Geology Section 3 Part 1

What share of Earth's liquid freshwater is groundwater?

94.05 percent

seasonal Floods.

Regional Floods

Complete this analogy: Bouncing is to sand as suspension is to_____________.

clay

flow

− material moves downslope as a viscous fluid.

What was the trigger for the landslide in Menton, France?

removal of stabilizing vegetation

According to the hydrologic cycle, once precipitation has fallen on land, what paths might the water directly take?

runoff into a river infiltration into the ground evaporation/transpiration runoff into the sea

Why the ground may subside after groundwater is pumped to the surface?

As water is withdrawn, the water pressure drops, and the sediment is left to support the weight on top of it. As a result, the sediment packs more closely together, causing the ground to subside.

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.

People want to build their houses where they will have the right amount of groundwater. If the aquifer is shallow, then it will be less costly to drill a well than if the aquifer is deep. But if the aquifer is limited in size and is not recharged with water, a well might run dry eventually. Running out of water because a shallow well runs dry is a better option than having to dig deeply to find a new water source. It is actually cheaper to run piping from one source to another than to dig very deeply for a well and pump it to the surface.While it is flowing underground, water may encounter zones of weak or easily dissolved rock, usually limestone. Water can dissolve rock and cut underground streams and lakes. This is how caves form in limestone rocks. On the surface, the ground may cave in, forming sinkholes, or streams may disappear underground and then reappear. This type of landscape is called karst topography. While the land surface in areas with karst topography might be unsteady and ill-suited for building, freshwater just below the surface is an abundant resource. Below is an image of different sites for houses: a shallow aquifer, a deep aquifer, and a karst area with lots of caves near the surface. Sort the sites in terms of the best to worst places to build a house considering both the availability of water resources cost and how water affects the land surface.

Best to Worst: Shallow Aquifer Deep Aquifer Area with Karst Toppography

Floods with high precipitation in a short time.

Flash Floods

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.

What depositional feature is visible here?

Delta

At approximately what velocity will a 0.1 mm sediment particle begin moving in the stream?

0.6 cm/sec

A stream is transporting Particle A. The velocity of stream is decreasing, but for the moment, Particle A is still moving. However, when the water drops below 50 cm/sec, Particle A falls below its fall velocity and is deposited. Based on this information, what is the likely particle size for this object?

10 mm

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

97%

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.

How does groundwater create caverns?

Caverns are created when acidic groundwater dissolves and carries away limestone over time.

artificial containment structures fail.

Dam-Failure Floods

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.

In order for an aquifer to be useful for reliable water extraction, what kind of porosity and permeability should it have?

High porosity, high permeability

frozen material creates a temporary dam on a thawing river.

Ice-Jam Floods

How might a stream channel become braided?

If a large portion of a stream's sediment load consists of coarse material and the stream has a highly variable discharge, a stream channel can become braided.

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.

Assume that the irrigation well in the middle of this image was installed by a seed corn company and not by the farmers who own the local wells on either side. If irrigation were stopped immediately, would this localized lowering recover immediately? Why or why not?

No. The average aquifer has a groundwater flow rate of 4 cm/day.

What geologic process is responsible for warming the water at nonvolcanic locations such as Hot Springs National Park, Arkansas, and Warm Springs, Georgia?

Normal geothermal gradient as groundwater circulates at depth

What is base level?

The downward limit of erosion.

Freshwater is less dense than saltwater.

True

What causes cavern formation to stop at one level (depth) but not continue or begin at a lower level?

When the entrenchment of streams is slow or negligible, the groundwater level does not drop, and cavern formation does not begin at a lower level.

An artesian well must tap into ______.

a confined aquifer

The lowest level to which a stream can erode is called _______

base level

What are the three types of loads carried by streams?

bed load, suspended load, dissolved load

Fall

detached material moves in a free-fall.

"De-watering" a slope could include constructing horizontal ________ to remove the water.

drain pipes

Incised meanders and terraces are __________.

erosional features

Geysers are more common in the western United States because ______.

igneous activity has occurred more recently in the western United States

Which of the following are part of the bed load?

sand gravel

What ways material can move during mass movement events?

slide flow fall

A(n) ______ is the remnant of a former floodplain.

terrace

Repeat laser or radar surveys, photogrammetry from ground or air, and satellite measurements (InSAR) provide motion assessments of large areas and provide a good indication of changes occurring on the landscape.

true

The weathering process of frost action can make a slope less stable.

true

How do a gaining stream and a losing stream differ?

