides in part by

answer

anchoring the slope materials

question

Why might the infiltration of water deep into a slide mass increase landslide hazards?

answer

the water increases the pore water pressure, effectively lifting the slide mass from stable ground beneath

question

How did geology influence the Vaiont Dam disaster?

answer

the geology in the adjacent hillslopes was dominated by weak rocks

question

How does road construction associated with timber harvesting contribute to landslide hazards?

answer

the roads alter the movement of surface water and groundwater

question

What aspect of hillside development has contributed to the frequency of landslides in southern California?

answer

grading of hillslopes to create pads for home construction

question

On what information is a landslide hazard map based?

answer

geology and inventory of past landslides

question

Why is drainage control sometimes an effective method of landslide control?

answer

it reduces the amount of water in the hillslope materials

question

How might the 1983 Thistle landslide have been prevented?

answer

examination of landslide history and installation of drains

question

Why does withdrawal of fluids sometimes lead to subsidence?

answer

the fluid pressure provides partial support for the overlying rock mass

question

Hillslopes typically are static systems.

answer

False

question

Slumps and debris flows tend to occur separately in time and space.

answer

False

question

A safety factor of 1 implies that driving forces are 10 times greater than resisting forces.

answer

False

question

The expense of preventing landslides is usually too great for the prevention strategies to be feasible.

answer

False

question

Hillslopes in weaker rocks tend to be more gently sloped.

answer

True

question

Debris avalanches tend to occur on steep slopes.

answer

True

question

Climate influences landslides by determining the vegetation present on a slope.

answer

True

question

Erosion of the base of a slope may increase landslide hazards.

answer

True

question

Grading of slopes can either increase or decrease landslide hazards.

answer

True

question

Sinkholes often result from water table fluctuations.

answer

True

question

All slope movements fall under the term _________ _____________.

answer

mass wasting

question

_____________ is the downslope movement of a coherent block of Earth material.

answer

Sliding

question

The lower portion of a slump typically evolves into a ____________.

answer

flow

question

The ratio of resisting to driving forces is called the ______________ ______________.

answer

safety factor

question

The noncohesive downslope movement of saturated Earth materials is called an _______________.

answer

earthflow

question

The spontaneous liquefaction of clay-rich sediment is called _____________ ___________.

answer

quick clay

question

The Thistle landslide, in the state of _____________, was one of the most expensive landslides in U.S. history.

answer

Utah

question

One of the most effective methods of stopping an active slide is _____________ ___________.

answer

water drainage

question

Snow avalanches tend to move down tracks called ___________.

answer

chutes

question

______________ are caused by the collapse of caverns.

answer

Sinkholes

Geol 2001 Exam 2 – Flashcards

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