While the eruption in El Hierro volcano ended some time ago, there has been an constant earthquake activity ongoing in El Hierro volcano. While this earthquake activity has not been in high volume at the moment. It has been deep. Suggesting that this earthquake activity has its source in inflow of new magma at depth. But it is the depth of those earthquakes it is the clue that magma is flowing again into El Hierro volcano.
This however does not mean that an new eruption is going to happen soon. So far the magma seems to be at the depth of 20 to 10 km and at the moment it is not moving at all. It is impossible to know when or if this magma is going to move at all.
Hydro-thermal zone off the coast of El Hierro Island
In the area where the eruption took place from October 2011 to February 2012. This area now has highly active hydro-thermal area. It is hard to know for sure how long it is going to be active. That depends on many factors. But activity should be noticed for at least next one to two years, possible even longer. But this hydro-thermal area off the coast of El Hierro Island is going to continue to create discoloration of the ocean for some time now. So when discoloration happens, it is not because the eruption has started again. It is because the hydro-thermal area activity is changing or some chemicals are getting mixed into the ocean creating discoloration of it.