Sunday, September 19, 2021, at 2:13 p.m. local time, a volcano erupted on the island of La Palma, in the Canary archipelago. The volcanic eruption monopolizes the news media due to its exceptional nature, but above all because it is taking place in a populated area.
In the first days, the lava flows, pyroclasts and gases emitted by the volcano mainly affected four municipalities, with more than 7,000 people evacuated. After the first week, it is estimated that the economic damage far exceeds 400 million euros.
Fortunately, the effective development of the Special Plan for Civil Protection and Emergency Assistance for Volcanic Risk (PEVOLCA) is minimizing the impact of volcanic products on the population, without causing any casualties among the inhabitants of the area.
The following lines explain the causes of volcanism on the island of La Palma, the relative dimension of the Cumbre Vieja eruption on a terrestrial scale, and the following reflection is invited: is economic investment in geological research necessary?
The oceanic islands
La Palma is an oceanic island (708 km²) formed by the progressive eruption and accumulation of lavas from the earth’s mantle on the ocean floor. That island corresponds to a huge volcano of conical geometry, with an almost circular plan of 75 km in diameter and a height of 6.5 km. Indeed, it rises from a depth of almost 4,000 m to a height of more than 2,400 m above sea level.
The location of the oceanic islands is not random, but is related to the existence of thermal anomalies in certain areas of the earth’s mantle called “mantle plumes”.
The mantle is a region of the earth’s interior of approximately 2,890 km thick whose lithological composition differs from that of the most superficial layer, called crust (whose average thickness in oceanic areas is 6 km and in continental areas 30-35 km) .
The temperature of the surface mantle (800-1,000 degrees) contrasts with that of its base (2,600 degrees), causing the formation of convective cells inside that transport heat and matter to the surface. On occasions, this convective phenomenon triggers in the lower 200 km of the mantle (in the area of contact with the earth’s core) the formation of plumes or plumes of rocky masses that rise towards the surface, developing a geometry similar to that of the fungi of nuclear explosions.
The diameter of the heads of these feathers is of the order of 2,000 km. Their ascents are slowed in the upper part of the mantle, of a rigid character, which is called the lithospheric mantle. The retained plumes cause the bulging of the lithosphere which, together with the accumulation of thermal energy and the decompression of the mantle rocks, generate the basaltic magmas and, by extension, the volcanism of the oceanic islands.
Volcanism in the Canary archipelago
In the Canary Islands, the location of volcanism has progressively changed place, since the African lithospheric plate, on which this archipelago is located, moves with respect to the underlying plume at about 9 millimeters per year. The formation of the first islands (Lanzarote and Fuerteventura) began 20 million years ago (Ma).
The progressive displacement towards the northeast of the African lithospheric plate brought with it the extinction of volcanism in those first islands, but the emergence of new ones on the oceanic waters (Gran Canaria, 15 Ma; Tenerife, 12 Ma; La Gomera, 10 Ma) . The westernmost islands, La Palma and El Hierro, are the youngest (1.8 Ma) and are in a stage of active growth, which is why they present historical volcanic activity.
On the island of La Palma, the most recent volcanic activity is located in the southern half, along the Cumbre Vieja volcanic rift, which integrates several eruptive centers aligned in a north-south direction along 17 km. In that area of the island there have been nine volcanic eruptions in the last 550 years.
Magnitude of the La Palma eruption
Although it may seem surprising to us, the Cumbre Vieja volcanic eruption is a modest eruption according to the volcanic explosivity index (VEI), which allows measuring the magnitude of volcanic eruptions. The VEI takes into account, among other parameters, the volume of pyroclastic material emitted and the height of the eruptive column, which is proportional to the explosiveness of the volcano.
Depending on these parameters, the VEI scale varies from a value of 0 (only effusive eruption) to a maximum of 8 (maximum explosiveness). Although it is still too early to make an adequate assessment, the eruption of La Palma probably does not exceed the VEI value 2 (volume of lava emitted between 0.001 km³ and 0.01 km³; height of the eruptive column less than 5 km).
The eruption, in terms of explosiveness, is thus far behaving like a typical Strombolian eruption with some exceptional Vulcan pulses. For comparison, VEI 8 eruptions emit more than 1,000 km³ of pyroclastic materials and form eruptive columns that exceed 25 km in height.
On the other hand, the lava flows emitted in the current La Palma eruption have modest dimensions compared to other flows emitted throughout geological time. So far, the lava flow of the Cumbre Vieja volcanic apparatus covers about 250 hectares, with a maximum power in its advance front that does not reach 25 m.
The Roza stream, in the Columbia River region (States of Idaho and Oregon, USA), was emitted 15 Ma ago with a lava emission rate of 1 km³ / day. This stream has a length of 400 km, an average power of 50 m and covers an area of 40,000 km², 57 times the area of La Palma.
Invest in geological research
Geological research is making it possible to predict with greater precision when and where volcanic eruptions will take place, including the possible level of explosiveness. In addition, it has also made it possible to identify volcanic eruptions, some of them catastrophic on a terrestrial scale, which have not yet been observed by humans, but which will probably occur again.
Approaching to observe what happens in an erupting volcano is tremendously dangerous. However, it is possible to study extinct volcanic devices, partially eroded, in which their deposits and internal structures emerge.
The basic geological research carried out in extinct volcanoes, undertaken by a few researchers during the last decades, is contributing to the knowledge of the behavior of active volcanoes. That is the challenge facing the scientific-geological community today.
To paraphrase Derek Bok, rector of Harvard University between 1971 and 1991, “whoever thinks that investment in basic research is expensive and expendable, let him try ignorance.”
This article has been published in ‘
The Conversation‘.
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