Volcano Watch: The hypothesis of the “mega-tsunami” of the Canary Islands and why it does not carry water


The recent eruption of La Palma in the Canary Islands has sparked speculation that the volcano could collapse, creating tsunamis that would devastate the east coast of North and South America. But is such a scenario possible or probable?

“Volcanoes watchers” are probably aware that an eruption started in La Palma in the Canary Islands on September 19. The eruption style is similar to Hawaiian eruptions, and both locations share the potential for flank collapses and tsunamis.

Islands in the basaltic ocean, such as the island of Hawaii and the Canary Islands, tend to experience catastrophic landslides every few hundred thousand years – a discovery made for the first time by the scientist in charge of the USGS Hawaiian Volcanoes Observatory, Jim Moore, in the early 1960s. A significant portion of an island is removed during collapse and has the potential to displace huge amounts of water of sea, generating local tsunami waves that are said to be over 100 meters (300 feet) in height. From this understanding arose the idea that the collapse of volcanoes – particularly in the Canary Islands – could generate an ocean-wide “mega-tsunami”.

In 2001, an academic article suggested that the collapse of La Palma could cause tsunami waves up to 25 m (about 80 feet) high along the eastern coasts of North and South America. This scenario made headlines in the media, which inaccurately portrayed a huge wave devastating New York City.

But can collapses really generate these “mega-tsunamis” far from their sources? Further research casts doubt on this idea.

The Canary Islands ‘mega-tsunami’ scenario assumed a single, cohesive and massive collapse block that reached high speed very quickly. Mapping of the ocean floor surrounding the Canary Islands, however, indicates that the collapses are rather occurring in an incremental or piecemeal fashion. In addition, geomorphologists have discovered, through slope stability analysis, that the potential collapse volume is much smaller than what was simulated by the 2001 article.

Tsunami modeling has also advanced considerably since 2001. Studies of landslide-induced waves show that they move at different speeds and interact more over long distances, leading to a smaller wave height. far from their sources. Better knowledge of ocean bathymetry, island and coastal topography, and energy transfer between landslide blocks and water also contributed to more accurate modeling.

These new simulations suggest that the maximum wave heights along the east coast of the Americas from a “worst case” La Palma collapse would be in the range of 1-2 m (3-7 feet) – still dangerous, but similar to a common storm surge.

A lack of geological evidence also calls into question the “mega-tsunami” hypothesis. Tsunamis leave characteristic sediment deposits on the coasts they impact. But no such deposit has ever been identified on the east coasts of North and South America.

Canary Island volcanic collapses are rare, occurring on timescales of hundreds of thousands of years, and should be preceded by signs of flank instability: increased earthquakes and deformation of the ground surface. Volcanoes in the Canary Islands also erupt regularly – La Palma last erupted in 1971 and 1949 – and slope stability analyzes conducted in La Palma indicate that the structure is stable. The volcano is expected to grow significantly before a collapse is likely.

This abundant evidence refutes the “mega-tsunami” hypothesis, showing that it does not withstand rigorous scrutiny. However, tsunamis generated by volcanoes are a real process and a significant threat. For example, the 1883 explosive eruption of Krakatau, Indonesia, triggered a local tsunami that killed tens of thousands of people on nearby coasts. In 2018, a smaller eruption and the collapse of Anak Krakatau, an island that developed into the 1883 caldera, also resulted in a local tsunami that left hundreds dead.

Local tsunamis can also be generated by other volcanic processes. On the island of Hawaii, the collapse of the lava delta at the inlets to the lava ocean can cause small tsunamis that impact areas adjacent to the delta. A slide on the underlying fault in the southern flank of Kilauea, associated with the M7-8 earthquakes, caused a local tsunami in 1868 and 1975 that left people dead. These are processes that have occurred several times in the history of mankind; they will happen again and the dangers associated with them deserve our attention.

While the scientific view of the “mega-tsunami” hypothesis has evolved over the years since 2001, this original work has led others to initiate investigations that have contributed to new knowledge that has improved our understanding of landslides. terrain and tsunamis generated by volcanoes. In this way, the story is a wonderful example of exactly how science happens.

Volcano activity updates

The Kilauea volcano is erupting. Its USGS volcanic alert level is at WATCH (https://www.usgs.gov/natural-hazards/volcano-hazards/about-alert-levels). Kilauea updates are released daily.

Lava continues to emerge from a single vent in the western wall of Halema’uma’u Crater. All lava activity is confined to Halema’uma’u Crater in Hawaii Volcanoes National Park. Sulfur dioxide emission rates remain high and were estimated at around 2,700 tonnes per day on October 17. Seismicity is high but stable, with few earthquakes and an ongoing volcanic tremor. Summit inclinometers have remained relatively stable over the past week. For more information on the current eruption of Kilauea, see Recent Eruption (usgs.gov).

Mauna Loa is not erupting and remains at the ADVISORY volcanic alert level. This alert level does not mean that a rash is imminent or that progression to a rash from the current level of unrest is certain. Mauna Loa updates are released weekly.

Last week, around 114 low-magnitude earthquakes were recorded beneath the summit and upper elevation flanks of Mauna Loa – the majority of them occurred at depths below 10 kilometers (6 miles). Global Positioning System measurements show no major distortions over the past week. The gas concentrations and the temperatures of the fumaroles at the summit and at the sulfur cone in the southwest rift zone remain stable. The webcams do not show any change in the landscape. For more information on the current monitoring of Mauna Loa, see: https://www.usgs.gov/volcanoes/mauna-loa/monitoring.

There have been 9 events with 3 or more felt reports in the Hawaiian Islands in the past week. Here is the list of felt events of magnitude 3 and above: an M3.6 earthquake at 91 km (56 mi) WNW from Kalaoa at 7 km (4 mi) deep on October 17 at 10:56 p.m. HST, an M3. 1 earthquake 4 km (2 mi) southwest of Pahala 36 km (22 mi) deep on October 17 at 7:34 p.m. HST, an M3.3 earthquake 4 km (2 mi) at l east of Pahala at 35 km (21 mi) depth on October 17 at 12:58 p.m. HST, an M3.8 earthquake 2 km (1 mi) south of Pahala at 37 km (23 mi) deep on October 17 at 5:52 a.m. HST, an M3.2 earthquake 4 km (2 mi) ENE of Pahala at 0 km (0 mi) depth on October 16 at 5:41 p.m. HST, an M3.0 earthquake 5 km (3 mi) SSW of Pahala 32 km (19 mi) deep on October 16 at 2:08 p.m. HST, an M3.0 earthquake 4 km (2 mi) S of Pahala at 33 km (20 mi) deep on October 16 at 13:35 HST, and an M3.6 earthquake 10 km (6 mi) east of Pahala at a depth of 31 km (19 mi) on October 15 at 12:03 am HST

The HVO continues to closely monitor the ongoing eruption of Kilauea and Mauna Loa for any signs of increased activity.

Please visit the HVO website for past Volcano Watch articles, Kilauea and Mauna Loa updates, photos of volcanoes, maps, information on recent earthquakes, and more. Email your questions to [email protected]

Volcano Watch is a weekly article and activity update written by scientists and affiliates of the US Geological Survey Hawaiian Volcano Observatory.

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