Thursday, February 16, 2012

VolcanoDiscovery.com | El Hierro volcano (Canaries): increase in small earthquakes, almost no visible activity


February 16, 2012
The submarine eruption south of El Hierro Island could be in a process of change: While visible activity on the sea surface above the vent, as well as harmonic tremor signal (thought to be more or less proportional to erupting magma flux) have nearly ceased, the number of earthquakes under the island has increased sharply since yesterday.
On 15 February, more than 20 quakes were measured. Most of the earthquakes were very small, well below magnitude 2, and were clustered beneath the NW and SW sectors of the island at depths of around 10 km.
There is no conclusive interpretation of this measurement. A possible (and usually assumed) scenario is that rising new magma from the mantle reservoir is creating new intrusions and rupturing rock to create pathways in the crust under El Hierro, not using the same paths as until now. That would explain why less magma is currently being erupted at the current vent(s). In that scenario, the eruption will continue, perhaps even from a different vent, and an increase in magma output is going to be expected any time soon. However, this is speculation.
The earthquakes could as well be related to some other (known or unknown) process, e.g. gravity-induced adjustments that respond to pressure changes and occur within previously ruptured areas of the crust beneath the island.
The next days or weeks will show what happens next.
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