Term
| 1. What is magma? What is it composed of? |
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Definition
| Magma is very thick underground liquid derived from melted rock material that contains small but significant amounts of dissolved gas, mostly water vapor and dissolved carbon dioxide. Most magmas come from the asthenosphere, the weak layer that underlies the lithospheric plates. |
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Term
| 2. What is viscosity, and what determines it? |
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Definition
| Viscosity is the measure of resistance to flow in fluids (it is the opposite of fluidity). Viscosity is determined by both silica content (as silica content increases viscosity increases) and temperature (as temperature increases viscosity decreases). Thicker fluids have greater viscosity. |
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Term
| 3. Explain the relationship between magma composition, viscosity, and gas content. |
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Definition
| Silicic magmas have longer chains of silicate minerals and are more viscous than mafic magmas. Silicic magmas also tend to have more dissolved gases in them than mafic magmas and are more explosive when they erupt. |
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Term
| 4. List the major types of volcanoes and the type of magma associated with each. |
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Definition
• Shield volcano (Basaltic magma)
• Composite volcano (Combination of basaltic, andesitic and rhyolitic magma)
• Volcanic Dome (Rhyolitic magma)
• Cinder cone (Basaltic magma) |
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Term
| 5. Describe the major types of volcanoes and their eruption styles. Why do they erupt the way they do? |
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Definition
Shield volcanoes form from relatively nonexplosive lavas due to their low silica content and low dissolved gas content. However, shield volcanoes can produce tephra, which is explosively ejected material.
Composite volcanoes, also called stratovolcanoes, are composed of both pyroclastic debris and less explosive lava flows. If one could cut these volcanoes in half from top to bottom, the alternating types of flow create a striped effect. Volcanic domes form from highly explosive eruptions, when highly viscous magma rises to slowly fill the volcanic vent after a major eruption. These are explosive because they are highly viscous and have large amounts of dissolved gas.
Cinder cones form by the accumulation of tephra around a volcanic vent. Hot-spot oceanic basaltic volcanoes typically form shield volcanoes, or smaller volcanoes known as seamounts and guyots. These have little dissolved gases and are not particularly explosive.
Hot-spot continental rhyolitic magma forms large caldera complexes, such as Yellowstone caldera. These may accumulate large amounts of dissolved gases and produce tremendously explosive and powerful eruptions. |
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Term
| 8. Explain the relationship between the Hawaiian Islands and the hot spot below the big island of Hawaii? |
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Definition
| The hot spot below Hawaii is responsible for creating the entire island chain. The hot spot appears to have been stationary for millions of years while the Pacific plate was moving over the hotspot and toward the northwest. As the plate moved, the hot spot essentially burned a hole in the overriding plate, erupting a series of volcanoes that are older to the northwest, and ending with the currently active calderas on Hawaii. The period of time that the hot spot has been active is the period of time in which the Hawaiian Islands formed. Currently, another "island" to the southeast of the big island of Hawaii is beginning to form. |
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Term
| 9. How do geysers work? How can they be hazardous? |
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Definition
| Geysers originate when groundwater comes into contact with hot rock in an underground thermal chamber. As the water gets closer to the hot rock, the water begins to boil, producing sporadic or episodic stream-driven releases of water and steam. Geysers can be unpredictable and as the caldera in which they form remains active there is a potential hazard from future volcanic eruptions. |
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Term
| 10. Explain how large caldera eruptions occur and why they are so dangerous? |
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Definition
| Caldera eruptions are dangerous because they are formed during explosive ejections of magma. Calderas contain volcanic vents that spew forth lava and pyroclastic debris in huge quantities. Some caldera eruptions have changed global climate for years. |
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Term
| 1. Explain how levees and floodwalls can actually worsen flooding. |
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Definition
| Levees adversely affect the natural processes of the river, and actually make floods worse. The first effect they have is to confine the river to a narrow channel, causing the water to rise faster than if it were able to spread across its floodplain. Additionally, since the water can no longer flow across the floodplain it cannot seep into the ground as effectively, and a large amount of water that would normally be absorbed by the soil now must flow through the confined river channel. The floods are therefore larger because of the levees. |
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Term
| 2. How is a drainage basin defined? |
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Definition
• Drainage basin, watershed, river basin, or catchment
• Area drained by a single stream |
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Term
| 3. What are the three components that make up the total load of a stream? |
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Definition
| The total load of a stream is made up of bed load (sand and gravel particles that slide, roll, and bounce along the channel bottom in rapidly moving water), suspended load (very small silt and clay particles that are carried above the stream bed by the flowing water) and dissolved load (dissolved chemical materials). |
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Term
| 4. What were the lessons learned from the 1992 flood of the Ventura River? |
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Definition
| We learned that a river's flooding history needs to be studied as part of the flood hazard evaluation; engineering models that predict flood inundation are inaccurate when evaluating distributary channels on river deltas where extensive channel filling, scouring, and lateral movement are likely to occur; historical documents such as maps should be evaluated. |
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Term
| 5. Differentiate between braided and meandering channels. |
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Definition
• Braided channels
• Contain sand and gravel bars that divide and unite a single channel
• Meandering channels
• Migrate back and forth within a floodplain
• Cutbanks
• Point bars |
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Term
| 6. Differentiate between pools and riffles. |
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Definition
o Riffles
• are formed in shallow areas by coarser materials such as gravel deposits over which water flows.
