Hali Jane Klein, age 9, of Tulsa, Oklahoma, for her question:

How do stalagmites form in caves?

A cave may have spiky stalagmites poking up from its floor and matching stalactites hanging from its ceiling, like stony icicles. Sometimes a pair meets and forms a stony column between floor and ceiling. These artistic formations are created by drip dripping water    with the help of air and limestone rock. Caves tend to form in thick layers of limestone. This pale, spongy rock contains soft calcite, a mineral that likes to dissolve and lose itself in moving water.

Raindrops seep through the ground and carry dissolved calcite away in fragments too fine to be seen. But when the water evaporates, it must leave this calcite behind. Sometimes it drips through a crack in the ceiling of a cave    and splashes down on the floor. The air in the roomy cave makes the water evaporate but its dissolved calcite must stay behind. As the splashes dry up, the fine fragments build a pile of solid calcite stone. If the ceiling leaks for ages, the calcite builds a high, spiky stalagmite on the floor of the cave.