4. EXTERNAL AGENTS OF RELIEF - RELIEF: Is also shapedby external agents:water, Wind, Ice, changes of temperature and human action. EROSION CYCLE - Relief modify by three proccesses: erosion, transport and deposition. - EROSION: - Materials (rocks and soil) are broken up and moved around by external agents. - TRANSPORTATION: Then, materials are transported by : - seas - rivers - glaciers - wind - DEPOSITION: Eroded rocks, sand and mud are deposited in low areas where sediments accumulate.
4. EXTERNAL AGENTS OF RELIEF We are talking about 5 agents:
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WATER:- Has an important role in erosion,transportation, and deposition.
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WIND: - causes aeolian erosion:- When wind erodes and transports rocks and sand. It occurs in dry climates where ther is little vegetation to protect the soil.
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ICE: - Causes glacial erosion: - It occurs in very cold areas and in mountainous areas. - When water enters the cracks in glaciers, it freezes and breaks rocks and these are transported by glacier. - when glaciers melt create: lakes and U-shaped valleys.
- Sudden CHANGES OF TEMPERATURE:- It occurs in deserts and in mountainous areas, that is to say, where there are big differente between the temperature during the day and day. - it can breaks up rocks. - water enter the cracksin rocks, it may breaks if water freezes and expands. - HUMAN ACTION: modify relief through: - activities such as agricutures, deforestation and mining - with man – made buildings such as roads and reservoirs.