Dignayan Biyernes – Formation of Speleothems

It’s Friday again! In today’s #DignayanBiyernes, let us talk about how the natural sculptures inside our caves are formed – the stalactites and stalagmites, or collectively, speleothems. 

The word speleothem comes from the Greek words “spelaion” which means cave and “thema” meaning deposit. It refers to cave features that are formed through the deposition of minerals dominantly calcite. We know them better as stalactites which hang like icicles from the ceiling and stalagmites which rise from the ground or the cave floor. 

These are created because of the rainwater that seeps through cracks in the rocks over a long period. Do you know that it takes about hundreds to thousands of years for a speleothem about 10 centimeters long to be formed? 

The weak acid that is made by the interaction of rainwater to the atmosphere and other organic materials dissolves the mineral calcite in which a cave is formed. When this water that contains dissolved minerals is exposed to the air, calcite is redeposited on the cave walls, ceiling, and floor. When the redeposited minerals continue to build up, stalactite is formed. And when the water that still contains dissolved minerals drops to the floor, stalagmites will be created. 

Speleothems are extremely fragile as they are covered by a very thin layer of water with dissolved minerals which also makes them grow. So the next time you visit a cave, try not to touch an actively growing stalactite or stalagmite as you may disrupt its formation that started hundreds to thousands of years ago. 

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Text and image by the NMP Geology and Paleontology Division

© National Museum of the Philippines (2022)