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.

Explore the phenomenon of mass wasting, its causes, and the contributing factors that influence its occurrence. Understand the interplay of gravity, slope, soil moisture, and vegetation in stabilizing or destabilizing slopes. This quiz covers essential concepts and scenarios related to mass wasting.