o Pools
• are deeper and calmer areas whose bed load (in general) is made up of finer material such as silt. |
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Term
| 7. How do the characteristics of upstream and downstream floods differ? |
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Definition
Downstream/regional
• cover a wide area
• large river valleys with low topography
• produced by storms of long duration
• widespread cyclonic systems → prolonged, heavy rains |
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Term
| 8. What are the primary and secondary effects of flooding? |
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Definition
• primary effects
• Injury and loss of life
• Damage caused by currents, debris and sediment to forms, homes, building, railroads, bridges and roads
• Erosion and deposition of sediment related to loss of soil and vegetation.
• Secondary effects
• River pollution
• Food supply problems
• Disease
• homelessness |
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Term
| 9. What are the major factors that control damage caused by floods? |
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Definition
• Land use on flood plain
• Depth and velocity of floodwaters
• Rate of rise and duration of flooding
• Season
• Quantity and type of sediment deposited
• Effectiveness of forecasting, warning, and evacuation |
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Term
| 10. What is flashy discharge? How is it hazardous? |
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Definition
| Flashy discharge is a type of flood characterized by short lag times between rainfall and the very rapid rise and fall of floodwater. These types of floods are characteristic of urbanized areas where ground surfaces have been paved over and the rain waters cannot infiltrate the ground, resulting in hazardous fast moving high floods that rapidly dissipate. |
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Term
| how does urbanization affect the flood hazard? |
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Definition
• Increases magnitude and frequency of floods
• Urban areas have impervious cover and greater storm sewers.
• Carries water to stream channels more quickly
• Decreases lag time
• Bridges block debris, creating dams.
• Changes shape of hydrograph, making curve much steeper
• Good news: urban flood might only last 20% as long
• Bad news: urban flooding could be four times higher |
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Term
| 12. What do we mean by floodplain regulation? |
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Definition
• Floodplain Regulation
• Land-use specification for floodplains in urban areas |
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Term
| 13. What constitutes channelization? |
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Definition
| Engineering technique to straighten, widen and deepen, or otherwise modify a natural stream channel. |
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Term
| 14. What is channel restoration? |
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Definition
| The process of returning a stream and adjacent areas to a more natural state. |
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Term
| 15. Describe the techniques that are used for flood proofing. |
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Definition
• Raising foundation above flood hazard
• Construction flood walls or mounds
• Using waterproofing construction
• Installing improved drains and pumps |
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Term
| 16. What do we mean when we say that a 10-year flood has occurred? |
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Definition
| A 10-year flood means that a given level/magnitude of flooding is likely to reoccur once every 10 years. There is a 10% chance per year that a 10-year flood will occur. 1 year/10 years = 10% |
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Term
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Definition
| A landslide is any type of downslope movement of earth materials including earthflows, debris flows, rock falls, and avalanches. |
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Term
| 2. What are slope segments? |
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Definition
| Slope segments are the different parts of a slope that may be straight or curved, and have different dips and characteristics from adjacent segments. |
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Term
| 3. What are the different types of slope segments and how do they differ? |
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Definition
| A free face is a nearly vertical segment. The talus slope forms at the base of the cliff and is composed of fallen rock fragments. An upper convex slope makes up what would be the top of a hill as it begins to slope down. The lower concave slope makes up the valley area and the straight slope is between the two. |
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Term
| 4. What are the three main ways that materials on a slope may fail? |
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Definition
| Materials may fall (freefall), slide, or slump (flow) off the face of a slope. |
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Term
| 5. What is the safety factor and how is it defined? |
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Definition
| The safety factor (SF) is the ratio of the resisting forces to the driving forces. |
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Term
| 6. How do slumps (rotational slides) differ from soil spits and rock slides (translational slides)? |
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Definition
| Slumps have curved slip surfaces, while translational slides have planar slip surfaces. |
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Term
| 7. How does the slope angle affect the incidence of landslides? |
