The Cumbre Vieja (; meaning "Old Summit") is an active volcanic ridge on the island of La Palma in the Canary Islands, Spain. The spine of Cumbre Vieja trends in an approximate north–south direction, comprising the southern half of La Palma, with both summit ridge and flanks pockmarked by dozens of craters and cones. The latest eruption began on 19 September 2021 in a forested area of Las Manchas locality known as Cabeza de Vaca. Voluminous lava flows quickly reached populated areas downslope, fanning out across settlements and banana plantations, destroying thousands of buildings and ultimately pouring over steep cliffs into the ocean to enlarge the island at several locations. The volcano went quiet on 13 December 2021, and on 25 December 2021, the local government declared the eruption to be over.
Cumbre Vieja erupted twice in the 20th century, in 1949 (Volcán San Juan) and in 1971 (Volcán Teneguía).
Volcanic history
La Palma is a volcanic ocean island located on the African Plate and is currently—along with Tenerife—one of the most volcanically active of the Canary Islands.Carracedo, J.C. 1996. "A simple model for the genesis of large gravitational landslide hazards in the Canary Islands". In McGuire, W: Jones, & Neuberg, J. P. (eds). Volcano Instability on the Earth and Other Planets. Geological Society, London. Special Publication, 110, 125–135. Since about 125,000 years ago (~125 ka), all subaerial eruptions on La Palma have been associated with the Cumbre Vieja, with eruptions ranging over the whole 25-kilometre-long ridge. Submarine surveys show that the Cumbre Vieja continues south of (the "Point of the Hot Source"), but no volcanic activity connected with the submarine extension has yet been observed. Historical eruptions on the Cumbre Vieja occurred in 1470, 1585, 1646, 1677, 1712, 1949, 1971, and 2021.
Detailed geological mapping shows that the distribution and orientation of vents and feeder dykes within the volcano have shifted from a triple rift system (typical of most volcanic ocean islands) to a single north–south rift.Carracedo, J. C; 1994. "The Canary Islands: an example of structural control on the growth of large oceanic-island volcanoes". J. Volcanol. Geotherm Res. 60, 225–241.Carracedo, J. C; 1999. "Growth, Structure, Instability and Collapse of Canarian Volcanoes and Comparisons with Hawaiian Volcanoes". J. Volcanol. Geotherm. Res. 94, 1–19. It is hypothesised that this structural reorganisation is in response to evolving stress patterns associated with the development of a possible detachment fault under the volcano's west flank. Siebert (1984)Siebert, L; 1984. "Large volcanic debris avalanches: characteristics of source areas, deposits and associated eruptions". J. Volcanol. Geotherm Res. 22, 163–197. showed that such failures are due to the intrusion of parallel and sub-parallel dykes into a rift. This causes the flanks to become over-steep and this inevitably causes the structure of the volcano to become unstable to the point that catastrophic failure may occur. There is no evidence beyond its surface expression that the 1949 section of the rift extends in a north–south direction, nor that there is a developing detachment plane. Research is ongoing.
1949 eruption
The only contemporaneous account of the eruption was published in 1950 by one of the scientists—Juan Bonelli-RubioBonelli-Rubio, J. M; 1950. "Contribucion al estudio de la erupcion del Nambroque o San Juan". Madrid: Inst. Geografico y Catastral, 25 pp. who witnessed the eruption first hand and recorded details of the various phenomena that occurred during the eruption. All other published accounts are based upon Bonelli-Rubio's observations. The next report regarding the eruption was a joint publication by Ortiz and Bonelli-Rubio published in 1951.Ortiz, J. R., & Bonelli Rubio, J. M; 1951. "La erupción del Nambroque (Junio–Agosto de 1949)". Madrid: Talleres del Instituto Geográfico y Catastral, 100 pp. This drew heavily on Bonelli-Rubio's observations and also analysis of various phenomena associated with the eruption. Both accounts are published in Spanish.
The eruption started on 24 June 1949, the feast day of St John, which is why in Spanish texts the eruption is referred to as , which in English is "The Eruption of the Nambroque or St John's volcano". During the 1949 eruption, eruptive activity was located at three vents—Duraznero, Llano del Banco, and Hoyo Negro—mild strombolian activity occurred at the Duraznero vent. Lava was erupted from the Llano del Banco vents, whilst only mild phreatomagmatic emissions occurred at the Hoyo Negro vent. Then on 30 July—the last day of eruptive activity, lava was erupted at the Duraznero fissure and vent. During the eruption on 1 and 2 July, two strong earthquakes with an estimated intensity of VIII on the Modified Mercalli Scale also occurred, the epicentre was calculated to be near Jedey. Following the earthquakes a fracture was noted and it had a length of approximately one and half kilometres. It was traceable to the Hoyo Negro and Duraznero vents, making a total length of about two and half kilometres or about 1/10 of the exposed length of the Cumbre Vieja, and parts of the western half of the Cumbre Vieja ridge had apparently moved about 1 metre sideways and 2 metres downwards towards the Atlantic Ocean. It was only in the vicinity of the Duraznero and Hoyo Negro vents that the vertical displacement attained about 4 metres. As of 2009, the fracture is still visible and still has the same dimensions recorded in 1949.
