No major quakes for nearly a month now but no such problems with volcano activity as the Volcan Santo Tomas, Galapagos Island is the latest to rumble back to life.
A seismic crisis has started under the volcano recently, suggesting that the volcano could be approaching a new eruption in the near or medium-term future.
The Geophysical Institute of Ecuador (IG) reported last week that seismic activity now has reached levels that could be interpreted as signs of an approaching eruption.
Seismic activity at the volcano has been gradually increasing over the past two years but reached and maintained very high levels since mid-May, with an average of 42 local events per day.
A record number of 104 quakes occurred on 25 May.
The largest-so-far quake was a magnitude 4.8 on 8 June.
This and several others have been widely felt by people in the vicinity.
In addition to the dominant so-called volcano-tectonic earthquakes, which are related to internal rock fracturing due to fluid (magma) pressure creating space inside the edifice, a significant number of tremors reflecting fluid (magma, water, gas) oscillations and movements inside the volcano have also been detected.
The earthquakes have been clustering in two SW-NE trending alignments touching the NW-N rims and S-SE rims of the caldera.
Over the past weeks, most quakes have been concentrated in the eastern and southeastern segments, suggesting that this could be a likely area of new fissures opening up in the case of a new eruption.
In line with the elevated seismic activity, monitoring data shows strong ground deformation in the summit area, suggesting that a new body of magma has been intruding inside the upper volcanic edifice.
IG concludes that the recent increase of seismic activity "suggests an increase of pressure inside the volcano, which could be related to an advance of a magmatic intrusion towards relatively shallow depths", or in other words, a new eruption could be in the making although it is difficult to give a time-scale.
It should be noted that the current unrest does not automatically lead to an eruption, but if it does, the most likely outcome would be a moderate-sized eruption in the Volcan Chico sector (SE).
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