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Transcript
Weathering & Erosion Weathering Weathering – the process by which natural forces break down rocks Types of Weathering •Mechanical Weathering •Chemical Weathering Rate of Weathering •Surface Area – the more of a rock’s surface that is exposed to air and water, the faster the rock will break down because there are more surfaces to be weathered Rate of Weathering •Rock Composition – different kinds of rocks break down at different rates, because some rocks contain softer minerals than others Rate of Weathering •Climate •Chemical weathering occurs faster in hot, wet regions •Mechanical weathering caused by freezing and thawing occurs more in cold regions Weathering •Mechanical Weathering – the breakdown of rocks into smaller pieces of the same material without any change in its composition Mechanical Weathering •Ice Wedging – when water freezes in the cracks and pores of rocks, the force of its expansion is strong enough to split the rocks apart •Occurs where there are frequent freezes and thaws •Can cause potholes to form in pavement Mechanical Weathering •Abrasion – the process of wearing down by friction (wind and water) Mechanical Weathering •Pressure Release – Earth’s forces can push rock that formed underground up to the surface, the release of pressure causes the rock to expand and crack •Exfoliation – in geology, the process in which layers or sheets of rock gradually break off Mechanical Weathering •Plant Roots – when plants grow in cracks in a rock, their roots can widen the cracks and force the rock apart Weathering •Chemical Weathering – the breakdown or decomposition of rock that takes place when minerals are changed into different substances Chemical Weathering •Dissolving – the slightly acidic water breaks down minerals in rocks •Acid rain can cause holes to form in rocks and/or smooth out rough edges •Carbonic acid in water dissolves calcite, which can hollow out underground caverns Chemical Weathering •Rusting – oxygen in the air and water combine with iron to produce iron oxides, or rust Soil Destruction •Farming •Farmers clear trees and other plants and plow up the soil to plant crops, but without its natural plant cover, the soil is more exposed to rain and wind and therefore more likely to get washed or blown away •Overgrazing by animals destroys natural vegetation and causes the soil to wash or blow away more easily Soil Destruction •Construction •Exposed soil at construction sites washes or blows away and ends up in nearby water sources Soil Destruction •Mining •Exposing rocks and minerals to the air and rainwater speed up the rate of chemical weathering Soil Destruction •Desertification – the expansion of desert conditions in areas where the natural plant cover has been destroyed Soil Conservation •Crop Rotation – the practice of planting different crops on the same field in different years or growing seasons to maintain soil fertility Soil Conservation •Conservation Tillage – a system of cultivating the land that reduces soil and water loss by leaving at least 30% of the crop residue on the surface at the time of planting Soil Conservation •Terraces – flat, step-like areas built on a hillside to hold rainwater and prevent it from running downhill Soil Conservation •Contour Plowing – the practice of plowing along the curves, or contours, of a slope helping channel rainwater so it doesn’t run straight downhill Soil Conservation •Windbreaks – rows of trees planted between fields to reduce the force of winds that can carry off soil Erosion •Erosion – the process in which sediment is picked up and moved from one place to another •Deposition – the process in which transported sediment is laid down •Mass Wasting – the downhill movement of loose rock or soil Erosion •Rockslide – a large mass of rock slides as a unit down a slope Erosion •Mudflow – a mixture of soil, water, and debris flowing downward, picking up sediment as it rushes down Erosion •Slump – a slide of loose debris that moves as a single unit Erosion •Creep – the soil closer to the surface moves faster than the soil farther down Glaciers Glacier •A mass of ice that exists year-round and moves over land •Glaciers move lots of sediment that can carve striations (grooves) into rocks •The glacier deposits debris as it melts Glaciers •Alpine Glacier – form in mountains and flow down through valleys (also called valley glaciers) Glaciers •Continental Glacier – much larger than alpine glaciers, they can cover entire continents (also called ice sheets) Glaciers •Till– sediment of different sizes left directly on the ground by a melting, or retreating, glacier Glaciers •Erratic– large boulders left behind by glaciers Glaciers •Kettle Lake – a bowl-shaped lake that was formed as sediment built up around a block of ice left behind by a glacier Running Water/Stream Erosion Streams •Flowing water will lift and carry small sediments such as silt and sand •Where water moves more swiftly there will be more erosion Running Water/Stream Erosion •Where the water slows down, sediments will be deposited •The steeper the slope, the faster erosion will occur Stream Erosion •Meander – curves and bends that form a twisting, looping pattern in a stream channel Water Erosion •Oxbow Lake – a crescent-shaped lake formed when a stream cuts a new channel that by-passes a meander during a flood Stream Erosion •Waterfall– soft rock erodes, leaving a hard ledge over which the stream falls Stream Erosion •Delta– an area of land formed by the buildup of sediment at the end, or mouth, of a river Stream Erosion •Floodplain– the area of land on either side of a meandering stream that is underwater when the stream floods •Often have rich, fertile soils due to minerals and fine sediments that have been deposited by past floods Stream Erosion •Canyon– the result of a stream cutting its way deeper and deeper through the underlying rock layers Stream Erosion •Cave– forms as acidic rainwater chemically reacts with limestone or dolomite rock layers underground, slowly creating larger and larger spaces as the rock is worn down and washed away Stream Erosion •Sinkhole – a basin that forms when the roof of a cave becomes so thin that it suddenly falls in Wind Erosion Wind Erosion •Carries fine, dry sediments over long distances •Can carve out landscapes as it carries sediment •Loess: fine particles of silt and clay deposits Wind Erosion •Dune – a mound of sand built up by wind Wind Erosion •Desert Pavement – the layer of stones and gravel left behind after wind blows away all the smallest particles of sand and silt Wave Erosion Waves •The crashing of waves on a shoreline combined with storms continually shape the beach •Tidal action and waves carry away weathered materials Wave Erosion •Longshore Drift – the zigzag movement of sand along a beach, caused by the action of waves Wave Erosion •Sandbar – a ridge of sand built up by the action of waves and currents (under water) Wave Erosion •Barrier Island – a long, narrow island that develops parallel to a coast as a sandbar builds up above the water’s surface Wave Erosion •Sea Arch– a natural opening eroded out of a cliff face Wave Erosion •Sea Stack– a steep, vertical column of rock near a coast Wave Erosion •Sea Stump– the collapsed remnants of an eroded sea stack