A gaining stream gains an influx of groundwater through the streambed, whereas a losing stream loses water to the groundwater through the streambed. A gaining stream exists when the elevation of the water table is higher than the surface of the stream. In contrast, a losing stream exists when the elevation of the water table is lower than the surface of the stream.

What is drawdown, and how does it relate to the cone of depression?

Drawdown is when the water table around a well is lowered because of water discharge. This depression in the water table is conical and is called a cone of depression.

Which rapid form of mass wasting is found at the base of slump blocks?

Earthflow

Which of the following factors does not influence mass wasting?

Geologic Age

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. Groundwater moves more quickly down steeper slopes than down shallow slopes. For this reason, the water table is known as the hydraulic gradient.

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.

What geological roles does groundwater play?

Groundwater sustains streams during periods of no rainfall. Groundwater erodes bedrock through dissolution.

What is the relationship between earthquakes and landslides?

If a slope that has not previously experienced mass wasting is covered by surface materials that are saturated with water, the vibrations of an earthquake may trigger liquefaction of these materials, causing them to travel downslope. If a slope exists under conditions that favor mass wasting but has not had any movement occur, the shaking force from an earthquake may jar the material loose from the slope.

India's population has more than doubled in the last 40 years. What is its population now?

India's current population is 1.2 billion people

Which type of motion will supply material to and maintain talus slopes?

Fall

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.

What is the difference between an aquifer and an aquitard?

An aquifer is a rather permeable rock, whereas an aquitard is an impermeable rock.

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.

How does an oxbow lake form?

An oxbow lake forms when the bend of a meandering river is isolated from the river because erosional forces create a cutoff in the main river channel. This isolated bend becomes the oxbow lake.

Recall from the introduction that karst topography exists because some minerals dissolve when they come into contact with rainwater. Minerals that contain calcium carbonate are especially susceptible to dissolving. Sinkholes and springs are common karst landforms that have the following characteristics: Sinkholes can develop slowly where rainwater infiltrates the dissolving soil and rock, slowly lowering the ground surface of an area. In these instances, sinkholes are shallow with gently sloping sides. Sinkholes can also form rapidly and catastrophically when the cave ceiling collapses, resulting in deep sinkholes with steep walls. Rainwater in karst landscapes flows on the surface differently than other types of terrain. Streams are fewer and less developed in karst areas because water readily infiltrates the ground. Limestone dissolution is often not spatially uniform. In some circumstances, nonuniform dissolution can lead to the formation of tower karsts, which are large structures of rock that have dissolved at a much lower rate than the surrounding rock that has eroded away. Which of the following is true about karst landscapes?

Karst topography erodes at different rates, meaning that tall karst towers might form. Sinkholes form from the same process as cave formations: the dissolution of minerals.

Groundwater refers to all the water flowing underground. Water can flow through permeable materials in the ground such as unconsolidated sediment and porous rock. The figure below shows the different zones of groundwater. The upper groundwater zone, called the vadose zone, consists of material whose pores are filled with water and air. The lower groundwater zone, called the saturated zone, consists of material whose pores are saturated with water. The water table is the boundary between the vadose zone and the saturated zone. The movement of water between the oceans, atmosphere, and land is called thehydrological cycle. Groundwater flow represents a critical part of the cycle. Approximately 40% of all water on land is returned to the oceans via a combination of surface runoff and groundwater flow. The other 60% is transported to the atmosphere by either evaporation or evapotranspiration (a type of evaporation facilitated by vascular plants). All of the water lost from the land is returned via precipitation from the atmosphere, after condensation initiates cloud development and subsequent rain cloud formation. The surface water can then migrate underground to form new groundwater in a process called infiltration.

Left to Right: Rain Cloud Cloud formation precipitation evapotranspiration evaporation surface runoff infiltration

Caves are erosional features, although depositional features form within them. Flowing and dripping water leave behind calcium carbonate, which is the precipitate of limestone dissolution. This precipitate in turn creates a form of limestone called travertine that is often white or cream-colored. Where and how these precipitates are deposited depends on how the water is dripping or flowing at a given location within the cave. Geologists have identified common formations within caverns, which are: Crystal formations that grow from the ceiling of a cave are called stalactites. These features have a cylindrical or conical shape and are formed as water leaves behind calcium carbonate when it is dripping off the ceiling and conical structures. Conversely, formations that grow from the floor of a cave are called stalagmites and are formed as water leaves behind calcium carbonate when it drips onto the floor or conical structure. Columns are stalagmites and stalactites that have joined. A flowstone forms where water flows on the walls or floor of a cave. The result is a sheet-like feature that is typically whitish or semi-translucent. Identify the above formations in the image below.

