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Geology 100 Final

Terms in this set (67)

Which of the following processes generates most earthquakes?
movement along faults
When do rocks along a fault have the highest amount of stress and stored elastic strain?
right before an earthquake
If an area has shallow, intermediate, and deep earthquakes, what can you infer about the area?
--it is near a subduction zone
--the shallow earthquakes will be closer to the trench than deeper ones
--the depth pattern of earthquakes can be used to determine which way the slab is inclined
--this area has the potential for large earthquakes

ALL of the ABOVE
The characteristics of S-waves include:
Both b and c
--they can travel through liquids
--they shear rock from side to side or up and down
How do we determine the location of a recent earthquake?
use seismic records from three or more stations
Shaking during an earthquake can:
liquefy unconsolidated sediments, causing destruction of buildings on top of them
generate a tsunami
trigger landslides
cause rigid buildings to collapse
Correct!
ALL OF THE ABOVE
The diagram indicates that
P-waves arrive first, followed by S-waves
Sudden movement on a fault can cause a tsunami when:
the fault suddenly uplifts or downdrops the seafloor
Areas of high earthquake risk are mostly located:
near a boundary between tectonic plates
What is one way that we determine the depth to the base of the crust?
observing whether seismic waves that travel through the crust arrived after those that traveled through the mantle
What are some uses of magnetic reversals?
matching the patterns of reversals in a rock sequence to the magnetic time scale
studying magnetic stripes on the seafloor
calculating rates of seafloor spreading
ALL OF THE ABOVE
Why are the patterns showing the age of the seafloor symmetrical in the Atlantic Ocean but not the Pacific Ocean?
both a and b
-spreading along the Atlantic ridge added seafloor to plates on both sides
-subduction has consumed large areas of old oceanic crust in the Pacific
In the Atlantic Ocean, where is the oldest oceanic crust?
abyssal plain next to the continents
How do most oceanic islands and seamounts form?
they are constructed by volcanic eruptions that first occur under water
What processes can occur in front of or behind some island arcs?
a and b only:
trench rollback
back-arc rifting
What is a popular model for the formation of an atoll?
a volcanic island forms and subsides
If you were looking for graded beds, where would be a good place to start?
in a submarine fan
What has happened to the Pacific Ocean in the last 200 million years?
it became smaller as the Atlantic Ocean opened
What causes the seafloor to deepen across a typical continental slope?
BOTH a and b
thinning of continental crust because of normal faults
a transition from continental crust to oceanic crust
If you drilled into an oceanic plateau, what would you most likely find?
large amounts of basalt derived from melting in the mantle
What could cause a region to be higher in elevation than an average part of a continent?
less dense continental crust
Regional elevation can be increased by:
ALL of these
thrust faulting that thickens the crust
constructing huge volcanic fields
adding a significant amount of magma at depth
heating a region's crust and mantle
Which of the following is NOT a setting in which regional mountain belts form?
passive margin
Which of the following occurs when mountain belts are eroded?
a. erosion is accompanied by isostatic rebound
b. the continental crust becomes thinner
c. deep metamorphic and plutonic rocks can be uplifted to the surface
Correct!
d. all of the above
Which of the following regions below would you predict to have the thickest continental crust?
the Colorado Rockies and adjacent Great Plains
The basin shown in this figure was actively subsiding during the formation of unit:
C
Which of the following processes forms basins in an ocean-continent convergent boundary?
a and b only
a. flexing and bending of the oceanic plate into the subduction zone
b. flexing of the continent by weight of the thrust sheets
What can occur during the evolution of a hot spot?
formation of rifts that radiate out from the hot spot
What is the main reason why the age of oldest rocks can vary from one part of a continent to another?
parts of the continent have been added by the accretion of tectonic terranes
Which numbered area on this geologic map of North America would contain the oldest rocks exposed at the surface
3, continental shield of eastern Canada
Which of the following has the lowest potential for landslides?
florida
Which of the following does NOT physically loosen rocks on the surface?
water contracting as it freezes
Some rocks and minerals are not stable at the surface because they:
are exposed to water
formed in high-temperature environments
formed in high-pressure environments
are exposed to oxygen
ALL OF THE ABOVE
Where does the quartz in granite typically end up?
it ends up as sand in rivers, dunes, and beaches
How does the character of a rock influence weathering
rocks that are broken have more surface area and so weather faster
Which of the following factors does NOT control the stability of a slope?
the angle of repose for intact bedrock
Which of the following factors is typically NOT used to classify slope failures?
the climate in which the failure occurs
Which of the following factors favors movement of a rock slide?
a valley or other open space downslope from the rock slide
Which of the following slope failures is least likely to cause casualties?
creep
The amount of kinetic energy that stream water has varies directly with its velocity (i.e., higher velocity = higher energy content). When streams transport sediment, they are using some of that energy to do work. In general, how does energy needed to transport sediment change as sediment size increases?
Energy required for transport increases with sediment size.
The change in the elevation of two locations on a stream divided by the distance between those locations is the stream ____________.
the gradient
Low-gradient portions of streams often meander. Within a meander, where does sediment deposition occur?
On the point bar of the meander.
What requires more energy, erosion or transport of sediment?
erosion
If a stream channel has a cross-sectional area of 5 m^2 and the water flows through the channel with an average velocity of 3 m/sec, what is the stream's discharge? (Note - your units must be correct. m^2 is meters squared.)
15 m^3/sec
Using the diagram below, which of the following statement is true with a river velocity of 10 cm/s?
none of these
Which of the following could trigger flooding?
all of these
Urbanization
Snowmelt
Regional precipitation
irrigation
If a stream delivers sediment to the ocean faster than waves and currents can carry the sediment away, what forms?
delta
Which of the following materials probably has the highest porosity?
sediment composed only of rounded cobbles that rest directly on one another
This cross section shows the location of 5 wells and the water table (dashed line). Which well is most likely to be an artesian well?
Well E
Under what conditions is it possible for a material to have both high porosity and low permeability?
c. it is possible if the void spaces are not well connected
d. it is possible if the void spaces are small enough

