BY CHIARA CIVIERO
Why are the rocks at the bottom of a river often round? Why usually do lakes get muddy after a rains storm? How do valleys form?
The answer to all these questions is erosion, the process that moves rocks and soil that make up the Earth’s surface from one place to another. Erosion constantly changes the shape of the landscape and can be caused by natural elements such as water, air and even ice that tend to flow from an upper position to another down.
Water is likely the most powerful force that causes erosion. If water is muddy, it is a sign that erosion is taking place. The brown colour indicates that bits of rock and soil are suspended in the water and being transported. The ways that it acts are:
– Rivers: they break up particles at the bottom and carry them downstream (e.g. Grand Canyon).
– Rainfall: the rain hits the surface of the Earth (splash erosion) or accumulates and flow as small streams.
– Floods: they act very quickly as powerful rivers and the erosion rates are greatly accelerated.
– Ocean waves: cause rock and coastline to break off changing the coastline over time. Erosion happens faster when shingle is thrown against the cliffs by the waves.
In dry regions as deserts (e.g., Sahara, Atacama) wind is the most frequent agent of erosion because there are few plants to hold the soil in place and there is no rain to bind the soil particles together. It erodes in two ways:
– Deflation: wind forces pick up and carry loose particles and dust away.
– Abrasion: flying particles strike the land and break off more particles.
Sometimes in mountain environments as Himalayas, Andes, but also near the North and South Poles, giant masses of ice that slowly move called glaciers, can carve out valleys and shape mountains. However, there are other minor forces that can cause erosion and these include: living organisms (i.e., insects, small animals, worms) can speed the erosion process by breaking up the soil and thus the water and/or wind can act on the surface more quickly; an increase of temperature may heat up a rock. This can lead the rock to expand, crack and break off in pieces over time; the force of gravity can pull rocks and other particles down the side of a mountain or cliff in form of landslides causing erosion.
COULD HUMANS CAUSE EROSION?
Erosion is a natural process, but human activity can make it happen more quickly. Humans have increased the rate of erosion through farming, ranching, cutting down forests, and the building of roads and cities. However, it is possible to control this phenomenon planting trees around farmland to protect it from the wind, moving herds around so that grasslands will grow back, and planting new trees to replace the ones cut down.