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Definition
| In general, the steeper the slope the greater the driving force, and therefore as the slope angle increases, the incidence of landslides will increase as well. |
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Term
| 8. How and where do debris flows occur? |
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Definition
| Debris flows are thick mixtures of mud, debris, and water that form on slopes after rainfall. They occur on mountains in North America, more specifically the Great Plains, the Arctic, the Great Lakes, and the southwestern United States. |
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Term
| 9. What are the three ways that vegetation is important in slope stability? |
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Definition
| Vegetation is important because it provides a protective cover that cushions the impact of falling rain, plant roots add strength and cohesion to slope materials, and the vegetation also adds weight to the slope. |
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Term
| 10. Why does time play an important role in landslides? |
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Definition
| Time plays an important role because forces often change with time. What may be affecting a slope one year may have no effect in subsequent years. |
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Term
| 11. What variables interact to cause snow avalanches? |
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Definition
| Snow avalanches are affected by steepness of the slope, stability of the snowpack, and the weather. |
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Term
| 12. What is the angle of repose? |
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Definition
| The angle of repose is the steepest angle at which any snow or loose material is stable. |
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Term
| 13. What are the two types of snow avalanches and how do they differ? |
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Definition
| The two types of snow avalanche include loose snow avalanches—which start at a point and widen as they move downhill—and slab avalanches, which start as cohesive blocks of snow and ice that move downslope. |
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Term
| 14. How might processes involved in urbanization increase or decrease the stability of slopes? |
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Definition
| Urbanization, the expansion of urban areas, transportation networks, and natural resource use, has increased the number and frequency of landslides. Many slopes are over steepened to make way for roads, buildings, and other features. Natural vegetation is sometimes removed, further reducing slope stability. However, where these problems are recognized, the number of events has decreased due to preventative methods. |
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Term
| 15. What types of surface features are associated with landslides? |
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Definition
| Surface features associated with landslides are crescent-shaped cracks on a hillside, a tongue-shaped area of bare soil on a hillside, large boulders at the base of a cliff, exposed bedrock laying parallel to the cliff, tongue-shaped masses of sediment, and irregular land surface at the base of the slope. |
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Term
| 16. What are the main steps that can be taken to prevent landslides? |
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Definition
| Some of the main steps taken to avoid landslides are drainage control, grading, and slope supports. |
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Term
| 6. Explain the relationship between plate tectonics and volcanoes. |
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Definition
| Tectonic setting determines the type of volcano. Mid-ocean ridges produce lava plains. Subduction zones produce composite volcanoes. Hot spots beneath oceans produce basaltic shield volcanoes, while hot spots beneath continents produce caldera-forming eruptions and rhyolitic magma. |
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Term
| 7. How do lava tubes form and move magma far from the erupting vents? |
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Definition
| Lava tubes help move magma far from the erupting vents because the tubes insulate the magma, preventing a drop in temperature which would cause solidification of the magma closer to the eruption site. |
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Term
| 11. Describe the primary and secondary effects of volcanic eruptions. |
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Definition
Primary effects of volcanic eruptions are direct results of the explosion. These effects include lava flow; pyroclastic activity, such as ash fall, pyroclastic flows, and lateral blasts; and the release of volcanic gases.
The primary effects cause secondary effects of volcanic eruptions. These effects include debris flow, mudflows, landslides, debris avalanches, floods, fires, tsunami, atmospheric changes, loss of crop productivity, disease, and displacement of populations. |
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Term
| 12. What methods have been attempted to control lava flow? |
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Definition
| Some methods which have been attempted to control lava flow include bombing, hydraulic chilling with fire hoses, and wall construction. |
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Term
| 13. Differentiate between ash falls, lateral blasts, and pyroclastic flows. |
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Definition
Ash falls are fine-grained rock and volcanic glass fragments and gas blown high into the air by volcanic explosions that settle back to earth.
