37 terms

mass waqsting, floods, and field trip

Natural Disasters BYUI Nelson Fall 2011
What forces will effect mass wasting
Slope -stable vs. unstable
pore h2o -unsaturated, partially, saturated
material -igneous, layered, sediment
orientation-dips upslope, horizontal, dips downslope
vegetation -no development, moderate, extensive
what changes the resistant forces and driving forces as conditions/factors on the slope charge
Saturation of the material
Over-steepening of the slope
Slope Modification
Ground vibrations
Expansion/contraction cycles of soil/regolith
what processes/events enhance the likelihood of mass wasting
examples of how these factors change the resistant and driving forces and what impact this may have on a slope
saturation of the material-increase pore pressure (increase downslope force decrease cohesion force)
over steepening increases weight, decreasing the resisting force
slope modification -a decrease in cohesive force &/or increase downslope force due to added weight will occur
ground vibrations-decrease in cohesive force
expansion/contraction cycles of soil/regolith-
identify localities that may be vulnerable, what factors are influencing this risk
how are mass wasting events classified
type of material (bedrock, unconsolidated material--soil, regolith, sediment)
rate of movement (mm/yr, km/hr)
Water content (dry, wet)
Type of motion (fall, slide, flow)
free fall of detached particles, slope teep enough that material falls to base
material remains cohesive and moves along a well-defined surface
material moves downslope as a viscous flow/ most are saturated with water
two types of slides
translational and rotationals
type of slide-donward rotation of rock along a concave upward curved surface (block remains relatively undisturbed) leave scarps on hill slopes--generally as a result from human activity--heavy rain and earthquakes can also trigger slumps
DEBRIS FLOW often associated
why do rotational slumps occur?
water often squeezed out of top material and redistributed to lower portion of the slide causing it to flow and form in lobate structures
sediment flow
mixture of rock with some water or air that begin to flow down slope due to gravitational forces
slurry flow
material moves as a viscous fluid or diplsays plastic movement
common in arid and semi arid enviornments triggered by rain
generally around pre-existing channels
the very slow (mm/yr) usually continuous movement of regolith down slope
expansion/contraction cycles play a key role
evidence of creep
bent trees, offests in roads and fences and inclined utility poles
expansion/contraction cycles
movement of material due to wetting and drying cycles
freeze-thaw cycles
flowage of regolith where material remains saturated for very long periods of time
produces distinctive lobes on hill slopes. similar to creep
occurs mainly in regions underlain by permafrost (permanently frozen water bearing ground)
during warm periods top portion thaws and becomes saturated
saturated zone flows over frozen layers
debris flow
flowing regolith with velocities between 1m/yr and 100m/hr caused by saturation of the regolith with water
-occasionally start with slumps then flow down hill forming lobes with an irregular surface consisting of ridges and furrows
common after heavy rains
common in semi-arid regions and along volcanoes (some lahars)
what is in a debris flow
mixture of rocks, mud, and water
Aberfan Wales
debris flow--school crushed
highly fluid, high velocity mixture of sediment and water that has a consistency ranging between soup-like and wet concrete
result of heavy rains in areas were there is a lot of loose sediment
mudflows can travel for long distances over gently sloping stream beds
common near volcanoes
Snow avalanche
loose snow type=start at a point and gets wider
slab type--cohesive blocks move downhill
Slope mitigation-stop the flow
barrier walls
rock dams
wire mesh
slope mitigation-stabilize the slope
slope mitigation-divert the flow
diversion channels
rock ledges
slope mitigation-remove the hazard
change the slope
scaling and trimming
slope mitigation-remove the water
driving drainpipes into the hillside
-remove some sub-surface water and help stabilize a hillside
landslide control is all about....
drainage and slope angle
--diversion channels, benches, vegetation
slope mitigation-mapping hazards
slope stability map
combine a slope map, landslide deposit map, susceptible rock map
Indication of unstable ground conditions
-springs, seeps, or saturated ground in areas that have not typically been wet before
-new cracks or unusual bulges in ground, street pavements, or sidewalks
-soil moving away from foundations
-structures such as decks and patios that tilt or move relative to main house
-tilting or cracking of concrete floors or foundations
=broken water lines or other underground utilities
-leaning telephone poles, trees, retaining walls or fences
-offset fences
-sunken or down dropped road beds
-sticking doors and windows or visible open spaces indicating frames are out of plumb
gros ventre, montana
landslide-river--water saturated shale beds lubriacted base of slide--slide debris in valley
Thistle, Utah
landslide-began moving in the spring of 1983 in response to groundwater buildup from heavy rains the previous september and the melting of deep snowpack for the winter of 1982-83 within a few weeks the landslide dammed the Spanish Fork River obliterating US highway 6 and the main line of the denver and rio grande western railroad. the town of thistle was inundated under the floodwaters rising behind teh lanslide dam
Provo rock fall 2009
47 hours after a snowstorm--contraction/expansion cycle
the breakdown and alteration of rock
mass wasting
the down slope movement of weathered material (under the influence of gravity)
the physical removal of material (water, air, and ice)