Yesterday evening, the north-western flank of the cone collapsed after the volcano had its strongest daytime activity since the beginning of the eruption (Sept. 19th). Large amounts of lava flowed out.
Apparently, the upper vents have been clogged during the collapse, meaning that the material could no longer be ejected.
This resulted in a floor elevation of at least 17 centimeters within 24 hours as shown in the GPS data below:
This new ground inflation shows that an enormous pressure is building up under the volcano. Consequently Pevolca issued a warning of possible explosions over the next few days.
The latest GPS data are very worrying. If this is not a measurement error, we could see a sharp increase in activity in the next few hours or days.
Residents have also reported an increasing, whistling noise since Sunday. This could be related to a Glissando effect, which normally occurs before or during a volcanic climax.
Like a scream before a blast
The subterranean magma plumbing systems that sit beneath volcanoes feed pressurised molten rock toward the surface before eruptions. As the magma flows through deep conduits and cracks, it generates small seismic tremors and earthquakes, typically around magnitude 1.
Sometimes these small earthquakes are spasmodic and episodic, but sometimes they appear to take a more harmonic and almost musical tenor, as was reported recently in a study of the Redoubt volcano, Alaska.
Ksenia Dmitrieva, from Stanford University, and colleagues measured seismicity leading up to an eruption of Redoubt in 2009. Small earthquakes occurred in rapid succession, blurring to a continuous high-frequency tremor, and ceased abruptly to immediate silence for about half a minute before the eruption.
The magma plumbing system appears to act like a giant organ pipe or flute, playing the music of the depths in response to the flowing magma as it judders through the system in a frictional tremor.
It is rather akin to the ringing of a wine glass made with a wet finger, but with the frequency ever increasing in a rising glissando – a musical glide from one pitch to another.
If these data are really correct, we could be at a terrifying turning point of this La Palma volcano eruption.
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