The Volcano Listening Project

The eruption of Mount Redoubt, Alaska, in 2009

was characterized by a number of volcanic explosions that ocurred over several days. The ground shaking from these explosions was recorded on nearby seismometers operated by the Alaska Volcano Observatory.

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Mt. Redoubt, Alaska (from Schaefer, 2012)
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Locations of major Alaskan volcanoes


Many of the explosions were preceded by strange gliding signals, in which volcanic tremor increased in frequency over time, followed by seismic silence, followed by the explosion.

Lets listen to one of these "screams"!

Direct sonification + post-processing

The sonification method here is "direct": we simply speed up the original datastream, sampled at 100 Hz, so that the frequencies of interest lie within the human auditory band. In the above example we used a speed factor of 150x.

We also did a bit of post-processing, to really bring out some of the features of interest. This was performed in the software package Ableton, using multiband compression and EQ, with a side-chained duplicate track with different filtering to emphasize the scream and bring out some of the overtones. We also added some subtle flanging and delay for aesthetics.

Compare this with pure direct sonification (here of multiple events on September 28, 2009)

This is now 12 hours of data, using two speed factors to "fast forward" through the boring bits... 300x... then 150x for the screams.

Listen to how different they are!

What could produce such signals?

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An interesting idea from Dmitrieva and others (2013) is that the gliding seismic tremor we hear as screams is actually composed of many small repeating earthquakes, occurring on a frictional fault along the volcanic conduit path. The frequency of these earthquakes is set by the stressing rate: higher stressing rates, higher frequency.
A transition from stick-slip to stable sliding (similar to what may happen on tectonic faults!) caused the silence before the explosion.


Dmitrieva, K, Hotovec-Ellis, A J, Prejean, S, Dunham, E M (2013) "Frictional-faulting model for harmonic tremor before Redoubt Volcano eruptions" Nature Geoscience Volume: 6, Pages: 652–656 Year published: (2013) DOI: doi: 10.1038 / ngeo1879

Schaefer, J (2012) "THE 2009 ERUPTION OF REDOUBT VOLCANO, ALASKA", US Geological Survey Report of Investigations 2011-5.