A piece of supervolcano and extracted quartz crystals analyzed for titanium Photo Credit: Rensselaer Polytechnic Institute/David Wark

Searing ash rained from the skies, blanketing half the United States. The sun was erased behind dense black smoke and hot lava oozed across hundreds of miles of forests and fields. It might have occurred more than 760,000 years ago, but the eruption of one of the country’s only “supervolcanoes” still has researchers and the public riveted.

Using a new technique developed at Rensselaer, a team of researchers has now determined that there was a massive injection of hot magma underneath the surface of what is now the Long Valley Caldera in California some time within 100 years of this gigantic volcano’s eruption. The findings suggest that this introduction of hot melt led to the immense eruption that formed one of the world’s largest volcanic craters. 

The research, which is featured in the March 2007 edition of the journal Geology, sheds light on what causes these large-scale, explosive eruptions, according to David Wark, research professor of earth and environmental sciences and lead author of the paper. 

The 20-mile-long Long Valley Caldera was created when the supervolcano erupted. The geologists focused their efforts on Bishop Tuff, an expanse of rock that was built up as the hot ash cooled following the eruption. The researchers studied the distribution of titanium in quartz crystals in samples taken from Bishop Tuff. 

A team from Rensselaer previously discovered that trace levels of titanium can be analyzed to determine the temperature at which the quartz crystallized. By monitoring titanium, Wark and his colleagues confirmed that the outer rims of the quartz had formed at a much hotter temperature than the crystal interiors. The researchers concluded that after the interiors of the quartz crystals had grown, the magma system was “recharged” with an injection of fresh, hot melt. This caused the quartz to partly dissolve, before starting to crystallize again at a much higher temperature.

Analyses of titanium also revealed that the high-temperature rim-growth must have taken place within only 100 years of the massive volcano’s eruption. This suggests that the magma recharge so affected the physical properties of the magma chamber that it caused the supervolcano to erupt and blanket thousands of square miles with searing ash. 

The research was funded through a grant from the National Science Foundation.

Wark was assisted in his research by Wes Hildreth of the U.S. Geological Survey; Frank Spear, Rensselaer professor of earth and environmental sciences and department chair; Bruce Watson, Institute Professor at Rensselaer, and Daniele Cherniak, research associate professor of earth and environmental sciences at Rensselaer.

Published March 12, 2007