At 04:18 UTC on 10 October, 2011 a eruption did start somewhere close to the El Hierro volcano Island (but inside El Hierro volcano system). So far nothing has been seen to this eruption, so location is uncertain at the moment. At the moment this eruption has only been confirmed by harmonic tremors seen on seismometers on El Hierro island.
From what I can tell, based on the harmonic tremor plots. It seems that the eruption has been growing in size since it started well over 12 hours ago. This suggests that the eruption is growing in size. That also brings up the issue that new fissures might open, both into deeper ocean and on shallower depth and even on land without any warning at all.
The harmonic tremor from El Hierro at 21:08 UTC on 10 October, 2011. Copyright of this picture belongs to Instituto Geográfico Nacional.
A location for the eruption has been suggested, as can be see on this map here.
Lack of earthquakes does not mean that magma is not the move and has not reached the surface already. But this however suggests that magma now has a free flow upwards to the surface since sometimes yesterday, when the earthquake activity did drop suddenly from ~100 earthquakes to ~30 earthquakes over the day.
Current earthquake activity in El Hierro. It is my personal opinion that the eruption is around -18.05 and 27.65 to 27.70 (middle of that area, around 450 meter depth). Copyright of this picture belongs to Instituto Geográfico Nacional.
Spectral image of the harmonic tremor. This image clearly shows that the orgin of the harmonic tremor is magma on the move. Not something else. Copyright of this picture belongs to Instituto Geográfico Nacional.
I am going to update this blog post as more is known about the eruption in El Hierro.
Canary Island news about this. With thanks to Dr. John v. Kampen how did send them to me in a email.
Blog post updated at 21:49 UTC on 10 October 2011.