The Cumbre Vieja is an active volcanic ridge on the island of La Palma in the Canary Islands, Spain. It reaches a height of 1,949 m above sea level at the vent of La Deseada. The spine of Cumbre Vieja trends in an approximate north–south direction, and covers the southern half of La Palma, with both summit ridge and flanks pockmarked by over a dozen craters.
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 Punta de Fuencaliente (the "Point of the Hot Source"), but no volcanic activity connected with the submarine extension has yet been observed.
Cumbre Vieja, meaning 'Old Summit', is in fact older than its younger counterpart Cumbre Nueva, which in turn means 'New Summit.' This paradox is owed to the fact that in mainland Spain, rugged mountain ranges with sharper summits—such as the Cantabrian Mountains—were traditionally referred to as 'new', whereas softer, eroded landscapes—such as the Galician Massif—were referred to as 'old'. While this naming system is geologically accurate in mainland Spain, it has lead to an incoherent interpretation in the Canary Islands. Due to orographic similarity and not because of their geological genesis, the older, rugged mountain ridges of La Palma—the Caldera de Taburiente and Cumbre Nueva—were considered to be new, and the softer mountain ranges pockmarked by recent volcano eruptions—Cumbre Vieja—were considered to be old.
Eruptions in the last 7,000 years have originated from abundant cinder cones and craters along the axis of Cumbre Vieja, producing fissure-fed lava flows gushing abruptly to the sea.
~125 ka: Formation of the volcanic ridge of Cumbre Vieja.
6,050 BCE ± 1,500: Eruption.
4,900 BCE ± 50: Eruption.
4,050 BCE ± 3000: Eruption of l'Amendrita and Birigoyo.
1,320 BCE ± 100: Eruption of La Fajana.
360 BCE ± 50: Eruption of El Fraile.
900 CE ± 100: Eruption of Nambroque II-Malforada.
Subhistorical and historical eruptions
From the first contacts of the European navigators who first visited the Canary Islands around the 15th century, 18 eruptions have occurred, of which 7 took place on La Palma. They mostly produced light explosive activity and lava flows that damaged the populated areas. On every occasion, alcaline basaltic lavas were emitted: true basalts, ankaramites and/or basanitoids. A differentiation process always took place in the magma chamber and a sequence from amphibole to olivine-bearing lavas was erupted. These variations of the chemistry and mineralogy of the lavas were related to the different stages of the eruption and the height over sea level where the corresponding eruptive vents opened. The duration of these historic eruptions ranges between 1 and 3 months, and the area covered with lava and pyroclasts is 39 km², 5.5% of the total surface of the island.
The 7 historic eruptions of La Palma have occurred in the southern half of the island, known as Cumbre Vieja, which spans from El Paso to the southernmost tip of the island in Fuencaliente. All eruptions began after a more or less prolonged period of earthquakes, whose magnitude never exceeded 6 on the Richter scale. These quakes were always restricted to some zones of the island, and increased their intensity and frequency on the days and hours preceding the eruptions. The eruption starts with the opening of little fissures of the ground following directions prefixed by the main structural patterns of the island. From the first moments, this fissuration is accompanied by the emission of gases and small lava fountains from several points along the whole extension of the main fissure that can attain several kilometers in length. Within a short time during the first hours of the event, these multiple incipient volcanic vents remain restricted to a few ones, increasingly active, where the construction of heaps of tephra increasingly grow and coalesce to the typical volcanic cones with their corresponding craters.
When the fissure opens in a terrain with a considerable slope and in its direction, high pressure lava fountains, pyroclastic materials and gases are emitted from the higher volcanic vents, while from the lower vents only more or less degasified lava pours out with a much lower explosivity. This pattern is more noticeable when the difference in height of the volcanic vents is greater, and the duration of the eruption is long-lived. In the most typical instances, the higher vents grow to volcanic cones a couple of hundreds of meters, while in the lower ones, only some eruptive fissures with outpouring lava remain. This pattern is very clear in eruptions such as that of Tigalate, El Charco, San Juan and Tajogaite, where the difference in height of the vents is very noticeable.
During the course of the eruption, it is also frequent that secondary cracks and fissures develop near the main volcanic vents, following also the main structural trends of the island.
The eruption continues with changes in the activity of the several vents, until suddenly and without a marked and gradual decrease of the explosivity and lava outpour, the activity practically ceases. Subsequently, the entire eruptive area suffers a period of slow degasification, gradually becoming weaker in the following 2 or 3 years. After this period, all volcanic manifestations cease, starting a new eruption, after an irregular period of time that normally lasts for several years, in other parts of the same island.
