Tsunami La Palma

A theory has been presented that a volcanic eruption could heat the water that is within the Cumbre Vieja and make it explode.  Fortunately, the explosion of water vapor in the interior of a volcano or caldera is a rather rare phenomenon, since it usually causes the formation of geysers instead.  In some cases on the Canary Islands (as in Lanzarote) this is a possibility, although dry weather is necessary so that water thrown into the opening can cause the eruption of steam.

The eruption of 1949 supports this theory.  This eruption showed how a flaw was opened, causing the southern part of the island to sink four meters into the Atlantic.   In some cases it is possible to generate a tsunami of catastrophic dimensions.

Furthermore, other scientists believe some eruptions may not generate a tsunami, or will generate one of only low intensity, but will cause fragmentation.  This was the case in 1949, when the western area of the island fragmented into small parts.  In any case, most scientists agree there is no evidence today suggesting that this could happen in the coming decades.

The geological history readily ascertainable on the island of La Palma supports this idea.  While La Palma is a very volcanic island with hundreds of craters of all sizes and types, a huge explosion on the island is not expected because there is no magma chamber common to all these craters.  The eruption of a volcano on La Palma does not usually affect the other volcanoes that are close-by, suggesting that the expansive force of the eruptions would have to allocate a large number of openings to affect the whole island.

In a documentary for the BBC Horizon series issued on October 12, 2000, two geologists (Day and McGuire) cited the gap as evidence that half of the Cumbre Vieja had slipped into the Atlantic Ocean (Day et al., 1999, Ward and Day, 2001).  They suggested the pressure caused by rising magma heating the water trapped within the structure of the island ultimately caused the sinking.

The assumption is that a future eruption at the western flank of Cumbre Vieja, with a mass of about 1.5 x 15 kg, could cause the mass to slide into the ocean.  This could trigger a giant wave called a “megatsunami” with a height of 900 meters in the region of the islands.

The wave would move across the Atlantic and inundate the eastern seaboard of North America, hitting the United States of America, the Caribbean and the northern coast of South America some six to eight hours later.  They believed that the tsunami waves would probably reach 1000 feet or higher and would cause huge devastation along the coasts.

Representations in models indicate that the tsunami could inundate up to 25 km inland, depending on the topography.  The theory of Ward and Day (1999) should have resulted in the collapse of a much larger portion of the western flank; the cracked surface that is currently visible suggests the geological mapping of Day et al 1999 was faulty.  This paper argues that much of the western flank was built on the scar of a previous fall, and therefore sits on unstable debris.

This was also the subject of a docu-drama on the BBC called End of Days, which went through several scenarios of disastrous proportions.

However, the Tsunami Society (Carayannis, 2002), issued a statement that “… We would like to halt the scaremongering from these unfounded reports …” The main points raised in this report include:

The assertion that half of Cumbre Vieja fell 4 meters in the 1949 eruption is wrong, and contradicts the physical evidence.
It has not been discussed or shown that there is a dividing line that separates a “block” of La Palma from the other half.
Physical Evidence shows a line of 4 km long in the rock, but the models are a line of 25 kilometers, for which there is no physical evidence. Furthermore, no evidence indicates that the line of 4 km in length extends beyond the surface. There has never been a megatsunami in Atlantic history.

There are other studies also in disagreement with the hypothesis of Day and others (1999) and Ward and Day (2001).

However, there is a consensus by geologists and volcanologists that the “building” of a volcanic island may undergo major changes, lifting or subsidence and may have produced large tsunamis in the Atlantic Ocean in the geological past.  Despite this there is still no reliable evidence to prove a cause and effect.  All documents on the large-scale tsunamis in the Atlantic show the tsunamis have been attributed to earthquakes and not volcanoes.  One such case is the collapse of Port Royal in Jamaica.

Evidence of tsunami deposits have been reported from the Caribbean and the Canary Islands.  Since the 1990s the area has been (and remains) stable and movement has not detected.  Follow-up studies conducted in 2008 show that the dimensions of the island agree with those recorded in 1949.  This indicates the block has not moved since 1949.