Describe types and processes of weathering and erosion.

This section introduces you to weathering and erosion, both important parts of the rock cycle. You will learn how different rocks are weathered and eroded and the implications of this weathering.

Causes of Soil Erosion

Soil erosion, as with rock erosion in general– caused by the action of  water, wind, ice, or gravity.
Running water is the leading cause of soil erosion, but freeze/thaw and wind are significant factors in certain environments.
Vegetation is another important factor– instead of a cause for erosion, its presence tends to reduce the removal of soil by stabilizing the ground.

Farming and Grazing

Agriculture is probably the most significant activity that accelerates soil erosion because of the amount of land that is farmed and how much farming practices disturb the ground (Figure 1). Farmers remove native vegetation and then plow the land to plant new seeds.

Figure 1. (a) The bare areas of farmland are especially vulnerable to erosion. (b) Slash-and-burn agriculture leaves land open for soil erosion and is one of the leading causes of soil erosion in the world.

Grazing animals (Figure 2) wander over large areas of pasture or natural grasslands eating grasses and shrubs. Grazers expose soil by removing the plant cover for an area. They also churn up the ground with their hooves.

Logging and Mining

Figure 3. Logging exposes large areas of land to erosion.

Logging removes trees that protect the ground from soil erosion. The tree roots hold the soil together and the tree canopy protects the soil from hard falling rain. Logging results in the loss of leaf litter, or dead leaves, bark, and branches on the forest floor. Leaf litter plays an important role in protecting forest soils from erosion (Figure 3).

Much of the world’s original forests have been logged. Many of the tropical forests that remain are currently the site of logging because North America and Europe have already harvested many of their trees (Figure 4). Soils eroded from logged forests clog rivers and lakes, fill estuaries, and bury coral reefs.

Figure 4. Deforested swatches in Brazil show up as gray amid the bright red tropical rainforest.

Construction

Constructing buildings and roads churns up the ground and exposes soil to erosion. In some locations, native landscapes, such as forest and grassland, are cleared, exposing the surface to erosion (in some locations the land that will be built on is farmland).(Figure 6).

Figure 6. Urban areas and parking lots result in less water entering the ground. Water runs off the parking lot onto nearby lands and speeds up erosion in those areas.

Recreational Activities

Recreational activities may accelerate soil erosion. Off-road vehicles disturb the landscape and the area eventually develops bare spots where no plants can grow. In some delicate habitats, even hikers’ boots can disturb the ground, so it’s important to stay on the trail (Figure 7).

Figure 7. (a) ATVs churn up the soil, accelerating erosion. (b) Hiking trails may become eroded.

Activities like motor bikes, or mountain bikes, or hiking are all great things to do.  We just need to be cognizant of WHERE we do them and best practices for land and soil conservation!

Summary

• Although soil erosion is a natural process, human activities have greatly accelerated it.
• The agents of soil erosion are the same as of other types of erosion: water, ice, wind, and gravity.
• Soil erosion is more likely where the ground has been disturbed by agriculture, grazing animals, logging, mining, construction, and recreational activities.

The Dust Bowl

What would cause such a tremendous dust storm?

Farmers were forced off their lands during the Dust Bowl in the 1930s when the rains stopped and the topsoil blew off these former grasslands. A wind storm blew huge amounts of soil into the air in Texas on April 14, 1935. This scene was repeated throughout the central United States.

Preventing Soil Erosion

Soil is a natural resource that is vitally important for sustaining natural habitats and for growing food. Although soil is a renewable resource, it is renewed slowly, taking hundreds or thousands of years for a good fertile soil to develop.

Figure 11. Steep slopes can be terraced to make level planting areas and decrease surface water runoff and erosion.

Most of the best land for farming is already being cultivated. With human populations continuing to grow, it is extremely important to protect our soil resources. Agricultural practices such as rotating crops, alternating the types of crops planted in each row, and planting nutrient-rich cover crops all help to keep soil more fertile as it is used season after season. Planting trees as windbreaks, plowing along contours of the field, or building terraces into steeper slopes will all help to hold soil in place (Figure 11). No-till or low-tillage farming helps to keep soil in place by disturbing the ground as little as possible when planting.

The rate of topsoil loss in the United States and other developed countries has decreased recently as better farming practices have been adopted. Unfortunately, in developing nations, soil is often not protected.