Weathering, Erosion & Deposition — Practice · Grade 9 Science

Chapter: Rocks, Landscapes & Water

What this practice covers

By the end of Weathering, Erosion & Deposition you should be able to:

11 questions, multiple choice, written answer and numeric, each with a worked explanation.

Vocabulary used: weathering, erosion, deposition, sediment.

Problem 1

Which term describes rock breaking down into smaller pieces WITHOUT being moved from its original location?
  1. Erosion
  2. Deposition
  3. Weathering
  4. Lithification
Answer and explanation

Weathering

Weathering breaks rock down in place; erosion is what moves the pieces away.

Problem 2

Rainwater is naturally slightly acidic and slowly dissolves limestone over many years. This is an example of…
  1. Physical weathering
  2. Chemical weathering
  3. Erosion
  4. Deposition
Answer and explanation

Chemical weathering

Dissolving is a chemical change to the rock's composition, so this is chemical weathering.

Problem 3

Which of these can act as an agent of erosion?
  1. Only earthquakes
  2. Wind, water, ice, and gravity
  3. Only chemical reactions
  4. Only volcanic eruptions
Answer and explanation

Wind, water, ice, and gravity

Erosion transports sediment via wind, water, ice (glaciers), or gravity (mass wasting).

Problem 4

Explain why deposition happens where a fast river meets a calm lake or ocean, rather than somewhere in the middle of the river's fast-flowing course.
Answer and explanation

Deposition happens when a carrying agent loses energy and can no longer hold its sediment load. A fast-flowing river has plenty of energy to keep sediment moving, but when it enters a calm lake or ocean it slows down sharply, loses that energy, and drops its sediment, often building a delta right at the river's mouth.

Problem 5

Much of Westchester County's landscape, including ridges and hills of unsorted rock debris, was shaped mainly by which process during the last Ice Age?
  1. Volcanic eruptions
  2. Glacial erosion and deposition
  3. Chemical weathering from acid rain
  4. Wind erosion in a desert
Answer and explanation

Glacial erosion and deposition

Advancing and retreating glaciers eroded the landscape and deposited moraines and other ridges across the Hudson Valley region during the last Ice Age.

Problem 6

A glacier deposits a moraine ridge that grows by about 2 meters of debris thickness every 100 years it remains in one place. At that rate, how many meters thick would the deposit be after 1,500 years?
Answer and explanation

30 meters

1,500 ÷ 100 = 15 hundred-year periods; 15 × 2 = 30 meters.

Problem 7

A stream slows on entering a lake and deposits gravel near its mouth and finer sediment farther out. Explain. Explain the reasoning in your own words.
Answer and explanation

Deposition and sorting occur as the stream loses energy; size, density and shape influence settling.

Reduced flow speed lowers transport capacity.

Larger grains commonly settle earlier under these conditions.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 8

Water freezes in rock cracks and widens them. Classify the weathering. Show the reasoning, not just the conclusion.
Hints

Identify breakdown, movement and settling separately.

Answer and explanation

Physical weathering by freeze–thaw action, where freezing water expands in suitable conditions.

Problem 9

Why might sediment settle when a river enters a lake?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Flow speed often falls, reducing transport capacity; particle size and density affect settling.

Problem 10

Deposition can occur while water is still movingDeposition can occur while water is still movingFaster channelFlow spreads into a basinReduced carrying conditions can favor deposition.Water can keep moving while material accumulates.
Original channel-to-basin deposition schematic. The deposit is a selected accumulation and its triangular shape is explanatory rather than surveyed geometry. Arrows are qualitative; the diagram does not claim a numeric settling speed or a universal grain-order sequence.
Interpret the supplied visual model. Why could some grains settle while fine material continues farther into the basin?
Answer and explanation

Different grain sizes, densities and shapes have different settling/transport behavior under the changed flow conditions. Depositing one fraction does not stop all water or all material transport.

Trace water into the wider basin and identify the accumulating sediment wedge. Width and arrow lengths indicate a qualitative contrast only.

Different grain sizes, densities and shapes have different settling/transport behavior under the changed flow conditions. Depositing one fraction does not stop all water or all material transport.

Response criteria

  • Read the labeled quantities, reference frame or objects correctly.
  • Explain the relation between the visual evidence and the mechanism.
  • Keep the drawing’s stated assumptions and limits in the conclusion.

Problem 11

Trial A produces 12 g of sediment in 120 mL runoff; trial B 9 g in 60 mL. Compare total sediment export and concentration, then name two conditions to control when testing a surface cover.
Answer and explanation

B exports less mass (9 vs 12 g) but greater concentration (0.15 vs 0.10 g/mL). Control rain input, slope, material and collection interval, except for the planned cover change.

Calculate A: 12/120 = 0.10 g/mL.

Calculate B: 9/60 = 0.15 g/mL.

Distinguish total export from concentration and match test conditions.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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