Cumbre Vieja
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Cumbre Vieja (Spanish: "Old Summit") is a volcanic ridge on the island of La Palma in Spain's Canary Islands.
This ridge passes roughly in a north-south direction and covers the southern third of the island. It is lined by several volcanic craters. Location: .
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[edit] 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.
[edit] 1949 eruption
During the 1949 eruption, a two kilometer-long fracture opened and parts of the western half of the Cumbre Vieja ridge slipped several meters downwards towards the Atlantic Ocean. The fracture 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 vaporizing water trapped within the structure of the island.
[edit] 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 tons, will slide into the ocean -- a so called "lateral collapse". Should that happen, the resulting megatsunami would reach local heights of well over 300 meters 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 eight. This could greatly damage if not completely destroy cities along the United States' east coast, such as New York, Boston, Washington, DC, Norfolk, Virginia, and Miami with 25 to 30m 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 at Cumbre Vieja, with indications that usually the landslides there are gradual, and unlikely to generate tsunamis. Others, who have studied localized megatsunami in the Hawaiian Islands, draw distinctions between the tsunami wave periods caused by landslides and subduction-zone earthquakes, arguing that a similar collapse in Hawaii would not endanger Asian or North American coastlines. [2]
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). In recorded history, the Krakatoa and Santorini eruptions have generated devastating and deadly tsunamis, yet the damage was local and did not propagate across long distances. 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.
As of 2004, there is very little seismological monitoring of Cumbre Vieja in progress.
[edit] External links
[edit] Information and sources
- Discussion
- Benfield Hazard Research Center: Why the only certainty about the La Palma tsunami is that it will happen
- Benfield HRC Q&A
- Pictures of Cumbre Vieja
- A rebuttal of Cumbre Vieja
- Another rebuttal of the possible disaster
[edit] 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.
