8.3 NOTES
How does running water cause erosion?
Objective: describe how running water causes erosion
Running water changes more of Earth’s surface than any other agent of erosion.
Rivers, streams, and run-off are forms of running water. Runoff is water from rain
or snow that flows over Earth’s surface. It empties into streams and standing
bodies of water such as lakes and ponds.
As runoff flows over the earth’s surface, it carries away soil particles. The faster it
moves the more particles it carries away. Runoff is affected by the amount of
rainfall, plant growth, and shape of the land. Heavy rains cause more runoff.
Plants help to stop erosion from runoff, because of their roots. Areas with more
plant growth have less runoff. Furthermore, areas with gentle slopes will also
have less runoff than areas with steep slopes.
River systems are made up of a river’s main stream and all of the smaller streams
that flow into it. The smaller streams, or branches, are called tributaries. For
example, the Mississippi River system is made up of many tributaries. The
Missouri and Ohio River are two tributaries that flow into the Mississippi River.
A river system is usually formed
in mountains or hills. The place
where a river starts is called its
source. When water cannot soak
into the ground, it begins to flow
down a slope. Over time, it cuts
gullies into the slope of the
eroded soil. A small channel
forms and eventually joins other streams. These streams will join a larger stream
forming tributaries of the main stream, or river. The end of the river, or mouth, is
where the river empties into a larger body of water, such as a lake or ocean.