Subhistorical eruptions are represented by a single event:
Tacande, Tacante or Montaña Quemada: VEI 2, 1470-92, 462 ha (unknown duration).
Historical eruptions on La Palma occurred as follows:
Tehuya, Tahuya, Tihuya, Roques de Jedey or Los Campanarios: VEI 2, 1585, 24×10⁶ m³, 400 ha, 84 days.
San Martín, Tigalate or Tagalate: VEI 2, 1646, 26×10⁶ m³, 610 ha, 82 days.
San Antonio: VEI 2, 1677-78, 66×10⁶ m³, 446 ha, 66 days.
El Charco or Montaña Lajiones: VEI 2, 1712, 41×10⁶ m³, 535 ha, 56 days.
San Juan (western vent of Llano del Banco and eastern craters of Nambroque, Hoyo Negro and Duraznero—the latter two jointly known as Las Deseadas): VEI 2, 1949, 51×10⁶ m³, 392 ha, 47 days.
Teneguía: VEI 2, 1971, 31×10⁶ m³, 317 ha, 24 days.
Tajogaite: VEI 3, 2021, 215×10⁶ m³, 1,237.3 ha, 85 days and 8 hours (Sept. 20 14:11 UTC—Dec. 13 22:22 UTC).
Magmatic activity underneath Cumbre Vieja
Partial fusion of the mantle occurs in the superior section of the upper mantle, between depths of 70 and 40 km. 3% magma is produced, and the remaining 97% is composed of peridotitic rock derived from the Earth's mantle. From 40 km upwards, the build-up of liquid rock is higher, with magma comprising about 10 to 15%. The rising diapirs intrude into fissures up until depths of 30 km, creating small magma pockets which exert an elevated pressure and create earthquakes. Between 30 and 15 km below the island, few earthquakes occur. Most earthquakes in La Palma are recorded between 15 and 10 km depth, at the Mohorovičić discontinuity, where the boundary between the oceanic crust and the Basal Complex of the island is located. A great concentration of magma is located here, which exerts high pressures on the oceanic crust and the insular edifice which fractures the crust and creates fissures, resulting in earthquakes.
Landslide and mega-tsunami misconception
Detailed geological mapping shows that the distribution and orientation of vents and feeder dykes within the Cumbre Vieja volcano have shifted from a triple rift system (typical of most volcanic ocean islands) to a single north–south rift. 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. 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, leading to a giant landslide along the detachment fault which trigger a potentially huge tsunami. 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.
One such mega-tsunami resulted when ~3×10¹⁰ m³ of volcanic material collapsed, forming the Güímar Valle on Tenerife ~830 ka, leaving marine deposits located between 41 and 188 metres above sea level in the Agaete Valley of Gran Canaria. So, while it is true that such landslides have occurred in the past on most of the Canary Islands, it is important to note that these events are rare and occurred at large time intervals spanning many tens of thousands of years, and that it is almost impossible for a trans-oceanic mega-tsunami to be generated in the basin of the Atlantic Ocean by a failure of the western flank of the Cumbre Vieja.
Unfortunately, most media are driven by sensationalism and report about it as if there was strong evidence that such a partial collapse of La Palma could occur in the somewhat near future—including potential horror scenarios such as mega-tsunamis devastating the east coast of the United States. There is, however, no scientific evidence to support this scenario. In fact, the section of the western flank of the Cumbre Vieja is far too stable to collapse within the next 10,000 years.
The Güímar landslide is—reportedly—the only plausible source for the marine deposits in Gran Canaria’s Agaete Valley, but there is no indication that the tsunami propagated beyond Gran Canaria. In the worst-case scenario for La Palma, with the most massive slide that could happen, the waves would dissipate as they propagate into the Atlantic. A height of 40 m is predicted for some nearby island systems. For continents, the worst effects are in northern Brazil (13.6 m), French Guiana (12.7 m), Mid-Atlantic United States (9.6 m), Western Sahara (37 m), and Mauritania (9.7 m). This is not large enough to count as a mega-tsunami, with the highest prediction for Western Sahara comparable to the 2011 Japanese tsunami, so it would only be a mega-tsunami locally in the mid-Atlantic Ocean.
Nevertheless, as was mentioned earlier, a failure of the western flank of Cumbre Vieja is extremely unlikely and probably impossible right now with the present-day geology.