By Boise State Geologist Jeffrey Johnson
See below for a video slide show
Seven weeks ago Volcan Villarrica erupted in southern Chile. While the suddenness and vigor of its lava fountain was surprising, the volcano’s increasing unrest had been anticipated. The Chilean volcano monitoring agency, SERNAGEOMIN, had raised alert levels from green, to yellow, to orange, then finally red, less than a day before the paroxysm. The forecast proved to be exceptionally timely and SERNAGEOMIN’s monitoring efforts are to be highly commended.
Volcan Calbuco, on the other hand, gave almost no warning prior to its powerful eruption just days ago. It had been quiescent for 42 years and had produced very little precursory earthquake activity prior to its reawakening on April 22. In fact, Calbuco started shaking earnestly only a few hours before exploding with a 10-mile high plinian column. The eruption took everyone by surprise.
About nine of ten volcanoes erupt after weeks or months of anomalous seismicity, making Calbuco’s short notice an outlier. Unfortunately, poorly behaved volcanoes provide little consolation to the public or to the volcano monitoring institutions, which are often (unfairly) accused of non-prediction. Those of us who are volcanologists who study volcanoes for academic pursuit have a great luxury when it comes to eruptions. We are absorbed by the challenge of trying to understand how, when and why volcanoes erupt as they do. Our goals might be to infer dynamical magmatic processing through inspection of seismic waveforms, or analysis of erupted gas, or through numerical models. Many of us hope that our science has application for hazard monitoring, but this is not our primary responsibility.
I am one of these scientists who have the luxury to study volcanoes motivated by the pursuit of research. On the morning after the April 22 paroxysm, I eagerly downloaded infrasound data from my sensors located here near Villarrica, including those in the yard at my rental house. These sensors were deployed here months earlier to track the ongoing crisis of the nearby volcano Villarrica, but they also serendipitously recorded the volcanic events 250 kilometers (155 miles) south. The records show hours of powerful, sub-audible sound produced on the afternoon of the 22nd and, after a few-hour respite, again on the morning of the 23rd. These incredible sounds propagated more than 15 minutes before being recorded with fist-sized sensors deployed next to the woodpile in my backyard.
As a scientist I was ecstatic to see the Calbuco eruption recorded in such high fidelity, as if it had occurred next door! I’m awed by the fact that the volcano produced forceful sounds equivalent to an unfathomable terajoule of acoustic energy (a preliminary calculation). That these sounds traveled more than 50 kilometers (31 miles) into the stratosphere before bending back to Earth permits us an improved understanding of the physics of wave propagation, as well as the source processes of volcanic eruptions.
In terms of volcano monitoring, these low frequency sounds also can give us the capability to track an eruption sequence from safe distances when the volcanic activity might not be visible due to inclement weather, volcanic fume or night time. Toward this end, I was honored to be invited by my Chilean colleagues to install near-vent infrasound hardware during the past few days.
My trip to the devastation area was sobering. Remarkably, no fatalities were reported due to Calbuco’s misbehavior, but collapsed roofs at 10 miles from the crater, and cattle unable to reach the grass through six inches of tephra attest to the very real impact of the eruption. People reported to me stories of their rapid escape amidst rock raining out of the sky and I saw bombs the size of my fists that had punctured roofs nearly five miles from the summit.
Within the 12-mile restricted zone, a region where only homeowners are temporarily permitted to enter, everyone is in face masks, digging out with shovels or tractors. Beyond the acute damage, most of which is uninsured, the psychological impact of an uncertain future beneath the still-venting, and potentially exploding, Calbuco is intense.
At noon the school called us to pick up the children early. They were canceling school for the rest of the week.
About the author: Johnson, a Boise State University Department of Geosciences professor, and his family are temporarily living in Chile supported by the U.S. Fulbright program, in connection with the University of Concepcion, and through a research grant from the National Science Foundation. Since March his children’s school has been canceled seven days due to excitement from two different volcanoes.
BY: KATHLEEN TUCKÂ Â Â PUBLISHED 1:34 PM / APRIL 27, 2015