Weathering, Erosion, Deposition, and Landscapes
Weathering – the breakdown of rocks into smaller pieces, called sediments.
Erosion – the process where the sediments are transported by wind, gravity, glaciers, man, and running water.
Deposition – the process whereby these sediments are released by their transporting agents (dropped).
Weathering breaks down the rocks, erosion moves the particles, and deposition drops the sediments in another location.
Mrs. Degl
There are two primary types of weathering:
Chemical and Mechanical(physical)
1. Mechanical Weathering – the breakdown of rocks and minerals into smaller pieces without a change in chemical composition.
Root/Plant Wedging/Action
Ice/Frost Wedging/Action
Exfoliation and Abrasion are also types of physical weathering.
Mechanical Weathering
Rock breaks apart in layers that are parallel to the earth's surface; as rock is uncovered, it expands (due to the lower confining pressure)
Weathering
Mechanical Weathering
Shattered rocks are common in cold and alpine environments where repeated freeze-thaw cycles gradually pry rocks apart.
Mount Rushmore
There is a pile of weathered material at the bottom. It is slowly being eroded down hill by gravity.
It will not be there forever!!
Chemical weathering
2. Chemical Weathering – the breakdown of rocks and minerals into smaller pieces by chemical action. The rocks breaks down at the same time as it changes chemical composition. The end result is different from the original rock. There are 3 types of chemical weathering:
1. Oxidation – oxygen combines with the elements in the rock and it reacts. This the scientific name for rust.
2. Water – water can dissolve away many earth materials, including certain rocks.
3. Acid rain/acid in ground water – carbon dioxide dissolves in water to form carbonic acid. This makes acid rain which chemically weathers (dissolves) rocks. Other acids also combine with water to make acid rain.
H2O + CO2 + CaCO3 --> Ca+2 + 2HCO3-
water + carbon dioxide + calcite
dissolve into calcium ion
and bicarbonate ion
Biological activity in soils
generates substantial CO2
Bicarbonate is the dominant
ion in surface runoff.
This photo of Lime Sink was taken on 20 July 1932, over a week after the drawdown, which occurred over the night of 9-10 July.
‘Karst’ landforms develop in areas underlain with limestone
Biological Weathering
Can be both chemical and mechanical in nature.
that dissolve rocks.
What type of weathering occurs in an area that has an average of 165 cm of rain each year and an average temperature of 18°C? ________________________
What type of weathering occurs in an area that has about 140 cm of precipitation each year and an average temperature of 5°C? _________________________
Erosion (transport)
There are 5 main agents of erosion:
Weathering has to happen before erosion. The rocks have to be broken into smaller sediments before they can be eroded away.
Wind Erosion
Glacier
Melbourne dust storm, 1983
Extreme Wind Erosion
The rocks to the right were transported by running water. How can you tell? _______________
Glacial Striations
(scratches)
Which rock layer appears to be the least resistant (weakest)? _______
Resistant rocks usually form steep cliffs and waterfalls, by sticking out further than the lower layers.
Which rock layer appears to be the most resistant (strongest)? _______
Stream erosion is the greatest at waterfalls. Erosion at waterfalls is called undermining.
Deposition – the process where sediments are released/dropped by their agent of erosion, such as water or wind.
Most deposition happens in standing/still bodies of water (oceans/lakes).
Deposition is caused by the slowing down (loss of kinetic energy) of the agent of erosion.
Below is the Mississippi delta. You can see the sediment flowing into the ocean.
What else is in that sediment?
Where can you see the deposition?