La Palma volcano update: Volcano remains calm, but small quakes continue

View of La Palma’s new volcanic edifice from the Llano del Jable Astronomical Viewpoint at 11.00 am Canarian time (image: INVOLCAN / Twitter)

For 3 days, no eruptive activity has taken place, and the likelihood that the eruption is actually over is clearly increasing. The cone only shows mild degassing and no lava flows are active any more.

Official confirmation when the eruption is declared over will likely need to wait a little longer. Some doubt remains as to the significance of the continuing earthquake activity: although of low energy and overall on a decreasing trend, it remains significant, and could indicate that magma at depth is still able to pressurize and fracture rocks at depth and create intrusions that might eventually allow it to rise further. However, this is far from certain – it could also be adjustments of the system triggered by the massive shifts of masses that has occurred during the eruption. In the latter case, the quakes should slowly die out.

During the past 24 hours, there were 3 quakes of magnitudes 3.3-3.5 at 35-36 km depth, in addition to many more smaller quakes (22 quakes of magnitudes 2.0-2.9 and 48 quakes below magnitude 2.0). If looking at the various maps published of recent quakes, it might seem that there is a a strong increase of quakes. This apparent increase, however, is mostly in the number of quakes, especially for those in the deeper region around 30-40 km. This is mostly an artifact caused by the absence of volcanic tremor, which acted as noise during the eruption and was simply hiding smaller quakes in its signal. Now, the very sensitive seismic devices are again able to pick up very small quakes below magnitudes 2, as well as quakes deeper down (whose signals at the surface are much weaker). In other words, most of the apparent increase of quakes is only an increase in detection sensitivity. Still, a weak increase in the total energy of the seismic activity remains visible for the past 48 hours or so. With most likelihood, it is part of a normal fluctuation, but nobody can be sure.

Depth vs time of quakes under La Palma showing an apparent increase of quake numbers, especially at depth