Lateral blasts happen when an explosion destroys part of the volcanoes as gas, ash, and rock fragments are blown horizontally from the sides of the mountain. The eruption of Mount St. Helens in 1980 involved a lateral blast. The eruptions move at high speeds and can be very destructive. Ash flows, also known as nueé ardentes, are avalanches of very hot pyroclastic material blown out of a vent moving rapidly down the side of the volcanoes. |
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Term
| 14. What are the major gases emitted in a volcanic eruptions? How can they be hazardous? |
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Definition
| The major gases emitted in a volcanic eruption are water vapor, carbon dioxide (CO2), carbon monoxide (CO), sulfur dioxide (SO2), and hydrogen sulfide (H2S). Carbon dioxide can flow from volcano into valleys below, displacing the air and suffocate people and animals. Carbon monoxide, hydrogen sulfide and sulfur dioxide are toxic. In addition, Sulfur dioxide can react in the atmosphere to produce acid rain. The most dangerous gases include carbon dioxide, sulfur dioxide, and hydrogen sulfide. |
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Term
| 15. Explain how volcanoes can produce gigantic debris or mudflows. |
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Definition
| Volcanoes can produce debris flows and mudflows when large amount of loose volcanic ash and other tephra are saturated with water, become unstable and suddenly move downslope. In some cases volcanic eruptions cause quick melting of ice and snow on the volcano, suddenly adding huge quantities of water to the slope. |
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Term
| 16. What kinds of information help geologists forecast volcanic eruptions? |
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Definition
| Some possible methods for forecasting volcanic eruptions are monitoring seismic activity; monitoring thermal, magnetic, and hydraulic conditions; monitoring the land surface to detect tilting of swelling of the volcano; monitoring of volcanic gas emissions; and studying the geologic history of a particular volcano or volcanic center. |
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Term
| 17. Explain the USGS alert notification system for volcanic eruptions. |
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Definition
| This system has two components: ground-based volcanic alert levels and aviation-based color code levels. Each component has four levels and for most monitored volcanoes and eruptions, the alert and aviation code will be at the same level. For some eruptions, the hazard posed to either those on the ground or in the air will differ. |
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Term
| 1. How does limestone bedrock dissolve? |
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Definition
| Limestone will dissolve if the percolating water—fresh surface water that flows through holes in the rock—is acidic. |
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Term
| 2. Which rock types are especially susceptible to dissolution? |
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Definition
| Several common sedimentary rocks—rock salt and rock gypsum, limestone and dolostone, and marble—are easily dissolved. |
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Term
| 3. What features are found in karst areas? |
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Definition
| Sinkholes, rolling hills (caused by an area of subsidence), cave systems, disappearing streams, collapse sinkholes, tower karst, and springs are all found in karst areas. |
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Term
| 4. Describe the two processes by which sinkholes form. |
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Definition
Solutional sinkholes form by dissolution on the top of a buried bedrock surface. This occurs where the downward infiltration of acidic groundwater becomes concentrated in holes created by joints and fractures. In the formation of these sinkholes, groundwater is typically drawn into a cone above a hole in the limestone, like water being drawn into a sink drain.
Collapsible sinkholes develop by the collapse of surface or near-surface material into an underground cavern. |
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Term
| 5. How do cave systems form? |
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Definition
| Cave systems form when solutional pits enlarge and move downward. The primary system for cave forming is groundwater moving through rock, typically following joint systems. |
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Term
| 6. Describe the natural cycle of permafrost thawing and how climate change has influenced this cycle. |
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Definition
| Permafrost occurs in polar regions and at high altitude where much of the soil and underlying rock remain frozen year round. As the ice in permafrost soil melts, there can be great subsidence of several meters or more. Without human impact, permafrost thawing will melt the few meters of soil and will refreeze in the winter; however, irregularly large amounts of permafrost have thawed due to global warming. This irregularity is referred to as thermokarst terrain. |
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Term
| 7. What keeps a delta plain from subsiding? |
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Definition
| In a delta plain, natural subsidence must be balanced by additional sediment to keep the land surface of the delta from sinking below sea level. Without the addition of sediment a delta plain tends to subside. |
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Term
| 8. What happens to organic soils when they are drained of water? |
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Definition
| When organic soils are drained of water, they dry out and compact. After they are exposed for a period of time to weathering processes, they literally disappear. |
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Term
| 9. Explain how expansive soils shrink and swell, how frost heaving occurs, and how collapsible soils subside. |
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Definition
| Expansive soils swell due to the absorption of water during wet seasons, and they shrink as water evaporates during dry seasons. Frost heaving occurs because of the 9 percent volume increase that occurs when water changes to ice. Collapsible soils subside due to percolating water weakening the bonds of clay particles and dissolving minerals that hold the soil together. |
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Term
| 10. What natural and artificial features might indicate the presence of expansive soils? |
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Definition
| Deep cracks, popcorn like weathering texture, an alternating pattern of mounds and depressions, a series of waves and bumps in asphalt soils, tilting and cracking of concrete in sidewalks and foundations, and random tilting of gravestones and utility poles are all signs of expansive soils. |
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Term
| 11. What factors influence the moisture content of expansive soils? |
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Definition
| Climate, vegetation, topography, drainage, and quality of construction are all factors that affect the moisture content of a soil. |
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Term
| 12. Explain how subsidence might be connected to earthquakes in subduction zones. |
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Definition
| Subsidence may be connected to earthquakes in subduction zones because the strain between great earthquakes which builds up due to "locked" plates may cause the continental plate to buckle. This drags the underwater seaward edge of the continent downward and produces an upward bulge along the coast. |
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Term
| 13. What causes subsidence on a volcano? |
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Definition
| When the magma is forced out of the volcano, the magma chamber contains less material because the lava is now on the surface. The drained magma chamber buckles under the weight of the volcano, causing subsidence. |
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Term
14. Identify the types of subsidence hazards that are likely to be found in the:
a. Eastern United States:
b. Western United States:
c. Alaska and Canada: |
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Definition
a. Eastern United States: Karst subsidence and groundwater withdrawal subsidence.
