New Area of Focus Weathering and Erosion Weathering

• New Area of Focus. Weathering and Erosion

Weathering The process that breaks down the materials of Earth’s crust (rock) by the action of physical or chemical processes into smaller pieces called sediments.

Mechanical Weathering l Process by which rocks are broken down into smaller pieces by physical means (ice, wind, water, plants, animals) l Types of Physical/mechanical weathering Frost heaving and Frost wedging (ice) B. Plant roots C. Friction and impact (Abrasion with H 20 and wind) D. Burrowing of animals A.

A. Frost Wedging l Water freezes in crack and expands while breaking surrounding rocks.

Frost Heaving • A section of ruptured pavement caused by the expansion of freezing water immediately under the road.

Mechanical weathering-Plant Roots Plant roots can sprout and cause existing cracks in rocks. Growth causes the root to expand, forcing the crack to widen. l The force can eventually split the rock apart. l

Abrasion- by wind or water Abrasion – the grinding and wearing away of rock surfaces through mechanical action of other rock or sand pebbles or when one rock hits another. https: //www. classzone. com/books/earth_science/terc/content/visualizations/es 1601 page 01. cfm? cha pter_no=visualization Mechanical weathering examples of abrasion include: A. Wind Abrasion: wind blows sand silt against exposed rock eventually wearing away the rock’s surface (ex. Sandblaster) B. Water Abrasion: as rocks and pebbles roll along the bottom of flowing water, they bump and scrape against each other, causing these rocks to become rounded and smooth.

Burrowing of Animals or insects that tunnel underground or that live in the soil break up soil and loosen rocks to be exposed to further weathering l Examples: Dogs or worms l

Discuss with a peer…. . • What are other animals that burrow or dig underground? • moles, prairie dogs, insects, worms, gophers • Where have you seen examples of mechanical weathering?

Chemical Weathering l Chemical weathering is the process by which rocks break down as a result of chemical reactions. Examples: Water, weak acids, and air can cause chemical weathering l The agents of chemical weathering Water l Oxygen l Carbon dioxide l Living organisms l Acid rain These agents weaken the bonds between minerals grains of the rock. l

Water • Water can cause rock to be broken down and dissolve. Can take thousands of years to take place.

Oxygen • Iron (element) combines with oxygen in the presence of water in a process called oxidation • The product of oxidation is rust

Weak acids chemically weather: Carbonic acids in groundwater • Decay of plants leaves carbon dioxide in soil. • Reacts with rocks in the ground, causing a chemical reaction, eating away at the rock. • Carbonic acid easily weathers limestone and marble • Example: Creates CAVES!

Living Organisms • Lichens that grow on rocks produce weak acids that chemically weather rock

Acid Rain • Compounds (nitrogen oxide, Sulfuric oxide, Carbon Dioxide) from burning coal, oil and gas are present in air. • It dissolves in rain water and creates acid rain • Acid rain causes very rapid chemical weathering

Features of chemical weathering: Sinkholes

Features of chemical weathering: Caves

Summary • Ice wedging is a form of mechanical weathering in which water seeps into rock cracks and then freezes and expands. • Wind, water, and gravity cause mechanical weathering by abrasion. • Animals and plants cause mechanical weathering by turning the soil and breaking apart rocks. • Water, acids, and air chemically weather rock by weakening the bonds between mineral grains of the rock.

Rates of weathering l What is differential weathering? l How does surface area affect the rate of weathering? l How does climate affect the rate of weathering? l Why do mountaintops weather faster than rocks at sea level?

Differential Weathering l Differential weathering is a process by which softer, less weather resistant rocks wear away and leave harder, more weather resistant rocks behind. l Hard rocks weather more slowly than softer rocks.

The Shape of Rocks l l l Weathering takes place on the outer surface of rocks. The more surface area exposed to weathering, the faster the rock will be worn down. As the surface area increases, the rate of weathering also increases. If a large rock is broken into smaller pieces, weathering of the rock happens much faster. The rate of weathering increases because a smaller rock has more surface area to volume than a larger rock. More of the smaller rock is exposed to the weathering process.

