Stalagmites grow upwards from the floor of caves as minerals are deposited by dripping water.
How the Growth Process Works
The formation of stalagmites is a fascinating geological process driven by the interaction of water, rock, and air within a cave environment. Based on the provided reference, stalagmites are deposits that form when water dissolves overlying limestone then re-deposits calcium carbonate along the ceilings or floors of underlying caves. For stalagmites specifically, this deposition occurs on the cave floor.
Here's a breakdown of the process:
- Water and Limestone: Rainwater absorbs carbon dioxide from the atmosphere and soil, becoming slightly acidic. This acidic water seeps down through the ground.
- Dissolving Rock: As the water passes through layers of rock, particularly limestone (which is primarily calcium carbonate), it dissolves small amounts of the mineral. This creates a solution rich in dissolved calcium carbonate.
- Reaching the Cave: This mineral-rich water reaches the cave ceiling and often hangs as a drop before falling.
- Deposition on the Floor: When a drop of water falls from the ceiling onto the cave floor, it slightly degasses (loses some carbon dioxide). This causes the water to be less acidic and less able to hold the dissolved calcium carbonate in solution. As a result, a tiny amount of calcium carbonate precipitates out of the water and is left behind on the floor.
- Upward Growth: Each subsequent drop deposits another small layer of calcium carbonate at the same spot on the floor. Over thousands and millions of years, these layers accumulate, building a conical or mound-shaped formation that grows upwards from the cave floor – this is a stalagmite.
While the reference mentions deposition on both ceilings (forming stalactites) and floors (forming stalagmites), the upward growth from the floor is the defining characteristic of a stalagmite.
