The Volcanism Blog and the Eruptions blog have both been keeping us up to date with the waxing and waning of these eruptions. However,given my past interest in possible seismic triggering of volcanic eruptions, it’s possibly no surprise that I’ve been wondering whether the near-simultaneous eruption of three volcanoes in the same geographic region is entirely a coincidence. Could the eruption of one have triggered the others?
Note that this triggering does not involve causing a completely inactive volcano to suddenly reactivate; it’s more about pushing a volcano that is already building up to an eruption over the threshold a little earlier than it would have done otherwise. In this case, could the seismic energy released by the first eruption of Okmok on July 12th have provided that extra little push to Cleveland and Kasatochi needed? Out of curiousity, I used the reports from the Alaska Volcanic Observatory (see here, here, and here) to roughly plot the activity of the three volcanoes against each other.
At first glance, there’s some evidence of a possible connection. Okmok has been erupting fairly continuously in the last few weeks, but there have been a few distinct periods of heightened seismic and eruptive activity (the thicker parts of the line). Cleveland’s latest eruption (one of a series that have occurred over the last couple of years, including this one) began on the 21st of July, 1-2 days after one of Okmok’s bursts of activity. Kasatochi erupted on August 6th, 4 days after another period of increased rumbling from Okmok on August 2nd. However, as we all know, correlation is not causation, and it all depends on the sort of timescales over which you’d expect a volcano to respond to a seismic jerk, and whether a few days reasonably falls within that range. I’m not so sure it’s not a little to long.
Additionally, you can also see from the above figure that the activity at Cleveland began to peter out on July 29th, right in the middle of another period of vigorous eruptive activity at Okmok. This stronger, negative, correlation seems to rule out the idea of any strong linkage between activity at these two volcanoes. Still, it was worth a look…