Weathering and Erosion

By Maggie Bagatta and Cadence Jegers

Weathering

Weathering is the process of rocks and sediment slowly wearing away.

Physical/Mechanical Weathering

Physical weathering caused by physical changes like temperature, freezing and thawing, wind, and water.

Physical weathering by temperature change

Physical weathering by temperature change occurs when the suns energy heats up a rock, causing it to expand, and then when the temperature goes back down the rocks contract This causes pressure on the outer layers of the rock which cause them to crack and eventually the rock falls away. This type of weathering only works on rock types such as granite, that expand under the heat of the sun and then contract when the temperature goes down.

Physical weathering by wind, rain, and waves

Physical weathering by wind is when wind blows on a weaker sediment like sandstone and causes particles of the stone to wear away. Rain water weathers stone over a long period of time, especially because it is not a very strong force. Waves weather at rock by crashing on the the rock and, like rainwater, takes a long period of time, but eventually eats away at the sediment. One last way is when rocks that sit in a river are weathered and made round by the water rushing over the rocks. This picture, taken at 7 bridges South Milwaukee, Wisconsin, is an example of water from a stream weathering away at the stones under and around it.

Physical Weathering by freezing and thawing

Physical Weathering by freezing and thawing is when water gets in between the cracks in a rock and freezes. When water freezes, it expands, so when it does this it also causes the crack in the rock to expand. Then when the ice melts, that causes the crack to close slightly, without the pressure of the ice. After this process is repeated, and there is enough stress on the rock, it breaks off. This picture is an example of a rock that had cracked because of Freeze-Thaw weathering.

Biological Weathering

Biological weathering is when animals or plants cause plants to wear away.

Biological Weathering plants

Biological Weathering by plants occurs by plant and tree roots growing in between rock. This causes weathering because when the roots grow bigger in between the rocks, the rock breaks off.

Biological Weathering by animals and humans

Biological Weathering by humans and animals is simply when animals or humans walk on rock and sediment over and over again, causing it to weather away. Another way that humans and animals weather is digging into sediment, using tool that they made or are on their body.

Chemical Weathering

Chemical Weathering is simply when rock and sediment is weathered away by chemicals.

Chemical Weathering by Acid Rain

When fossil fuels like coal are burned they release carbon dioxide which is dissolved into the clouds, making the rain more acidic than usual. Acid Rain causes weathering to certain rocks, such as chalk and limestone, when acid rain falls on them, it causes the rock to crumble/weather away. This picture, taken at 7 bridges, South Milwaukee, is an example of rocks that were weathered to this texture due to acid rain.

Chemical Weathering by Oxidization

Oxidization is when a rock (usually containing iron) reacts with oxygen, this causes it to rust and crumble or break the rock.

Erosion

Erosion is the act of broken of pieces of rock and sediment moving away from the site of weathering.

Erosion by Wind, how it occurs.

Erosion by wind occurs when wind carries rock and sediment pieces from place to place.
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This is a picture is an example of Erosion by Wind, wind created small sand dunes on the shores of Lake Michigan at Grant Park, South Milwaukee. The picture below is an example of larger sand dunes created by Wind Erosion located at Outer Banks, North Carolina.
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Sediment Sizes that Wind Can Carry & Why

Wind can carry small sediment such as dust, sand, and volcanic ash. Wind cannot carry sediment any larger than this because wind alone is not dense or powerful enough to hold the sediment up without it being dragged down by gravity.

Effects of Wind Erosion on Landforms and Other Structures

Some effects that Wind Erosion can have on landforms and other structures are the creation of sand dunes, stone arches, and the flattening of whole mountain ranges. An example of Erosion by Wind eroding a mountain range is in central Australia, a whole mountain range, that is now called Ayer's Rock. An example of Wind Erosion creating stone Arches is at Arches National Park, in eastern Utah, or Mackinac Island in northern Wisconsin, as seen in this picture.

Erosion by Water, How it Occurs

One example of Erosion by Water is by Rainwater, this is when rain comes down on broken of sediment, and washes it slowly away. Another example of Erosion by Water is waves from an ocean or lake crash onto the beach and pull the sediment into the water, and move it to another spot, or push it farther onto land. One last example of Erosion by Water is rivers, depending how strong their current is they can move almost any size of sediment.
The video above shows Water Erosion by the stream located in Grant Park, Milwaukee.

Sediment Sizes Water Can Carry & Why

Rivers- Rivers with a stronger current can carry or move considerably large rocks, while small streams may only be able to erode pebbles and anything smaller.

Rainwater- Not being very powerful, can only only erode small sediment such as sand or volcanic ash.

Ocean/Lakes- Ocean and Lake waves carry smaller sediment like sand and smaller rocks depending on how large the waves are, they could also erode larger.

Effects of Water Erosion on Landforms and Other Structures

One example of the effects Water Erosion has on landforms and other structures are when waves of an ocean or lake can either erode a beach away, or push more sand onto it. If the beach is eroded away and a man made structure was on the beach, it will likely not withstand the water and will need to be removed or pushed back. For example at Outer Banks, North Carolina, a light house had to be moves over 900 yds. inland due to the beach being eroded away.

Erosion by Gravity and How it Occurs

Gravity by Erosion is when rock or sediment is loosened on a slope, and gravity causes it to roll or slide down the hill. Depending if it is dry sediment or wet, it will create a talus, which is a pile of dry sediment (rock slide), or wet sediment, creates a mudslide.
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Sediment Sizes Gravity Can Carry

Depending on the slope, gravity can move any size of sediment.

Effects of Gravity Erosion on Landforms and Other Structures

An example of some effects that Gravity Erosion can create mud and rock slides and piles of rock at the end of slopes. For example at the end of slopes of the Colorado Plateau there are piles of rock from Erosion by Gravity pulling them down the hill.

Erosion by Glaciers, How it Occurs

Erosion by glaciers is when glaciers (large sheets of ice) either slowly move down hill or across land and pick up sediment that gets stuck in them or push sediment in front of them.
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This is a picture of Lake Michigan, which is one of the Great Lakes that were created by Glacier Erosion.

Sediment Sizes Glaciers Can Carry

Glaciers can pick up any sediment size in their path, from the size of sand and soil to boulders.

Effects on Land forms and Other Structures

Some effects glaciers can have on land forms are the creation of lakes, kettles, and ponds. For example, the 5 Great Lakes located in northern America were created by glaciers.

Sources

  • BBC
  • National Geographic
  • Geological Society
  • Discovery Education