Volcanoes almost always make some noise before they erupt, but they don't erupt every time they make noise.
In a new research, scientists have determined that like an angry dog, a volcano growls before it bites, shaking the ground and getting "noisy" before erupting.
This activity gives scientists an opportunity to study the tumult beneath a volcano and may help them improve the accuracy of eruption forecasts, according to Emily Brodsky, an associate professor of Earth and planetary sciences at the University of California, Santa Cruz.
Each volcano has its own personality.
Some rumble consistently, while others stop and start. Some rumble and erupt the same day, while others take months, and some never do erupt.
Brodsky is trying to find the rules behind these personalities.
"Volcanoes almost always make some noise before they erupt, but they don't erupt every time they make noise," she said. "One of the big challenges of a volcano observatory is how to handle all the false alarms," she added.
Brodsky and Luigi Passarelli, a visiting graduate student from the University of Bologna, compiled data on the length of pre-eruption earthquakes, time between eruptions, and the silica content of lava from 54 volcanic eruptions over a 60 year span.
They found that the length of a volcano's "run-up"- the time between the onset of earthquakes and an eruption - increases the longer a volcano has been dormant or "in repose."
Furthermore, the underlying magma is more viscous or gummy in volcanoes with long run-up and repose times.
Scientists can use these relationships to estimate how soon a rumbling volcano might erupt.
A volcano with frequent eruptions over time, for instance, provides little warning before it blows.
The findings can also help scientists decide how long they should stay on alert after a volcano starts rumbling.
"You can say, 'My volcano is acting up today, so I'd better issue an alert and keep that alert open for 100 days or 10 days, based on what I think the chemistry of the system is'," Brodsky said.
Volcano observers are well-versed in the peculiarities of their systems and often issue alerts to match, according to Brodsky.
"But, this study is the first to take those observations and stretch them across all volcanoes," she said.
"The innovation of this study is trying to stitch together those empirical rules with the underlying physics and find some sort of generality," Brodsky said.
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