(1) Q: My uncle's house was swallowed up by a
sinkhole! What happened?
A: Luckily this is rare, but items like this have shown up on the
evening's news. Sometimes humans are responsible for places where the
land subsides and/or sinkholes develop. If large amounts of ground
water are pumped from an area that is composed of a thick layer of
fine-grained material then the land can become more compacted once the
water is removed. In other words, the water keeps the soil from
settling, and once the water is gone, the soil settles -- too bad if
there is a house on top.
Some parts of the country are
susceptible to sinkholes -- places where the land is
underlain by limestone that can be dissolved by ground water.
Also, a house could be sitting on a salt bed that dissolves, leaving a
cavern in the ground. Some homeowners have become cave-dwellers overnight!
(2) Q: My mom drinks "
artesian well water." What is it?
A: It means she is drinking water from a well that taps an aquifer that is "confined." This aquifer is water-bearing rock below ground that is surrounded by other rock or material that does not allow water to pass through. So, the water in this aquifer is squeezed by the other rocks, creating pressure in the water-bearing aquifer. When an artesian aquifer is tapped by a well the pressure pushes the water up the well, sometimes all the way to the surface, creating a flowing well. Imagine it as a very wet sponge contained in a closed plastic bag. Put a straw through the bag into the sponge, hold the bag tightly around the straw, and SQUEEZE - that would be artesian water squirting you in the face.
(3) Q: I've seen ice flowing out of hills in the winter. Why?
A: Probably you've seen this when driving on a road that has been cut
through a hill. You are really seeing an exposed portion of
water-bearing subsoil and bedrock. The water table is the part of the subsurface ground
where the material below it is saturated with water - this is the
material that wells tap into to get water. Water will flow along the
water table at a downward angle, similar to how it flows on the earth's surface.
It follows soil and rock that are permeable (allows water to move through it)
and eventually will find its way to stream beds, lakes, and the ocean. But if a
road is cut deep enough and goes into the water table then the water
can emerge from the rock.
Next time you are at the beach try
digging a hole at a place that is just out of reach of where the waves
are washing up. You'll start off in solid sand but soon the bottom of
the hole will fill with water, and no matter how deep you try to dig
it will stay full of water. In a way, the point at where the water
starts filling the hole is the water table boundary.
U.S. Department of the Interior | U.S. Geological Survey
URL: http://ga.water.usgs.gov/edu/qaother.html
Page Contact Information: Howard Perlman
Page Last Modified: Friday, 07-Nov-2008 15:45:18 EST
