Forces of Erosion and Deposition

Science, Grade 6


Table Of Contents: Forces of Erosion and Deposition

1. Natural Forces of Erosion and Deposition
Many natural forces cause erosion and deposition, including gravity, moving water, glaciers, ocean waves and wind. These forces continuously wear down and build up material on the Earth’s surface.
2. Gravity and Mass Movements of Rock
Gravity can cause unstable rock material to move suddenly. Landslides and mudflows occur when loose soil and rocks slide down steep slopes. Slump is the sudden movement of a single large mass of rock material. Creep is caused by gravity, but is a slow downhill movement of sediment over time.
3. Moving Water Carries Sediment
Rivers and streams move across the Earth's surface and shape the landscape. Flowing water has enough energy to move large amounts of sediment, composed of soil, rock, clay and sand. The amount of sediment that is carried by a river or stream is called its load.
4. Deltas and Alluvial Fans
When a river empties into an ocean or lake, sediments are deposited and a triangular-shaped delta is formed. When water transports sediments from a hilly area to a flat area, the water slows down and sediment forms an alluvial fan.
5. Glaciers Shape the Land
Glaciers are massive sheets of ice that form over continents and in high altitude mountains.Glaciers move and shape the land by grinding, breaking and transporting rocks. Continental glaciers create flat landscapes while alpine glaciers create rugged, mountain features.
6. Glacier Landforms
Glacial erosion creates many landforms including mountain horns, cirques, aretes and U-shaped valleys. When a glacier melts, the deposited sediment left behind is called glacial drift. Moraines, drumlins and kettle lakes are landforms created by glacial drift.
7. Waves and Rock Formations
Ocean waves contain energy that breaks down rock and shapes coastlines. Rock formations created by wave erosion include headland cliffs, sea caves, sea arches and sea stacks.
8. Waves and Deposition
Waves also move and deposit rocks, sediment and sand. Beaches are composed of different sources of eroded rock. Barrier spits are created from longshore wave currents, and sandbars are built up offshore by incoming storm waves.
9. Wind Erosion and Deposition
Wind causes erosion through deflation, the blowing away of surface materials, and through abrasion, the grinding down of rock by blown particles. Wind also deposits sand into land formations such as sand dunes and loess deposits.