Volcano activity of September 8, 2012 - San Cristobal eruption (Nicaragua), Apoyeque, Krakatoa, Bagana, Nevado del Ruiz, Galeras, Costa Rica volcanoes and Tungurahua

This (almost) daily post intends to follow up the activity changes of volcanoes all over the world.
This post is written by geologist Richard Wilson who specializes in Volcano seismicity and Armand Vervaeck. Please feel free to tell us about new or changed activity if we haven't written about it. -

September 8, 2012 volcano activity

Eruption San Cristobal volcano earlier today -Image courtesy Ineter, Nicaragua

Nicaragua’s largest volcano erupted three times this morning, belching gas and ash 1,500 meters into the sky and forcing the evacuation of thousands of families in the rural northwestern department of Chinandega, according to government media sources. No damages or injuries have been reported. San Cristobal’s eruption is being monitored by the government officials and could result in the evacuation of 20,000 people, according to first lady and government spokeswoman Rosario Murillo.
Update : Nearly 3000 people living in La Bolsa, Versalles, El Pando, Pellisco and Apazate are relocated. President Ortega is carefully following up the situation and says that he may order a second eveacuation for approx. 20000 people. 400 people from the Civil Defense have been asked to be ready in case the evacuation will be ordered.

Likely pre-eruptive seismicity continues at Little Sitkin volcano (AK) this morning. Several episodes of larger magnitude events occurred overnight within the background activity comprised of numerous smaller earthquakes. (station LSSN)
A small swarm of earthquakes occurred early yesterday within the Yellowstone caldera complex (WY).  Swarm activity at the volcano has been meager since the big earthquake swarms of 2008-9 and 2009-10.
Low level seismicity, in-concert with low-level surface activity, affects Popocatepetl volcano (Mexico) today.
Pulsatory, low-level volcanic tremor continues at Pacaya volcano (Guatemala) (station PCG).
Despite a recent dramatic increase in fumarolic temperatures, seismicity (consisting of tremor pulses) is relatively low at Telica volcano (Nicaragua) today. (station TELN)
 Volcanic, low-frequency earthquakes remain visible on seismograms at Nevado Del Ruiz (Colombia). (station OLLZ)
 Small earthquakes are apparent on seismograms at Galeras volcano (Colombia) this morning. (station ANGV)
Numerous low-frequency volcanic earthquakes rumble within Tungurahua volcano (Ecuador), although magnitudes seem to be diminishing over the past day.  (station RETU)
 Across the pond, in New Zealand, continuous volcanic tremor rattles White Island volcano again today.
Recent satellite data show significant SO2 emission from Popocatepetl, Nevado Del Ruiz, Ambrym (Vanuatu), Bagana (Bougainville Island), and Krakatoa (Sunda Strait) which apparently experienced a large eruption on 04 September (judging from imagery on that date).
There's still something "fishy" with the seismogram depictions at Apoyeque but, upon second glance, I would believe those small events are small earthquakes. Not a good scenario given the proximity of Managua if Apoyeque is indeed waking-up!
 Large earthquakes in Central America frequently result in internal activity at nearby volcanoes.  For Managua's sake, let's hope it stays internal!

Costa Rica volcanoes and the massive earthquake
After the Mw 7.6 earthquake on September 5th., 2012 (08:42 local, 14:42 GMT) on the Nicoya Peninsula, Costa Rica, concern raised about the possibility of depressurization in the volcanic range and consequently changes in the volcanic activity. Preliminary results do not show any affectation on the volcanic activity. The seism that took place ~35km depth, 20 km south of Sámara (9.696N, -85.49W) on the Nicoya Peninsula (NW of the country) had minor effects in the country considering the magnitude, and aftershocks (more than a 1,000 on September 7th) are occurring around the epicentral area and beyond the volcanic range.
After field investigation and collection of information, the scientists of the volcano observatory (OVSICORI-UNA) are reporting that only small gravitational collapsed occurred without modifying the volcanic activity of the five monitored volcanoes.
The most affected volcano, Arenal, suffered moderate rock avalanches up to the middle of the flank, mainly from the unstable blocks on the north rim of the crater. Minor rockfalls were reported from Irazú´s main crater walls. Rincón de la Vieja, Poás and Turrialba do not show significant changes related to this seismic event.

Video eruption San Cristobal volcano