Fig. 10.2. True springs and high
altitude aprings.
These depend on the existence of the 39°F
(+4°C) denser water level which is called the
centre stratum. This gets squeezed between the
weight of water in the rocks above, and the water
strata below. At 39°F (+4°C) it will compress
no more, and has to move vertically or laterally,
eventually emerging as a spring. This is why they
are normally very cold and may appear on
mountain tops.
springs. The difference here is that, emerging in the high moun-
tains, these waters are then augmented by rich glacial waters, and
by minerals from the action of the aggressive mountain streams
eroding the surface rocks.
The rainwater penetrates the ground surface under the influ-
ence of a positive temperature gradient, in a way similar to that
of a seepage spring. But it is drawn down much more deeply,
helped by the increasing pressure, so that it condenses and cools
to around +4°C (39°F). Being immature water, it will absorb what
it can, so it removes salts from the upper layers of the ground,
depositing them later as the water condenses and cools with
depth. This makes the upper layers more fertile, and the salts are
now available to deep-rooted trees that have the ability to metab-
olize them, converting them to nutrients for more shallow-rooted
plants.
The downwards-percolating rainwater increases the pressure
on the groundwater body, pressing the lowest layer into rocks thatHIDDEN NATURE