Volcanic events large enough to devastate Earth have taken place in a number of places worldwide in the recent geological past. It seems inevitable that another super-eruption will strike in the future.
Now scientists say the warning signs would probably show up about a year before a big eruption.
That’s the conclusion of a new microscopic analysis of quartz crystals in pumice taken from the Bishop Tuff in eastern California, which is the site of the super-eruption that formed the Long Valley Caldera 760,000 years ago.
“The evolution of a giant, super-eruption-feeding magma body is characterized by events taking place at a variety of time scales,” says Guilherme Gualda, associate professor of earth and environment sciences at Vanderbilt University.
Tens of thousands of years are needed to prime the crust to generate sufficient eruptible magma. Once established, these melt-rich, giant magma bodies are unstable features that last for only centuries to few millennia.
“Now we have shown that the onset of the process of decompression, which releases the gas bubbles that power the eruption, starts less than a year before eruption.”
Gualda and Stephen Sutton at the University of Chicago analyzed dozens of small quartz crystals from the Bishop Tuff. Previous investigations of quartz crystals from several super-eruptions, including Long Valley, have noted that they have distinctive surface rims. These studies concluded that the rims formed in less than a century before eruption.
The new study, published in PLOS ONE, uses a more accurate method for measuring rim growth times pinned on variations in the concentration of titanium in the crystal.
Days to Months Before Eruption
Titanium is one of the few impurities that is incorporated into quartz in appreciable amounts and it diffuses fast enough to permit probing of time scales as short as minutes. However, it is extremely difficult to measure the small levels of titanium involved at sufficient spatial resolution. So the researchers established that the concentration of titanium in quartz directly correlates with the amount of light produced when a material is bombarded by electrons, an effect called cathodoluminescence.
