Cave and Sinkhole Explorer: Water That Eats Rock
Link chemistry to landscape: rainwater with dissolved carbon dioxide is a weak acid that dissolves limestone along cracks, forming caves over millennia until a thin roof collapses.
Before you try
What if it rained on granite for a million years? Would you get a cave?
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What happened?
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One round cave growing at a rate set by rain and acidity with a simple roof-span rule; real karst depends on the cracks in the rock.
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Try these ideas
- Run 50,000 years in limestone, then the same in granite.
- Double the rainfall and see how much sooner the roof collapses.
- Set the acidity to zero. Does the cave still grow?
Why it works
Rain is never pure water. It takes in carbon dioxide from the air and much more from the soil, becoming weak carbonic acid. Limestone is calcium carbonate, which that acid slowly dissolves, so water seeping down cracks widens them into passages and, over tens of thousands of years, caverns. Dripping water later leaves the calcium behind as stalactites and stalagmites. Granite and sandstone hardly dissolve, so they rarely form caves this way.
When a cave roof becomes too thin for its width it can no longer hold itself up and falls in: a sinkhole. Landscapes riddled with caves and sinkholes are called karst; the caves of Meghalaya and the Borra caves in Andhra Pradesh are examples. In this explorer you set the rainfall, the acidity and the rock, run the millennia, and see the cave grow and the roof thin.
Check your understanding
Question 1 of 4
Rainwater dissolves limestone because it contains
Which rock forms caves most easily?
A sinkhole opens when
Stalactites form from
Explain it in your own words
What changed? Why did it happen? Where might you notice this in everyday life?
What will you discover next?
Try Groundwater Explorer: Will the Well Run Dry? next.
For parents & teachers
- Drop a piece of chalk in vinegar and watch it fizz.
- Ask: why is well water in limestone areas often “hard”?
- Look up the Meghalaya cave systems and how long they are.