Most of us who follow volcanoes over time have been asked at some point if there is a connection between earthquakes and volcanic eruptions, that is to say, can an earthquake set off an eruption at a volcano? I’ve recently been asked this question again, and I will reply with a firm yes.
Now I know that some of you may be skeptical, and some are asking “Why should we believe a woman who puts mayonnaise on hot dogs?” Leaving aside whether that’s a fair question or not, let’s move on to what’s happened recently, and then look at the past.
The most striking evidence of the link between earthquakes and volcanoes is readily apparent in Google Earth as we look at the subduction zones of the Pacific, which have volcanoes all along them. It’s pretty hard to miss the co-relation. Subduction zones are noted for lots and lots of earthquakes, and not coincidentally lots and lots of volcanoes.
If you have been reading here, and elsewhere in such circles, you know that their has been a recent series of earthquakes in the Fox Islands of the Aleutian arc, not far from the also recently active Cleveland volcano. You also know that a 5.5 earthquake struck yesterday just off the east coast of Kamchatka, where three volcanoes are currently active.
I think it very logical that there should be interplay between earthquake activity and volcanic activity, and it should not surprise us at all that one affects the other, albeit somewhat indirectly and over periods of time. In the course of monitoring both earthquakes and volcanoes I sometimes happen upon some interesting interplay between the two, and that happened August 24th after the 6.6 quake hit northern Sumatra near Toba.
I also monitor the seismographs at Galeras in southern Columbia far far away, and saw the quake in Sumatra appear on seismograph station CR2R SHZ OP. That the quake showed up there is not my point, what happened after that is. Large quakes send shock waves all over the planet beneath the lithosphere, and they affect magmatic systems the world over to a lesser or greater extent depending on the state of each one and it’s distance from the quake. What I saw in Columbia after the quake in Sumatra was interesting.
Over the next few days the seismographs at Galeras showed activity I’d not seen there before the quake in Indonesia, and it’s still going on to some extent. Galeras shows no signs of erupting, but it’s magmatic system has clearly been affected and was responding to the shock waves of that quake.
This was on Sept. 5th, and it’s still going on. Activity at Ruiz in Columbia has also picked up since then as I reported here earlier this week. Elsewhere I’d seen the Mt. St. Helens magmatic system respond to a distant quake on Sept. 2nd.
The blue trace is the quake being picked up, and immediately following that we see the energy of those shock waves, approximating a long sine curve, in an oscillation of decreasing amplitude over 30 minutes or so reflecting around the magmatic system beneath St. Helens.
It is a well known fact that 12 years before the 79 AD eruption of Mt. Vesuvius there was a large and quite destructive earthquake in Italy northeast of the volcano. Research has also shown that every major eruption of Vesuvius was preceded by a significant earthquake some years in advance. More recently Merapi in Indonesia became significantly more active following two 6 point quakes there in 2006, and later erupted.
This is not to say that an earthquake today is going to immediately set off a volcano nearby, or anywhere else, but rather that the shock waves of a quake can affect changes in the stability of magmatic systems at a distance, by inducing gas bubble formation in magma or changes in it’s density and viscosity, and that those changes can result in an eruption over time.
Changes in the pressure of a magmatic system can either increase or reduce the pressures on the ground above it, and magma chambers under volcanoes. Either change can destabilize it and stimulate magma intrusions or weaken the geologic structures in and around volcanoes. Unfortunately we cannot monitor those changes as they happen, and even seismic tomography cannot tell us whether earthquake induced changes in particular magmatic system might produce a volcanic eruption, but the correlation between earthquakes and volcanic activity is clear.