View over the western flank of Cumbre ridge, La Palma island. As seen from Miradoro El Time on October 18, 2021. Day et al. (1999) indicated that the Cumbre Vieja may be in the initial stages of failure. The authors of the paper also said that the geological development of La Palma had undergone changes due to the southerly migration of the hotspot and the collapse of the earlier volcanoes. Subsequent to this, a triple-arm rift system had evolved with the eventual closing down of volcanic activity associated with two of the arms – the north-west and north-east rifts. The reasons can only be hypothesised. This caused the southern arm – the Cumbre Vieja – to be the sole location of volcanic activity. As a result, they postulated that the western flank may be in the initial stages of failure.

In October 2000, the British Broadcasting Corporation (BBC) transmitted a Horizon programme called "Mega-tsunami: Wave of Destruction", which suggested that a future failure of the western flank of Cumbre Vieja could cause a megatsunami. On 18 April 2013, the BBC transmitted a follow-up programme entitled Could we survive a Mega-Tsunami? The programme was presented in a "breaking news" reporting style. It painted a scenario in which the western flank of the Cumbre Vieja had collapsed and the initial wave had an amplitude of about 1,000 metres. The programme used computer generated graphics to present a story line that is based on a hypothesis. The programme interviewed several scientific personnel to give credence to the story. One scientist claimed, "This is a true story – only it hasn't happened yet!"

Day et al. (1999), Ward and Day (2001) and Ward and Day (2005) hypothesize that, during an eruption at some future date, the western half of the Cumbre Vieja — approximately 500 km3 (5 x 1011 m3) with an estimated mass of 1.5 trillion metric tons — will catastrophically fail in a massive gravitational landslide and enter the Atlantic Ocean, generating a so-called mega-tsunami.

There is controversy about the threat presented by the Cumbre Vieja. Moss et al.; (1999) reported that the western flank of La Palma is static and there is no indication that it has moved since 1949, confirming the dimensions provided by Bonelli-Rubio (1950).

Carracedo et al (2001) state that they consider the crack to be a surface expression which is of a shallow and inactive nature. They also indicate that it should be monitored, but consider the possibility that the edifice is unstable as being almost non-existent.

The Tsunami Society (2002) claim that the model used by Day et al.; (1999) and Ward and Day (2001), and Ward and Day (2005) is wrong. They cautioned about the claims made by Day et al.; and Ward and Day, stating that there is no evidence of a mega-tsunami having been generated by volcanic edifice failure.

Murty et al.; (2005) claim that it is almost impossible for a trans-oceanic tsunami to be generated in the basin of the Atlantic Ocean, which — if correct — supports the work by many other researchers that the failure of the western flank of the Cumbre Vieja would be unlikely to generate a "mega-tsunami".

Pérez-Torrado et al.; (2006) indicate that marine deposits located between 41 and 188 metres above sea level in the Agaete Valley of Gran Canaria resulted, when ~3 x 1010 m3 — one order of magnitude less than that of models of Day et al.; (1999), Ward and Day, (2001); and Ward and Day, (2005), — of volcanic material collapsed, forming the Güimar Valle on Tenerife ~830 ka and generating a tsunami. They indicate that this collapse is the only plausible source, and also report that there is no indication that the tsunami propagated beyond Gran Canaria. These deposits date from between 32,000 and 1,750,000 years ago.

Scientists at TU Delft in the Netherlands reported in 2006, that the section of the western flank of the Cumbre Vieja that was conjectured as potentially failing and falling into the Atlantic Ocean to create the hypothesised La Palma mega-tsunami was both too small in mass and volume, and far too stable to break away within the next 10,000 years. A 2008 paper looked into this very worst-case scenario, the most massive slide that could happen (though unlikely and probably impossible right now with the present day geology). They find wave heights in the range 10 to 188 metres in the Canary Isles themselves. But the waves interfere and dissipate as they head out into the Atlantic. They predict a height of 40 metres for some nearby island systems. For continents, the worst effects are in northern Brazil (13.6 metres), French Guiana (12.7 metres, Mid-Atlantic United States (9.6 metres), Western Sahara (largest prediction at 37 metres, and Mauritania (9.7 metres). This is not large enough to count as a megatsunami, with the highest prediction for Western Sahara comparable to the Japanese tsunami, so it would only be a megatsunami locally in the mid-Atlantic Ocean.

#LaPalma #CanaryIslands #CumbreVieja

INFO - WIKIPEDIA

свернуть