Cumbre Vieja - Future Threats

Future Threats

In October 2000, the BBC transmitted “Mega-tsunami; Wave of Destruction”, which suggested that a future failure of the western flank of the Cumbre Vieja would cause a "mega-tsunami".

Day et al. (1999) and Ward and Day (2001) hypothesize that during an eruption at some unascertained future time, the western half of the Cumbre Vieja—approximately 500 km3 (5 x 1011 m3) with an estimated mass of 1.5 x 1015 kg—will catastrophically fail in a massive gravitational landslide and enter the Atlantic Ocean, generating a so-called 'mega-tsunami'. The debris will continue to travel along the ocean floor as a debris flow. Computer modelling indicates that the resulting initial wave may attain a local amplitude (height) in excess of 600 metres (1,969 ft) and an initial peak to peak height that approximates to 2 kilometres (1 mi), and travel at about 1,000 kilometres per hour (621 mph) (approximately the speed of a jet aircraft), inundating the African coast in about 1 hour, the southern coast of England in about 3.5 hours, and the eastern seaboard of North America in about 6 hours, by which time the initial wave will have subsided into a succession of smaller ones each about 30 metres (98 ft) to 60 metres (197 ft) high. These may surge to several hundred metres in height and be several kilometres apart while retaining their original speed. The models of Day et al. and Ward and Day suggest that the event could inundate up to 25 kilometres (16 mi) inland. This would greatly damage or destroy cities along the entire North American eastern seaboard, and tens of millions would be killed as Boston, New York City, Miami, and many other cities located near the Atlantic coast are leveled.

Detailed geological mapping shows that the distribution and orientation of vents and feeder dykes within the volcano have shifted from a triple rift system (typical of most oceanic island volcanoes) to one consisting of a single north-south rift. It is claimed that this structural reorganisation is a response to evolving stress patterns associated with the development of a possible detachment fault under the volcano's west flank. Siebert (1984) showed that such failures are due to the intrusion of parallel and sub-parallel dykes into a rift. Eventually the structure becomes unstable and catastrophic failure occurs. There is no evidence that the 1949 section of the rift extends in a north-south direction or that there is a developing detachment plane. Research is ongoing.

There is controversy however, about the threat presented by Cumbre Vieja. Current indications are that recent landslides may have been gradual, and therefore may not generate tsunamis unless they increased in magnitude. Studies of possible local 'mega-tsunamis' 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.

Sonar surveys around many volcanic ocean islands including the Canary Islands, Hawaii, Réunion etc., have mapped debris flows on the seafloor. Many of these debris flows are about 100 kilometres (62 mi) long and up to 2 kilometres (1 mi) thick, contain mega-blocks mixed up with finer detritus.

Moore (1964) was the first geologist to interpret such features depicted on a United States Navy bathymetric chart. The chart showed two features that seemed to originate from the Hawaiian islands of Oahu and Molokai.

In recorded history, the Krakatau eruption generated devastating tsunami, yet the damage was local and did not propagate across long distances. This may have been due to the confining geography of the areas.

Approximately 3615 years ago, the volcano on Santorini exploded with a VEI estimated at 7. Research suggests that the eruption generated a tsunami which inundated Crete, possibly triggering the downfall of the Minoan civilization.

An earthquake and landslide in Crillon Inlet at the head of Lituya Bay, Alaska, on 9 July 1958 generated a 'mega-tsunami' with an initial amplitude (height) of ~525 metres (1,722 ft), which stripped trees and soil from the opposite headland and inundated the entire bay, destroying three fishing boats anchored there and killing two people. Once the wave reached the open sea, however, it rapidly dissipated.

Lateral collapse events at stratovolcanoes, similar to the current threat posed by the western flank of Cumbre Vieja, could increase due to the physical effects of global warming on the Earth from increases in deviatoric stress from post-glacial rebound, while the size and frequency of eruptions are also likely to increase.