geology test 3

What is the difference between terrane and terrain?

"Terrane" describes a crustal fragment consisting of a distinct and recognizable series of rock formations that has been transported by plate tectonic processes, whereas "terrain" describes the shape of the surface topography.

Correctly describe four types of drainage patterns.

(1) rectangular pattern, which develops on highly jointed bedrock; (2) trellis pattern, which develops in areas of alternating weak resistant bedrock; (3) dendritic pattern, which develops on relatively uniform surface materials; (4) radial pattern, which develops on isolated volcanic cones or domes

When did Pangea begin to break into smaller fragments?

180 million years ago

What percentage of Earth's water is in the form of seawater?

97.2%

Select the correct description of a passive continental margin and the correct description of an active continental margin.

A passive continental margin is tectonically inactive and features a continental shelf, a continental slope, and a continental rise (from land toward the sea). An active continental margin is located along a convergent plate boundary, has a deep-ocean trench where subduction takes place, and may have evidence of an accretionary wedge or of subduction erosion.

Why can rock avalanches move at such great speeds?

Air becomes trapped and compressed beneath the falling mass of debris, which allows the debris to move as a flexible sheet across the surface of the slope.

How does an accretionary wedge form?

An accretionary wedge forms at an active continental margin when the subducting oceanic slab scrapes pieces of itself onto the more buoyant continental slab.

What is an accretionary wedge, and how does it form?

An accretionary wedge is an accumulation of deformed, thrust-faulted sediments and scraps of ocean crust. This wedge is plastered against the edge of the overriding plate from the subducting plate.

Briefly describe a general drainage basin.

An area drained by a stream is called a drainage basin, which is bounded by an imaginary line called a divide. The divide can be clearly visible as a sharp ridge, or it could be difficult to determine in subdued topography.

How do mantle-derived magmas that have a basaltic composition generate magmas that exhibit an intermediate to felsic composition?

As basaltic magma ascends through the thick continental crust, ferromagnesian minerals crystallize and drop out of the melt, thus creating a secondary melt of an intermediate or a felsic composition.

How did the Mississippi River delta form?

As the Mississippi River enters the Gulf of Mexico, its velocity decreases and it begins to drop its sediment load.

Which of the choices below correctly defines base level and differentiates between ultimate base level and local (temporary) base level?

Base level is generally defined as the lowest elevation to which a stream can erode its channel. The ultimate base level is sea level; local base levels are lakes, resistant layers of rock, and rivers that act as base levels for their tributaries.

Where are bedrock channels more likely to be found?

Bedrock channels are typically found in the headwaters of river systems where streams have steep slopes.

What is the difference between capacity and competence?

Capacity is the maximum load of solid particles a stream can transport per unit of time, whereas competence is a measure of a stream's ability to transport particles based on size rather than quantity.

What causes creep, and how can it be recognized?

Creep is caused by the repeated expansion and contraction of the regolith, which may be caused by repeated freezing and thawing or wetting and drying. Creep can be recognized by tilted trees, tilted fences, and displaced retaining walls.

What is the difference between an earthflow and a debris flow?

Debris flows generally occur within semiarid areas and tend to be restricted to channels, whereas earthflows most often occur on hillsides in humid areas.

Part complete How are deep-ocean trenches related to plate boundaries?

Deep-ocean trenches are sites of plate convergence where an oceanic plate subducts under another plate.

What has caused the hypoxic "dead zone" to form off the coast of the Gulf states?

Fertilizers promote the growth of algae. When they die and decompose, oxygen is depleted in the Gulf of Mexico.

How does hydrothermal metamorphism alter saltwater and the basaltic rocks that make up the seafloor?

Hydrothermal metamorphism causes the minerals olivine and pyroxene in basalt to form new minerals, such as chlorite and serpentine. It also dissolves various ions in the hot seawater, which eventually rise along fractures and spew out on the ocean floor.

_____ is the principle that explains why materials uplift to a certain elevation.

Isostasy

What is mass wasting, and how does it differ from other erosional processes (e.g., streams, glaciers, wind)?

Mass wasting is the downslope movement of rock material driven by the force of gravity. It differs from other erosional processes in that mass wasting does not require a transporting medium.

How do oceanic ridges differ from continental mountain ranges?

Most mountain ranges form through the collisions of two continents, whereas oceanic ridges form when material upwells from the mantle and generates new oceanic crust.

How does the formation of a natural levee impact flooding?

Natural levees raise the height of the stream channel, reducing the amount of flooding that will occur on the floodplain.

What happens as plates diverge at an oceanic ridge?

New oceanic crust and lithospheric mantle are generated by the cooling of molten rock upwelling from the mantle.

Where are the headwaters of the Mississippi River?

Northern Minnesota

How does a guyot form?

Over time, guyots lose their original shapes and sizes through the process of weathering, after moving away from their original locations over hot spots.

What is permafrost, and what can result from disturbing it?

Permafrost is permanently frozen ground. If the thermal balance of permafrost is disturbed, ice within the permafrost may melt, causing the ground to slide, slump, or subside.

Contrast spontaneous subduction with forced subduction.

Spontaneous subduction, which occurs at Mariana-type subduction zones, takes place when old, dense lithosphere subducts beneath the other plate at a very steep angle. In contrast, forced subduction, which occurs at Peru-Chile-type subduction zones, takes place when hot, low-density lithosphere subducts beneath the other plate at a shallow angle because of compressive forces.

Part complete How can the Appalachian Mountains be considered a collision-type mountain range when the nearest continent is 5000 kilometers (3000 miles) away?

The Appalachians were created by the closing of three ocean basins during the formation of Pangaea.

Compare the Mid-Atlantic Ridge and East Pacific Rise.

