Weathering and Erosion — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. Which process creates caves in limestone regions?
A) Wind abrasion wearing away the rock surface
B) Acidic groundwater dissolving the limestone
C) Glaciers grinding through the rock layer
D) Tree roots splitting the rock apart
Caves form through chemical weathering when acidic groundwater dissolves limestone over thousands of years. The acid slowly eats away the rock, creating tunnels and chambers underground.
2. A farmer notices that topsoil washes away during every rainstorm. Which solution would best reduce this erosion?
A) Remove all plants so water runs off faster
B) Add more gravel to the surface
C) Plant cover crops with deep roots
D) Dig deeper channels for the water
Deep roots hold soil firmly in place and slow water runoff, which prevents rain from washing topsoil away. Cover crops also shield bare ground from the direct impact of raindrops.
3. What evidence shows that a glacier once moved through a valley?
A) Sand dunes on the valley floor
B) A V-shaped valley with a river at the bottom
C) A U-shaped valley with scratched bedrock
D) Sea arches along the valley walls
Glaciers carve wide, U-shaped valleys and leave scratches (striations) on the bedrock beneath them. Finding both a U-shaped valley and scratched rock together is strong evidence that a glacier once moved through the area.
4. Which pair correctly matches the weathering type to its example?
A) Physical — acid rain dissolving marble
B) Chemical — ice splitting a boulder
C) Physical — roots prying apart sidewalk cracks
D) Chemical — wind blowing sand against a cliff
Roots growing into sidewalk cracks use physical force to push the concrete apart. Since no chemical change happens to the material, this is physical weathering, not chemical.
Part B: Fill in the Blank
Write the correct answer on each line.
1. A meander is a wide, looping curve in a river caused by erosion on the outer bank.
A river erodes faster on the outside of a bend because the water moves faster there. This creates a wide, looping curve called a meander that gets more exaggerated over time.
2. Lichens release acids that slowly dissolve the surface of rocks they grow on.
Lichens produce weak acids as part of their life processes. These acids react with and dissolve the minerals on the rock surface, causing chemical weathering over many years.
3. An oxbow lake forms when a river meander gets cut off from the main channel.
When a river meander loops so far that the two ends nearly touch, the river breaks through and takes the shorter path. The abandoned loop fills with still water, forming a crescent-shaped oxbow lake.
4. The breakdown of rock by heating and cooling throughout the day is called physical weathering.
Heating and cooling makes rock expand and contract without changing its chemical makeup. Because only the shape and size of the rock are affected, this is classified as physical weathering.
5. Retaining walls along highways prevent rocks from sliding onto the road.
Retaining walls act as barriers that hold back loose rocks on steep roadside slopes. Without them, gravity would pull those rocks downhill onto the highway, creating a dangerous hazard for drivers.