Geology Reference
In-Depth Information
Springs are locations where groundwater flows out onto the surface. You often find
springs on slopes where the change in elevation of the ground surface intersects the el-
evation of the water table, allowing groundwater to flow to the surface out of the hill-
side, as illustrated in Figure 12-8.
Figure 12-8:
Springs often oc-
cur on hillsides,
where groundwa-
ter flows out onto
the surface.
Confining an aquifer
An aquife r is any rock or sediment where fresh water is stored. The saturated zone be-
low the water table that you tap into with your well is one example of an aquifer. It is an
unconfined aquifer, which means that the rocks and sediment above the stored water are
permeable (water can flow through them).
Conined aquifers, or artesian aquifers, are layers of rock or sediment filled with water
that have an impermeable layer above them. This means that water does not easily infilt-
rate down to a confined aquifer directly from the earth's surface; it can't pass through
impermeable layers. Instead, water enters a confined aquifer by flowing horizontally
through other permeable rocks or sediment.
An interesting feature of artesian aquifers is that due to the pressure of the water being
trapped between two impermeable layers, the water may be forced upward against the
pull of gravity. The next time you buy bottled water from an “artesian spring,” you'll un-
derstand that the water flowed up to the surface from a confined aquifer beneath the
earth's surface!
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