Geography Quiz: Landslides and Earth Flows

Earth Movements and Flow Types

• Earth Flows: Slow movements of soil; distinct from mudflows.
• Mudflows: Fast-moving mixtures of mud and water; can be triggered by earthquakes or volcanic eruptions. Common in sloped, semi-arid regions during intense rain.
• Avalanches: Landslides in mountainous areas; typically occur on slopes of at least 35°. Often caused by sun melting surface snow, which later refreezes, creating instability.

Avalanche Statistics

• Approximately 10,000 avalanches occur annually in western US mountains.
• Avalanches can achieve speeds of up to 300 km/h.

Rockfall Characteristics

• Defined as rock volume that free falls and impacts a surface; typically occurs in mountainous regions.
• High velocity is common, leading to the formation of talus slopes—cone-shaped piles of debris.

Debris Avalanche

• Characterized by very high velocity and medium moisture content.
• Example: A 1970 event in Peru involved over 100 million m³ of debris, traveling 10 miles and resulting in 18,000 deaths.

Scarification

• Refers to human activities that destabilize slopes, such as construction and mining.

Fluvial Geomorphology

• Involves stream-related processes of erosion, transportation, and deposition; studies landforms created by these activities.

Drainage Basin Information

• Everyone lives within a drainage basin, classified by characteristics such as drainage density, patterns, and stream orders.

Arid Regions and Characteristics

• Arid and semi-arid climates occupy 35% of Earth's surface; wind significantly influences erosion in these areas, making deserts prime environments for sediment transport.
• Examples of arid regions include Sonoran, Taklimakan, Atacama, and Kalahari Deserts.

Aeolian Erosion

• Deflation: Removal of loose particles, creating desert pavement and blowout depressions.
• Abrasion: Grinding of rock surfaces via particles suspended in air.

Aeolian Sediment Transport Methods

• Saltation: Jumping of sand particles along the surface.
• Creep: Gradual movement of larger particles.
• Other methods also involve the movement of sediments.

Karst Landscapes and Mass Movement

• Karst Topography: Formed by the dissolution of soluble bedrock like limestone; requires specific conditions including high calcium carbonate content and vegetation.
• Approximately 15% of Earth's land area exhibits karst features, including sinkholes and caves.

Mass Movements

• Defined as any movement of soil, rock, or debris driven by gravity; can be sudden (slope failure) or gradual (creep).
• Triggering factors include precipitation, earthquakes, volcanic activity, and human interventions.

Angle of Repose

• The maximum slope at which material remains stable, typically ranging from 25° to 40°, influenced by material size and moisture content.

Triggering Mechanisms for Mass Movements

• Various events like heavy rainfall, volcanic eruptions, and human activities can trigger mass movements.

Classes of Mass Movements

• Include processes like creep, sliding, flowing, and falling of materials due to gravitational pull reaching a critical shear-failure point.

Creep

• A slow mass movement resulting in the gradual downward movement of sediments, often exacerbated by freeze-thaw cycles; trees and structures can lean downhill.

Solifluction

• A type of earth flow occurring in periglacial regions with permafrost; involves saturation of the surface layer leading to slow movement (1-10 cm/week).

Landslides and Flows

• Sudden and rapid movements of soil or bedrock, often medium moisture content, can be triggered by earthquakes.
• Flows occur when the addition of water leads to instability, turning earth materials into thick, liquid-like movements.