Weathering and Erosion

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September 19, 2016

Weathering and Erosion

Weathering- a natural process that causes rocks to change, breaks them down, and causes them to crumble.

*Freezing and thawing, oxygen in the air, and even plants and animals can affect the stability of a rock. These are some of the things that cause rocks on Earth's surface to weather, and in some cases, to become soils.

http://www.brainpop.com/science/weather/weathering/

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Mechanical Weathering

Mechanical Weathering breaks down rocks into smaller pieces without changing them chemically. For example, a sidewalk breaking apart is mechanical weathering.

Two of the many causes of mechanical weathering are:1. Ice wedging2. Living organisms

http://www.youtube.com/watch?v=lyysL02ZvQ8

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September 19, 2016

Ice Wedging

In some areas of the world, air temperature drops low enough to freeze water. Then, when the temperature rises, the ice thaws. This process of freezing and thawing breaks up rocks.How does this happen?

*Ice wedging also causes potholes to form in roadways.

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Plants and Animals (aka living organisms)

Plants' roots grow deep into cracks in rock where water collects. As they grow, roots become thicker and longer, slowly exerting pressure and wedging rocks apart.

Gophers and prairie dogs also weather rock (and other burrowing animals). As they burrow through sediment or soft sedimentary rock, animals break rock apart.

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Chemical Weatheringhttp://www.youtube.com/watch?v=6VnVRHIV6j4

Chemical weathering occurs when the chemical composition of rock changes. Chemical weathering is rapid in tropical regions where it's moist and warm most of the time.

*Natural Acids *Plant Acids *Effect of Oxygen

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September 19, 2016

Natural AcidsSome rocks react chemically with natural acids in the environment. When water mixes with carbon dioxide in air or soil, for example, carbonic acid forms. Carbonic acid can change the chemical composition of minerals in rocks.

limestone dolomitemarble

Although carbonic acid is weak, it reacts chemically with many rocks.

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September 19, 2016

Plant AcidsPlant roots also produce a substance called tannin that can react with rocks. In solution, tannin forms tannic acid. This acid can dissolve some minerals in rocks.

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September 19, 2016

Effect of Oxygen

Think about how many times you see rust on a car, reddish soil, or reddish stains on a rock. When you see this, oxidation has occurred. Oxidation is the chemical effect caused by oxygen. When iron-containing minerals (rocks) are exposed to oxygen, they can weather to minerals that are like rust.

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September 19, 2016

Soil

Soil isn't just dirt under your feet! Soil is a mixture of weathered rock, organic matter, water, and air that supports the growth of plant life.Organic matter includes decomposed leaves, twigs, roots, and other material.

Some factors that affect soil formation include:*parent rock *slope of land *climate *time *organisms

http://www.brainpop.com/science/earthsystem/soil/

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September 19, 2016

Parent Rock

The kind of parent rock that is being weathered can affect the soil fomation. For example, where limestone is chemically weatherd, clayey soil is common because clay is left behind when the limestone dissolves.

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September 19, 2016

The Slope of the Land

The topography, or surface features of an area also influence the types of soils that develop. Soil has little chance to develop on hillsides. Why do you think that is?

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ClimateIf rock weathers quickly, deep soils can develop rapidly. This is more likely to happen in tropical regions where the climate is warm and moist.

Climate also affects the amount of organic material in soil. Soil in desert climates contain little organic material. However, in mild, humid climates, vegetation is lush and much organic material is present.

When plants and animals die, decompostion by fungi and bacteria begins. The result is the formation of a dark-colored material called humus. Humus helps soil hold water and provides nutrients that plants need to grow.

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September 19, 2016

Time

It takes time for rocks to weather. It can take thousands of years for some soils to form.

In young soils, the parent rock determines the soil characteristics. As weathering continues, however, the soil resembles the parent rock less and less.

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September 19, 2016

Organisms

Organisms influence soil development. Lichens are small organisms that consist of an alga and a fungus that live together for mutual benefit.You may have seen lichens in the form of multicolored patches growing on tree branches or cliff faces. Lichens can grow directly on rocks! As they grow, they take nutrients from the rock that they are starting to break down, forming a soil.

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September 19, 2016

Erosion of Earth's Surface

Erosion- The wearing away and removal of rock or sediment.

Erosion occurs because gravity, ice, wind, and water sculpt Earth's surface.

gravity ice

wind water

http://www.brainpop.com/science/earthsystem/erosion/

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Gravity*Gravity is a force that pulls every object toward every other object. *Gravity pulls everything on Earth toward its center. *As a result, water flows downhill and rocks tumble down slopes.

