Monday, May 29

This is how the underground tubes created by the La Palma volcano are: speleologists carry out an exploration that could last for years

A team of espeologists has entered the system of lava tubes that has been created on La Palma after the volcanic eruption in Cumbre Vieja. This exploration began in June 2022 when the first accesses documented by specialists were made to find out in situ the large number of possible existing entrances. The accesses to these tubes have been made in different degrees of cooling.

Now, the first steps are taken in important galleries. Scientists have confirmed the presence of another chasm on the north face of the volcano, which is the second vertical development cavity after the one found at the end of the eruption. These multidisciplinary works have been coordinated by the Volcanic Speleology Team of the Canary Islands Federation of Speleology and include obtaining laser point clouds, temperature measurements and microbiological studies, with the participation of the Geological and Mining Institute of Spain (IGME-CSIC), the Department of Engineering and Land Morphology (Caminos – UPM), the company Geoavance SL (official distributor of Leica – Geosystems in the Canary Islands) and the Institute of Natural Resources and Agrobiology of Seville (IRNAS – CSIC).

The drone-view thermal images of June 2022, as explained in a press release, began to show accesses suitable for exploration, given their relatively low temperature. The heat on the surface of the lava flows for most tours, which allows a small caving team to move around in detours to avoid problem areas, also meant a limit to be exceeded for the exploration on foot of the new volcanic tubes of La Palma started. This exploration, which will last for years, seeks to answer the question of whether the largest volcanic tube in the Canary Islands has been formed on La Palma.

On the 21st of that same month, after a thermal overflight with a drone, for the first time a woman from the Volcanic Speleology Team agreed to the call southern tube one of the superficial drainages of the emitting centers of Montaña Cogote, 9 meters long, at 30 degrees.

As a result of these walks through the lava fields, it has been possible to confirm the rapid cooling of the tubes formed in more superficial lava flows, although only a tiny number of the mouths observed from the air have been reached. Being closer to the outside, and also aided by its location at high altitude or by the characteristics of its mouth, these shallow tubes can surprisingly become completely cold, even if the lava on their sides is not completely cold. It is not surprising that a volcanic tube, which represents the now empty arteries of the lava flow, will cool before the core of the rock, because where lava flowed before, now air does and the conduit acts as a cooling circuit.

The tubes of the main system, deeper and with galleries of greater internal dimensions, are still at temperatures that do not even allow them to come close to the mouths, most of them fluctuating between 200 and 400 degrees. But once again, the peculiar characteristics and arrangement of the entrances in one of these main tubes have allowed speleologists to find a series of refuge zones in which to move significant distances of between 60 and 80 meters.

The call red tubea branch of one of the labyrinthine systems that in November 2021 flowed towards where the town of Todoque was located, presents surprising internal characteristics, not only because of the peculiar red color that gives it its name, but also because of the profusion of lava stalactites and, above all, for its special ventilation characteristics: in this place it is possible to be inside a branch between 40 and 60 degrees, observing another at more than 200 degrees a few meters away.

The fact of being able to access these extreme temperature conditions represents an opportunity for speleologists and geologists to improve the understanding of the cooling of these structures, for which there are no clear figures regarding the time that must elapse for them to reach the outside ambient temperature. . After the observations made in other volcanic areas such as Hawaii, we can say that two years after their formation they are normally accessible in various sections, and that in general these cavities cool before the rock that surrounds them. La Palma is currently a new laboratory in which to improve general knowledge about the formation of volcanic tubes, and also has the ideal showcase to present the results as it has the Caños de Fuego Volcanic Cavities Interpretation Center very close to these localities.

As part of the exploration, the first tests of topographical surveys of the new cavities are being carried out, seeking the highest resolution and versatility that allows obtaining clouds of laser points quickly and with little restriction for explorers. It is here where the collaboration between Volcanic Speleology, the Department of Engineering and Terrain Morphology (Caminos – UPM), Geoavance SL & IGME–CSIC has managed to show the first results obtained using portable laser scanners with SLAM technology, with which it is intended to map the thickness of the new volcanic tubes and chasms as their temperature allows it. These tests have been possible thanks to the funding provided by the UPM within the framework of the KUK_AHPAN2 project and the collaboration of Geoavance SL – Leica Geosystems Canarias.

The prior knowledge of the cavities of La Palma by the IRNAS-CSIC staff, who since 2012 have been studying the microbiology of the subsoil of La Palma in collaboration with local speleologists, provided the necessary impetus to obtain the financing that allows today to carry out the first sampling of bacterial fauna in the new tubes and continue laser scanning after the initial tests, within the framework of the MICROLAVA3 project financed by the Junta de Andalucía.

Precisely one of the first samples of microbiota and laser clouds have been obtained in a new volcanic chasm, small but geomorphologically complex, which has been located on the north face of the cone and which is linked to the emitting centers that developed there at the end of November 2021. This small cavity, which has already been partially explored and studied, turns out to be a fissure-type chasm; that is to say, one of the multiple dykes that conducted lava inside the cone, which, when it reached the outside, was emptied and allowed speleologists to enter. Who knows if when the temperature drops it will also allow us to delve into the secrets of this colossus that has changed the face of the Aridane Valley on the surface and left behind a vast legacy of volcanic cavities.

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