By Sid Perkins
From London, at the Environmental Catastrophes and Recovery in the Holocene conference
Analyses of toppled stalagmites and other fallen rock formations in two Israeli caves may provide hints about the rate of ancient earthquakes in the area.
Stalactites, stalagmites, and other speleothems–or cave formations–grow as water travels through rocks, dissolves minerals, and then seeps into caves and redeposits those substances. Scientists can find out the age of layers within many such formations by determining the ratios of various chemical isotopes within the layers and comparing the numbers with those from nearby rocks of known ages, says Elisa J. Kagan of the Geological Survey of Israel in Jerusalem. Furthermore, by dating the youngest material in a fallen speleothem and the oldest material that accumulated on the formation after it fell, scientists can bracket the period when the breakage occurred.