Plate tectonics

Deep Heat May Have Spawned One of the World’s Deadliest Tsunamis

Sumatra quake
DEADLY DISASTER The quake that ruptured off the coast of Sumatra on December 26, 2004, was one of the deadliest earthquakes in history, mostly because it set off an enormous tsunami that destroyed nearby island communities.

Chemical transformations in minerals deep beneath the seafloor could explain why Indonesia’s 2004 mega-earthquake was unexpectedly destructive, researchers report in the May 26 Science.

The magnitude 9.2 quake and the tsunami that it triggered killed more than 250,000 people, flattened villages, and swept homes out to sea across Southeast Asia. It was one of the deadliest tsunamis in recorded history.

“It raised a whole bunch of questions, because that wasn’t a place in the world where we thought a magnitude 9 earthquake would occur,” says study coauthor Brandon Dugan, a geophysicist at the Colorado School of Mines in Golden.

The thick but stable layer of sediment where tectonic plates meet off the coast of the Indonesian island of Sumatra should have limited the power of an earthquake, seismologists had predicted. But instead, this quake was the third-strongest on record worldwide.

Dugan spent two months aboard a boat with 30 other scientists collaborating through the International Ocean Discovery Program. The researchers drilled down 1,500 meters below the seafloor in two places off the coast of Sumatra, extracting narrow cylinders of sediment. This sediment is very slowly moving toward the fault where the 2004 earthquake occurred — a zone where one massive tectonic plate slides over another, pushing that plate downward.

Analyzing how sediment changes with depth can give scientists a snapshot of the geological processes at play near the fault zone.

In particular, the researchers noticed that the deeper they drilled, the lower the salinity of the water surrounding the sediment. Since seawater seeping into the sediment would be salty,…

50 years ago, continental drift began to gain acceptance

map of Earth
FULL OF PLATES Earth’s outer crust is composed of more than a dozen large pieces, known as tectonic plates, which bump or slide against each other.
Science News cover from April 29, 1967

Drifting theories shake up geology

Continental drift, a theory often considered amusing but rarely important, seems about to become the focus of a revolution in geology. At the least, it has already split the geological community into those who find the evidence…