Re: Why does rivers (springs) always come from a mountain top ?

Dear Hendrik:
The short answer to your question is that rivers and springs DON'T always
come from mountain tops. However, they often do, and the reason is part of
what is called the water cycle. 

The water cycle is the name for the process by which water moves from one
place to another on and in the Earth. This goes on all the time. Water runs
down rivers to the sea. In the sea, some water evaporates and eventually
becomes clouds. Clouds produce rain, snow, and so on, and much of this
precipitation falls on the land. Precipitation that reaches land either
soaks into the ground, runs off to rivers and lakes, or re-evaporates. The
key here is gravity, which makes water run down hill. 

Imagine that a drop of water hits the ground in a valley and soaks into the
ground. This water may be used by a plant, or evaporate from the soil, but
if it does not it will move down and join the ground water. There is water
everywhere underground, and this is the ground water. Ground water moves,
but slowly, and like all water, it moves downhill. So our little rain drop,
now part of the ground water, moves downhill until it either comes out of
the ocean floor, or comes out on the bed of a lake or river. If it does
that, it joins the river and flows downhill to the sea. 

Now, imagine a different drop of water that lands high up in the mountains.
It might evaporate or be used by plants, but if it does not it has two
choices. It can run off into a little mountain valley and join a stream, or
it can soak into the soil and move downhill with the ground water to the
nearest mountain stream. This is how mountain streams form--from
precipitation in the mountains. 

So streams form everywhere, in valleys and mountains, from individual bits
of water joining them here and there, but the water always moves downhill.
It looks like the stream starts in the mountain and goes to the sea, but
really the stream isn't moving. It's the WATER that's moving, and it has to
go down to the sea because of gravity. (Streams do move, but very very
slowly, because of erosion.)

Springs form in places where ground water comes out of the ground, for
reasons that have to do with what the rocks and sediments are like
underground. 

If this message makes you want to know more, there are many web sites with
information about water. I will give you a url to a list of earth-science
education web sites; part of the list is about water web sites.
 http://www.gsa.state.al.us/gsa/Education/edpglnk3.html

Best regards,
David Kopaska-Merkel
Geological Survey of Alabama
P.O. Box 869999
Tuscaloosa AL 35486-6999
(205) 349-2852
fax (205) 349-2861
www.gsa.state.al.us