This is a short analyze of what is happening in El Hierro volcano. What is taking place in El Hierro volcano has an simple explanation. What is taking place in El Hierro volcano is an dike intrusion. This creates earthquakes as new magma is injected into the crust. This is also creating inflation on the surface. It has been reported so far the inflation is 20mm up, 20mm east, 20mm north. This can clearly be seen on GPS data that was released today.
The dike intrusion into El Hierro volcano is creating sill in it. While new magma is being injected into the volcano. It is going to mean earthquake activity and a lot of it. Currently there are three older sill that have formed in El Hierro volcano. This sill clearly appear on images that show the earthquake pattern over the past one year in El Hierro volcano.
What happens if the new injection gets into contact with the old inection is anyone guess. But new magma, if it gets in contact with an older magma might mobilize it. It might not mean an eruption. But earthquake activity might get really intense for a while. A lot more intense then it already is today. With earthquake well above magnitude ML3.0 and up to ML5.0 (depending on the stress of the crust in the area).
Earthquake activity in El Hierro volcano today. So far no harmonic tremors have been detected. But that might change without warning if the magma finds a path to the surface. Copyright of this image belongs to ING/AVCAN
When I write this I see that El Hierro volcano has had it first ML4.0 earthquake as I did fear yesterday might happen. But I made a comment on that on AVCAN Facebook page yesterday (Somewhere, I have no idea where it is located).
Dike (geology) (Wiki)
Intrusion triggering of the 2010 Eyjafjallajökull explosive eruption (http://geoscience.wisc.edu/)