D - Mass Movements Flashcards
What is a mass movement in geomorphology?
Any large-scale movement of the Earth’s surface not accompanied by a moving agent (river, glacier, or ocean wave).
How are mass movements classified by speed?
They range from extremely slow (soil creep, solifluction) to very fast (rockslides, debris avalanches).
What is the difference between a ‘flow’ and a ‘slide’ in mass movements?
Flows involve material moving as a fluid mass (e.g., mudflows, earthflows), while slides involve coherent blocks moving along a defined plane (e.g., landslides, rockslides).
Name one factor that increases shear stress on a slope.
Removal of lateral support (e.g., undercutting by rivers or waves), loading of the slope (e.g., weight of water or debris), or earthquakes.
How can the removal of lateral support lead to slope failure?
Undercutting by erosion or faulting steepens or destabilizes the slope, reducing the support that keeps the slope material in place.
What does ‘removal of underlying support’ refer to?
Processes like undercutting by rivers/waves or dissolution of subsurface material, leading to a collapse of overlying layers.
Give an example of how slope loading can increase shear stress.
Accumulation of water or debris adds weight to the slope, increasing gravitational pull and stress.
What are transient stresses that can trigger slope failure?
Earthquakes, strong winds on trees, or sudden shocks that increase shear stress.
Name a factor that reduces shear strength in slope materials.
Weathering, which can disintegrate rocks or dissolve cementing minerals.
How does pore water pressure affect slope stability?
Increased pore water pressure can saturate and soften materials, reducing their internal friction and cohesion.
What structural changes can reduce shear strength?
Creation of fissures, remolding of sands or clays, and any process that weakens the internal structure of the soil or rock.
How can organic effects (e.g., burrowing animals, root decay) reduce slope stability?
They disturb or loosen soil, creating voids and reducing the cohesive strength of the material.
Give an example of a slow mass movement and a fast mass movement.
Soil creep or solifluction (slow) and debris avalanche or rockslide (fast).
Why are debris avalanches considered extremely rapid mass movements?
They involve large volumes of material moving downslope at very high speeds, often triggered by sudden slope failures.