b. Western United States: Karst, subsidence caused by compaction of sediment, expansive soils, groundwater withdrawal subsidence, and seismic related subsidence.
c. Alaska and Canada: Permafrost, expansive soils, and seismic related subsidence. |
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Term
| 15. Which subsidence or soil volume change hazards cause the most economic damage? Why are these hazards so costly? |
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Definition
| Karst and expansive soils cause the most damage each year. Karst damage is expensive because it causes sinkholes, groundwater pollution, and variable water supplies. Expansive soils are expensive because they cause damage to highways, buildings, bridges, pipelines, and other structures. |
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Term
| 16. What factors contribute to the formation of sinkholes? |
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Definition
| Some factors which contribute to the formation of sinkholes are the lowering of groundwater, dissolution of limestone, and human activities that cover any evidence of a possible sinkhole, causing huge amounts of damage after building construction after the evidence was buried. |
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Term
| 17. Why is groundwater sometimes polluted in karst terrains? |
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Definition
| Sometimes pollution comes from sinkholes which have been used for waste disposal, or when polluted surface water flows into groundwater through caves and fractures in the rock. |
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Term
| 18. What are the natural and anthropogenic causes for subsidence of the Mississippi Delta and New Orleans? |
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Definition
| New Orleans is below sea level. The only thing preventing it from disaster is the ring of levees surrounding the city. If a hurricane comes. many people will be trapped as there is only one exit out of the city, and a large tidal surge could inundate much of the city. Further, if the Mississippi changes course, then the current Mississippi delta will subside below sea level. |
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Term
| 19. What types of damage are caused by the thawing of permafrost, shrinking and swelling of soil, and frost heaving? |
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Definition
| The damage caused from the thawing of permafrost includes damage to highways, buildings, and other structures. Shrinking and swelling of soil causes similar damage; as the volume of the ground and soil changes, overlying buildings, roads, and buried pipelines must also change shape or fracture to accommodate the changing soil volume. Most structures crack. |
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Term
| 20. How are subsidence and soil volume change hazards linked to changes in climate? |
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Definition
| Drought conditions lower the groundwater table, resulting in shrinkage of unconsolidated earth materials. As global warming melts the permafrost in the Arctic, it contributes to the increasing sea level. |
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Term
| 21. What are the natural service functions of subsidence? |
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Definition
| Karst terrains are some of the world's most precious sources of drinkable water. Forty percent of the U.S. population relies on karst terrains for drinking water. |
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Term
| 22. Explain how fluid withdrawal and mining can increase subsidence. |
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Definition
| Both fluid withdrawal and mining increase subsidence because the techniques remove material from the ground. The surface above the void exerts force downward. Eventually there is a point where the surface can no longer be supported at its original height and so it subsides. |
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Term
| 23. How can we minimize or adjust to subsidence and soil volume change hazards? |
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Definition
| Injection wells can minimize or stop subsidence from fluid withdrawal. Preventing mining in urban areas will prevent the damage caused by subsidence. Buildings on permafrost are now installing screw jacks or lattice-like foundations to allow for the freezing and thawing. For communities on deltas, the only option is to continue to raise the levees and allow swamps in nearby unpopulated areas. In general, people should avoid building on subsidence-prone areas. |
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