Cave Formations Carry Clues About Ancient Earthquakes
Researchers have found that stalagmites can help determine if and when a region was struck by an earthquake.
Researchers studying stalagmite formations in the Wabash Valley fault system have found that stalagmites can yield clues to the timing of ancient earthquakes. (Courtesy Samuel Panno)
By Ker Than
SMITHSONIANMAG.COM
SEPTEMBER 12, 2016
While exploring a pair of cave in Illinois in 2008, Samuel Panno noticed a peculiar thing: some of the stalagmites—rocky, cone-shaped formations that rise up from cave floors—had smaller, neighboring growths that were lighter in color, suggesting they had formed more recently.
The offset, white stalagmites were about two inches tall and were growing on taller, brown stalagmites throughout both caves. "It looked like somebody had dropped the ice cream from their cone on top of [the bigger stalagmites]," said Panno, who is a researcher at the University of Illinois and the Illinois State Geological Survey.
When he and his colleagues spotted similar stalagmites pairings in caves in two other Midwestern states, they decided to investigate. Using rock dating techniques, the scientists calculated the ages of the new stalagmite growths, and were surprised to find that they were all roughly 200 years old. "That correlated really well with a series of earthquakes in the region that happened in 1811 and 1812," Panno said.
An idea began to form in the scientists' minds: perhaps the stalagmite pairs they had uncovered were due to earthquakes disrupting the normal stalagmite-formation process. Stalagmites are formed by mineralized water droplets falling from cave ceilings, and earthquakes could leave their mark on stalagmite growth by shifting the ground and altering the flow of a water drip.
More:
https://www.smithsonianmag.com/science-nature/cave-formations-carry-clues-about-ancient-earthquakes-180960419/