Left to Right: Column Stalacite Flowstone Stalagamite

The topography and subsurface of karst regions evolve together. The image below depicts how landforms and underground features form in this landscape over time. As described in the introduction, naturally acidic rainwater plays an important role in cave formation.Sinkholes develop on the ground surface as limestone dissolves. Cracks and crevices form along with sinkholes.With flowpaths now established from the surface to underground, rainwater passes into the subsurface.Eventually enough rock is dissolved so that a large airspace is opened, resulting in a cave. Formations begin developing once airspace is created. The action of water dripping and flowing in this airspace is what allows these formations to "grow."Caves often form within limestone rock at about the elevation of the water table. The elevation of the water table changes over time, which allows caves to expand vertically once the cave is established. Rank the following events in a single row from initial stages of cave development (left) to later stages of cave development (right).

Left to Right: Cracks and crevices develop in limestone in the subsurface. Water infiltrates the ground and flows through cracks and crevices. Limestone that is exposed to water dissolves, which widens the airspace. A cave forms now that much limestone has dissolved and a large airspace has been created. Formations such as stalactites and stalagmites form. Caves expand vertically due to water table elevation change.

When water winds up underground, it becomes part of the groundwater cycle. Water can only be present underground in areas where rocks have porosity—spaces or voids within the rock material. Well-rounded coarse-grained sediments usually have higher porosity. For water to move underground, rocks need to have permeability, or connections between pore spaces. Water seeped into the ground becomes part of the zone of soil moisture in areas where the ground is covered with soil. Typically, soil moisture and the rocks below are part of the unsaturated zone —an area above the water table where rocks and soil are not completely filled with water. The depth of the unsaturated zone depends on climate, depth of soil, and the type of vegetation. This is the zone from which plant roots draw water. The water table is the boundary between the unsaturated zone above and the saturated zone below. The saturated zone is where rocks are entirely saturated with water. If there is a significant and useable amount of water present in the saturated zone, it is called an aquifer.

Left to Right: Material of high porosity and permeability saturated zone unsaturated zone zone of soil moisture water table

Look at the figure below and determine which of these is true in terms of relative pressure and water table depth at locations A and B.

Location A has a higher pressure

Permeable rock strata that allow for the easy flow of groundwater through pores are called an aquifer. Groundwater moves by twisting and turning through small, interconnected openings. The smaller the pore spaces, the slower the groundwater flow. Porosity, the amount of pore spaces in a rock, and permeability, the ability of a material to transmit fluid, are two important concepts in groundwater movement and the formation of aquifers. Most sedimentary rocks, such as cavernous limestone, have a lot more pore spaces than igneous and metamorphic rocks, and in the case of igneous and metamorphic rocks, fractures must be present to provide voids or pores for an aquifer to develop. Porosity alone cannot measure a rock's capacity to yield groundwater, because rocks or sediments may be very porous, yet still not allow water to easily move through them. For example, clay has a high water storage capacity (porous), but its pore spaces are too small to make it a good aquifer. Hence, a rock or material has to have a high level of porosity and permeability to have the likelihood of being a good aquifer.

Low: Granite (igneous rock) with very few to no cracks Gneiss (metamorphic rock that used to be granite and underwent intense pressure) High: Conglomerate (sedimentary rock composed of various sizes of sediment such as pebbles and sand grains) Unconsolidated gravel and sand Sandstone (sedimentary rock composed of sand grains)

These Google Earth photos show the Colorado River, which has incised downward due to uplift of the Colorado Plateau. The canyon cut by this river is currently flooded due to a dam installed in northern Arizona in 1963, creating Lake Powell. A rincon, or an incised and abandoned meander, can be seen in the following images. The previous and present paths of the river are also outlined. You can see from the north-south line and elevation profile below that the rincon is higher in elevation than the current flooded canyon. This suggests that the river abandoned this meander while it was downcutting. This shortened the river course by six miles. Take a moment to think about how the Colorado River has evolved through time. Focus on how changing base level and stream incision created landforms, such as incised meanders and rincons, and arrange these events accordingly.

