Unit 3 - Page 77 - 78

Which of the following best describes falls in mass movement?

• Slow, downward movement of soil

• The rapid free-fall of rock from a steep slope

• The gradual sliding of soil layers

• The flow of mud mixed with water

Answer explanation

Answer: B) The rapid free-fall of rock from a steep slope

• Explanation: A fall happens when rocks or debris suddenly break off a steep slope and drop due to gravity.

• Example: If you kick a rock off a cliff, it falls straight down quickly instead of sliding.

Falls are most common on slopes with an angle greater than:

• 20°

• 30°

• 40°

• 50°

Answer explanation

Answer: C) 40°

• Explanation: The steeper the slope, the more likely rocks will break off and fall freely.

• Example: A cliff with a near-vertical face is more likely to have falling rocks than a gentle hillside.

What is a major cause of rock falls?

• Soil erosion

• Water infiltration

• Weathering processes such as freeze-thaw

• Wind erosion

Answer explanation

Answer: C) Weathering processes such as freeze-thaw

• Explanation: Water gets into cracks in rocks, freezes, expands, and forces the cracks to grow. Eventually, pieces break off.

• Example: In cold mountain areas, rocks break apart due to freezing and thawing cycles.

What happens to rocks after they detach from a cliff in a fall?

• They roll and form talus slopes

• They dissolve into sediment

• They remain suspended in midair

• They move slowly downslope over time

Answer explanation

Answer: A) They roll and form talus slopes

• Explanation: After falling, rocks often bounce or roll down the slope, collecting at the bottom.

• Example: At the base of a cliff, you often see a pile of broken rocks.

Which of the following is NOT a characteristic of falls?

• Rapid movement

• Occurs on steep slopes

• Influenced by gravity

• Requires water to initiate movement

Answer explanation

Answer: D) Requires water to initiate movement

• Explanation: Falls happen mainly due to gravity and weathering, not water.

• Example: A dry rock face can still have rockfalls if the rocks are weak.

What is surface wash?

• Water flowing in a river channel

• The unchanneled flow of water over a soil surface when infiltration capacity is exceeded

• Water seeping into the ground

• The downward movement of rocks due to gravity

Answer explanation

Answer: B) The unchanneled flow of water over a soil surface

• Explanation: When the ground can’t absorb water fast enough, the water runs off the surface.

• Example: After heavy rain, water runs over a dry road instead of soaking into it.

Surface wash commonly occurs when:

• The soil is frozen

• The soil's infiltration capacity is exceeded

• The slope is covered with vegetation

• Wind speed is high

Answer explanation

Answer: B) The soil’s infiltration capacity is exceeded

• Explanation: When soil is already wet or too compacted, water stays on top and flows downhill.

• Example: When a sponge is full of water, extra water just runs off.

What is a major consequence of surface wash?

• Increased vegetation growth

• Formation of new landforms

• Removal of soil and creation of erosion features

• Strengthening of soil structure

Answer explanation

Answer: C) Removal of soil and creation of erosion features

• Explanation: The flowing water carries away soil, making the land uneven.

• Example: In farming areas, bare soil can be washed away after heavy rain, forming small trenches.

In which type of environment is surface wash most common?

• Wetlands

• Deserts

• Semi-arid and temperate regions

• Coastal areas

Answer explanation

Answer: C) Semi-arid and temperate regions

• Explanation: These areas don’t have much vegetation to hold the soil in place.

• Example: In dry farmland, water washes soil away because there aren’t many plants to stop it.

What is sheetwash?

• A type of landslide

• Water flowing in narrow, deep channels

• Unchanneled water flow transporting sediment downslope

• The process of soil expanding and contracting

Answer explanation

Answer: C) Unchanneled water flow transporting sediment downslope

• Explanation: Sheetwash happens before the water forms visible streams or rills.

• Example: After a storm, water spreads evenly over a parking lot before flowing into drains.