mass wasting/landslides 2 Flashcards
what is fall?
A material dropping through air, vertically or almost vertically.
what is slide?
A material moving as a mass along a SLOPING surface (NOTE: there is NO internal motion
within the mass itself).
what is flow?
Downslope movement of a material that also has internal motion, like a fluid (e.g., water, lava).
do most mass wasting examples include only one type of it?
no, most MASS WASTING examples include two or more of the above (e.g., stones can SLIDE before FALLING off cliff)
what are the characteristics of falls?
are an EXTREMELY RAPID or VERY RAPID form of MASS WASTING seen with rocks (ROCKFALL) and unconsolidated materials (SOIL FALL)
what is rockfalls?
✓ rapid downslope movement of dislodged rocks that originate above a steep enough slope
✓ rocks may experience falling, rolling, bouncing, and/or sliding
✓ falling rocks include broken chunks from BEDROCK OUTCROPS or BOULDERS coming
down mountainsides/cliffs.
what is bedrock?
✓ hard, solid rock (i.e., CONSOLIDATED ROCK) under UNCONSOLIDATED surface materials such as SOIL, SAND
or GRAVEL.
✓ can extend hundreds of meters below Earth’s surface
✓ exposed (i.e., above Earth’s surface) BEDROCK seen on mountain tops, along coastlines, in quarries and on plateaus
(plateau = region of relatively level/flat ground with a higher elevation than surrounding areas)
what is outcrops?
visible exposures of BEDROCK occurring due to EROSION or TECTONIC PLATE activity.
what is hydrostatic pressure?
Pressure exerted by any fluid (e.g., water) in a confined space.
what factors can rockfalls and soil falls can driven (in part) by aside from SHEAR
FORCE, SHEAR STRENGTH, ROCK STRENGTH?
✓ HYDROSTATIC PRESSURE and the presence of water in BEDROCK cracks
✓ Freeze (i.e., expansion) and thaw (i.e., contraction) cycles
✓ heavy snowfall and subsequent melt
✓ plant roots in BEDROCK cracks.
✓ erosion by rivers/streams and/or wave action below (aka. UNDERCUTTING)
✓ quarrying (i.e., mining) activities.
what are 3 types of slides?
- rock slide:
✓ sliding motion of rocks along a sloped surface
✓ can range from VERY SLOW to MODERATELY FAST. - rock avalanche:
✓ sliding motion of rocks along a sloped surface
✓ larger rocks moving downhill quickly (at speeds on the order of meters/second) fragment (i.e., BREAK DOWN) to form smaller rocks/pieces that keep moving down hill/slope - slump:
✓ sliding encountered when have thick (> 10 meters) layer/slice of UNCONSOLIDATED MATERIAL on a CURVED SLOPE.
✓ (may also observe same for rock layer on CURVED SLOPE)
✓ can occur EXTREMELY SLOWLY to MODERATELY FAST.
✓ mass of UNCONSOLIDATED MATERIAL gradually moves DOWNWARD and spreads OUTWARD.
✓ often caused by presence of excess water between UNCONSOLIDATED layer and CURVED SLOPE
what are the characteristics of slides?
SLIDES can range from EXTREMELY SLOW to EXTREMELY RAPID. This form of MASS WASTING is seen with rocks and
unconsolidated materials.
what are the characteristics of flows?
FLOWS can range from EXTREMELY SLOW to
EXTREMELY RAPID. This form of MASS WASTING is generally associated with unconsolidated materials.
what are 3 types of flows?
- creep:
✓ very slow (mm/year to cm/year) movement of soil/UNCONSOLIDATED materials down a SLOPE.
✓ prevalent on SLOPED surfaces
✓ an example of very slow FLOW but difficult to rule out some SLIDING in many cases.
✓ results in cracked roads
✓ results in trees, fenceposts, grave markers, etc… that lean DOWNHILL. - mudflows and debris flows:
✓ often RAPID to EXTREMELY RAPID movement of soil/sediment/UNCONSOLIDATED materials down a SLOPE.
what can creep down a sloped surface can be enhanced by?
✓ frozen subsoil preventing water drainage and wet material above slowly moves downhill
✓ freeze/thaw
✓ frequent wetting/drying of soil
what is solifluction?
✓ CREEP triggered by freeze-thaw in colder climates.
✓ gradual movement of wet soil/wet UNCONSOLIDATED materials
down a slope
what happens to SEDIMENT/UNCONSOLIDATED MATERIALS
SATURATED with water (e.g., due to heavy rain, ice/snow thaw)?
- lose strength and ability to stay/stick together
- SEDIMENT/UNCONSOLIDATED MATERIAL grains are pushed apart to extent that SATURATED MIXTURE can actually FLOW.
why mudflows and debris flows flow?
Since SEDIMENT/UNCONSOLIDATED MATERIALS are SATURATED with water, then FLOW can occur even down GENTLE SLOPES
what is mudflow?
FLOW of (water) saturated UNCONSOLIDATED material whose grains are SAND-SIZED or smaller.
what is debris flow?
FLOW of (water) saturated UNCONSOLIDATED material whose grains are GRAVEL-SIZED or larger.
into what do scientists classify soil particles?
1.CLAY particles are smallest with DIAMETERS < 0.002 mm.
2. SILT particles have DIAMETERS ranging from 0.002 mm to 0.05 mm.
3. SAND particles have DIAMETERS ranging from 0.05 mm to 2.0 mm.
4. GRAVEL/STONES have DIAMETERS > 2.0 mm.
what is pore space?
size of spaces that exist between SOIL
PARTICLES.
what is the biggest to smallest pore space size from the soil categories?
GRAVEL > SAND > SILT > CLAY
what happens when all pores spaces (i.e., the entire PORE VOLUME) is filled with water?
SOIL is SATURATED