Oldest to Youngest A stream migrates laterally across its floodplain developing meanders. This stream terminates at a lake, which is its base level The base level of the stream is lowered by crustal uplift and the river begins to incise downward. Incised meanders form. A rincon forms by the cutoff of an incised meander, which shortens the river.

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.

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 do stalactites and stalagmites form?

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. 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.

Why do the Koli insist that they will never leave their waterfront community?

The Koli believe that the sea is their god and it is what feeds their children and how they make their living.

Why do the Koli believe they are deliberately being denied community services?

The Koli believe they are deliberately being denied community services as a means to force them to move from their valuable waterfront property.

What is the biggest threat to the Koli way of life?

The biggest threat to the Koli way of life is the overall decrease in the number of fish because of significant water pollution and Mumbai's population explosion.

What is the source of heat for most hot springs and geysers, and how is this reflected in the distribution of these features?

The heat sources for most hot springs and geysers are magma bodies and igneous rocks. Thus, hot springs and geysers are often located where igneous activity occurs.

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.

What factors led to the massive rockslide at Gros Ventre, Wyoming?

The sandstone layer had almost no support at the bottom of the slope, as it had been undercut by the Gros Ventre River. Heavy rains and meltwater seeped through the sandstone and saturated the clay underneath.

How does the water table change around a pumping water well?

The water table elevation decreases.

Various sources of pollution can contaminate groundwater. Groundwater can carry this pollution to surface-exposed waters such as oceans and rivers, thereby impacting marine and freshwater ecosystems. Groundwater can also transport pollution to wells used for drinking water or for farm irrigation. See the figure below for examples of groundwater pollution sources.

Top to Bottom: Uncontaminated Well Contaminated Well Uncontaminated Well

A type of aquifer called an unconfined aquifer is a good source of freshwater wells but can become easily contaminated because pollutants can easily flow into the water. Unconfined aquifers are not bound by aquitards. Confined aquifers have layers of impermeable material—aquitards—above and below. The aquifer may be under high pressure, which means that it requires little to no pumping to pull water to the surface at a well. Also, the impermeable layer on top of the aquifer protects it from surface contamination. Perched aquifers are usually small and sit atop an impermeable aquitard layer above the surrounding water table. Below you will find a rendering of the different aquifers and an aquitard.

Top to Bottom: Perched aquifer unconfined aquifer Aquitard confined aquifer

Which of the following is an erosional feature?

Tower karst

Caves, as formed from dissolution, are most commonly formed in limestone, but are occasionally found in other rock types, like gypsum.

True

Most caverns are created at or near the water table.

True

La Cañada Alamosa is a tributary of the Rio Grande, located in central New Mexico. Due to climatic changes, the local base level for this stream was lowered. This occurred many times as evident by the presence of multiple terraces. Rounded gravels present on the terraces represent former channel deposits. Using the following photos, classify the observations according to whether they are "true," or " false."

True: At least two episodes of downcutting have occurred. Rounded gravels provide evidence that these flat-topped features are terraces. False: Only one terrace is present at La Cañada Alamosa. The local base level for this stream is sea level.

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 geologic process is responsible for the geothermal features in Yellowstone National Park?

Volcanic activity

What is infiltration?

Water soaking into the ground

What factors cause water to follow the paths shown in the above diagram?

Water that enters the groundwater at the recharge areas moves downward due to gravity and then loops upward to the discharge areas due to water pressure.

How might a wildfire influence mass movement?

Wildfire destroys plants which anchor soils and loosen upper layers of soils, increasing mass movement events.

Wildfires, such as the ones in Montecito, California in 2018, contribute to mass wasting. What effect do they have?

Wildfires clear the slope of vegetation, leading to a more unstable slope.

