La Palma volcano update: Why activity is different at different vents
Wed, 20 Oct 2021, 07:3107:31 AM | BY: T
Volcanes de Canarias (link to twitter) published a simplified sketch to illustrate the current arrangements of vents at the eruption site, to help to better understand how the activity is different at each vent. Ultimately, this is a function of how gasses, present as bubbles inside the magma as well as still in solution in it, separate from the liquid magma column when it rises to the surface, and might form different regimes within the system:
Cartoon showing the different activity at the vents of La Palma at the moment (image: Volcanes de Canarias)
For example, if gas bubbles form a type of conduit within the magma column, aggregating along a specific area, they likely will erupt as gas jets with little liquid and more ash, something typically observed at the upper vents. Areas at the margins of the main column might be largely degassed on the other hand; these will form liquid, but lower fountains or entirely effusive vents.
Another important factor includes how much external water (i.e. from the groundwater system) interacts with the magma. Depending on how much water is present and able to interact with the magma, this interaction can completely change the dynamics of the activity at some (or even all vents). Water can absorb a lot of energy, but if in contact with magma, it typically transforms into steam as result, which goes with a thousand (1000!) times increase of volume. If the generated steam is not easily released, it becomes over-pressured, and once, this pressure overcomes the surrounding containing pressure, will. result in violent explosions known as phreatomagmatic.
Phreatomagmatic activity is more likely to occur at the vents furthest away from the center, where magma rises through older rock layers that might still contain water or are in connection with aquifers.
The sketch only illustrates what might be happening very close to the surface, i.e. the very top of the feeding system, not the magma chamber. The magma erupted as lava comes from deeper storage systems much less understood, but there is obviously a currently very effectively working connection from there way up to the surface. This connection is commonly imagines as a series of "dikes" - sheet like fissures filled by moving magma, but not necessarily exactly vertical, so the magma source might very well be under the center of the volcano (where the quakes are being detected), then migrates both vertically and horizontally to reach the current vents near El Paraiso.
Wed, 20 Oct 2021, 06:00
La Palma volcano (Spain) - Smithsonian / USGS Weekly Volcanic Activity Report for 20 October-26 October 2021 (New Activity / Unrest)
The eruption at La Palma continued during 20-26 October, characterized by Strombolian explosions, lava fountaining from multiple vents, advancing and branching lava flows, and daily ash emissions. Eruption details are based on official sources including PEVOLCA (Plan de Emergencias Volcánicas de Canarias) steering committee summaries issued daily. Seismicity remained elevated, with most earthquakes located 10-15 km deep (though some were as deep as 39 km); dozens of events were felt by local residents and some were felt across the entire island. ... Read all
Tue, 19 Oct 2021, 23:19
The strongest-so-far quake, a magnitude 4.8 event at 39 km depth, occurred at 10.48 p.m. on Tuesday evening under the island. Whether it is an indication of another pulse magma going to fuel the eruption remains to be seen, but a possible scenario, in which case activity should be picking up even more in the near future. ... Read all