Buzz
Well-intentioned geologists unintentionally caused confusion when they named stalactites and stalagmites. Both of these similarly named formations, typically found in limestone caves, can grow up to 27 feet long. But what sets them apart, and how do these unusual formations develop in the first place?
Let’s clarify the terminology. Here’s a simple and widely-recognized saying to help you distinguish between the two: “Stalactites hold tight to the ceiling, while stalagmites might reach the ceiling.” In other words, stalactites form from the cave ceiling, hanging down like rocky icicles, while stalagmites grow from the floor upwards, occasionally touching the ceiling above them.
Another way to remember: “Stalactite” has a “t” for “top,” and “stalagmite” has a “g” for “ground.”
The Oxford English Dictionary explains that both terms trace their origins to the Greek word stalaktos, meaning “to drip.” This reflects the way trickling rainwater contributes to the formation of these cone-shaped structures. As rainwater flows through limestone, it absorbs carbon dioxide from the rock, creating a weak carbonic acid that seeps into the stone. This acid leaves behind calcite deposits on the cave ceiling. With every additional drip, more calcite accumulates, eventually forming a stalactite.
What about stalagmites? These formations are typically found beneath stalactites, as the constant flow of water has to land somewhere. When a drop finally falls to the cave floor, it deposits more calcite in a small mound. As the water continues dripping from the stalactite, the mound rises, gradually creating a stalagmite. This process is extremely slow, with growth rates in limestone caves generally under 10 centimeters per millennium.
It's also important to note that both stalactites and stalagmites are part of a larger geological family called “speleothems.” This broad group of mineral formations includes not only these classic shapes but also intriguing features like globular “cave popcorn” and striking “flowstones.” In some cases, lava even plays a role in stalactite formation, leading to some truly unusual appearances.