Mass Movement- When gravity alone causes rock or sediment to move down a slope, the erosion is called mass movement.*These can occur anywhere near hills, mountains, or volcanoes.

The Four Mass Movements are:Creep, Slump, Rock Slides, and Mudflows

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September 19, 2016

Mass Movements

Creep- When soil on a slope moves very slowly downhill, a mass movement called creep occurs. Some of the trees, poles, and fences gradually bend because of creep's pressure on them.

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September 19, 2016

Slump

A slump occurs when a mass of rock or sediment moves downhill along a curved surface.

Slumps frequently occur on slopes that have been undercut by erosion, such as those above the bases of cliffs that have been eroded by waves.

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Rock Slides

During a rock slide layers of rock break loose from slopes and slide to the bottom. The rock layers often bounce and break apart during movement. Rock slides can be destructive, sometimes destroying entire villages or causing hazards on roads in mountainous areas.

http://www.youtube.com/watch?v=ZVYGJYnJTi0

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MudflowsWhen heavy moisture saturates sediments, mudflows can develop, sending a pasty mix of water and sediment downhill over the ground's surface.

http://www.youtube.com/watch?v=AEny25AocYw

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September 19, 2016

Ice

In cold regions, more snow might fall than melts. Over many years, the snow can accumulate to form large, deep masses of ice called glaciers.

*There are 2 types of glaciers:~CONTINENTAL GLACIERS

*These are huge glaciers in polar regions that cover about 10% of Earth. These glaciers are so thick that they can bury mountain ranges!~VALLEY GLACIERS

*These are much smaller and are found in high mountains where the average temperature isn't warm enough to melt the glaciers.

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September 19, 2016

Glacial Erosion

There are 2 ways glaciers can erode rock:

1. Pulling out loose rock:If the rock that the glacier is sliding over has cracks in it, the ice can pull out pieces of rock. This causes the rock to erode slowly.

2. Scratching:When loose pieces of rock freeze into the bottom of the glacier and are dragged along as the glacier moves. (Act like giant sheets of sandpaper)

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Effects of Glacier Erosion

*Valley glaciers form large bowls called cirques in mountains.

*Glaciers can widen valleys giving them a wider U-shaped profile.

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Glacial Deposition

Glaciers can also deposit sediments. When stagnant glacier ice melts or when ice melts at the bottom of a flowing glacier or along its edges, the sediment the ice was carrying gets left behind on Earth's surface.

*Sediment deposited directly from a glacier is called till.Till- the mixture of different-sized particles, ranging from clay to large boulders.

Outwash- sand and gravel deposits laid down by rivers made by melting glaciers. All particles are about the same size.

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Wind

When wind blows across loose sediments like silt and sand, it lifts and carries it.

*Wind often leaves behind particles too heavy to move. This erosion of the land by wind is called deflation. Deflation can lower the land's surface by several meters.

Wind can also deposit sand. If sand deposits continue to grow, sand dunes form.

Sometimes wind carries only fine sediment called silt. When this sediment is deposited, an accumulation of silt called loess can blanket Earth's surface. It is very fine (like talcum powder) and is found in some large deserts and near glacial streams.

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September 19, 2016

Water

Water that flows over Earth's surface is called runoff and it is an important agent of erosion.

*Sheet flow is when water flows downhill as a thin sheet. This thin sheet of water can carry loose sediment grains with it, and cause erosion of the land (also known as sheet erosion).

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Rills and Gullies

Where a sheet of water flows around obstacles and becomes deeper, rills can form. Rills are small channels cut into the sediment at Earth's surface. These channels carry more sediment than can be moved by sheet flow.

As runoff continues to flow through the rills, more sediment erodes and the channel widens and deepens. When the channels get to be about 0.5 m across they are called gullies.

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September 19, 2016

Streams

*Gullies often connect to stream channels. Streams can be so small that you could jump to the other side or large enough for huge river barges to transport products along their course.*In mountainous or hilly regions, streams flow down steep slopes. This causes the streams to have a lot of energy and often cut into the rock beneath their valleys. *All streams must eventually flow into the ocean or a large lake.***STREAMS ARE THE MOST IMPORTANT AGENT OF EROSION ON EARTH!!!***

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Effects of Erosion

All agents of erosion change Earth's surface.

*Rock and sediment are removed from some areas only to be deposited somewhere else.

*Where material is removed, canyons, valleys, and mountain bowls can form.

*Where sediment accumulates, deltas, sand bars, sand dunes, and other features make up the land.