What is a stream's longitudinal profile?

a cross-sectional view of a stream from the headwaters to its mouth

What is a floodplain?

a flat surface next to a river channel

What is a natural levee?

a ridge of flood deposits next to a river channel

water under pressure in a confined aquifer that will rise above the level of the aquifer.

artesian well

rock or regolith that can store and transmit water but is contained between two impermeable layers.

confined aquifer

If the velocity of a stream decreases, competence __________ and sediment is _____.

decreases, deposited

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

discharge

Mudflows are big enough to move in any direction, regardless of the orientation of the landscape.

false

Running water is the second most important erosional agent sculpting Earth's land surface.

false

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

floodplain

The flat, broad area surrounding a stream is referred to as a(n) _______

floodplain

A ________ is a process that can cause harm to people or property if they are sufficiently exposed.

geologic hazard

intermittent hot springs that periodically eject water into the air with great force.

geyser

Velocity and turbulence are _____ at the __________.

greatest; outside of a meander

Complete this analogy: Sliding is to gravel as dissolution is to_____________.

ions

In a river valley, mass-wasting processes can ______. CHOOSE ALL THAT APPLY.

make the valley walls less steep make the river valley wider

slide

mass movements in which there is a distinct plane of weakness between the slide material and underlying stable material.

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

Worldwide, the largest percentage of freshwater readily available to humans is stored in _______.

pore spaces between rocks and sediments

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

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

rolling, sliding, bouncing

Which type of mass wasting forms a crescent-shaped scarp at the head of movement?

slump

− a natural outflow of water where the water table intersects the surface.

spring

Which of the following can result from excessive pumping of groundwater? CHOOSE ALL THAT APPLY.

subsidence reversing the direction of flow in the aquifer saltwater contamination

Transpiration moves water from _______.

the biosphere to the atmosphere

What is suspended load?

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

What warms the waters that flow at Hot Springs National Park, Arkansas, and at Warm Springs, Georgia?

the geothermal gradient

When rain falls on land, what factors influence the amount of water that soaks in?

the nature of the surface material the intensity of rainfall the steepness of the slope the amount of vegetation on the surface

Why do some artesian wells not flow at Earth's surface?

the pressure surface is below ground level

What is the cone of depression?

the shape that the water table takes on near a pumping well

Which of the choices below is not a factor that causes infiltration and runoff to vary from place to place and from time to time?

time of the day

a type of calcite that is deposited at geothermal springs like Mammoth Hot Springs.

travertine

Creep is the most widespread mass-wasting process.

true

Point bars are locations where deposition occurs whereas cutbanks are locations where erosion occurs.

true

Trees will result in more slope stability than grasses.

true

rock or regolith that can store and transmit water and receives its recharge directly from the atmosphere.

unconfined aquifer

Which factor exerts the greatest control over the velocity of debris flows and the distance they will travel?

water content

dividing line between the vadose zone and the zone of saturation.

water table

When will a cone of depression stop enlarging?

when the amount of water flowing toward the well equals the amount of water being pumped out of the well

When might a well, Well A, go dry?

when the cone of depression of a second well intersects the deepest part of Well A

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

The following photo shows a typical cut bank on the Missouri River (iPhone for scale). Note the steep profile with fine-grained sediments above coarser sands and gravels.

A cut bank is located on the outside of a meander bend.

Why are urban areas susceptible to flash floods?

A high percentage of the surface area is covered with cement, asphalt, and other impervious materials

The Goosenecks of the San Juan River are located in southeast Utah. At this location, the San Juan River has cut a gorge through at least 1,000 feet (300 m) of Paleozoic sedimentary rocks. As mentioned in the video, this region was affected by uplift of the Colorado Plateau during the Cenozoic era. Base level was lowered and this river began to incise downward due to a steepened gradient. A raft on the San Juan would float more than 6 miles to match a crow flying straight for 1.5 miles above this landscape. The Google Earth image and photo below, which depict the same location from different angles, show two features, labeled A and B, that were created by downcutting of the San Juan River. Choose the correct pair of terms from the choices below.

A) incised meanders, B) terraces

The creation of which sedimentary feature is controlled in part by debris flows exiting a narrow canyon?

Alluvial fan

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.

Why might West Virginia have the landslide risk that it does?

Appalachian Mountains

X marks the site of oil drums that were illegally buried by the Shay-Dee Oil Corporation. These oil drums have begun leaking and the leaking oil has flowed downslope to the stream below, contaminating the stream. Which stream drainage basins would be affected by this oil?

C and A

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.

________ are flat areas along streams that are created by the deposition of alluvium and is subject to periodic inundation.

Floodplains

Look at the two graphs below. Label each graph with the scenario it most likely represents. Notice that for each graph, a similar rainstorm occurs, releasing a certain amount of water into the environment. The horizontal (x) axis represents time. The light blue curve shows the amount of streamflow (called river discharge) in each environment.