The Mid-Atlantic Ridge is spreading at a much slower rate than the East Pacific Rise.

Using what you know about isostasy, how would the crust behave if a large glacier were removed?

The crust would move up in elevation.

What landscape feature indicates that mass wasting has helped shaped a river valley?

The river valley is much wider than it is deep.

If the Rocky Mountains were eroded, what would happen to the roots of the mountains?

The roots would rebound upward.

How can satellites orbiting Earth determine features on the seafloor without being able to directly observe them beneath several kilometers of seawater?

The satellite measures the variation in the sea-surface elevation by bouncing microwaves off of the water's surface, which mimics the shape of the seafloor.

What happened when the spreading center that generated the Farallon plate collided with the North American plate?

The spreading center ultimately subducted beneath the coast of California. This event destroyed this spreading center and replaced it with a transform fault system.

Rapid mass-wasting events do not always need a trigger. (T or F)

True

Running water is the single most important erosional agent sculpting Earth's land surface. (True or False)

True

How can the addition of water make a slope fail, creating a landslide?

Water makes the slope material heavier. Water can easily flow downslope. Water in pore spaces reduces cohesion between particles.

What role do mineral phase changes play in plate subduction?

When an oceanic slab reaches 400 km within the mantle, the mineral olivine changes to its more dense spinel structure. This increase in density helps pull the slab farther down into the mantle.

What is a process that accounts for the elevated topography of some fault-block mountains?

When tensional forces stretch and thin the lithosphere, hot mantle rock upwells and heats this lithosphere, making it less dense and causing it to rise.

What does a turbidite sequence consist of?

a blanket of sand overlain by a sheet of mud

What is a floodplain?

a flat surface next to a river channel

What is a black smoker?

a particle-filled cloud resulting from metallic-rich solutions gushing form the seafloor into the ocean water

What are the features associated with a divergent boundary that is spreading quickly?

a relatively smooth swell with gentle slopes

What is a natural levee?

a ridge of flood deposits next to a river channel

In which environment are rapid mass-wasting processes most likely to occur?

among rugged, geologically young mountains

Where are most modern divergent plate boundaries found?

at mid-ocean ridges

What are the three types of loads carried by streams?

bed load, suspended load, dissolved load

Bouncing is to sand as suspension is to_____________.

clay

What are the three major topographic provinces of the ocean floor?

continental margins oceanic ridges deep-ocean basins

Water erodes the outside of a river bend to form a __________.

cut bank

What causes melting of material under divergent plate boundaries?

decompression of rock

The volume of water flowing past a certain point in a given amount of time is a river's

discharge

The geographical area where all surface water converges to one location is called its

drainage basin

Point bars are locations where erosion occurs whereas cutbanks are locations where deposition occurs. (True or False)

false

A river with a well-developed _________ has a flat low-lying channel and experiences flooding during periods of high discharge.

floodplain

Which geologic features would be present in compressional mountain belts?

folds thrust faults intrusive igneous rocks

Which of the following is the major contributing factor in all landslides?

gravity

The __________ of a river have a steep gradient, high channel roughness, and low water volume.

headwaters

Sliding is to gravel as dissolution is to_____________.

ions

The oceanic ridge system _____.

is transected along its length by transform faults at irregular intervals and winds through all of the major oceans on Earth

What is meant by a nonstructural approach to flood control?

limiting certain activities or land uses and implementing appropriate zoning regulations in high-risk flood areas

In a river valley, mass-wasting processes can ______.

make the valley walls less steep and make the river valley wider

Which of the following contains the entire ophiolite suite, in order from the mantle to the seafloor?

mantle peridotite, gabbro, sheeted dike complex, pillow lavas, deep-sea sediments

What are stromatolites?

mats of blue-green algae that grew in mounds up from the sea floor

A stream with a low to moderate gradient, carrying most of its load in suspension, should be characterized by many curves and bends called

meanders

Which of the following is a characteristic of a graded stream?

meanders and well-developed flood plain

Which landscape is most prone to generating landslides?

mountains

A delta forms at the _____ of a river, where the velocity of the water flow decreases and deposition is highest.

mouth

Which type of faulting is associated with the development of new ocean floor?

normal faulting

What features on the ocean floor most resemble flood basalt provinces on the continents?

oceanic plateaus

____ is a trigger for mass wasting.

oversteepening of a slope and adding water to sediments and a wildfire

What two layers of the ophiolite sequence are compositionally similar, but formed in different areas with respect to the crust?

pillow lavas and gabbro

How can pieces of rock in contact with a stream bed move?

rolling, sliding, bouncing

Which of the following are part of the bed load?

sand and gravel

Which of the following rocks are characteristic of compressional mountain building?

schist

What terms are used to describe the way material moves during mass wasting?

slide fall flow

What caused metamorphism to occur in the Blue Ridge District during the Alleghanian Orogeny?

strong differential stress generated by compressional stress as rocks were thrust westward

What is the geologic term for folded rocks with the bend at the bottom?

syncline

What is discharge a measurement of?

the amount of water flowing in a river

Transpiration moves water from _______.

the biosphere to the atmosphere

What is orogenesis?

the collection of processes that produce a mountain belt

What is suspended load?

the fine-grained particles that travel in the water column above the stream bed

What is bathymetry?

the topography of the ocean floor and the measurement of ocean depths

Which of the following scenarios could result in the development of a compressional mountain belt?

two landmasses collide

Batholiths, such as those that make up the Sierra Nevada Mountains of California, form at great depth in the crust. How could they have been exposed at the surface?

uplift and erosion

When do new oceans form?

when a continent is broken apart by a divergent boundary

Where do most divergent boundaries originate?

within continents

What are the three main zones of a river system from highest to lowest?

zone of sediment production, zone of transportation, and zone of deposition