An artesian well allows water to rise to the
surface that has traveled through porous rock from a higher
elevation. This pumpless well seems to defy gravity because the
pressure that builds up between layers of rock gets relieved when
the water finds a path to the open air. For nearly a thousand
years, people have drilled wells to drink such cold, filtered water
that doesn't need to be hauled up from the depths. An aquifer
provides the water source for an artesian well. An aquifer is the
layer of permeable rock, like limestone or sandstone, that absorbs
water from an inlet path at high elevation such as the top of a
mountain. The water source might be fed by snowmelt or
precipitation. Porous stone is sandwiched between a top and bottom
layer of an impermeable substance like clay soil or shale rock.
This keeps the water pressure high, so that when you get to a point
below the entryway of the flow, there is enough pressure to bring
the water up. Natural springs form in the same way when a gap in
the impermeable rock, maybe triggered by an earthquake, allows the
water to rise to the surface. Entire cities have relied on giant
underground aquifers to provide fresh, cold water when there are no
above-ground rivers. In 1126, monks used a rod with a sharp end,
called a bore, to penetrate a layer of impermeable rock. Their
percussive drilling, just hammering on the end of the bore, broke
through with sheer human force. The water that rose had percolated
through the pores of the rock, so that many contaminants have been
filtered out, and it proved safer to drink than standing or river
water.
Nowadays, if a town or residency needs water
closer to the top of a mountain, they might lie above the line
where there is enough pressure to push the water all the way to the
surface. In this case, the aquifer can be accessed by drilling a
relatively shallow well and then pumping the water up to ground
level. Our well-drilling has progressed from hammers and bores, to
machinery that twists a giant drill into the ground. Sometimes, if
the pressure is especially strong, because the well is lower in
elevation, the water might thrust up like a fountain, and form a
geyser. This particular artesian spring is less dramatic than a
geyser, but it still provides a steady source of fresh, clear
water.
In order to log this cache, please complete
the following tasks:
1. Take a picture of the water outflow
location with yourself or your GPSr in the picture, and
2. Measure the water flow in units per
minute. For example, record the time it takes to fill a litre,
gallon, quart or whatever size container you have, and convert that
result to give a "units per minute" waterflow.
