Geology Final Exam
What factors led to the massive rockslide at Gros Ventre, Wyoming? Please select all that apply.
-The sandstone layer had almost no support at the bottom of the slope, where it had been undercut by the Gros Ventre River. -Heavy rains and meltwater seeped through the sandstone and saturated the clay underneath.
When was the last time North America had major ice sheets?
18,000 years ago
What is drawdown and how does it relate to the cone of depression?
A lowering of the water table in response to pumping by wells is called drawdown. Cones of depressions are conical depressions in the water table around wells that form from pumping of groundwater. If the well is deep, and the withdrawal of water high, this can cause nearby shallower wells to run dry if they are within the cone of depression.
What type of variations in the earth's orbit might help explain the alternation of glacial and interglacial periods? What was the name of the scientist who built a model based on these variations?
A scientist by the name of Milutin Milankovitch built the mathematical model that explained the alternating glacial and interglacial stages as the result of three different kinds of orbital variations: 1) Variations in the shape of the Earth's orbit around the Sun (Eccentricity) 2) Changes in the angle of the Earth's axis (Obliquity) 3) Wobbling of the Earth's axis (Precession)
What is a spring? What usually causes them?
A spring is a natural outflow of groundwater at the surface. This happens when the water table intersects the surface, often due to aquitard layers preventing water flowing downward and forcing it to move laterally (sideways) instead.
What is the difference between an aquitard and aquifer? What type of rock(s) make good aquitards? Aquifers?
An aquitard is an impermeable layer (that does not allow the movement of water through it) while an aquifer is a rock unit with high porosity and permeability good for storing large quantities of groundwater. Clay (or shale) make good aquitards while sand and gravel layers (or sandstone) make good aquifers.
List and describe five effects of Ice Age glaciers aside from the formation of major erosional and depositional features.
Animal and plant migration (some plants and animal that could not adapt became extinct), adjustments in Earth's crust (isostatic rebound of the crust is still taking place today), sea level changes (sea level rose following the end of the Ice Age), large-scale change in river routes and drainage patterns, formation of proglacial and pluvial lakes.
Which two regions currently contain the world's last remaining ice sheets?
Antarctica and Greenland
Please select the picture of a slump.
B
How might a wildfire influence mass movement?
Because plants on a slope bind the regolith with their roots and shield the soil surface from raindrops, a wildfire that destroys these plants would render the soil looser and more susceptible to the erosional force of rain.
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 calving and what does it create?
Calving is the process of ice breaking off glaciers as they flow out onto water. This produces icebergs.
Which aquifer would be most effective in purifying polluted groundwater: coarse gravel, sand, or cavernous limestone? Why?
Coarse gravel and cavernous limestone have such large openings and pore spaces that water moves rapidly through these layers not allowing contaminates to be filtered out by chemical reactions or organisms. Sand would be best for purifying polluted groundwater because the water moves through much more slowly allowing natural filtration processes to remove contaminates.
Define: Crevasse. Why do crevasses form in the upper portion of a glacier but not below a depth of about 50 meters?
Crevasses are cracks in the brittle upper layer (uppermost 50 meters) of a glacier that form due to the topmost part of a glacier being brittle and cracking while the ice at lower depths is under higher pressure which causes it to deform and flow plastically.
How is a lahar different from a debris flow that might occur in southern California?
Debris flows are composed of soil and regolith, whereas lahars are composed of volcanic materials.
Moving from the headwaters to the mouth, in most streams, which of the following is true?
Flow velocity generally increases.
How are geysers different from hot springs? Describe how geysers periodically erupt. (Hint: look at figure 14.19)
Geysers involve periodic eruption of hot water ejected with great force while hot springs are simply hot pools of water usually 10 to 15 degrees warmer than the mean annual air temperature of the locality. Geysers erupt when groundwater nearest the heat source reaches near its boiling point while water closer to the surface also expands due to heating. The expansion of the upper water lowers the pressure on the deeper water, causing it to flash into boiling and generating stream which propels water upward explosively. After the release the process continues and repeats.
What is glacial drift? What is the difference between till and stratified drift?
Glacial drift is any sediment of glacial origin. Till is unconsolidated, unsorted mixtures of sediment of all different sizes while stratified drift is unconsolidated but sorted by size (from deposition by meltwater).
Where are glaciers found today? What percent of the Earth's land surface do they cover today?
Glaciers are found today near the Earth's poles (high latitudes) and in mountainous regions (high elevations). Today they cover approximately 10% of the Earth's land surface.
Name and describe the two ways in which glaciers erode the landscape.
Glaciers erode by plucking (the process of picking up chucks of rock and incorporating them into the mass of ice as it flows over the ground). They also erode by abrasion (rocks being carried by the ice grind against the rocks of the ground as the ice flows overland). This essentially scratches and pulverizes rock which can produce glacial striations (scratches left behind on ground rocks) or glacial flour (finely ground up rock).
