Weathering and Erosion — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
Sand dunes are created by rivers depositing sand at the bottom of the ocean.
Corrected: Sand dunes are created by wind depositing sand in dry, open areas like deserts or coastlines.
Sand dunes are built by wind, not rivers. Wind carries loose sand grains and deposits them in dry, open areas like deserts or beaches, where they pile up into hills.
2. Fix the sentence:
Physical weathering changes the minerals inside a rock into new substances.
Corrected: Chemical weathering changes the minerals inside a rock into new substances, while physical weathering only breaks the rock into smaller pieces.
Physical weathering only breaks rock into smaller pieces without changing what it is made of. Chemical weathering is the type that actually alters the minerals inside the rock, turning them into new substances.
3. Fix the sentence:
A moraine is a valley carved by flowing water over thousands of years.
Corrected: A moraine is a ridge of rocks and sediment left behind by a glacier as it melts or retreats.
A moraine is not a valley -- it is a ridge or mound of rocks, dirt, and gravel that a glacier pushes ahead or leaves behind as it melts. Valleys carved by water are a different landform.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. Ocean waves pounding against sea cliffs is an example of physical weathering.
Waves crashing into cliffs use force to chip and break the rock apart without changing its chemical makeup. Since the rock is only broken physically, this is physical weathering.
2. A glacier is a large, slow-moving mass of ice that reshapes the land as it flows.
A glacier is a huge, slow-moving sheet of ice that carves valleys and moves boulders as it flows. Its massive weight and grinding motion reshape the land over thousands of years.
3. The wearing away of rock by particles carried in wind, water, or ice is called abrasion.
Abrasion happens when small particles carried by wind, water, or ice scrape against rock surfaces. Over time, this grinding action wears the rock smooth or wears it away completely.
4. When a river slows down and drops the sediment it was carrying, the process is called deposition.
Fast-moving water has the energy to carry sediment, but when a river slows down, it loses that energy and drops the material. This dropping process is called deposition.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Give one example of chemical weathering and explain what causes it.
Sample answer: When rainwater mixes with carbon dioxide in the air, it forms a weak acid. This acid slowly dissolves limestone and creates caves or sinkholes over time.
Rainwater absorbs carbon dioxide from the air and becomes a weak acid called carbonic acid. Over time, this acid dissolves limestone, hollowing out caves and sinkholes underground.
2. Why does a river carry more sediment during a heavy rainstorm than on a calm day?
Sample answer: During a heavy rainstorm the river flows faster and has more water. The extra speed and force allow it to pick up and carry larger and heavier pieces of sediment.
Heavy rain adds more water to the river, making it flow faster. The extra speed gives the water more energy, so it can pick up and carry larger and heavier pieces of sediment than it could on a calm day.