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Topic 3 – Erosion 1. Erosion: the movement of rock and mineral grains from one place to another. Sediments come from larger rocks that have broken down or worn away through weathering. 2. Weathering is the breaking down of rocks mechanically, chemically, or biologically. There are 3 Types of Weathering. Please read p. 373-374 for key pts. and examples below. 1. Mechanical Weathering - The physical break-up or disintegration of rocks Example: gravity causing rocks to fall and break apart; rocks bumping together in a river, frost wedging, wind, water (rain). Mechanical Weathering is the part of the process responsible for wearing away. Sedimentation is the part of the process responsible for building up. 2. Chemical Weathering - the breaking down of rocks and minerals through chemical reactions Example: Acid Rain – acidic rainwater caused by air pollution dissolves some types of rock (ex. Limestone) 3. Biological Weathering - the physical or chemical breakdown of rock caused by living organisms such as plants, animals, bacteria, and fungi Example: Tree roots getting into cracks in rock and wedging the rock apart, acids produced by living organisms can dissolve rocks *The physical environment and natural processes such as earthquakes and volcanic eruptions can also cause rocks and the landscape to change. 3. 4 Key Agents of Erosion – p. 376 Glaciers, gravity, wind and water are the 4 Key Agents of Erosion. 1. Glaciers – glaciers erode the land as they pass over it (Striations – grooves left behind by rocks in a glacier, erratics – large rocks left behind by a glacier, moraines – piles of sediment in front of glacier, melt water – washes away/moves sediment) 2. Gravity – responsible for rockslides and landslides; can be unexpected (retaining walls, better drainage, monitoring) 3. Wind – picks up loose sediment and wears away rock through abrasion (plant vegetation, contour farming, reduced tillage) 4. Water – most powerful cause of erosion (rivers, meandering streams, heavy rain, coastlines) – break down rocks, rocks can rub against each other, and be deposited far downstream. Define Abrasion- windblown particles of rock strike other rocks and wear it down (ex. Like a sandblaster) 4. What is a Striation? P.376 - rocks frozen into glaciers scrape across the bedrock as the glacier moves, leaving behind grooves in the bedrock 5. What is a Moraine? P.376-377 - eroded sediments get pushed in front of a glacier and piled up along its sides in formations called moraines 6. What is an Erratic? P.377 - Large rocks left behind by a glacier, often many kilometers from their source 7. Gravity is one force that is responsible for landslides and rockslides. What can be done to prevent slides from happening? Describe Frank Slide p. 377 - Adding retaining wall, improving drainage, monitoring dangerous slopes - In 1903, rock from Turtle Mountain in Alberta sent over 80 million tons of rock onto the town of Frank in less than 100 seconds. 8. How does a V-shaped valley form? - Rivers can cut straight into rock to form canyons, gorges, and V-shaped valleys * Topic 3 Review p. 380 - # 1-4