Chapter 14 - Mass Wasting
creep details
aided by alternate expansion and contraction of surface material - freezing and thawing, imperceptibly slow - cannot be seen
stable slope angle
angle of repose, different for various materials
landslides occur..
as a result of earthquakes, rain
rockslide
blocks of bedrock break loose and slide downslope
soil
combination of regolith, organic matter, water and air
slow
creep, solifluction
slow mass wasting
creep, solifluction
unconsolidated material
debris, mud, earth
type of material
debris, mud, earth, or rock
role of water
diminishes particle cohesion (friction), adds weight
earthquakes as triggers
dislodge rocks and unconsolidated material
mass wasting
downslope movement of rock, regolith and soil via gravity
slump
downward sliding of mass of rock or unconsolidated material as unit along curved surface
type of motion
fall, slide, or flow
fall
free-falling pieces
slopes form
from mountain building and volcanic processes
rockslide details
generally very fast and destructive, occurs where rock strata are inclined or joints and fractures in the rock are parallel to slope, triggered by rain or melting snow - common in spring
creep
gradual downhill movement of soil and regolith
solifluction
gradual flow of saturated surface layer underlain by impermeable layer (permafrost)
control of mass wasting
gravity, other factors overcome inertia to enable mass wasting to occur
distinct from erosion b/c
it does not require a transporting medium
regolith
layer of rock and mineral fragments produced by weathering
slope materials weaken over time b/c
long-term weathering, infiltration of water
damage
mass wasting caused by earthquakes can cause more damage than the earthquake itself
when slope becomes unstable..
mass wasting occurs
translational slide
material moves along a flat surface - joint, fault, bedding plane
slide
material moves along a surface as a coherent mass
flow
material moves as a viscous fluid
debris flow details
mudflows, often confined to canyons and channels, common in semiarid regions - limited vegetation, rate of flow depends on slop and water content
earthflow details
occurs on hillside in humid area, water saturates soil, material breaks away leaves scar that forms tongue or lobe that flows downhill, highly viscous - slower than debris
slump details
often consists of multiple blocks, occurs along oversteepened slopes, materials above held in place by material below, anchor at base is removed, unstable material above reacts to gravity
permafrost
permanently frozen ground (below zero Celsius for two or more years), ice underground affects behavior at surface, thawing produces unstable ground (slide, slump, subside)
removal of vegetation
plant roots bind soil, becomes unstable (?)
solifluction (soil flow)
promoted by a dense clay hardpan or impermeable bedrock layer, common in regions underlain by permafrost, can occur on gentle slopes
debris flow
rapid flow of soil and regolith containing large amount of water
rate of movement
rapid or slow
prevent mass wasting
revegetation, regarding terraces, reduce subsurface water, prevent undercutting (relocate river channel), prevent undercutting (add rip rap), construct safety structures (retaining wall, rock bolts)
mountains are eroded by
rivers and glaciers to form steep, unstable slopes
bedrock
rock
in order for mass wasting to occur, there must be..
slopes
mass wasting and erosional processes...
slowly lower land surface
rapid mass wasting
slump, rockslide, debris flow, earthflow
fast
slump, rockslide, debris flow, earthquake
effects of mass wasting and running water produce
stream valleys
rotational slide
surface of rupture is concave upward, descending material moves downward, with outward rotation
processes based on
type of material, type of motion, rate of movement
earthflow
unconfined flow of clay-rich soil on hillside after heavy precipitation
lahar
volcanic mudflow, triggered by volcanic activity - eruption
liquefaction
water-saturated surface materials behave as fluid-like masses that flow, caused by earthquakes
process that follows
weathering