ch.15 mass wasting and hazards
Terms in this set (25)
1.) discuss the meaning of the term landslide
-a sudden event in which large quantities of rocks and soil plunge down steep slopes
-example of geologic process of mass wasting
-can occur in connection with other major natural disasters including earthquakes, volcanic eruptions, wildfires, and sever storms
after weathering breaks rock apart gravity moves the debris downward , can be a slow or fast movement
2.) what is the controlling force of mass wasting?
-the downslope movement of rock, regolith, and soil under the direct influence of *"gravity"
-it is a distinct from other erosional processes bc it doesn't require a transporting medium such as water, wind, or glacial ice
weathering and mass wasting
-once weathering weakens and breaks the rocks apart, mass wasting transfers the debris downslope, where a stream or glacier acting as a conveyor belt, usually carries it away
3.) in what environment are rapid, mass-wasting processes most likely to occur?
-most rapid and spectacular mass wasting events occur in areas of rugged, geologically young mountains
-newly formed mountains are eroded by rivers and glaciers into regions w steep and unstable slopes--- then landslides happen
1.) How does water affect mass-wasting processes
-mass wasting is sometimes "triggered" when heavy rains or periods of snow-melt saturate surface materials
-the water does not transport the material, rather it allows gravity to more easily set the material in motion
2.) Describe the significance of the angle of repose
-it is the stable slope loose, granular particles assume
-steepest angle at which material remains stable
-angle can vary from 25 to 40 degrees
-oversteep slopes are another trigger of mass movement
3.) how might a wildfire influence mass wasting?
-when anchoring vegetation are removed by forest fires or by people for (timber, farming, houses) surface materials frequently move downslope
-plants contribute to stability of slopes bc their roots bind soil together
4.) describe the relationship between earthquakes and landslides
-can be a trigger for landslides/mass wasting
-an earthquake and its after shocks can dislodge enormous volumes of rock and unconsolidated material
1.) what terms are used to describe the way material moves during mass wasting?
-different types are classified based on the type of material involved, the kind of motion displayed and the velocity of the movement
-fall, slide, flow
when the movement in a mass wasting event involves the free fall of detached individual pieces of any size
-common when slope are so steep that loose material cannot remain on the surface
-way "talus slopes" are built
are a type in which debris piles up to a characteristic angle of repose. When new debris is added to the slope, thereby locally increasing the angle, the slope adjusts by movement of the debris to reestablish the angle.
**type of mass wasting it results in ROCK FALL
-when there is a distinct
zone of weakness
separating the slide material from the more stable underlying material
when the surface of the rupture is a concave upward curve that resembles the shape of a spoon and the descending material exhibits a downward and outward rotation
when a mass of material moves along a relatively flat surface such as a joint, fault, or bedding plane
-exhibit little rotation or backward tilting
occurs when material moves downslope as a vicious fluid
-most flows are saturated with water
2.) why can rock avalanches move at such great speeds?
-avalanche is most rapid type of mass movement
-high velocities result when air becomes trapped and compressed beneath the falling mass of debris, allowing it to move as a buoyant flexible sheet across the surface
2.) Both slumps and rockslides move by sliding. How do these processes differ?
-slumps: downward sliding of a mass of rock or unconsolidated material moving as a unit along a curved surface
-usually slumps don't move fast or far, earth flows frequently form at base of slump
-ex: of a rotational slide
-rockslides: occur when blocks of bedrock break loose and slide down a slope , very fast and destructive
-debris slide, when material involved is largely unconsolidated
3.)What factors led to massive rockslide at Gros Ventre, Wyoming
-water from heavy rains and melting snow seeped through the sandstone saturating the clay below
-bc much of the sandstone layer had been cut through by the Gros Ventre river the layer had virtually no support at the bottom of the slope
-the sandstone could no longer hold its position on the wetted clay and the gravity pulled the mass down the side of the valley
4.) How is a lahar different from a debris flow that might occur in southern california?
-debris flow is a relatively rapid type of mass wasting that involves a flow of soil and regolith containing a large amount of water (mudflow when material is fine grained)
-debris flow poses a serious hazard to development in relatively dry mountain areas such as southern california (house building, removal of vegetation by wildfires can increase this)
-lahars are debris flows composed mostly of volcanic materials on the flanks of volcanoes
5.) contrast earth flows and debris flows
-debris flows are frequently confined to channels in semiarid regions
-earth flows most often form on hillsides in humid areas during times of heavy precipitation or snowmelt, are generally more viscous so slower moving
1.) describe the basic mechanisms that contribute to creep. how might you recognize that creep is occurring?
-is a type of mass wasting that involves the gradual downhill movement of soil and regolith
-one factor that contributes to creep is the alternating expansion and contraction of surface material caused by freezing and thawing or wetting and drying
-aided by anything that disturbs the soil (raindrop impact, disturbance by plant roots, burrowing animals, saturation by water)
-bent rock layers, curved tree trunk, titled fence
2.) During what season does solifluction in the arctic occur? explain why it occurs only during that season
-common wherever water cannot escape from the saturated layer by infiltrating to deeper layers
-common in regions with permafrost(permanently frozen ground) -- aka arctic climates
is a special type of creep that occurs in areas of permafrost. Permafrost refers to the layer of groundwater that fills in the pore spaces of soil and rock that is permanently frozen.
3.) what is permafrost? how might disturbing permafrost lead to unstable ground that may slide, flow or subside?
-permanently frozen ground
-occurs where summers are too short and cool to melt ground more than a shallow surface layer
-when people disturb the surface such as by removing insulating vegetation or by building houses/roads the delicate thermal imbalance is disturbed and permafrost can thaw
-thawing produces ground that may slide, slump, subside
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