Under what circumstances will the front of a glacier advance? Retreat? Remain stationary?
Glaciers have budgets. The zone where snowfalls and ice accumulates is called the zone of accumulation. As glacial ice flows downslope it reaches an elevation where melting begins. This is called the zone of wastage. If a glacier is "advancing" it means more snow is falling in the zone of accumulation than is being lost by melting in the zone of wastage (this glacier has a net positive budget). If the opposite true, more volume is lost from melting than is being added in the zone of accumulation then the glacier has a net negative budget and will "retreat". If the budget of additions and losses is balanced and in equilibrium then the front face of the glacier will seemingly remain stationary. (In reality, the glacier is still flowing but additions and subtractions are the same).
List and briefly describe the two mechanisms by which glacial ice moves.
Glaciers move by plastic flow (movement within the ice) and basal slip (movement of ice as a unit). Studies of glaciers have found that different parts of glaciers move and flow at different rates.
What percentage of Earth's total freshwater supply is groundwater? What share of Earth's liquid freshwater is groundwater?
Groundwater is 30% of Earth's freshwater supply, 96% if only liquid water is considered.
List two geologic roles that groundwater plays.
Groundwater is important as an erosional agent and as an equalizer of streamflow (storing water that allows streams to continue to flow even during dry periods).
What natural acid does groundwater contain? How does groundwater create caverns?
Groundwater is slightly acidic and contains natural carbonic acid. Groundwater creates caverns in soluble rock layers such as limestone by moving through cracks and fractures and dissolving the carbonate minerals that make up these layers.
How does a glacier lose ice through sublimation?
Ice changes from solid to gas.
Explain why post A has moved farther than posts B and C.
Ice in the center of a glacier has the least friction with the surrounding bedrock and can flow faster.
What is the difference between an ice sheet and an ice shelf? How are they related?
Ice sheets are larger than ice caps. They are both masses of glacial ice covering large areas of the land surface.
What is the difference between a gaining stream and a losing stream?
In a gaining stream, water from the zone of saturation moves into the stream channel. This happens when the water table line is higher than the surface of a stream. In a losing stream, the water table is at some depth below or sloping away from the stream and may not intersect the stream channel. This results in a stream losing water to the groundwater system by flowing out from the stream channel into the surrounding sediments or rock.
What is the difference between the zone of saturation and the unsaturated zone? Which holds the groundwater?
In the zone of saturation, all open pore spaces in the rock and sediment are completely filled with water. The unsaturated zone does not have all empty spaces filled with water. Groundwater is stored in the zone of saturation, the water table marks the top of the zone of saturation.
In the first model, what happens as the layer of coarse material develops at the surface?
It blocks the fine-grained sediment below from the wind, which prevents the possibility of further deflation.
Consider a weathered rock or soil particle lying on a slope. How will the gravitational force pulling the particle downward along the land surface vary with the inclination of the slope?
It will decrease as the slope angle is lessened.
What is karst topography? Describe two ways in which sinkholes form.
Karst topography is a term used to describe a landscape that has been significantly shaped by the dissolving power of groundwater. Karst areas typically have irregular terrain punctuated with man depression called sinkholes and a lack of surface drainage (rivers). Sinkholes can develop gradually over many years without any physical disturbance to rock and a gradual lowering of the surface around the solution cavity (end up as shallow depressions with gentle slopes) or they can form by sudden collapse without warning (forming steep sided and deep depressions).
What is land subsidence and how can it occur due to groundwater withdrawl?
Land subsidence is the lowering of the elevation of the ground surface in response to the withdrawl of water from sediments. As water is withdrawn, sediments can become more tightly compacted and reduce porosity of the rock and sediments which causes subsidence.
Compare and contrast an end moraine with a ground moraine.
Moraines are piles or ridges of till that accumulate around the edges of glacial ice. End moraines form at the terminus and mark the furthest extent reached by the glacial ice. Ground moraines are gently rolling layers of till deposited as the ice front recedes and retreats.
Which of the following budget scenarios describes a glacial advance?
More ice and snow accumulates than melts each year.
__________ are defined as a chain of glacial lakes where each lake flows into the next.
Pater noster lakes
What is a pluvial lake? What pluvial lake is the Great Salt Lake a remnant of (Fig. 15.29)?
Pluvial lakes are remnant lakes found in now arid or semi-arid climate zones that originally formed when cooler, wetter climates conditions once prevailed. The Great Salt Lake is the evaporating remnant of a much larger lake (Lake Bonneville) that once existed during the Ice Age.
Describe how the shape of a mountain valley changes after glaciation.
