Phil
My only knowledge is based on ancient A-level
geography, so it is definitely neither
up-to-date nor dependable, especially
considering the state of my little grey cells.
But your question interested me, so please
forgive me a few thoughts...
I am not familiar with the lake you mention, but
why do you believe the water cannot come from
the surrounding higher ground, however little
you consider that to be? Extinct calderas at the
tops of mountains often contain lakes. Often
very deep, yet apparently with little run off
from the surrounding higher ground. And do not
forget that a great deal of the water enclosed
in Britain's lakes was probably left behind
following the ice age and a minimal amount of
water would be needed to "top up".
Given our climate in the British Isles
(especially 1999-2000) a postage stamp would
collect a great deal! The amazing thing is that
it does not overflow! Indeed, if there is no
run-off by rivers or waterfalls, my primary
question would be the opposite to yours: "Where
does all the water go?" Evaporation is certainly
not a major factor here, eh? :-)
Apart from the site within the landscape, the
local geology would be the most important thing
to investigate when considering a particular
example. The water table is going to be
influenced by that and it is going to be the
most important factor. Yes, water rises with the
lay of the ground along with the water table,
but I would think it is general and not very
localised, as in a spring.
For example, in the case of springs which have
dried up, the felling of trees (which help to
keep the water table near the surface) have
often been a major influence, rather than a
change in direction of water "flowing"
underground.
Water stored in underground aquifers should not
be seen as a body of water like a lake. This
complex water storage system is similar to a
sponge, not a water container with holes in it.
Squeeze or extract water from one point and the
sponge dries out at that point, but remains wet
elsewhere. Dig a well to extract water and the
surrounding rock will dry out, creating a blip
in the underground water level. The sponge will
gradually even out the moisture through osmosis,
but only very slowly, unless more water is
added. I believe the same goes for rocks. Hence
all the rain of the past couple of years has not
replaced all the water removed by the water
companies.
When a sponge is saturated, it also drips... I
have always thought of springs as being
similar... The drips from the huge underground
reservoir which is full and overflowing at the
point of least resistance or along a
particularly impervious layer of rock thus
produce springs. Including or even producing the
fissures someone else mentioned. This is usually
a hillside spring.
Of course underground "water pressure" must also
be an added factor where thousands of gallons of
water flow but there is no apparent stream or
water course. Heat will be another factor... We
probably underestimate that influence, except
when contemplating hot springs.
There is also the spring which bubbles up from
the ground... I think this is usually when the
surrounding geology creates a storage sponge
which collects so much water, that the immense
pressure results in the water being pushed
upwards. Again at a point of least resistance.
I wish more hydro-whatsits were part of this
list! My schoolgirl memories are hardly going to
add to the sum and total of mankind's knowledge!
Janet Kaiser
Criccieth
----- Original Message -----
From: Philip David
> What I'm curious about is
> water rising underground. One model that I
have in mind is a very deep (and
> quite large) lake only slightly below the two
summits of Slieve Gullion, Co.
> Armagh, which is very steep on all sides below
the lake. It doesn't seem
> plausible that all that water comes from the
two summits. Does water rise
> under the ground, and if so, how? Could
"syphonic action" account for this?
> Phil
>
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