View Full Version : Volcanic Tremors May Help Predict Massive Eruptions

08-05-2012, 12:06 AM
Earthquakes often precede explosive volcanic eruptions such as the devastating outburst from Mount St. Helens in 1980. But attempts to use tremors to predict the timing and force of such explosions have proved unsuccessful for decades. Now multidisciplinary teams of researchers have developed models that could help warn of disastrous eruptions hours to days before they happen.

A group of scientists at the University of Leeds in England investigated the mystery of why volcanic tremors come in clusters and why they can occur at multiple depths within volcanoes. The answer may lie in how magma behaves: much like Silly Putty, it shatters if pulled apart quickly. When magma rising within a volcano’s main conduit ruptures, the magma develops deep cracks. These cracks weaken the magma, helping it rupture at other points and flow more quickly, which causes still more shattering to occur.

Such a series of ruptures may explain the swarms of low-frequency earthquakes that past research has detected from volcanoes. Analysis of such tremors could determine how fast magma is ascending “and thus can be used to forecast explosions,” says geophysicist Jürgen Neuberg of Leeds. Neuberg and his Leeds colleague Mark Thomas detailed their findings online March 2 in Geology.

A model developed by another team considers tremors created by columns of magma within a volcano that wag back and forth within its main conduit like a metronome rod. The rate at which the magma wagging occurs matches the dominant frequency of most volcanic tremors, reports volcanologist and geophysicist Mark Jellinek of the University of British Columbia, who described his team’s work in the February 24, 2011, issue of Nature. (Scientific American is part of Nature Publishing Group.)

As explosive eruptions near, this model indicates the volcanic tremor frequency would rise in a predictable manner: explosive eruptions would generate gas that would constrict the magma column into a stiffer, thinner shape that would wobble faster. Both research teams say they need to further refine their models with additional data from volcanoes. Any future attempts to predict explosive eruptions will also need to look at changes in gas emissions and how volcanoes physically deform before explosions. “If we take all these data together, we might be able to prevent tragedies,” Neuberg says.

[Link (http://www.scientificamerican.com/article.cfm?id=volcanic-tremors-may-predict-massive-eruptions)]

Regarding the unsuccessful previous prediction attempts;

Dilatancy Theory

Most of the prediction research is centred around the theory of Dilatancy. It has been noticed that when a rock is stressed it begins to expand; to dilate. This is caused by micro-cracks and fractures in the rock opening up and becoming larger. This only seems to start when a rock is roughly half way toward its breaking point.

Visually monitoring the size of a rock sample underground is not possible, but there are several indirect ways to gather the information. When a rock becomes stressed it begins to change physically. It transmits seismic waves at changing speeds, its magnetic properties can alter and its electrical resistance will also vary. The physical change in rock size may lead to a general uplifting of the ground surface or a change in the groundwater pressure and levels. Scientists monitor all these factors and are beginning to find generalized patterns of activity.

The hope is that patterns of activity can be identified which can be associated with the build up of significant earthquakes.
There has been some success with these methods, especially in relation to volcanic eruptions such as that of Mount St. Helens, USA, but accurate predictions are still not possible.

[Link (http://www.geography-site.co.uk/pages/physical/earth/pred.html)]

That has clarified how patterns of seismic activity take place (Dilatancy of rocks causes physical changes as it is contorted). Now, I am curious as to why measuring the electromagnetic changes within the rocks cannot be measured. Surely those resistance changes can be measured by opposing poles running a current through rock "sample sites" in hotspot areas of the world with a continuous feed keeping researchers up to speed? I suppose it's the practicalities of monitoring such phenomena I am more intrigued by.

11-06-2015, 07:19 AM
Regarding Mount St. Helens: