Geology Reference
In-Depth Information
Lakes:
Water that enters a lake — either from the sky, from a stream, or as surface
runoff — stays in the lake for a long time before evaporating back into the atmo-
sphere, being carried away by another stream, or becoming groundwater.
Streams:
Most of the water on the earth's surface is carried by streams. This water
may begin as surface runoff, snow, rain, melting ice, or even groundwater. As it
makes its way downhill, it accumulates into running bodies of water such as rivers
or creeks. Geologically speaking, a
stream
is any moving body of water that carries
sediment,
or rock particles. I explain streams in detail in the next section.
It may take many years, but the water eventually makes its way back to the ocean,
where once again it can be evaporated into the atmosphere by the sun's heat.
Streams: Moving Sediments toward the
Ocean
People use terms such as
rivers, creeks,
and
brooks
to describe water that
runs across the earth's surface, but geologically speaking these are all streams. A
stream
is any flowing water in a channel on the surface of the earth.
A stream removes or
erodes
rocks and soil, carrying sediment toward lower elevations.
Eventually, a stream makes its way to the nearest ocean (or sea). On the way to the
ocean, a stream drops off, or
deposits,
sediment particles. The
erosion
and
deposition
of
sediments create geological features on earth's surface. In this section, I describe the
components of a stream, how streams carry sediments, and the marks they leave on the
landscape when they erode and deposit sediments on their journey to the sea.
Draining the basin
A basin or
watershed
is an area of land that supplies water to a stream from rainfall and
groundwater. The edges of a watershed are determined by the highest points on the
landscape so that a watershed contains all water flowing downhill to a common stream
that eventually empties into the ocean. Figure 12-2 illustrates how a watershed includes
all the land draining toward the same direction on one side of a
drainage divide:
the
highest point of elevation separating two watersheds.
