Explained: Stalagmites, How Do They Tell About Monsoon And Drought History Of A Region

Rainwater has been steadily dripping from the ceiling in the same locations in a remote cave in Cherrapunji, Meghalaya, for more than 1,000 years, according to a recent study that was published in the Proceedings of the National Academy of Sciences. Every drop of water deposits minerals into the ground below, where they gradually build up to form calcium carbonate towers referred to as stalagmites.

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Similar to tree rings, the strata of these stalagmites serve as a record of the history of rainfall in the area, making them more than just geological marvels. They also serve as a reminder that devastating multiyear droughts could occur in the future.

What are Stalagmites?

Stalagmites are a particular kind of rock structure that develops from a cave's floor as a result of the buildup of debris from ceiling drips that fall to the ground. The most common ingredient in stalagmites is calcium carbonate, but they can also be made of lava, clay, peat, pitches, sand, sinter, and amber.

Speleothems are stalagmites that are most prevalent and often form in limestone caves. Stalagmites in the cavern can only flourish in certain pH conditions. They are created by calcium carbonate and other minerals that condense from solutions of mineralized water deposited on the surface.

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Limestone serves as the most prevalent form of calcium carbonate rock, and in caverns, it mixes in water that contains co2 to create a calcium bicarbonate solution. Conventional stalagmite formation requires a difference between the partial pressures of carbon dioxide in the water and the cave chamber.

Skin oils can change the surface tension where the natural mineral hangs or flows, which can influence the development of the formation. Stalagmites are typically not to be touched since the rock accumulation is produced by minerals precipitating out of the liquid solution onto the surface layer. The structure can also get irreversibly stained by oils and grime (mud, clay) brought on by human interaction.

What does the new study say?

The abandoning of Fatehpur Sikri by the Mughals, the horrific Chalisa famine that killed 11 million people, and the 17th-century Deccan famine are just a few examples of significant historical events that occurred during the severe and prolonged droughts that have occurred in India during the previous 1,000 years, as demonstrated by the stalagmites in a Meghalayan cave.

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In a secluded cave in northeast India, rainwater has been continuously flowing from the roof at the same spot to create stalagmites for more than a thousand years. The strata of these stalagmites, like tree rings, preserve the history of the region's rainfall, making them more than just natural wonders. They also serve as a warning about the potential for disastrous, protracted droughts in the future, according to The Conservation.

A new study found that the Indian subcontinent commonly observed prolonged, severe droughts that were unheard of during the 150 years of accurate monsoon rainfall observations.

What does it reveal about the monsoon and drought history of India?

The observed instances of drought are strikingly consistent with prior accounts of famines, mass fatalities, famines, and geopolitical changes in the region.

They show how the collapse of the Mughal Empire and India's textile economy in the 1780s and 1790s paralleled the greatest 30-year drought of the century. The length and intensity of the drought, which caused widespread crop failures, would have contributed to the scope of the famine documented in historical writings from the time.

Another prolonged episode of the drought was the Deccan famine of 1630¨C1632, one of the worst droughts in Indian history. Numerous millions of people died as a result of agricultural failure.

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The majestic Mughal city of Fatehpur Sikri was abandoned during the same period as the Guge Dynasty in western Tibet.

The findings have important ramifications for water planning now that the world is warming, particularly for India, which is on the verge of overtaking China as the most populated country in the world as a result of its extensive agriculture industry, which is dependent on the monsoon.

How are monsoon histories preserved in stalagmites?

Researchers for the study took small samples of calcium carbonate out of its tree rings and then measured the oxygen isotopic composition to reconstruct the history of monsoon rainfall. They measured the uranium-to-thorium ratio to fix the climatic record to certain years on the calendar.

Small amounts of uranium as well as other minerals that were absorbed as rainwater seeped into the rocks and soil just above the cavern are retained inside the growth plates of rock formations. By analyzing the ratio of uranium to thorium, it is possible to determine the age of each stalagmite growth layer since the uranium contained in stalagmites decomposes into thorium over time at a consistent rate.