The BBC is reporting today on a study published in Earth and Planetary Science Letters that attempts to establish a connection between large earthquakes and subsequent volcanic eruptions. The study is focussed on large Chilean earthquakes over the last 200 years (Chile has had some of the biggest, hitting M9 on the Richter Scale) and then examining the number of volcanic eruptions that followed. They find that activity increased in the year after the earthquakes. This suggests that many volcanoes might be "primed" to erupt and just need a catalyst like a large seismic event to promote eruption.
This effect was seen as far as 500 km from the epicenter of the earthquake, which makes for some fascinating speculations for future volcano predictions. For instance, what happens when we have the next big Cascadia subduction zone earthquake in the Pacific northwest? The last major one was in 1700 (and yes, if you read Fire Mountains of the West, it does seem like the Cascades were much more active in the 18th and 19th centuries), so when the next one rolls around, might we expect more activity from the many potentially active Cascade volcanoes. The key to understanding this will be to discover what exactly does it mean for a volcano to be "primed" for eruption - in other words, where does the magma have to be in the system, what thermal condition should the magma be in, what amount of melt has to be present, how degassed can the magma be, how close to the epicenter is the volcano, what sort of shaking did it experience? These are just the first few questions that popped into my head concerning this connection. As usual, more work needs to be done to understand how robust this volcano-earthquake connection might be and how might it work.
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If that proves to be the case, I wonder if the strength of the eruptions is any different for these volcanoes then other eruptions of the same volcanoes not connected to a large earthquake.
Comment posted on March 6, 2010 @ Vulcanism blog:
I remember that after two days from the 9.5 earthquake in Valdivia (May 22, 1960), the Puyehue volcano located 200 km from the epicenter, erupted for several weeks.
http://www.ngdc.noaa.gov/hazard/img/200_res/45/45_913.tif
Furthermore, due to the same earthquake, several mountains collapsed blocking the drainage of Lake Riñihue. This lake is the last of Seven Lakes that are interconnected and is drained by the San Pedro River that runs through several towns (including Valdivia) before emptying into the Pacific.
It is also recorded in Chilean history that an estimated 8.5 earthquake hit Valdivia on December 16, 1575 and the drainage of Lake Riñihue was also blocked at that time.
Has anybody evaluated these possible scenarios with the current sismic activity?
There is one concept that the expulsion of water and volatiles from slab serpentinite makes it denser so the slab will sink. Usually under volcanic arcs there the angle of the slab bends down more at a steeper angle. There is a concept that the slab is buoyant and sticks up against the plate above until it gets under the volcanoes where the slab loses buoyancy and bends down to a steep angle that sinks more easily into the mantle. One questionable thought is: When a large volume of magma ascends from the slab up into a magma chamber, does the loss of this magma separated from the slab affect slab motion, such as increased rate of sinking? If so, then the increased rate of sinking would accumulate strain faster than usual and increase the stress of pulling motions through the locked zone until the subduction fault zone ruptures. Meanwhile, the magma has been filling the magma chamber, getting ready for the timely eruption.
and thats why we can't have nice things :(
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