Download Erosion – Level 1

Erosion – Level 1 (LEXILE 710 or lower)
The power of erosion produces geological wonders. The Grand Canyon. The Sahara sand
dunes. The fjords of Norway. The beaches of Malibu, California.
Erosion involves the wearing away of rock and soil. The forces behind erosion are many. The
most powerful include flowing water, ice, and wind. Of course, gravity helps as well.
River Erosion
Rivers may be the most powerful erosion force of all. The Colorado River carved the Grand
Canyon. Today, it continues to move some 500,000 tons of sediment each day. Rivers
continually pull soil, rocks, and other material from their banks and bottom. As this debris
tumbles in the water, it adds to the river's scouring action. In this way, rivers carve out valleys
and canyons. Eventually, rivers slow and drop their sediment. This produces new land. New
Orleans, for example, sits on a delta produced by the Mississippi River.
Wave Erosion
Water erodes in other ways as well. Ocean waves can pound rock into sand. They can also carry
that sand away. Waves can even grind away entire islands. Rain is another watery force for
erosion. A hard rain can quickly strip soil from a dirt field. Given enough time, even gentle rain
can dissolve solid rock. Acid rain, which contains pollutants, speeds this erosion.
Glacial Erosion
Ice, a form of water, is another powerful force. When water freezes, it expands. So, water that
seeps into cracks and then freezes can bust apart solid rock. Glaciers are enormous piles of
moving ice. As they inch along, they scrape the landscape clean. They pick up huge rocks and
tiny grains of soil. This debris adds to a glacier's scouring action. As a result, glaciers leave huge
scratch marks, called striae, in their wake. Large glaciers carve bowl-shaped valleys. When a
glacier finally stops or melts, it drops its load of debris. Huge piles of boulders mark the
boundaries of ancient glaciers.
Wind Erosion
Wind is yet another force for erosion. Wind piles up sand to create dunes. Then it moves the
dunes from one place to another. Wind that picks up sand becomes a more powerful erosive
force. The airborne grains literally sandblast objects in their path. Sandy winds created many
natural sculptures in the southwestern United States. Arizona's Monument Valley is full of
sandblasted arches and buttes.
Human Erosion
Natural erosion has been sculpting our planet for billions of years. But human activities can
increase erosion in destructive ways. Loggers, farmers, and builders strip forest from millions of
acres each year. Stripped of its natural cover, the land easily loses its fertile soil. In wet climates,
rain quickly washes this soil away. In dry climates, wind can blow it away.
Human activity and wind erosion have produced great disasters. In the 1920s, American farmers
plowed under millions of acres of grassland. Then a drought dried up their crops. With no grass
or crops to anchor the soil, it blew away. The result was the great Dust Bowl of the 1930s.
Humans can learn from such mistakes. We now understand the power of erosion and how we
must work with nature to control its force.