What’s the most likely location of the area’s next volcanic eruption?
“I can tell there are a lot of geologists in the room because of the facial hair. I’ve always been told I would be a lot more believable with facial hair,” opened the clean-shaven Dr. Brandon Browne at Tuesday evening’s SNARL (Sierra Nevada Aquatic Research Laboratory) lecture held at the Green Church.
Browne, a volcanologist, then began a presentation on one of his case studies – Mammoth Mountain. When did it erupt last, and when can it be expected to erupt again?
An Assistant Professor in the Department of Geological Sciences at Fullerton, Browne’s research looks at understanding magma reservoir processes and volcanic eruption styles as recorded by mineral compositions and textures as well as the physical characteristics of the resulting deposits. His current projects are focused on Augustine Volcano (Alaska) and several Quaternary volcanoes in the southern and central Sierra Nevada (California), according to the Cal State Fullerton website.
In his talk, “Mammoth Mountain’s Shaky Past,” Browne explained that the last time Mammoth Mountain erupted was approximately 57,000 – 67,000 years ago, but it was a Plinian eruption 90,000 years ago that left all the pumice still seen in the area today.
“A Plinian eruption shoots pyroclastic material up in the air, which then gets carried everywhere,” Browne explained. [So when you are out mountain biking this summer, blame any frustrations you have as you ride through the pumice on that darn Plinian eruption.]
Browne explained further that Mammoth Mountain is not a caldera like Long Valley. It is more of a dome and crater volcano. Whereas the magma in a caldera pulls the crust down and then the edges erode out, leaving a depression in the ground, a dome and crater volcano pushes the ground up.
“Domes are dangerous because the magma ascends slowly and often gets stuck,” Browne explained. “Then the gases build up and explode.”
According to the volcanologist, it is basalt that excites the magma into an eruption in the first place. Basalt comes from partially melted mantle. Areas like the Red Cones near Devils Postpile are visible signs that there is still basalt in the area, and Browne predicted that if there were to be another explosion in the Sierra Nevada, it would come from Red Cones, not Mammoth Mountain.
Which is a good thing for residents living here. An eruption at Red Cones, or Pumice Butte or Horseshoe Lake (other areas Browne predicted might be next) would have a low flow of lava and the eruption and dispersal of the lava would be over quickly.
“Much different than if Mammoth Mountain itself erupted,” Browne said, alluding that an eruption from Mammoth would be a much worse scenario.
With any eruption, however, there is time to get away. It’s not like the movies where you are instantly swept away in a lava flow.
“It can take a month to a couple of years for the magma to get activated,” he said. “Then it would take a week to a month for the magma to ascend to the surface. So you have about two months before the eruption would start. You could sell your house and no one would know.”
The length of the eruption once it begins, however, is completely variable. It could last a few years to a decade, according to Browne.
Of course, can you really trust a guy without facial hair from Southern California?
Please note, next week’s SNARL lecture, the final one of the 2011 series, takes place on Friday, June 3 (not Tuesday) at 7 p.m. The speaker will be Dr. Mark Chappell from the Department of Biology at UC Riverside. His talk is titled, “Combining Science and Art: A Biologist’s Images of the Natural World.”