Chapter 18 Mass Wasting (movement)
Mass Wasting – process in which gravity pulls soil, debris, sediment, and broken rock (collectively known as regolith) down a hillside or cliff Avoidance – approach for avoiding a geologic hazard such as mass wasting by learning to recognize the characteristics of an unstable slope and by not building or engaging in other activities there * with growing population, people are now building communities with neighborhoods in places like stream valleys that are prone to flooding, slopes of active volcanoes, fault zones with earthquakes hazards, shorelines where ocean is constant threat, and hillsides that are vulnerable to mast wasting * by moving onto and living on these areas, exacerbates the problem, makes area more dangerous Vaiont Dam
* dam in the Italian Alps, purpose to trap river in order to cerate reservoir and generate power for surrounding communities * building water level affected groundwater level, and walls of dam, accelerating downward movement of mountainside was filling the reservoir * massive block of soil 2 km long 1.5 km wide fell down the mountain into the reservoir, causing titanic wave 100 m high that overtopped the dam and slammed into town of Longarone, killing 2600 people Undercutting – river erosion removes rock at the base of the hillside that previously buttressed the limestone * dam survived and still stands, but dam closed and abandon Geological Engineering – study of geological processes and the role they play in engineering projects and safety, heavily focused on after the disaster Creep – slow, down slope migration of soil under the influence of gravity * occur over months to centuries
Solifluction – type of soil creep that occurs in water saturated regolith in cold climates * most is seen in permafrost zones – ground that is permanently frozen but develops a thawed layer in the summer * produces distinctive wave forms of slowly sliding soil on hill slopes where the top soil remains saturated with water for long periods but is able to slide on an underlying layer of weakness Slump – occurs when regolith suddenly drops a short distance down a slope, usually as a cohesive block of earth that simultaneously slides and rotates along a failure surface shaped like the bowl of a spoon * typically upper surface of the rotating block remains relatively undisturbed * especially common in places where clay rich sediments are exposed along a steep bank * often occur as result of human activity
Mud/Debris Flow – rivers of rock, earth, and other debris saturated with water * mud flows less viscous than debris flow because mud flow comprised of mud, while debris flow carry particles ranging in size as big as boulders distinguishing feature of debris or mud flow – tendency for material to exhibit turbulent flow characteristics (flows, not rolls or etc) * result from heavy rains in areas with abundance of sediment with steep slopes Rock Slides and Debris Slides – result when a slope fails along a plane of weakness * characterized by unconsolidated rock, debris, and regolith that have moved downslope along a relatively shallow failure plane * rock slide usually lacks debris instead consists of bocks or rock in a chaotic mass * popularly known as landslides
Rockfalls – occur when an accumulation of consolidated rock is dislodged and falls through the air, or free falls, due to force of gravity Debris falls – similar to rockfalls, but usually involce mixture of soil, regolith, vegetation, and rocks * closely associated with steep cliffs
Avalanches (type of debris flow) – fast-flowing, fluidized mass of snow, ice, air, and occasionally some regolith that cascades down a mountainside due to the collapse of a snowfield Lahars (type of mud flow)– mud flow composed of pyroclastic ash, lapilii, and water that flows down the slopes of a volcano * have consistency of concrete, fluid when moving but become...