This week in Frannie’s exploration of the Awesome Aquifer
Kit is about sinkholes and how they are formed.
A sinkhole is a hole in the ground caused by the erosion of
the soil or bedrock underneath. They
occur when acidic water seeps down and percolates through soluble, or easily
dissolved, layers of soil like sandstone, chalk, or limestone. Over hundreds or thousands of years, more of
the rock dissolves while loose soil and sand shifts down to fill the
cracks. For a long time, the land is
able to hold its own weight and even the weight of buildings constructed on top
of it. However, as even more of the rock
dissolves and becomes empty space, the land becomes too heavy and will collapse
suddenly.
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| For this activity, you will need a pitcher of warm water, sand, a piece of paper, a cup with a small-medium size hole, a coffee filter, scissors, and sugar or powdered creamer. |
Frannie starts by cutting a small hole, the same width as
the tube, in the bottom of the cup and placing the coffee filter on top of it,
keeping it in place with just a little bit of sand.
Next, she puts her tube over the coffee filter and fills the
tube a part of the way with sugar. The
sugar represents the soluble rock that will dissolve when the ground gets
wet. While the tube is still in the cup,
she pours in the sand so that it comes to about the same height as the
sugar. The sand represents the rest of
the ground and will hold the soluble layer in place.
Slowly remove the tube without disturbing the sand or sugar
too much and then pour more sand on top, just enough so that none of the sugar
is showing. Carefully pick up the cup
and place the bottom into the water and in just a few moments, the water will
infiltrate the sand and sugar, dissolving the sugar and creating our sinkhole.
Check out this cool graphic to see what's happening inside the cup!
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| Graphic by PBS |
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