Weathering and Erosion — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. Caves form when acidic groundwater dissolves limestone rock underground.
Limestone dissolves easily in acidic water because it is made of calcium carbonate, which reacts with acid. Over thousands of years, this chemical weathering hollows out underground caves.
2. A canyon is a deep, narrow valley with steep sides carved by a river.
A canyon is carved over millions of years as a river cuts deeper and deeper into rock. The steep, narrow walls on both sides are shaped by the constant force of flowing water.
3. When temperature changes cause the outer layers of rock to peel off, it is called exfoliation.
Repeated heating and cooling makes the outer layers of rock expand and contract at different rates than the inside. Over time, these layers crack and peel away like an onion skin, a process called exfoliation.
4. Muddy river water shows that the river is carrying sediment downstream.
Muddy water looks brown because tiny particles of soil, sand, and clay are mixed into it. These particles are called sediment, and the river carries them downstream through erosion.
5. A sea arch is a natural opening through a rocky headland formed by wave erosion.
Waves pound both sides of a rocky headland, eventually eroding a hole all the way through. The remaining rock above the opening forms a natural bridge called a sea arch.
6. Lichens growing on rock surfaces cause slow chemical weathering by releasing acids.
Lichens release weak acids as they grow on rock surfaces. These acids dissolve minerals in the rock, which changes its chemical makeup -- making this chemical weathering, not physical.
7. A floodplain is an area of flat land built by repeated deposition of river sediment.
Each time a river floods, it spreads sediment across the flat land beside it. Layer after layer of deposited sediment builds up the floodplain over many years.
8. Animals that dig burrows contribute to physical weathering by breaking apart soil and rock.
Burrowing animals like groundhogs and earthworms loosen and break apart soil and rock as they dig tunnels. This physical action exposes fresh rock to air and water, speeding up further weathering.
9. A cirque is a bowl-shaped hollow carved into a mountainside by a small glacier.
A cirque forms when a small glacier sits in one spot on a mountainside, scooping out rock through freezing, thawing, and grinding. The result is a bowl-shaped hollow, often holding a lake after the ice melts.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each erosion agent to the landform it creates.
river water
→ V-shaped canyon
U-shaped valley
ocean waves
→ sea cliff
sea cliff
wind
→ sand dune
V-shaped canyon
glacier
→ U-shaped valley
sand dune
Each erosion agent creates a signature landform: rivers carve V-shaped canyons by cutting downward, waves pound cliffs into sea cliffs, wind piles sand into dunes, and glaciers grind wide U-shaped valleys.