What cave formation grows upward from a cave floor?

A cave formation that grows upward from a cave floor is a stalagmite.

Stalagmites form when mineral-rich water drips onto the floor and leaves behind deposits, most commonly calcium carbonate. In limestone caves, rainwater absorbs carbon dioxide from soil, becomes mildly acidic, and dissolves small amounts of rock before entering the cave. When the water loses carbon dioxide, calcium carbonate can precipitate and slowly build a mound or pillar.

The classic mix-up is stalactite, which hangs down from the ceiling. A useful memory aid is that stalactites hold tight to the ceiling, while stalagmites might reach the ceiling. If a ceiling stalactite and floor stalagmite eventually join, they form a column, also called a stalagnate.

Growth is usually extremely slow, often taking centuries or much longer, though lava, ice, and concrete-derived examples can form under very different conditions and rates.