The timeline for the eruption, according to Bonelli-Rubio, is as follows: The first reported seismic activity was noted on the southern rim of the Caldera de Taburiente on 23 July 1936 at about 23:30 (11.30 pm) local time, with further activity noted over the next two days. During the following years periodic seismic activity occurred, but due to the absence of monitoring equipment, the only reports are those recorded in the media. Then at about 09:00 (local time) on 24 June 1949, the Duraznero vent opened with mildly explosive activity, venting of gases, and rocks; with eruptive activity continuing in this manner until 6 July. During this phase a strong earthquake occurred on 1 July and again on 2 July with an estimated intensity of VIII on the Modified Mercalli Scale. Visits to the summit region revealed a crack about 1.5 km (~1 mile) long which extended in a northerly direction from the ("Black Hole") and about 1 km (~0.5-mile) south to the Duraznero vent making a total length of about 2.5 km (~1.6-mile), (this crack is the subject of research and heated debate as to whether it indicates initial failure of the western flank—or not). Later analysis placed the epicentre north of the township of Jedey. Eruptive activity at the Duraznero vent ceased on 6 July with only degassing continuing. No eruptive activity occurred on 7 July. On 8 July eruptive activity commenced at the Llano del Banco vents—about 4 km (~2.8miles) north of the Duraznero vent, as lava was erupted and flowed down the western flank. The vents opened progressively up the barranco (ravine), forming a series of en echelon (diagonally side by side), vents. On 10 July the westward flow of lava from the Llano del Banco vents reached the coast at Puerto de Naos and entered the Atlantic Ocean, forming a lava delta, the velocity is estimated at ~14 metres (approximately 46 feet) per sec. On 12 July mildly explosive activity commenced at the Hoyo Negro (Black Hole) with emissions of rocks, fumes and some phreatomagmatic activity indicating that the eruption had encountered ground waters. Activity at the Hoyo Negro ceased on 22 July, but continued at the Llano del Banco vents until 26 July. Only residual fumarolic activity and thermal emissions then occurred until 30 July when the Duraznero vent and fissure re-activated. Lava then flowed from the Duraznero vent and fissure, filling the adjacent crater of El Fraile and created a lava lake. This subsequently overflowed and the lava flowed down the eastern flank towards the ocean. It finally stopped about 30m (about 100 feet) from the ocean. Also later, on 30 July all eruptive activity ceased and only residual fumarolic activity continued until 4 August; thereafter there was only thermal emissions. It is estimated that approximately 60 million cubic metres of lava was erupted during the eruption.Klügel, A; Schmincke, H –U; White, J. D. L; and Hoernle, K. A; 1999. "Chronology and volcanology of the 1949 multi-vent rift-zone eruption on La Palma (Canary Islands)". J. Volcanol. Geotherm. Res. 94, 267–282.
Volcanic explosivity index
The eruption style ranged from effusive—mildly explosive at the Duraznero and Llano del Banco vents—to mildly explosive at the Hoyo Negro vent and was strombolian in style. It is classed as having a volcanic explosivity index (VEI) of 2.
Earthquakes
The process creating the earthquakes of 1 and 2 July is considered to have been driven by the pressure caused by the rising magma super-heating water trapped within the edifice of the volcano.Day, S. J; Carracedo, J. C; Guillou, H. & Gravestock, P; 1999. "Recent structural evolution of the Cumbre Vieja volcano, La Palma, Canary Islands: volcanic rift zone re-configuration as a precursor to flank instability". J. Volcanol. Geotherm Res. 94, 135–167. It is unlikely that the trapped waters could vapourise due to being under considerable pressure. What is postulated is that the waters were heated to a point where they could not absorb further thermal energy in the available space. Continuing heating required the water to expand further and the only way it could do so was to move the flank of the volcano. This caused the two earthquakes that were reported as occurring during the eruption along with the development of the crack.
That the water entrapped within the edifice did not vapourise is shown by the absence of phreatomagmatic explosions except the mildly explosive eruptive activity that occurred at the Hoyo Negro vent from 12 to 22 July: steam escaping explosively from the ground is often a precursor of volcanic activity. Further evidence that vapourisation did not occur is that when Rubio Bonelli visited the rift the following day, the newly opened fissure "... Was not issuing fumes, vapour, steam, ashes, lava or other materials ..." In fact at no time during or after was steam or phreatomagmatic activity reported. This reinforces the claim that the waters trapped within the edifice never vapourised, which they would do if the pressure had fallen sufficiently to allow the super-heated water to flash into steam. Only at the Hoyo Negro did any phreatomagmatic activity occur. Unlike the northern sector of the island, the Cumbre Vieja is "dry". Unlike the northern sector there are no water galleries, and it is therefore unlikely that the earthquake was caused—as claimed by Day et al.; by water becoming superheated by rising magma. Research is continuing.
Due to the lack of seismic monitoring equipment on the island, any claims about seismic activity are based upon personal observation and may not be reliable.
1971 eruption The 1971 eruption occurred at the southern end of the Cumbre Vieja at the Teneguía vent. The eruption was mainly strombolian in style. Lava was erupted. Seismic activity did occur before and during the 1971 eruption but was not on the scale associated with the 1949 eruption. Residual thermal emissions continue.
2021 eruption