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Geology Exam 3
Terms in this set (67)
What is the difference between numerical dates and relative dates
Numerical dates specify an absolute age in number of years, whereas relative dates determine the order of events in relation to on another
Which of the geologic principles listed here is incorrectly defined
The principle of cross-cutting relationships states that the fault or intrusion that cuts across several rock layers is older than these layers
What is the significance of an unconformity
An unconformity represents an interval of time that is missing from the rock record.
What is rock deformation? How might a rock body change during deformation?
Deformation is a rock's reaction to stress, which can cause a rock to change its shape or position
Which of the descriptions below accurately describes the various types of differential stress
-Shear stress, which moves one part of a rock body past another, changes rock shape and can break rocks apart
-Tensional stress, which pulls rock apart in opposite directions, horizontally stretches and lengthens rock bodies
-Compressional stress, which squeezes rock, generally shortens rocks horizontally and thickens them
At which types of plate boundaries do the three types of differential stress occur
Shear stress occurs at transform boundaries, compressional stress occurs at convergent boundaries, and tensional stress occurs at divergent boundaries
Which of the characteristics below makes a rock very strong as opposed to very deformable
-having a very low temperature
-having a very high confining pressure
-having forces suddenly applied to it
-being a metamorphic rock composed of quartz
What is elastic deformation
The temporary and reversible deformation of a rock caused by the gradual application of stress. During elastic deformation, the chemical bonds within the rock do not break
Where do the youngest rocks in an eroded basin outcrop
-The youngest rocks of a basin are on top of all the other rock layers
-In top view, the youngest rocks of a basin are in the middle of a basin
How do monoclines form
Movement along a steep fault in basement rock pushes up a portion of the ductile rock layers above it.
The black hills of south Dakota are a good example of which type of geologic structure
How are joints different than faults
Faults are breaks within rock where appreciable displacement has occurred, joints are breaks within rock where no appreciable displacement has occurred
Which type of fault is associated with fault-block mountains
What is an earthquake, and how do earthquakes generally occur
a sudden shaking of the ground that is caused by the rapid movement of one block of rock past another block of rock at a fault
During an earthquake
the slippage continues along the fault until it reaches a point where rocks are not sufficiently strained to continue slippage
What characteristics do faults that experience fault creep exhibit
Fault creep tends to produce slow, gradual displacements of rock blocks with little seismic shaking
How does a seismograph work?
-A seismograph works by suspending a weight from bedrock, which remains motionless during an earthquake. A rotating drum that is affixed to the moving bedrock moves as the rock moves, recording the relative displacement between the stationary weight and the rotating drum
-A seismograph can measure P waves, S waves, and surface waves
What are the differences between P waves, S waves, and surface waves?
P waves are the fastest and have the lowest amplitudes; S waves are the second-fastest and have the second-lowest amplitudes; surface waves are the slowest and have the highest amplitudes
What information does a time-travel graph provide
the distance from the earthquake to the recording station
How does triangulation determine the epicenter of an earthquake
On a map, a circle is drawn around each of three recording stations, with the radius being the distance from the station to the epicenter of the earthquake. The epicenter is located where the three circles intersect
What information is used to establish the lower numbers on the Modified Mercalli intensity scale
how the earthquake is felt by people in an area
How much more energy does a magnitude 8.0 earthquake release than does a magnitude 7.0 earthquake
An earthquake with a magnitude of 8.0 releases 32 times more energy than an earthquake with a magnitude of 7.0
What causes a mineral phase change
the increase of pressure on a mineral when it is moved deeper within Earth
which phases below complete the following sentence? The force of gravity is
-not equal all over the world in part because of the centrifugal force created by Earth's rotation
-weaker at the equator than at Earth's poles because of the equatorial bulge
What is the difference between an aquifer and an aquitard
An aquifer is a rather permeable rock; whereas an aquitard is an impermeable rock
How does groundwater create caverns
Caverns are created when acidic groundwater dissolves and carries away limestone over time.
What is the difference between stress and strain
Strain is the change in rock shape that results from stress, which is the force that deforms the rock
Which statements below distinguishes between anticlines and synclines, domes and basins, and anticlines and domes
-Anticlines have hinge lines, whereas domes are roughly circular when viewed from above
-Folded rock layers in anticlines arch upward, whereas folded rock layers in synclines arch downward
-Folded rock layers in domes upwarp, whereas folded rock layers in basins downwarp
What is the relative movement along a strike-slip fault?
-the dominant displacement is parallel to the strike of the fault
-Both blocks of rock move horizontally past each other
How are reverse faults different from thrust faults?
A reverse fault is steeper than a thrust fault; thrust fault have dips that are lower than 45 degrees
How do geologists infer the orientation of rock structures that are mainly below Earth's surface
After measuring the strike and dip of several outcrops within an area, geologists graphically present these data in the from of geologic maps
Distinguish between the two measurements used to establish the orientation of deformed strata
-Strike is the direction of a line produced by the intersection of an inclined rock layer and a horizontal surface; dip is the angle of inclination of a rock layer from horizontal
-Strike is identified between two directions; dip is identified in one direction
-The strike and the dip are each represented on a geologic maps with their own symbols
How are faults, hypocenters, and epicenters related
The hypocenter is the exact point underground along a fault where the slippage of the two blocks of rock occurs. The epicenter is the point on Earth's surface that is directly above the hypocenter
What is meant by elastic rebound
Elastic rebound refers to how the slippage along a fault (i.e., earthquake) allows the deformed rock to regain its original shape in a new location.
