A 2008 image of the summit crater at Poas in Costa Rica. The summit crater lake helps drive some of the phreatic explosions that commonly occur at the volcano - and is one of two summit lakes (the other is cold). Image: Robert Nunnally / Flickr. Ever since the M7.6 earthquake off of Costa Rica earlier this year, we've been watching the volcanoes of the Central American country closely to see if they have any response to the significant seismic event. So far, nothing is conclusive but over the weekend, Poás did have one of its largest explosions in almost 6 years (only a few days after a M6.5 aftershock of the earlier earthquake). News reports from Costa Rica say that the volcano produced a half kilometer (~1500 foot) plume that rained ash on the national park that surrounds the volcano. Now, this is by no means a large volcanic eruption -- it is barely a blip for most volcanoes. However, this is the biggest event at Poás since 2006. Eliecer Duarte, from OVSICORI characterized the eruption was likely a phreatic explosion -- driven by superheated water rather than new magma at the surface -- and the descriptions I've seen would back that up as well. OVSICORI doesn't seem to think this is an event that is leading to something larger, as many phreatic explosions can be, "clearing the throat" of the volcano, so to speak. However, the volcano will remain under close observation to see if the situation changes. Poás erupts frequently but does not tend to have large eruptions - mostly VEI 1 to 2 explosions - at least over the last few thousand years.