Weathering and Climate l The rate of chemical weathering is faster in warm, humid climates than cold, dry climates because of oxidation. l Oxidation happens when the temperature is higher and when water is present. l Water increases the rate of mechanical (physical) weathering (ice wedging). l Repeated changes in temperature (freeze, thaw, freeze, thaw) is a major factor in mechanical weathering.

Weathering and Elevation Mountaintops weather faster than rocks at sea level because they are exposed to more wind, rain, and ice than rocks at sea level or lower elevations. l The increase in wind, rain, and ice increases the effects of mechanical and chemical weathering. This increase in elevation causes peaks of mountains to weather faster. l Gravity affects the rate of weathering: l l l Steepness Rainwater Removal of sediment exposes new rock to weathering Abrasion Increased surface area of mountain

Erosion The process by which water, ice, wind or gravity moves fragments of rock and soil. l The natural moving of material from one place to another l Erosion transports weathered rock and soil. l

Agents of Erosion l l WATER: Rivers, streams, and runoff WIND: Dunes and Loess ICE: glaciers GRAVITY/Mass Movement: Landslides, mudslides, slump, creep, rockslides, and avalanches

Water Erosion WATER: Rivers, streams, and runoff l As water moves in rivers and streams, weathering and erosion work together as sediments are pulled from the banks (sides) and transported downstream. *This helps the stream grow wider and deeper l Examples of geological features: Alluvial fans and deltas l

How do Streams Erode? http: //highered. mheducation. com/olcweb/cgi/pluginpop. cgi? it=swf: : 640: : 480: : /sites/dl/free/0072402466/30425/10_22_10_23. swf: : Figs. %2010. 22, %2010. 23%20 -%20 Meander%20 Cut-Offs%20 and%20 Oxbow%20 Lakes http: //www. classzone. com/books/earth_science/terc/content/visualizations/es 0604 page 01. cfm? chapter_no=visualization

Water Erosion l Rill Erosion starts when a small stream forms during a heavy rain. l Channel- is a groove created by water moving down the same path l Gully Erosion carries away large amounts of soil. l Sheet Erosion- occurs when water flowing as sheets picks up sediment and carries them away.

l http: //nroc. mpls. k 12. mn. us/Environmental %20 Science/course%20 files/multimedia/le sson 54/animations/4 c_Erosion. html l https: //ees. as. uky. edu/sites/default/files/e learning/module 11 swf. swf

Wind Erosion As loose sediments are laid on ground, wind picks them up and moves it to another location. l Once wind stops, it deposits the sediments and creates new geological features. l Examples: Dunes and Loess l

Erosion by Ice As glaciers move slowly, the glacier pick up loose sediments and deposit them in another location as the glaciers melt. l Examples of geological features: Morraines l

Mass Movements rocks and soil moving down slope under the influence of gravity Examples: Landslides, mudslides, slump and creep landslide clip. mpeg

Gravity • The greater an object’s mass, the stronger its gravitational pull. • Earth’s sediment is carried by mass movement, which is a kind of erosion in which gravity moves sediment down slope.

Types of Mass Movements • Slump: Slump occurs when a mass of material slips down a curved surface • Creep: Creep occurs as soils slowly move downhill. • Rock Slide: Slide occurs when layers of rock slip down a hill suddenly. • Mudflows: Mudflows occurs when there are thick layers of loose sediment

How are Mass Movements Alike? • All are most likely to happen on steep slopes. • Gravity is the cause of them all • They can occur after heavy rain • Water adds mass to the soil causing more pressure and weakens the sediment • All mass movements erode at the top of a hill and deposit at the bottom.

Consequences and Prevention of Erosion • Many homes are built on hills because people like the view but may not be safe • Growing plants on bare slopes helps hold the soil in place • Drainage pipes and tiles help make the slope more stable by allowing water to drain more easily • Concrete or stone walls help protect

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