May 4th - May 11th
Erosion and Deposition
You should now have a solid understand of how solid rock and mineral is broken up Physically and Chemically to produce sediment and soil, loose material on the surface of Earth. Next, you will explore the ways that the loose material is moved around on Earth's surface. This results in dramatic landscapes such as the Grand Canyon and Letchworth State Park, as well as simpler features like beaches and deltas. There are several ways that material can be moved on Earth's surface, and this next lesson will touch on each of the 5 ways that material is moved. Seeing it in action is the best way to learn about erosion, so each of the following methods will have videos of the erosion in action.
5 Agents of Erosion on Earth
1. Running Water (by far the largest erosional factor on Earth's surface)
2. Wind (generally only in dry, no-vegetation areas like deserts. Also can be a factor when plowed farm fields dry out and are plowed to reveal dry, dusty soil)
3. Glaciers (occurs only in high altitude, high latitude locations such as Antarctica, Greenland, Alaska, Himalayas, Alps, Andes)
4. Wave Action (along shorelines worldwide)
5. Gravity (occurs in steep terrain areas where landslides, avalanches, and rock slides can occur.
The amount of erosion is influenced by the speed of the water flow and also the amount of water in the river. Big rivers like the Amazon, Nile, Mississippi and even the Niagara River can erode more than a little creek by your house. Faster rivers, such as rivers in mountainous areas or during floods can also erode more than slow flowing "lazy rivers". The following videos will help illustrate this point.
Fast flowing Rivers
This is a local river, Cattaragus Creek in Gowanda (near Springville) during a flash flood in 2009.
Notice in both of these that the color of the water is brown, showing that lots of sediment (sand, silt, clay, and even pebbles and cobbles in these videos) is being eroded and carried downstream.
Slow flowing River
Now think about how the amount of erosion in each of these videos is different.
Even in the driest places on Earth, when it does rain, erosion from running water takes place. This photo is from the Sahara Desert, and evidence of river erosion is shown from the "tree branch" look of the dry riverbeds. Interestingly, Mars also shows this type of erosion, which tells us even though we have not found water on the surface, at some point in Mars' history it had streams of flowing liquid eroding its surface.
Wind is the primary method of erosion in deserts because it rarely rains. There is no vegetation to hold soil or sand in place, and so on any windy day, the tiny clay and silt is blown up into the sky as a dust storm (eventually deposited in oceans), and the sand is left behind to blow around on the surface and form sand dunes! This is why deserts are covered in sand. There are also plenty of boulders and cobbles, which over time will be weathered into sand too.