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Activity: Imagine that you are a tin can-shiny, new, and clean. But something happens, and you don’t make it to a recycling bin. Instead, you are left outside at the mercy of the elements. In light of what you have learned about physical and chemical weathering, write a story about what happens to you over a long period of time. What is your ultimate fate?
Erosion Do Now: Define chemical weathering and describe its causes. EQ- How do rocks and minerals break down?
Chemical weathering occurs when chemical reactions dissolve the minerals in rocks or change them into different minerals. This type of weathering changes the chemical composition of the rock, which can weaken the rock.
Erosion EQ- How do rocks and minerals break down?
Erosion • Erosion is the process of moving pieces of rock and sediment by wind, water, ice, or gravity.
Erosion Moving Sediment • Weathering breaks rock into bits and pieces called sediment. How does sediment get from a mountain peak to a beach?
Erosion • Weathering breaks rock into bits and pieces called sediment. • Wind erodes mountains and moves sediment, but not as well as flowing water.
Erosion • Running water, wind and ice are all involved in moving sediment. Sediment generally moves downhill because of the force of gravity. • Running water- like that found in rivers, streams, and waterfalls carries sediment. - a river is a large, flowing body of water -a stream is a small river. -a channel is the path that a river or stream follows
Erosion Running water moves sediment • The process of depositing sediment after it has been • moved by water, wind, or ice is called deposition. • The amount of sediment carried and deposited by • water depends on many factors: • the volume of water, • the slope of the land, • how rocky or smooth the land is.
Erosion Volume: The volume of running water affects how much sediment can be carried. When the volume of flowing rainwater is small, some sediment is moved. After a heavy rainfall, the greater volume of water can move a lot of soil or sediment from yards. Slope: Slope refers to how steep the land is, another word for slope is gradient. The steeper the slope, the faster the water and sediment will move over land. Faster water means that larger particles can be moved and more particles can be moved at one time. Rocky vs. Smooth: Rocky landscapes can trap sediment causing the sediment not to travel far. A smooth landscape or river bed might mean that sediment can be carried a long way.
Erosion • A stream table can model how water flows over the land. • The steeper the slope, the faster the water and sediment will move over land.
Erosion Sorting sediment: How fast water moves is directly related to how much energy it has. Both the speed of water and its energy are directly related to how big a piece of rock can be moved. Fast, high energy water can move big pieces of rock. Slow-moving water can only move fine sediment. • You can tell the speed of flowing water by the size of the rock pieces found on a stream bottom. • The grains settle in order, making a pattern called graded bedding.
Erosion Interpreting layers of sediment: • Sedimentary rocks hold clues to their past. • If you know the up direction, you know the direction of younging —this is the directions of younger layers.
Erosion When sediment is carried by the wind or running water, it often forms a pattern of alternating beds where it is deposited, this pattern is cross bedding. • Cross bedding, is easy to recognize in sedimentary rocks where one layer ends and another layer passed over it.
Erosion Moving sediment by ice: • Particles that are trapped in ice or suspended in water can cause weathering. • As the ice of a glacier flows down a valley, it grinds the valley floor with pieces of rock caught up in the ice.
As the ice of a glacier flows down a valley, it grinds the valley floor with pieces of rock caught up in the ice.
Glaciers are formed from accumulation of snow over hundreds or thousands of years. • As snow piles up and pressure increases, it changes into ice.
The fine rock powder that results from glaciers is called “rock flour.” • Rock flour can be washed into lakes and make them a milky blue color.
Types of glaciers • Alpine Glaciers (Valley Glaciers) • - small to medium glaciers formed in mountains where the temperature is low enough to prevent snow from melting during the summer. • - Flow slowly down mountain slopes and valleys eroding as they go.
U-shaped Valleys Alpine glaciers typically follow a river bed and cut the deep V into a smoother but larger U-shape as they move down the mountain. The sides of the U-shaped valleys are much steeper and rugged than when they were shaped by a river. The ice in a glacier is much more destructive to the land than the running water in rivers.
Continental Glaciers • Huge continuous masses of ice that form from layers of snow that compact and freeze into ice.
How do Glaciers move? Glaciers move by two different methods: • when ice at the bottom of the glacier melts due to the weight of the glacier. The glacier begins to slide on the melted water. • when ice crystals within the glacier slip over each other
Glacial Erosion • As glaciers move they break off pieces of rock and sediment, pick them up and carry them with them. As the glacier begins to melt the sediment is deposited on land.
More on moving sediment • Wind can move particles of sediment from one place to another. • Beach dunes hold large amounts of wind deposited sand. • Loess is another wind-blown deposit of fine sediment.
More on moving sediment • Mass wasting is the downhill movement of large amounts of rock and sediment due to the force of gravity. • Mass wasting might occur as a landslide, rockfall, a mudflow, or a slump. • A landslide occurs when a large mass of soil or rock slides down a steep slope.
More on moving sediment A rockfall can occur when a big chunk of rock is split off of a large landform due to weathering (like frost or root wedging). Rockfall speeds up the weathering process by quickly breaking up large pieces of rock formation. A mudflow occurs when a large rock, sediment, and plant material flows down a mountain.
More on moving sediment • Slumping describes what happens when loose soil becomes wet and slides or “slumps”. • Slumping can happen after a period of very heavy rainfall.
