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Earthquake and eruptive activity at Poás volcano, Costa Rica

Updated Monday, 19th January 2009

The science goes on, despite experiencing an earthquake at the Poás volcano in Costa Rica

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We have a long term research project at active volcanoes in Central America. Our primary goal is a better understanding of the environmental and ecological hazards posed by gas emissions at persistently active volcanoes. Armed with this understanding, our second goal is to develop strategies to mitigate the environmental and ecological risk at these sites. We have chosen to conduct this interdisciplinary study at Masaya (Nicaragua) and Poás (Costa Rica) volcanoes because of the contrasting environmental conditions at each and the persistent, low level of eruptive activity. The aim is to track and quantify the volatile flux at each volcano from the source magma, through the volcanic plume, to the local environmental sinks in the soil and water, and the flora and fauna.

The local environmental effects of pyroclastic flows and lavas are obvious in their coverage and destruction of the land surface. Persistently active volcanoes by their very nature erupt in a regular manner and effects over time are not so obvious. These volcanoes may erupt magma - for example Stomboli (Italy) and Arenal (Costa Rica) typically erupt explosively every 20-30 minutes throwing magma tens to hundreds of metres into the air. For the most part however, persistently active volcanoes emit gases rather than rock.

We are investigating the processes that control volatile flux from magma and quantifying the long-term environmental and ecological effects of background degassing at these two persistently active volcanoes. The aim is to identify the relationship between acid rain and dry deposition of sulphur and to find out how this varies with local climate, soil type and volcanic activity. The idea is to uncover the path and ultimate fate of volatiles erupted at Masaya and Poás volcanoes from their magmatic source, through the gas plume and into the ecosystem. This will lead to a better understanding of the hazards posed by gas emissions at persistently and intermittently active volcanoes. Information on the transport mechanisms of pollutants will allow for more effective mitigation procedures to be adopted including (i) cultivation of acid tolerant crops to neutralise soil, (ii) evacuation of livestock and (iii) advice on the full evacuation or time-limited exposure for the human population as necessary.

As part of the monitoring programme, we are currently in Costa Rica and on 8th January 2009 there was a 6.2 magnitude earthquake at Poás volcano while we were working on the crater rim. We were making gravity and biological diversity measurements at the time.

There was intense shaking of the ground for several seconds and it was very hard to remain standing. New fractures opened up around the crater rim and there were several rock slides as parts of the crater wall crashed down to the crater floor. We moved back away from the rim and sheltered behind boulders to wait for aftershocks or in case there was an eruption. The degassing from the crater increased in intensity and the landslides and shaking caused sulphur pools in the crater bottom to be disturbed so that the lake changed colour on the surface as yellow sulphur streaks appeared on it.

We climbed out of the crater area and felt a few more aftershocks. Colleagues in the crater bottom also emerged safely. The visitor centre at Poás suffered some damage with broken windows. Further down from the summit, local villages were severely affected. Houses were destroyed, some completely disappeared in landslides and floods. More than 40 people lost their lives in these events and emergency services were hampered by blocked roads due to fallen trees, landslides and collapsed bridges. After shocks are still occurring more than 24 hours after the main event.

We will be going back to the volcano over the next few days to resume our work. The gravity measurements demonstrate that there has been an increase in sub-surface mass, which we interpret to be shallow intrusions of magma beneath the active crater. We are also measuring the rate of deposition of sulphur around the crater area and also the effect on biodiversity.

Hazel Rymer talking to a group of students on the crater rim of Poás volcano. [image by Michelle Spinosa © copyright Michelle Spinosa] Copyrighted  image Icon Copyright: by Michelle Spinosa © copyright Michelle Spinosa
Hazel Rymer talking to a group of students on the crater rim of Poás volcano.





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