Cumbre Vieja (Spanish: "Old Summit") is a volcanic ridge on the island of La Palma in Spain's Canary Islands.

Volcanic history

La Palma is not only the steepest island in the world but has also been the most volcanically active of the Canary Isles in the past 500 years. The last few eruptions in the ridge were in 1470, 1585, 1646, 1677, 1712, 1949, and 1971.

1949 eruption

During the 1949 eruption the western half of the Cumbre Vieja ridge slipped several metres downwards into the Atlantic Ocean. This also opened a two-kilometre-long fracture which can quite easily be seen to this day. It is believed that this process was driven by the pressure caused by the rising magma heating and vaporising water trapped within the structure of the island.

Future threat

Scientists warn that in some future eruption within the next few thousand years the western half of the island, approximately 500km³ of land weighing an estimated 500 billion tonnes, will slide into the ocean -- a so called "lateral collapse ". Should that happen, the resulting megatsunami would reach local heights of well over 100 metres and the speed of a jetliner, reaching the African coast in three hours, the coast of England in five, and the eastern seaboard of North America in twelve. This could greatly damage cities along the United States' east coast, such as New York, Boston, Washington, DC, Norfolk, Virginia, and Miami with 10 to 25 m high waves. It is observed that, over the last several thousand years, the distribution and orientation of vents and feeder dykes within the mountain have shifted from a triple rift system (typical of most oceanic island volcanoes) to one consisting of a single N-S rift with westward extending vent arrays. Some argue that these structural re-organizations are in response to evolving stress patterns associated with the growth of a detachment fault under the volcano's west flank.[1]

There is controversy about the seriousness of the threat, with indications that usually the landslides there are gradual, thus not likely to generate tsunamis. An earthquake and landslide in Crillon Inlet at the head of Lituya Bay on July 10, 1958 generated a monstrous megatsunami more than 500 m high, which stripped trees and soil from the opposite headland and consumed the entire bay, destroying three fishing boats anchored there and killing two people. By the time the wave reached the open sea, however, it dissipated quickly. Scientists have now identified the island of La Palma as such a potential hazard. History has also documented large and damaging tsunamis from far smaller lateral collapses of stratovolcanos and residual debris found on the seafloor does provide evidence of their abundance in recent geological time (see Storegga Slide).

As of 2004, very little seismological monitoring of Cumbre Vieja is being carried out.

External links

Information and sources

• Benfield Hazard Research Center: Why the only certainty about the La Palma tsunami is that it will happen
• Benfield HRC Q&A
• Pdf giving details
• Pictures of Cumbre Vieja
• discussion
• iberianatureA skeptical review of Cumbre Vieja

Press articles

• CNN: Scientists warn of massive wave
• BBC: Expert says threat is being ignored.
• BBC: Threat is stated to be a worse case scenario; it might not happen.