Water dripping onto the cave floor leaves behind tiny rocky particles that were dissolved in it. As the dripping continues, these particles can build up form a pillar of rock, or stalagmite.

Stalagmites have thicker proportions and grow up on the bottom of a cavern from the same drip-water source, the mineral from which is deposited after the water droplet falls across the open space in the rock. Not every stalactite has a complementary stalagmite, and many of the latter may have no stalactite above them. Where the paired relation exists, however, continual elongation of one or both may eventually result in a junction and the formation of a column.

 

Picture Credit : Google