Mass Wasting and Its Factors

Mass Wasting

• Mass wasting is the downhill movement of bedrock, rock debris, or soil, caused by gravity.
• It's a major, but easily avoidable, geological hazard.

Controlling Factors in Mass Wasting

• Driving Force: Gravity
  • Contributing Factors: 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 thickness, planes parallel to slopes and temperature above freezing.
  • Most Unstable Situation: Steep or vertical slopes, great thickness, planes perpendicular to the slopes, freezing/thawing, high precipitation, and little vegetation.

Shear Strength and Water

• 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.

Mass Wasting Triggers

• Seismic activity
• Heavy rainfall
• Construction
• Lack of vegetation

Classification of Mass Wasting

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

Types of Mass Wasting Movement

• Flow: Downward movement of the material
• Slide: Movement along a well-defined surface
• Fall: Free-fall, or bouncing, of material.
  • Examples of slide types: Translational slide and Rotational slide (slump).
  • Examples of fall types: Falling rock, waves.

Flows: Earthflow and Solifluction

• Flow: Mass moving downhill as a viscous fluid.
• Earthflow: Debris moves slowly or rapidly as a viscous liquid, downslope.
• Solifluction permafrost: Flow of water-saturated soil over impermeable material (common in colder climates).
• Flows (debris flow, mudflow, avalanche): Flowing mixture of debris and water; mostly down a channel. Mudflow is only soil and water.

Falls

• Material free-falls or bounces down a cliff.
• Rockfall: Block of bedrock breaks free and falls.
• Talus: Accumulation of fallen rock fragments.

Slides

• Descending mass remains relatively intact, moves along well-defined surface.
• Translational slide: movement parallel to motion.
• Rotational slide (slump): movement along a curved surface.
• Rockslide and rock avalanche: rapid mass movement of bedrock along an inclined surface of weakness below the surface. This can cause tsunami.

Preventing Landslides

• Remove loose materials
• Stitch slopes together
• Preventing mass wasting of soil
• Construct retaining walls with drainage

Streams and Floods

• Hydrologic Cycle: Movement and interchange of water between the sea, air, and land. (evaporation, precipitation, transpiration, runoff, infiltration).
• Running Water: Body of running water confined to a channel that runs downhill by gravity.
• Stream Features: Headwaters (upper part of stream near source), mouth (where it enters another body of water), stream banks, channel, floodplain, streambed.
• Drainage Basin: Total area drained by a stream and its tributaries.
• **Drainage Patterns:**Arrangement of stream and tributaries on a map. (ex. dendritic, radial, rectangular, trellis)

Factors Affecting Stream Erosion and Deposition

• Velocity: Maximum velocity near center of channel. Higher velocities promote erosion and transport of coarser sediments. Floods increase erosion.
• Channel Shape and Roughness
• Discharge: Volume of water passing.
• Stream Erosion: Cutting, deepening, and widening valleys over time and carrying away the sediment. Processes include hydraulic action, abrasion and solution.
• Stream Transportation: Bed load (large/heavy particles), suspended load (medium particles), dissolved load.
• Stream Deposition: Bars (sediments temporarily deposited), place deposits (concentrated heavy sediments).

Braided Streams, Meandering Streams and Meandering Cutoffs

• Braided Streams: Have many interconnected, rivulets.
• Meandering Streams: Have pronounced, sinuous curves called meanders.
• Meandering Cutoffs: When a shorter channel cuts through the narrow neck of a meander (can occur during floods).

Floodplains and Deltas

• Floodplains: Broad strips of land built up by sedimentation on either side of a stream channel, resulting from slow flood waters.
• Deltas: Bodies of sediment deposited at the river mouth when flow velocity decreases; surface marked by shifting distributary channels.

Stream Valley Development: Downcutting, Grading, Later Erosion, and Headward Erosion

• Downcutting: Erosion at the base of a valley.
• Grading: Balance between available sediment load and transport (lacks rapids and waterfalls)
• Lateral erosion: widens the valley by undercutting banks
• Headward erosion: growth of valley above its source

Glacial Erosion and Glacial Deposition

• Different glacial erosion landforms: U-shaped valleys, hanging valleys, truncated spurs.
• Glacially deposited features: Till (unsorted), lateral, medial, and end moraines, glacial lakes, outwash, eskers, kettles, kames,
• Glacial effects: carving valleys, creating lakes through ice erosion, and pluvial lakes from rainfall.

Other Glacial Landforms

• Cirques, horns, aretes: Erosional landforms created by glacial erosion.
• Glacial Deposition: Till, moraines, outwash materials.

Landscapes Associated With Continental Glaciation

• Features: rounded topography, grooved or striated rock, glacial deposition.

Deserts and Wind Action

• Deserts: Arid regions receiving less than 25 cm of precipitation per year.
• Wind: Predominant force shaping landscapes and landforms through transportation (dust and sand), erosion, and deposition (loess, sand dunes).

Rain Shadow Deserts

• Formed downwind of mountains; moisture falls on windward side, leaving little for the leeward (rainshadow) side.
• Dry conditions are the primary characteristic.

Desert Features in the Southwestern United States

• Colorado Plateau: Flat-lying sedimentary rocks; often heavily eroded into mesas and buttes.
• Basin and Range Province: Rugged, linear, fault-bounded mountain ranges separated by flat-floored valleys. Narrow canyons carry sediment to valleys.

Wind Erosion and Transportation

• Mechanical Erosion: Sandblasting of rock, abrasion, and deflation (removal of fine sediment)
• Transportation: Wind keeps dust in suspension; larger sand grains move by saltation.

Wind Deposition: Loess and Sand Dunes

• Loess: Wind-blown silt and clay deposits (fertile but easily eroded).
• Sand Dunes: Mounds of loose sand piled up by the wind, often shaped by wind direction, sand supplies, and vegetation.

Types of Dunes: Barchan, Longitudinal, Transverse, and Parabolic

• Descriptions and characteristics of these dune types.

Importance of Groundwater

• Groundwater is crucial resource.
• Contamination can be challenging and expensive to clean up.

Contamination of Groundwater

• Pollutants enter the groundwater from various sources:
  • pesticides, fertilizers, landfills, heavy metals, bacteria, viruses, industrial chemicals, acid mine drainage, and oil.

Balancing Withdrawal and Recharge

• Balancing groundwater withdrawal with recharge is crucial to avoid water table drop, potential subsidence and cracking of foundations.