River valleys start out "V" shaped and after being eroded and sculpted by glacial ice flowing through them often become "U" shaped.
When rainfall occurs, what three paths can it take? What factors influence the amount of water that soaks in?
Runs off (collects in lakes and streams) Evaporation and transpiration (returns to atmosphere) soaks into ground (becomes groundwater) Factors that influence the amount of water that soaks into the ground include: steepness of the slope of the land, nature of the surface material, intensity of the rainfall and type and amount of vegetation.
Which of these options accurately describes settling velocity?
Settling velocity is the speed at which a particle falls through a still fluid. This velocity is influenced by the size, specific gravity, and shape of the settling particle. Settling velocity has no effect on the dissolved load of a stream.
________ comprise the suspended loads of most rivers and streams.
Silt and clay-sized, detrital grains
Which of the following statements about mass movement is true?
Some mass movements occur with no discernible trigger.
What are some of the sources of contamination in groundwater?
Sources of contamination include sewage, highway salt, fertilizers, pesticides and industrial chemicals.
How do stalactites and stalagmites form?
Stalactites (hanging down) and Stalagmites (growing up) from caverns form by carbonate laden groundwater losing some of its dissolved carbon dioxide as it drips from the ceiling which, in turn, causes precipitation of calcite. The splashing of the water drop to the floor causes similar precipitation on the ground of the cavern. Speleothems form over time as this process repeats.
High Plains is an example of what kind of problem associated with groundwater pumping?
The High Plains aquifer is heavily utilized for agricultural irrigation. The region it occupies has high rates of evaporation with less precipitation, causing the natural recharge rate of the acquifer (rainfall) to be less than the amount withdrawn. As a result, parts of the aquifer are seeing depletion rates and lowering of the water table to depths that will soon make it uneconomical to use a water source for crops.
What causes streams that emerge from glaciers to be milk-colored?
The presence of finely ground sediment called rock flour in the meltwater.
How do freezing, thawing, wetting, and drying contribute to soil creep?
The soil expands and contracts, lifting particles and dropping them a slight distance downslope.
What is the source of heat for most hot springs and geysers? Why are most of the hot springs found in the western U.S.?
The source of heat for most hot springs is hot igneous rock or magma. Active volcanic zones are found in the western U.S.
What is the water table? Is it a flat, level surface?
The water table marks the boundary between the zone of saturation and unsaturated zone. The water table is rarely a level line, it most often mimics the topography of the surface, being highest under hills and deeper under valleys.
Which of the following is true of earthflows?
They are viscous and move at slower rates than debris flows.
What is the best way to describe the shape of a glacial valley?
U-shaped
What shape is a glacial trough?
U-shaped
What share of U.S. freshwater is provided by groundwater? What is most groundwater used for?
U.S. freshwater supplied by groundwater is approximately 25%
How is an artesian well different from regular wells? What are the two conditions that must be met in order to produce an artesian well?
Unlike in regular wells, artesian wells have groundwater that is under pressure rising above the level of the aquifer. In order to produce the conditions needed for an artesian well you must have 1) water confined to an aquifer that is inclined so that one side is open to water recharge and 2) aquitard layers present both above and below the aquifer, confining it.
List and briefly distinguish among four types of glaciers.
Valley (Alpine) glaciers - found in mountains, ice accumulates near peaks where it flows downward into surrounding valleys Ice sheets - largest of all glaciers, consist of thick ice sheets covering large areas of land currently found in Greenland and Antarctica (high latitudes) Ice caps - cover uplands and plateaus (smaller in scale than ice sheets). Examples: Iceland, some islands in Arctic Ocean. Outlet glaciers - Essentially alpine glaciers that have reached valley floors and spread out. Some of these reach coastlines and flow out onto water as ice shelves and produce glaciers as chunks of ice break off into the water.
Which statement best describes the way vegetation affects slope stability?
Vegetation protects against erosion from raindrops and helps bind together soil and regolith.
How does water affect mass-movement processes? Please select all that apply.
Water adds weight to the material on a slope. When only enough water is added to make the sediment on a slope slightly damp, the sediment sticks together and resists downward pull. Water fills the pores between sediment, destroying the sediment's overall cohesion.
Any theory that explains the cause of the glacial Ice Ages must answer what two basic questions?
What causes the onset of glacial conditions? What caused the alternating glacial and interglacial stages during the Quaternary period?
What causes a crevasse to form?
When ice flows around a bend or over an obstacle, it is stretched and torn, causing large cracks to form.
Which part of a glacier will see the build-up of ice and snow over the course of a full year?
