9.4 NOTES
What are rivers and streams?
Objective: Describe the three stages in the life cycle of a river or stream
A river is a large, natural channel containing flowing water. Gravity forces the
river water downhill. The main sources of the water in the river are runoff from
rainwater, streams that flow into the river, groundwater from springs, and
melting snow.
Rivers go through three stages in their development. The three stages are
youthful, mature, or old. Age is determined by the speed of the water flow, and
how steep the slope is.
A youthful river has a steep
slope and fast-moving
water. The fast-moving
water erodes the riverbed
and forms a V-shaped
valley. Two features of a
youthful river are rapids
and waterfalls. The
Yellowstone and Niagara
Rivers are youthful rivers.
Mature rivers move
slower than youthful
rivers do. Mature
rivers do NOT have
rapids and waterfalls.
Erosion widens slopes
and makes the sides
smoother and wider.
The river winds back
and forth in loops
called meanders. The
Missouri River and the
Ohio River are mature
rivers.
Old rivers
move very
slowly. They
have nearly
flat slopes and
can easily
flood.
Flooding
causes erosion
and deposition
along the
meanders.
Over time, they change position. Sometimes meanders are cut off from the rest
of the river and form C-shaped lakes called oxbow lakes.
Rivers can become endangered due to pollution from new energy sources.
Building dams for power, draining acid from coal mines, and drilling for oil and
natural resources can all endanger rivers. The most endangered river in 2001 was
the Missouri River.