Mass Movement

Question 1

Mass movement is the?

Answer 1

downslope movement of rock, regolith, or both, caused by the downward pull of the force of gravity.

Question 2

“Landslide” is a commonly used term referring to?

Answer 2

spectacular examples of mass movement, but has no formal meaning

Question 3

types of material. 2 types and what are they?

Answer 3

1. Debris, mud or earth – used when unconsolidated material (soil and regolith) dominate .
   2, Rock –used when a mass of bedrock detaches and moves downslope.

Question 4

Type of motion.? 5 types. what are they and then def?

Answer 4

1. Fall – material (rock) detaches from a slope and then free falls through the air, or bounces and rolls down slope.
2. Slide – material (rock or debris) that slides along a “flat” surface of rupture.
3. Slump – material (earth) that slides along a “curved”surface of rupture.
4. Flow – continuous movement of material (mud or debris) that behaves as a high-viscosity liquid.
5. Creep – migration, but not visible motion, of material (soil or rock) downslope.

Question 5

Mass movement happens if the? and what are the 4 forces?

Answer 5

gravitational force is greater than the resisting strength of the rock or regolith.

1. Gravity is the driving force.
   2 and 3. Friction and Cohesion are the resisting forces.
2. Motion results when driving force is greater than resisting force.

Question 6

Factors determining slope stability? 5 things and what are their def’s?

Answer 6

1. Water – commonly contributes to slope instability.
2. Slope – steepness of the slope increases instability.
3. Geologic Structures – presence and orientation of planar features in the rock that may form rupture surfaces.
4. Weathering – physical and chemical weathering can increase slope instability.
5. Vegetation – roots penetrate and bind soil together and absorb water from precipitation.

Question 7

Triggers of mass movement are factors that? 3 of them and what are their def’s?

Answer 7

change the balance of driving and resisting forces to permit mass movement.

1. Rainfall and Snowmelt (water) – water causes particles to lose contact, decreasing both friction and cohesion.
2. Earthquakes – strong ground shaking triggers mass movement. As shaking particles lose contact with one another, the frictional resistance to movement decreases and the fragments bounce and roll downhill.
3. Volcanic Eruption – the combination of decreased vegetation, unconsolidated ash, rapid melting of ice and snow, and ground shaking can make volcanic areas extremely hazardous zones for mass movement.