Zone of Accumulation
Briefly describe the following erosional features created by valley glaciers:
a) Hanging valley - These form in areas where smaller tributary glaciers feed into a larger, deeper main glacier. The depth of erosion of the different alpine glaciers will vary and when the ice melts the smaller tributary glaciers will leave a shallower valley "hanging" above a more deeply carved main valley. These often turn into the sites of waterfalls. b) Cirque - These are bowl-shaped depressions sculpted by valley glaciers as they flow down mountain peaks. c) Tarn - These are small lakes that form in cirque depressions after glacial ice melts away. d) Arete - These are sinuous, knife-edged ridges found in mountains glacially sculpted by valley glaciers. e) Horn - These are jagged, pyramid-like peaks found in mountains glacially sculpted by valley glaciers. f) Fiords - are deep, steep-sided inlets present at high latitudes where mountains are next to the ocean. They are drowned glacially sculpted valleys submerged after the ice melted and sea level rose following the Ice Age.
Briefly describe the following depositional features created by glaciers.
a) Kettle Lakes - basins or depressions filled with water that form when blocks of ice unevenly break off the front of a retreating glacier. Stranded blocks of ice often become partially buried in outwash sediments as the glacier continues to melt and deposit sediment. When the ice eventually melts it leaves behind a depression or basin where the ice once stood and these depressions often fill up with rain water and form kettle lakes. b) Drumlin - a streamline or assymetrical hill composed of till that has been smoothed and sculpted by glacial ice flowing over it. It usually has a steep side that faces the direction from which the ice advanced and a more gentle slope on the opposite side. c) Esker - a sinuous snake-like ridge composed of sand and gravel that was deposited by a meltwater flowing within, on top of, or beneath the glacial ice. d) Kame - an irregular steep-sided hill composed of sand and gravel from meltwater washing sediment into openings or depressions within glacial ice. When the ice later melts away the sediment is left behind as these irregular mounds or hills.
Smooth, rounded cobbles and pebbles are found in streams a result of ________.
abrasion
What glacial feature is circled in Figure 1?
arête
Which type of glacial movement is circled in Figure 1?
basal sliding
At what latitudes do the large-scale, convection cells bring dry air downward toward the Earth's surface?
between 20-30° north and south
Deflation leads to the formation of desert pavement by __________.
carrying fine sediments away and leaving a layer of larger particles at the surface
Which mass movement process has the slowest rate of movement?
creep
Wind erosion can cause __________, which can create shallow depressions called __________.
deflation; blowouts
A drainage pattern that resembles the branching pattern of a deciduous tree is called ________.
dendritic
The volume of water flowing past a certain point in a given unit of time is called ________.
discharge
What glacial landform is visible in Figure 1?
drumlin
What is the name for an isolated boulder of unexpected rock type that has been transported by a glacier and stranded after the ice melts?
erratic
he process by which liquid water changes into water vapor is called ________.
evaporation
During a glacial retreat, a glacier will flow _____ while the terminus moves _____.
forward; backward
All of the following are factors affecting mass movement EXCEPT for ________.
geologic age
What glacial feature is circled in Figure 2?
horn
The ________ describes the movement of water through Earth's hydrosphere.
hydrologic cycle
Which type of glacial movement will be responsible for the greatest amount of glacial flow?
internal flow
When water moves in nearly straight-line paths parallel to the stream channel, in slow moving streams, this is called ________.
laminar flow
The downslope movement of rock, regolith, and soil is called ________.
mass movement
Desert regions occur __________, and always have a(n) __________ climate zone adjacent to them.
on every continent; steppe
Which of the following are considered triggers for mass movement events? Choose all that apply.
oversteepening of the slope, ground vibrations, oversaturation of the material
What is the difference between porosity and permeability in rock?
porosity - total amount of storage space available in the pore spaces of rock to hold water permeability - how well connected the individual pore spaces are to each other, in other words, how easily can water move through the rock or sediment.
The removal of blocks from the bed of a stream channel is known as ________.
quarrying
A drainage pattern comprised of streams that diverge from a central area like spokes is called ________.
radial
Most modern glaciers are __________.
retreating
Of the following, which one would most likely be triggered by an earthquake?
rock avalanche
Which of the following sediments are unstable and at a high risk for mass movement?
sediments that are steeper than the angle of repose
When air __________, it is compressed and warmed.
sinks
What terms are used to describe how material moves during mass movement? Please select all that apply.
slide, fall, flow
Which type of mass movement involves a downward sliding mass of rock or unconsolidated material moving along a curved surface?
slump
Which one of the following operates primarily in areas of permafrost?
solifluction
What feature is responsible for creating eskers?
streams that flowed below, in, or on the glacier
Which landform marks the furthest extent of an advancing glacier?
terminal moraine
What serves as the ultimate base level for streams?
the ocean
Deserts that lie outside of the subtropics and mid-latitude belts are most likely the result of __________.
the presence of a rainshadow
Precipitation occurs on the __________ of the mountain range, while the __________ is dry.
windward side; leeward side
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
