Understanding Mass Wasting

Mass wasting is the downhill movement of bedrock, rock debris, or soil, driven by gravity.
It is a major geologic hazard, but often avoidable.

Driving Force: Gravity
- Contributing factors include: slope angle, local relief, thickness of soil over bedrock, orientation of planes of weakness in bedrock, climatic factors (ice in ground, water in soil, precipitation), and vegetation.
Most Stable Situation
- Gentle slopes or horizontal surfaces, low slope angle, slight thickness (usually)
Most Unstable Situation
- Steep or vertical slopes, high slope angle, great thickness.

Shear strength is the resistance to movement or deformation.
Saturated soil has reduced shear strength due to increased pore pressure.
A small amount of water in soil can prevent downslope movement (like building a sandcastle).

Rate of Movement: <1cm/year to 100km/hour
Type of Material: solid bedrock or debris (unconsolidated material at earth's surface)

Flow: downhill movement of a mass as a viscous fluid. Examples include creep, earthflows, debris flows, mudflows, and avalanches.
Slide: a mass moving downslope along a well-defined surface. Examples include translational slides (movement parallel to the surface) and rotational slides (slump) (movement along a curved surface).
Fall: a free-falling movement, such as rockfalls, or when rock bounces down a cliff.

Hydrologic Cycle: movement and interchange of water between the sea, air, and land, including evaporation, precipitation, transpiration, runoff, and infiltration.
Running Water: body of running water, confined to a channel that runs downhill under the influence of gravity.
Stream Components: headwaters (source), mouth (end), channel, stream banks, and streambed.
Drainage Basins: total area drained by a stream and its tributaries.
Drainage Patterns: arrangement of a stream's flow, including dendritic, radial, rectangular, and trellis patterns.

Velocity: maximum velocity is usually in the center of a channel and is affected by higher velocities, channel shape, and roughness, and sediment load.
Discharge: volume of water passing.
Erosion: process of streams acting on their valleys, carrying away sediment by hydraulic action and solution.
Abrasion: grinding away of the streambed, creating potholes.
Transportation: bed load (large/heavy particles), suspended load (medium particles), dissolved load (ions)
Deposition: accumulation of sediments, forming bars, place deposits

Braided streams: streams containing many bars around which water flows into highly interconnected rivulets.
**Meandering streams:**streams that develop pronounced sinuous curves called meanders; water currents are faster along the outside of meanders, causing erosion of cut banks and slower flow along the inside, depositing point bar materials.

Body of sediment deposited at a river mouth when flow velocity decreases.
Shape of a delta depends on whether it's wave-dominated, tide-dominated, or stream-dominated.

Large, fan-shaped piles of sediment formed where stream velocity decreases as it emerges from a narrow canyon.

Downcutting: deepening of a valley by stream erosion.
Grading: longitudinal profile that lacks rapids and waterfalls and represents a balance between sediment load and transport.
Later Erosion: widening of valleys by lateral erosion
Headward erosion: slow uphill growth of a valley above its original source, through gullying, mass wasting, and sheet erosion.
Terraces: step-like landforms above a stream and its floodplain; these form when a river rapidly cuts downward into its own floodplain.

Groundwater is water located beneath the Earth's surface.
Water Table: top of the saturated zone (all rock openings filled with water).
Porosity: percentage of rock or sediment that consists of void or openings.
Permeability: capacity of a rock's ability to transmit fluid through pores and fractures.
Aquifers: body of saturated rock or sediment through which water can move easily; unconfined and confined.
Aquitards: rock or sediment that retards groundwater flow because of its low porosity and/or permeability.
Wells: deep holes dug or drilled into the ground to obtain water.
Contamination: infiltrating water carries contaminants to the water table (pesticides, fertilizers, landfills, heavy metals, bacteria).

Springs are places where water flows to the surface from rock or sediment.
Gaining streams receive water from the saturated zone (water table is above the stream bed), and losing streams lose water to the saturated zone (water table is lower than the stream bed.)

Naturally formed underground chambers due to acidic groundwater dissolving limestone along joints and bedding planes.
Components include Stalactites, Stalagmites.

Glaciers are large, long-lasting masses of ice that move downhill under their own weight.
Types include alpine (in mountainous regions) and continental (covering large land masses in polar regions)

Glaciers erode underlying rock by plucking and abrasion, creating landforms such as U-shaped valleys, cirques, horns, and arêtes

Till is the general name for unsorted, unlayered glacial sediment deposited by glaciers.
Moraines are accumulation of till at the sides, medial, or end of a glacier.
Outwash is sediment deposited by large amounts of meltwater from a glacier; this is often in the form of a braided channel drainage pattern.
Glacial landforms may include Eskers (sinuous ridges), Kettles (glacial depressions), and Kames (low glacial mounds), among other features.

Deserts: any arid region receiving less than 25 cm of precipitation per year.
Formation of Deserts: associated with areas where air is descending.
Rain Shadow Deserts: form downwind of high mountain ranges where moist air rises and loses moisture.
Intermittent Stream Features: streambeds are dry most of the year, lacking continuous flow except after rains.
Desert Landforms in Southwestern US: characterized by Colorado Plateau and Basin and Range Province, featuring flat-lying sedimentary rocks, buttes, mesas, canyons, alluvial fans, and bajadas.
Wind Erosion and Transport: wind can keep dust in suspension, but larger grains like sand move by saltation.
Wind Deposition: Loess (unweathered silt and clay) and wind-blown sand dunes (mounds of loose sand piled up by wind).
Dune Types: barchan, transverse, parabolic, and longitudinal based on shape, wind direction, and sand supply.