Graph 1: Flooding in an urban area This setting is more likely to produce flash floods. Concrete surfaces mean water flows directly to the stream or river after a storm. Graph 2: Abundant open farmland allows for infiltration of water into the ground. Flooding in a rural area

How is it possible for a landslide to occur without a trigger?

Long-term weathering weakens the rock past the strength necessary to maintain stability.

Which of the following scenarios represents the best nonstructural approach to flood control?

Managing a floodplain to limit development in sensitive areas

Define mass movement. How does it differ from erosional agents such as streams, glaciers, and wind?

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

________ is the downslope movement of rock, regolith, or soil under the direct influence of gravity.

Mass wasting

Stream valleys are produced through combined effects of mass wasting and running water. If running water alone were responsible for creating stream valleys, how would they appear?

Narrow valleys with vertical walls

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.

Which of the choices below correctly describes four main types of drainage patterns and what causes them?

Rectangular pattern, which develops on highly jointed bedrock; Trellis pattern, which develops in areas of alternating weak resistant bedrock; Dendritic pattern, which develops on relatively uniform surface materials; Radial pattern, which develops on isolated volcanic cones or domes

What term is commonly used to describe a sudden event in which large volumes of rock move down steep slopes?

Rockslide

During which season does solifluction occur in the Arctic, and why?

Solifluction occurs during the Arctic's summer, when the top meter or so of the active layer thaws. Because the resulting meltwater has nowhere to go, it saturates the active layer, causing it to slowly flow.

Why doesn't sea level drop even though oceans have a higher rate of evaporation than precipitation?

Surface water running off into the oceans makes up the difference between evaporation from the oceans and precipitation into the oceans, creating a balance.

In general, how do the channel width, channel depth, flow velocity, and discharge change between the headwaters and the mouth of the stream?

The channel width, channel depth, flow velocity, and discharge all increase as the stream approaches the mouth.

How did the debris from the Gros Ventre Landslide of 1925 lead to another disaster in the same region in 1927?

The debris blocked the river, creating a lake that later burst.

What is the angle of repose?

The steepest angle at which a material remains at rest

A stream is cutting into a valley wall. Which of the following is the most likely trigger for a mass wasting event?

The stream erodes the toe of the slope, which results in the slope becoming oversteepened.

Central Wisconsin and south-central Minnesota both have regions with the potential for landslides. However, neither of these locations is located in mountainous areas. Why might landslides occur in these specific regions?

These locations have steep bluffs along rivers

A ________ is not the sole cause of a mass wasting event, but the last of many causes that initiate the downslope movement of materials.

Trigger

What is the risk for landslides in West Virginia?

Very high potential

How does an alluvial fan form?

When a stream with a steep gradient emerges onto a relatively flat lowland, its gradient drops, and it deposits a large portion of its sediment load in a pattern that looks like a fan from above.

In what ways does a stream transport its load, and which part of the load moves most slowly?

as a bed load, which is the slowest mode of particle transport in streams as a dissolved load as a suspended load

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

drainage basin

One main cause of creep is ________.

expansion and contraction of soils during freezing and thawing

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

headwaters

A(n) _______ is a bend in a steep narrow bedrock valley.

incised meander

Which mass wasting process involved volcanically derived material from the eruption of Nevado del Ruiz and destroyed the city of Armero in 1985?

lahar

Examples of local base level include a stream or a(n) ______

lake

A flood plain is the flat area around the river extending from its channel to the edge of the wide valley.

left to right: point bar scroll bars cut bank floodplain

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

A sweeping bend of a stream which is migrating laterally in a wide, flat valley is called a(n) ______

meander

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? CHOOSE ALL THAT APPLY.

meanders well-developed floodplain

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

mouth

____ is a trigger for mass wasting. CHOOSE ALL THAT APPLY.

oversteepening of a slope adding water to sediments a wildfire

Below is a photo from the meandering channels at Missouri Headwaters State Park, in southwest Montana. At this location, the Missouri River is formed at the confluence of the Gallatin, Madison, and Jefferson Rivers. This river flows 2,341 miles before joining the Mississippi River, and is considered the longest river in the United States. Different processes influence the lateral migration of a meandering channel in its valley. Erosion, transport, and deposition all play significant roles in shaping a river through time. Focus on the locations in the channel where velocity is fast and slow, where along the channel erosion and deposition is occurring, and which direction the channel will migrate through time.

top to bottom: left arrow deposition slower water velocity faster water velocity erosion