12 July 2017
Understanding the La Palma mega-landslide hypothesis: part 1
As I noted in an earlier post, I spent a part of last week on the island of La Palma in the Canary Islands. Whilst my visit was to mark the opening of the GOTO telescope in my Vice-President role, I also took two days to explore the supposed mega-landslide that, it has been suggested, could generate a huge and very damaging tsunami. I have noted before that I do not subscribe to this hypothesis, but welcomed the opportunity to explore the site. In this and at least one subsequent post I will try to explain the mega-landslide hypothesis, and will also seek to outline why I do not think it stands up to scrutiny.
The La Palma volcanoes
The Google Earth image of La Palma below shows the main features of the island. I have provided an annotated version on the left alongside an unannotated version for clarity:-
The main features are, first, the Taburiente Volcano to the north. This is a large shield volcano that reaches almost 2500 metres above sea level (and thus about 6500 m above the sea floor). This started to form about 2 million years ago, and slowly extended to the south to form a ridge, called Cumbre Nueva. This is the Taburiente Volcano from the south:-
About 560,000 years ago the Cumbre Nueva ridge underwent a giant landslide, when up to 200 cubic kilometres of the volcano slipped towards the west into the ocean, leaving the giant Cumbre Nueva scarp. This feature can be clearly seen in the satellite image and in the photograph above, and is more obvious in the image below. The presence of this giant landslide has also been detected in the offshore bathymetric data. It is likely that this event generated a large local tsunami, but as far as I am aware no evidence has been found of a tsunami deposit from this event beyond the Canary Islands.
The easterly winds cause clouds to form as the air rises up the slopes of the volcano. These clouds then tumble over the landslide scar to form the cloud waterfall shown above.
Bejenado volcano erupted into the scar left by the Cumbre Nueva landslide, blocking a part of the drainage from Taburiente. This led to rapid erosion and formation of the enormous Calder de Taburiente, which can be seen in the image below:-
Thereafter volcanic activity has been mainly focused on the volcanoes to the south, which form the Cumbre Vieja ridge. These volcanoes remain active, and indeed erupted in both the 1940s and the 1970s. It is this part of La Palma that, it has been suggested, may be structurally unstable. This image shows one of the many volcanic cones along Cumbre Vieja:-
Note the major lava flow at the foot of the volcano.
In the next post I will explore the idea that the Cumbre Vieja volcano system may undergo a flank collapse event.