Think They’re Just Rocks? Stalagmites and Stalactites Tell a 10,000-Year Story

The next time you visit another limestone cave, take a moment to look at the interesting, unusual shapes that take form as rocks hang from the ceiling or rise from the floor. Those are stalactites (the ones that hang) and stalagmites (the ones that grow). While they might simple cave formations, they are actually cave records of historic rainfall and other aspects of climate.

How Cave Formations Grow Over Time

Rainwater is captured in soil and rocks and becomes acidic due to the carbon dioxide in the air. When the rainwater drips in the cave, the slightly acidic water evaporates and leaves behind thin mineral layers. Over hundreds of years, they grow into the large formations. Each layer is made of the various minerals and elements that evaporate and drip during rain, which provide a detailed and chemical records of the rain sequence and its history.

Reading the Climate Story Hidden in Caves

Different periods of rainfall can be determined by studying the sequence of oxygen in the stalagmite layers. Reading the sequence of a stalagmite there is like counting the rings of a tree, only underground.

Researchers in India studied the growth layers of a stalagmite in Mawmluh Cave in Meghalaya to determine the historical pattern of monsoon rains of the Meghalaya region. Their work showcased the changes in the historical account of rainfall, which included periods of rains, and matches periods of known historical drought events.

Why These Natural Climate Records Matter

With changing rainfall patterns due to climate change, these cave formations act as long-term diaries documenting weather. They hold paleoclimate information for thousands of years and aid researchers to track and make projections on the changing monsoon patterns in India.

When you’re under a large stalactite, remember you are not viewing a rock. You are witnessing a part of climate history, painstakingly carved out and documented over time.

References

• Geological Survey of India – Speleothem Studies

• NOAA Paleoclimatology Program

• Nature Geoscience – Monsoon Variability from Mawmluh Cave, India

• Smithsonian Magazine – How Cave Formations Record Climate History

• Science Daily – Stalagmites Reveal Ancient Rainfall Patterns