e. both c and d
Which of the following materials would best to drill into for a good supply of groundwater?
shale and gravel
Most groundwater pumped in the United States is used for:
irrigation
Which of the following is true about the water table?
the water table can slope in opposite directions beneath a hill
Where on this cross section would water at the surface infiltrate to become groundwater?
1, 2, and 3
This map shows contours of the water table, the location of four factories (labeled A, B, C, and D), and contaminated (x) and uncontaminated wells (-). Which factory contaminated the groundwater?
factory c
Which of the following controls the rate of groundwater flow?
the slope of the water table
the permeability of the rocks
how fractured the rocks are
Correct!
ALL OF THESE
Each number on this figure refers to a location with groundwater in a subsurface material that is consistent in character across the entire figure. Of these locations, which would likely have the fastest groundwater flow?
1
If it contained oil, which layer would most likely produce an oil seep on the surface?
A, a permeable sandstone
Which site would most likely contain oil in the subsurface?
C, a permeable sandstone
Which of the following sites is the least common place in which oil is trapped?
the bottom of a syncline
Once oil and gas are formed, they:
ALL OF THE ABOVE
rise toward the surface
are lighter than water
flow most easily through permeable rocks, such as sandstone
can be prevented from reaching the surface if they are trapped by impermeable layers
Which site in the accompanying figure is the most likely setting for an oil field?
sandstone at D
For a rock to be considered an ore, it must:
contain enough of a commodity to be mined at a profit
What is the main way that gold ore forms in association with a caldera?
hot water flows along the margins of a caldera
How do modern gold placer deposits form?
pieces of gold are weathered and eroded from bedrock and carried and deposited by streams.
The percentage or concentration of the valuable commodity in a rock is called the:
grade
Which of the following processes CANNOT form a mineral deposit?
igneous crystallization
metamorphism
precipitation at low temperatures
weathering
Correct!
all of these processes can form a mineral deposit
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