Over the past few days there has been interesting development taking place in El Hierro volcano, Canary Islands, Spain. It is not the amount of activity that is interesting, or lack of it to be exact. It is where the activity is taking place and how it is manifesting itself currently. On 28-July-2013 a magnitude 2.8 (EMSC) earthquake took place in El Hierro volcano, at the near top of the volcano, on the central part of the Island. This earthquake only had the depth of 11 km, that is a shallow earthquake for this region since most of earthquakes so far have the depth of 28 to 20 km. Shallower earthquakes are not unheard of, but mostly happen in times with high earthquake activity. That is not the case now. Later that same day a magnitude 3.0 (EMSC) earthquake took place in El Hierro volcano, with the depth of 20 km. A more common depth for this area in past few months.
What is known about this is little at present time, since this activity has been getting a little attention from authorities and scientists (best to my knowledge at present time). What I do know however is that eruptions not always start with large earthquake activity (Eyjafjallajökull 2010). If that is going to be case now I do not know yet, current activity is far to small to be sure on this. But it is important to keep a eye on this activity in case changes take place in next weeks to months.
Local activity in El Hierro volcano, this is the magnitude 2.8 earthquake in El Hierro volcano. Copyright of this image belongs to EMSC.
The risk here is that magma has “boiled” the rock in El Hierro volcano, making it soft and soft rock does not make earthquakes, or earthquakes of less magnitude than normal rock. Since normal rock is hard and require more energy to fracture then rock that has been in part been melted by basaltic magma (more details here), as can be found inside El Hierro volcano at the moment. This change in the rock increases the risk of sudden eruption without much earthquake activity, even at current time when no major activity is taking place.
I however must stress that even if there is a risk of something, it does not mean it is going to take place now. Currently there are no sign if imminent eruption in El Hierro volcano.