Weathering and Erosion

Weathering and Erosion

Weathering is the process where rock is dissolved, worn away or broken down into smaller and smaller pieces. There are mechanical, chemical, and organic weathering processes.

Weathering process are primarily responsible for soil development. These process take thousands of years. Climate, vegetation, and rock type determine what type of soil forms. Soil contains organic matter from decaying plants and animals (humus) as well as sand, silt, and clay. It covers the landscape and provides a medium for plants to grow.

Weathering is caused by water, as it freezes and melt, as well as by chemical reactions that loosen the bonds holding rocks together.

1. Organic weathering happens when plants break up rocks with their growing roots or plant acids help dissolve rock.

       

2. Mechanical weathering physically breaks up rock. One example is called frost action or frost destroying. Water gets into craks and joints in bedrock. When the water freezes it expands and the cracks are opnened a little wider. Over time pieces of rock can split off a rock face and big boulders are broken into smaller rocks and gravel. This process can also break up bricks on buildings.

          

3. Chemical weathering decomposes or decays rocks and minerals. An example of chemical wethering is water dissolving limestone.

            

Once the rock has been weakened and broken up by weathering it is ready for erosion. Erosion happens when rocks and sediments are picked up and moved to another place by ice, water, wind, or gravity.

Erosion in Wet Climate

As soon as rock is exposed on the earth's surface, it is attacked by wind, water, or ice - a process known as "weathering". This prepares for erosion, when rock is broken down and removed. Weathering can be either physical (wearing away the rock itself) or chemical (attacking the minerals in the rock). Climate and rock type determine the kind of weathering that occurs. In wet climates, chemical weathering, mainly by rainwater, is dominant.

Mountain Stream

Cascading over steep gradients, a swift-flowing stream wears away softer rocks. Harder rocks remain and create rocky outcrops. These become steep rapids or waterfalls. 

                                  

  

Frost Shattering

This type of weathering occurs when water in cracks in the rock freezes and expands. Joints in the rock widen and the rock shatter

                                                

Clints and Grikes

Acid in rainwater seeps into limestone joints and dissolves the calcite in the rock. Ridges known as "clints" and grooves known as "grikes" form in the rock. 

Erosion in Arid Climate

In hot, dry, desert areas extremes of temperature cause rocks to fragment. By day, rock expands in the heat, and by night it contracts in the cold. It is mainly physical weathering that occurs in arid (dry) climate, chiefly caused by wind helps to erode rocks and build shifting sand dunes.

              

Onion-skin layering

In the heat of the desert, a rock's surface may expand, though the interior stay cool. At night, the surface of the rock cools and contracts. This daily process causes flaking on the surface of the rock, and the outer layers begin to peel and fall away.

       

Zeugens

Sand carried by the wind sculpts these strange forms called "zeugens". Sand wears away soft rock leaving behind areas of harder rock, worn into jagged shapes.

     

Mushroom rocks (Pedestal rocks)

The desert wind contains a great deal of sand, which scours away the surface of rocks. Mushroom-shaped rocks are a result of this action. Rocks are worn away most at their base by the sand, leaving behind a landscape of rock pedestals.

      

Sand dunes