Yesterday (21.03.2013) at 22:50 UTC an earthquake with the magnitude of 3.8 did happen in El Hierro volcano. This earthquake was felt on the Island from reports over Facebook. Since the earthquake activity has been growing with many earthquakes reaching the magnitude from 2.5 to 2.8. But so far not many earthquakes with the magnitude of 3.0 or larger have happened. The main earthquake activity now takes place a bit off the coast of El Hierro volcano. So it is not focused on dry land as it currently stands. It is impossible to know if that is going to change or not at the present time. What is happening in El Hierro volcano is that magma injections (dike intrusions) are most likely forming an sill inside the volcano where the magma can reside until it erupts or just stays there and cools down to form a granite slap in the crust. It is impossible to know what is going to happen at present time.
It is important to note that earthquakes in this location does not equal that an eruption is going to take place there. As it stands now if there is going to be an eruption. It is going to take place where there is a weak spot in the crust. But at the moment that has to be somewhere where the magma has access to. It is impossible to know if that is going to happen this time around or not. If an eruption starts out at sea there is going to be fast drop in earthquake activity and steady harmonic tremor is going to be detected. That are the signs on the instruments that are at El Hierro volcano. Other signs are going to depend on the location if an eruption starts. For the moment however there is no eruption, just earthquakes. More earthquakes should be expected for as long there is clearly magma movement inside El Hierro volcano.
Current earthquake activity in El Hierro volcano. Please note that IGN has re-scaled the image. Why they do this I do not know. But I find it annoying and skewing my view of current events. Copyright of this image belongs to IGN.
While the earthquake activity is ongoing. Please in El Hierro Island should do there best to secure loose items in there homes (televisions, glass items and so on). Since more earthquakes over magnitude can and should be expected while this current activity passes over. There is also an chance no more earthquakes over magnitude 3.0 are going to take place. But that is an small risk given the current status of what is taking place in El Hierro volcano. This activity that is now taking place in El Hierro volcano is like earlier activity in El Hierro volcano. It is almost identical in how it started. But there is no way to know how and when it is going to stop. Since this activity is based on the magma that is being injected into the volcano at over 30 km depth. But earthquake activity now starts around 20 to 25 km from the current detected earthquakes.
The map above shows earlier magma injections into El Hierro volcano. The newest one is taking place at location where no earlier magma injection has taken place. Why that is I do not know. But this means the rock in this area is hard and that means the magma has to break it as the pressure from it increases. The what happens as this progresses. We are all just have to wait and see as I have told before. There is no good way to predict what is going to happen inside a volcano. This goes for both highly active volcanoes and volcanoes that almost never erupt (in human time scale).
I am now off to my weekend break. But if anything major happens in El Hierro volcano. I am going to post an update on it.