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Objectives Explain how flowing water causes erosion and deposition Describe how runoff, streams, and rivers change Earth’s surface Identify features caused by groundwater erosion and deposition Erosion – transportation of sediments Agents of erosion include flowing water, wind, waves, ice, or gravity. Eroded materials drop somewhere. This is called deposition. Rate of erosion depends on velocity of running water. Fast water larger particles and more particles transported Minerals that dissolve in water form salts. Small particles such as clay and silt are carried in a suspension, not dissolved in water. Medium sized particles as such as sand, moved by saltation. They jump at the bottom of the stream. Large particles like gravel and pebble move by traction – dragged at the bottom of the water. Eventually the particles are deposited. This can happen by runoff, streams, and rivers. Erosion by runoff – when rain is not able to absorb into the ground, it may pick up loose material on the surface and move it somewhere else. Erosion by streams – Mountain – steep slope carries a lot of sediment down V-shaped channel. If softer rock erodes next to harder rock waterfall can form. Slow-Flowing rivers ▪ ▪ ▪ ▪ Gentle slopes erode the sides of the channel more than the bottom. These large curves are called meanders. Meanders erode from side to side, create a floodplain. A meander may cut off from the rest of the river forming an oxbow lake. The slope has much to do with the sediment moving. Deposition occurs when the slope becomes more gradual and movement slows down. Alluvial Fan – deposits at the bottom of a mountain stream, flat land. Delta – deposits where a stream or river empties into still water. It forms a triangle shape. Flood waters will spread out sediment and deposit it over the land. Flood plain develops a thick layer of soil from all the deposits. Good for growing plants/crops. Forms natural levees – raised strip of sediments deposited close to the water’s edge. Some water soaks into the ground into the soil, seeps through the rocks, can erode/deposit materials. Water can dissolved rock and form caves. Water is dissolved in minerals. When minerals come out of a solution, they are deposited. Formations build up in caves – Stalactites – pointed, icicle-like mineral from ceiling of cave down Stalagmite – rounded mineral deposit from the bottom of the cave up Sinkhole – when the erosion continues and the ceiling of cave collapses. Objectives Explain how waves cause erosion on shorelines Describe features formed by wave deposition Identify ways to protect shorelines from wave erosion Waves – the way energy travel through matter. Ocean waves form when wind blows over the surface of the ocean. Wind energy is transferred to to the sea surface and is carried through by waves. Factors that determine size of waves Speed of the wind Length of time the wind blows Distance the wind blows Wave Erosion – Runoffs, streams, and rivers carry sediment to the oceans and act like sandpaper. They erode the shore. Landforms From Wave Erosion Sea Arches form when waves erode both sides of a cliff. Sea Stacks – form when waves erode the top of a sea arch, leaving behind pillars of arch. Wave-cut cliffs when rocks erode a rocky shoreline Beaches- sediment in the form of sand deposited in quiet areas along a shore. Shore can include rock and shell in addition to sand. Longshore drift – moves the sediment straight down the beach with the direction of the wave. Spit – deposits from longshore drift, a ridge of sand that extends away from the shore. Sandbars and barrier islands can form from wave deposits. Breakwaters – artificial barriers that protect the shoreline from incoming waves. Groins – A wall of rocks or concrete that juts out into the ocean perpendicular to the shore. Objectives Explain how wind causes erosion Describe sediment deposited by wind Identify ways to prevent wind erosion. Wind carries particles in the same way that water carries them. Tiny particles move through suspension, they hang in the air for days. They go far distances. Medium sized particles move by saltation. They move in short hops and stay close to the ground. Large sized particles move by traction. They stay on the ground. Abrasion is a form of wind erosion where rocks are scoured and polished from wind itself or by being dragged over surfaces. Like water, when wind slows down it drops the sediments its carrying. As wind slows down, it deposits the largest particles first. Sand dunes – deposits of sand found mainly in deserts and beaches. Formed from an obstruction slowing down wind, sand is then deposited. Loess – wind dropping fine particles of silt and clay, forms vertical cliffs. It can become a thick, rich soil. Covering soil with plants Plants and roots help the soil to stay in place Planting rows of trees around fields Fences at beaches Objectives Describe how continental and valley glaciers form Explain how glaciers cause erosion Identify landforms deposited by glaciers Glaciers are masses of flowing ice Two types of glaciers: continental and valley Continental glacier is spread out over a huge area. It may cover most of a continent or large areas such as Greenland or Antarctica. Valley glacier is long and narrow. It forms in mountains and flow downhill through mountain river valleys. Glaciers form erosion in two main ways: plucking and abrasion. Plucking – the process by which rocks and other sediments are picked up by glaciers. Abrasion – the process in which a glacier scrapes underlying rocks. Erosion by Valley Glaciers Carves out U-shapes valley with nearly vertical walls Cirque is a rounded hollow carved in the side of a mountain by a glacier. Arete – a jagged ridge that remains when cirques form on opposites sides of a mountain. Horn – a sharp peak that is left behind when glaciers erode all sides of a mountain Glacial till – a mixture of particles and rocks of all sizes Moraine – sediment deposited by a glacier. A ground moraine is a thick layer of sediment left behind by a retreating glacier. Drumlin – a long, low hill of sediment deposited by a glacier. Esker – a winding ridge of sand deposited by a stream of meltwater. Kettle Lake – occurs where a chunk of ice was left behind in the sediments of a retreating glacier. Objectives Identify causes and effect of landslide s and mudslides Explain how slump and creep occur Mass movement – the type of erosion and deposition by gravity. Gravity can pull soil, mud, and rocks down cliffs and hillsides. Landslides – most destructive type of mass movement. Happens when a large amount of soil and rock suddenly falls down a slope because of gravity. More likely if there has been heavy rain or an earthquake. If a landslide falls into a body of water tsunami could form Mudslide – a sudden flow of mud down a slope due to gravity. Occurs where soil is mostly clay. Forms usually with lots of rain mud slippery and slides Slump – a sudden mass movement of large blocks of rock and soil down a slope. Creep – slow movement of rock and soil down a hillside. Happens so slowly you can’t see it happening.