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Geology and Tectonics of La Palma

Updated: 2 days ago


Llano de los Jables in northern Cumbre Vieja, with the Caldera de Taburiente in the background and Valle de Aridane covered by a sea of clouds, bordered to the right by the Cumbre Nueva.

La Palma, historically known as San Miguel de La Palma, is the most north-westerly island of the Canary Islands, Spain. La Palma has an area of 708 km², making it the fifth largest of the eight main islands of the archipelago. Like the others, it is a volcanic ocean island located on the African Plate. La Palma is currently, along with Tenerife, the most volcanically active of the Canary Islands.


The main geographic feature of the northern part of La Palma is the Caldera de Taburiente, measuring 9 km wide and 1,500 m deep. It is surrounded by a circular range of mountains reaching 1,600 m to 2,400 m in height. Erosion has partially uncovered the seamount in the caldera. The only ravine leading into the interior of the caldera is the deep Barranco de las Angustias ('Ravine of Anxiety'). The exterior of the caldera is cut by many gorges which run from 2,000 m above sea level down to the sea. South of the Caldera de Taburiente runs the ridge of Cumbre Nueva ('New Summit'). Yet further south runs the Cumbre Vieja ('Old Summit', which despite its name is geologically newer than Cumbre Nueva), a volcanic ridge formed by numerous volcanic vents built of lava and scoria, and makes up the southern part of La Palma.


Geology and tectonics

The Canary Islands were formed as seamounts through submarine volcanic activity, and as volcanic activity continued, they emerged above the sea level. La Palma rises almost 7 km above the sea floor of the Atlantic Ocean; most of its volcanic structure is located underwater, its base being located almost 4,000 m below sea level, and its highest peak reaches 2,426 m above sea level. On the island, two volcanic domains can be distinguished: the rounded northern third, or Taburiente domain, and the elongated dorsal domain from Taburiente to the southern tip of the island.


The Taburiente domain is an enormous truncated cone with a quasicircular plant that currently rises to 2,426 m (Roque de los Muchachos), with a colossal central arcuate depression formed by heavy erosion: the Caldera de Taburiente. It was formed by the consecutive superposition of different stratovolcanoes due to progressive reactivation. Since the island emerged, successive volcanic activity has piled up materials to heights of over 3,000 m above sea level. The reactivation of the central volcano has resulted in the circular shape that characterizes the domain. The entire subaerial phase rested on the underwater volcanic materials that constitute the so-called Basal Complex (4 mya).


This formation eventually surpassed the sea level and was subsequently intruded by gabbros and dikes which were the magma chambers and conduits of the following eruptions. The first subaerial emissions constitute the so-called Garafía volcano (1.77 mya), which was mainly composed of basaltic flows intruded by basic vertical and subvertical dikes and largely covered by posterior volcanic phases. On top of this formation developed the Taburiente volcano (1.10 mya), with a thick lower section of agglomerates and basic slide breccias that covered almost the entire emerged island. A large pile of basaltic flows was formed above it. Subsequently, the upper section (1.1-0.80 mya) was emitted, with a similar composition to the previous one and crowned by frequent strombolian cones, also basaltic, some of them hydromagnetic. Finally, a subrecent phase (0.80-0.71 mya) of phonolytic and tephritic cones was produced.

Geological units of La Palma, based on information contained in the viewer of IDECanarias.

About half a million years ago, at the end of the construction of the Taburiente complex, the accumulation of material on the southern flank must have been so great that, due to gravitational instability or increasing lithostatic pressure, a great collapse occurred, known as the Aridane slide. The volume of the mobilized material has been estimated between 180-200 km³ and it is located at the bottom of the sea covering the slope of the island. The resulting depression created the Aridane Valley, which was occupied by the Bejenado volcano (1,854 m) emitted 0.530 mya, which was sustained by the materials that were left uncovered from the substrate of the Basal Complex. Phonolithic lava flows were emitted. Bejenado has steep slopes, the center of which must have been located further north, inside the Caldera. The rapid erosive widening of the caldera and the possible landslides it suffered have completely dismantled the northern flank of this building. The maximum thickness on the underwater substrate of the Basal Complex is about 600 m at Pico Bejenado.


On the sides of the mouth of the Las Angustias ravine there are thick deposits of sand and gravel that form two large walls. They extend upstream to the area of La Viña, and have a maximum thickness of about 300 m. The resulting sedimentation on reaching the edge of the sea forms a fan delta. In the lower parts of the deposit there are phonolytic lava flows interspersed, with a composition similar to that of the Bejenado building, which leads us to believe that both events were, in part, simultaneous.


The entire Taburiente Domain is, at present, totally inactive, and has probably not had any eruptions in the last 125 ka. Volcanism migrated southwards through the eruptive fissure of the Dorsal or Cumbre Vieja.


The dorsal domain corresponds to the southern half of the island and is structured by an eruptive axis in a north-south direction, in which two sectors with well-defined reliefs can be clearly distinguished: Cumbre Nueva, or northern sector, with a very regular height of around 1,400 m, a length of about 7 km and an arched shape. Cumbre Vieja, or southern sector, which constitutes a volcanic structure that reactivates towards 0.123 mya through the 21.5 km long N-S rift that builds what is called the Cumbre Vieja Ridge. The six historical eruptions (last 500 years) on the island have taken place on this ridge, the last two in the 20th century (1949 and 1971). It is mainly formed by the concentration of fissures and the rift zone, which individualize two very pronounced slopes, eastern and western. At all times, the lava flows ran along the sides and reached the coast most of the time, occupying the seabed and fossilizing the previous cliff which is now seen as a paleo-cliff. The materials that were emitted are mainly basic alkaline lava flows (alkaline basalts, basanites, trachyba-salts and tephrites) and strombolian-type pyroclastic deposits. There are also a significant number of phonolytic domes scattered over the rift, such as the Teneguía dome that gave its name to the forelast eruption on the island. The current seismicity of the island is clearly associated with this Cumbre Vieja ridge.

 

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