Click to edit Master subtitle style 12/13/10 Chapter 8 Erosional Forces

Click to edit Master subtitle style 12/13/10 Flatten the soil in your plate. Find 3 ways to move the soil from one side of the plate to the other. You may not touch the soil with your hands! But, you can touch the plate. Do not spill!

12/13/10 Erosion: process that wears away surface material and moves them from one place to another major causes: gravity, glaciers, wind, water they all need energy for motion! Deposition: the dropping of sediments that occur when an agent of erosion looses its energy of motion and is no longer able to carry the load drop when energy of motion decreases! What causes erosion and deposition? - Gravity! What is gravity? The force of attraction that exists between all objects - Since Earth is so large, all objects are attracted to it. - The Earth is the source of all our gravity. - Any loose material will be pulled down a slope (hill), due to gravity. - When gravity alone causes material to slide down a slope this is called mass movement.

12/13/10 Examples of mass movement: 1) Slump: mass movement that happens when loose rock layers slip down a slope. When a slope becomes too steep, the base material no longer can support the rock and sediment above it. The soil and rock slip downslope as one large mass or break into several sections. 2) Creep: sediments slowly inch their way down a hill…most common in freezing areas. Ex: Leaning trees and fence posts that lean downhill.

12/13/10 3) Rockfalls and Rock Slides: when large rocks break loose and tumble down a hill…can be very destructive! Rockfalls - As rocks fall and tumble through the air, they crash into other rocks and knock them loose. More and more rocks break loose and tumble to the bottom. Rock Slides – occur when layers of rocks – usually steep layers – slip down a slope suddenly. Happen most after heavy rain or earthquakes. 4) Mudflows: a thick mixture of sediment and water flowing down a slope…dry areas with thick layers of sediment that suddenly get really wet from rain…

12/13/10 All mass movements… Occur on slopes… Occur more often after a rain… Increase if vegetation has been removed… How can you prevent these problems? Strengthen slopes with vegetation…roots hold soil together Walls made of concrete… We can try all we want to avoid erosion and deposition problems, but in the long run…gravity will still be too powerful! IE – video of mudslide…

12/13/10 Review: 1. Define erosion. What force causes it? 2. Explain how deposition changes the surface of the Earth. 3. Describe the characteristics that all types of mass movements have in common. 4. Describe ways to help slow erosion on steep slopes. 5. What are the similarities and differences between rock falls and rock slides?

12/13/10 Erosion by Glaciers! Glacier – a large mass of ice and snow moving on land under its own weight. As glaciers pass over land, they erode it, changing features on the surface. They then carry eroded material along and deposit it somewhere else. Change large areas of the earth’s surface. Plucking – process that adds gravel, sand and boulders to a glacier’s bottom and sides as water freezes and thaws, breaking off pieces of surrounding rock.

12/13/10 Transporting and Scouring – as glaciers move forward over land, they can transport huge volumes of sediment and rock. Plucked rock fragments and sand at its base scour and scrape the soil and bedrock like sandpaper against wood, eroding the ground below even more. When bedrock is gouged deeply by rock fragments being dragged along, marks are left behind. Deep, long parallel scars are called grooves. Shallow marks are called striations. These indicate the direction in which the glacier moved.

12/13/10 Ice Depositing Sediment… When glaciers begin to melt, they are unable to carry much sediment and that sediment drops, or is deposited, on the land. When a glacier melts and begins to shrink back, it is said to retreat. As it retreats, a jumble of boulders, sand, clay and silt is left behind. The mixture of different sized sediments is called till. Till deposits can cover huge areas of land. Thousands of years ago, huge ice sheets in the northern US left enough till behind to fill valleys completely and make these areas appear flat. Ex: areas of Montana, Iowa, Ohio, Illinois, Indiana and New England.

12/13/10 Moraine Deposits – large ridges of rocks and soil deposited by a glacier when it stops moving forward. Outwash Deposits – material deposited by meltwater from a glacier. Eskers – a winding ridge of sand and gravel left behind when a glacier melts. Pg. 217

12/13/10 Continental Glaciers – huge masses of ice and snow that cover 10% of Earth…mostly near the poles of Antarctica and Greenland. Thicker than some mountain ranges and make it impossible to see most of the land features of those regions. Valley Glaciers – occur in high mountains where the average temperature is low enough to prevent snow from melting during the summer…these grow and creep along. Importance of Glaciers… Shaped mountain tops and transformed valleys. Left behind sediments that are economically important Ex: sand and gravel deposits are excellent starting materials for the construction of roads and buildings.

12/13/10 Wind! Wind erosion: air moves and picks up particles and deposits them in other places Air differs from other erosional forces because it can’t normally pick up heavy objects, but it can deposit sediment over a large area Wind erodes Earth’s surface by deflation and abrasion… Deflation: wind blows across loose sediment and removes small particles and leaves behind heavy material…big rocks… Abrasion: windblown sediment hit rocks and surface gets worn away – occurs everywhere…but mostly in deserts, beaches & plowed fields WHY? – fewer plants to hold sediment Sandstorms - sand is normally too heavy for wind…wind blows forcefully & sand bounces & hits other grains causing them to rise into air (low cloud just above ground…) Dust storms - dry soil picked up by wind and blown high into atmosphere because they weigh less than sand…carries particles far distances… IE – 1930…dust picked up in Kansas was found in New England… important part of soil erosion…

12/13/10 Reduce wind Erosion: Erosion is most common in areas with no plants… Stop erosion?…PLANTS! Vegetation will reduce erosion… Roots hold soil in place Windbreaks with trees – slow down wind… Stop energy of motion… IE – row of cottonwood trees reduced wind to 66% of normal speed But…strong wind with dry soil…nothing will stop erosion by wind!

12/13/10 Deposition by wind: sediments are eventually deposited in new areas… Creates a variety of land forms… Loess: wind deposits of fine- grained sediment…packed together creates a thick unlayered yellowed- brown colored deposit What happens when wind blows sediment against an obstacle? = dune! Dunes: created when sediment settles behind an obstacle Dunes can be moved as sand is lifted and deposited downwind…(picture ) Overall…Erosion and Deposition constantly shape and reshape the land!

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Create a Study Guide! Using key terms and main ideas from chapters 7 and 8, create a study guide AND answer key (on separate sheets of paper). 10 fill in the blank questions 5 multiple choice questions 5 true or false questions Ex: ______ is a mixture of weathered rock, organic matter, mineral fragments, water and air.