Who was the first to explain the mechanism by which most earthquakes are generated
H.F. Reid first explained the mechanism by which most earthquakes
Which type of fault tends to produce the most destructive earthquakes
Which type of seismic waves tend to cause the greatest destruction to buildings
What does the Modified Mercalli Intensity scale tell us about an earthquake
how intense an earthquake feels
What influences the amount of destruction that seismic vibrations cause to human-made structures
-the nature of building processes and construction processes used
-the nature of the ground underneath human-made structures
-intensity of the vibrations
-duration of the vibrations
For which reasons might an earthquake with a magnitude of 7.0 result in more death and destruction than a quake with a magnitude of 8.0
-The area with the 7.0 magnitude earthquake has a higher population than an area with the 8.0 magnitude earthquake
-the construction materials used in buildings in the area with the 7.0 magnitude earthquake are of poorer quality than those used in the area of the 8.0 magnitude earthquake
-The 7.0 magnitude earthquake lasts longer than an 8.0 magnitude earthquake
Which types of plate boundary are associated with earth's largest earthquakes
-ocean-oceanic convergent plate boundary
-oceanic-continental convergent plate boundary
Why would a repeat of the 1811-1812 New Madrid, Missouri, earthquakes be destructive to the Memphis, Tennessee, metropolitan area
The buildings in Memphis are on top of unconsolidated floodplain deposits and thus are more susceptible to damage than buildings on top of solid bedrock.
Aside from the answer to the previous question, in what other setting(s) do(es) strong earthquake activity occur
-along transform faults in continents
- along strike-slip faults in continent
What characteristic of seismic waves makes them useful for probing Earth's interior
The velocities and directions of seismic waves reliably differ when they encounter different materials within Earth.
What does a reflected wave tell us about Earth's interior?
The wave has hit a boundary between two different Earth materials, causing it to reflect back to Earth's surface.
Why do seismic waves travel along curved paths through the mantle
because mineral phase changes in the upper mantle cause sudden increases in seismic velocity
What is the Moho, and how is its depth determined?
The Moho is the boundary between the crust and the mantle. Its depth is determined by observing where refracted seismic waves and direct seismic waves cross over each other.
In general, how does temperature change between Earth's surface and its core
The temperature increases from Earth's crust to its core; the rate of increase changes within and between Earth's layers.
What were the main sources of Earth's original internal heat?
-kinetic energy from impacts on Earth's surface (which converted into thermal energy)
- radiogenic heat released during the decay of short-lived isotope
How do the positions of the magnetic poles change through time?
The magnetic north pole varies somewhat from the geographic North Pole while still remaining in the Northern Hemisphere. Additionally, periods of full magnetic reversals have occurred where magnetic north and magnetic south have switched places with each other. Both types of variation are caused by changes in the convection patterns within the outer core
What percentage of Earth's total freshwater supply is groundwater
What share of Earth's liquid freshwater is groundwater
What share of U.S. freshwater is provided by groundwater, and what is most groundwater used for
Groundwater provides 23 percent of the United States' freshwater. It is mostly used for irrigation and public use.
When rain falls on land, what factors influence the amount of water that soaks in?
-the nature of the surface material
-the steepness of the slope
-the intensity of rainfall
-the amount of vegetation on the surface
Is the water table usually flat like the surface of a kitchen table, and why or why not
Underground, the water table is shaped like a subdued replica of the land surface. Additionally, the water surfaces of rivers and lakes are the level of the water table.
What is groundwater, and how does it relate to the water table?
Groundwater is water that occupies the zone of saturation within the ground. The water table is the upper limit of the groundwater.
Please contrast porosity and permeability.
Porosity is the percentage of the total volume of rock or sediment that consists of pore spaces, whereas permeability is the ability of a rock or sediment to transmit fluid.
How does the movement of groundwater relate to hydraulic gradient and hydraulic conductivity?
Groundwater flows more rapidly through sediments having greater permeability than through materials having lower permeability. This factor is known as hydraulic conductivity.
How does the movement of groundwater in a near-surface local system contrast with that in a deep regional system?
Groundwater movement in a near-surface local system generally sinks down at recharge areas and loops up at discharge areas. In contrast, groundwater movement in a deep regional system generally flows laterally toward the direction of decreasing gradient.
List the features layered in the cross section of a flowing artesian well from top to bottom.
pressure surface, flowing artesian well, aquitard, aquifer (containing well base), aquitard
What warms the waters that flow at Hot Springs National Park, Arkansas, and at Warm Springs, Georgia?
the geothermal gradient
Which of the below circumstances can lead to the formation of a spring
An aquitard blocks the downward movement of groundwater, causing it to move laterally. Where the permeable crops out at the surface, a spring results.
What occurs to cause a geyser to erupt
The heat underground within a geyser causes the water to expand, and some water is forced out of to the surface. Water deep within the geyser quickly turns to steam, causing the geyser to erupt.
Which aquifer listed below would be the most effective in purifying polluted groundwater, and why
permeable sandstone; the pores between grains are large enough to let water through but small enough to block contaminants
What significant problem might arise when groundwater is heavily pumped at a coastal site?
If the groundwater withdrawal exceeds recharge, the saltwater will become high enough to be drawn into the wells.
What problem is caused by pumping groundwater for irrigation in the Southern High Plain?
A low precipitation rate and a high evaporation rate allow little water to recharge the aquifer.
How do stalactites and stalagmites form?
-Stalactites form on the ceiling when water seeps through the ceiling and deposits calcite. Eventually a soda straw develops, which develops into a stalactite after many more depositions of calcite.
-Stalagmites form when calcite-rich water falls to the floor from the ceiling, splattering minute amounts of calcite on the floor. After many such depositions, a stalagmite begins to take shape.
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