The Geological and Mining Institute of Spain (IGME-CSIC) and the Complutense University of Madrid have launched the first Global Catalog of Historical Megatsunamis (GHMCat), in which the 40 documented events from 1674 to the present with at least 35 meters of maximum wave height are collected, in order to know the impacts of these phenomena given its increase due to climate change.
The catalog includes descriptions of maximum wave heights, causes and sources, according to available data and with the main bibliographic references that support the data collected.
This inventory, recently published in the scientific journal GeoHazardsreveals that megatsunamis originate from massive landslides or large rock avalanches, sometimes induced by large earthquakesand details its location and geographical distribution, with a notable concentration in the glacial fjords of Alaska and Norway.
Likewise, warn about the Potential increase in these extreme events in glacial areas, as a direct consequence of global warming.
The study by IGME-CSIC and the UCM began with the analysis of the relationship between the maximum heights of the waves and the causes of historical tsunamis documented in the world – mainly caused by earthquakes (75%) and landslides (14%). – and shows that those of seismic origin rarely generated waves of more than 20 meters. Above 30 meters, the vast majority were caused by subaerial or submarine landslides.
forty events
The research proposes a definition of megatsunami, based on objective criteria of the maximum height reached by the waves, 35 meters or more. This threshold distinguishes an exclusive group of 40 events, representing 1.5% of all documented historical tsunamis.
They were used as main sources of information the two existing global historical tsunami databases, completed with numerous publications. In these bases there are about 2,800 recorded events, 700 of them with waves more than one meter high.
“This catalog represents a crucial tool to understand the connection between geological risks and climatic conditions and can help prevent risks,” says Mercedes Ferrer, researcher at IGME-CSIC and co-author of the research.
Megatsunamis or giant waves are extreme episodes that impact cliff coasts in any region. They are conditioned by the presence of a body of water and the occurrence of a large landslide that, upon entering the body of water, causes a sudden vertical displacement of the same.
Until now there was no universal definition and accepted term, which was associated with prehistoric oceanic events linked to large asteroid impacts, gigantic collapses of volcanic islands or very destructive transoceanic earthquakes, such as those in Indonesia in 2004 and Japan in 2011.
Unlike tsunamis, megatsunami waves reach enormous heights –up to several hundred meters – upon impact on the coasts.
The main problem when investigating these phenomena is the scarcity of well-documented geological and historical records. Although megatsunamis must have been relatively frequent throughout Earth’s history, the vast majority were not observed or documented and They have left no geological record.
The oldest
He recorded event oldest was triggered by the massive explosive eruption on the island of Thera (Santorini) in Greece, around 1600 BC. c.
Of those that have been documented, most were generated by large subaerial landslides, in some cases by submarine landslides, and only a few are related to violent volcanic eruptions.
The first were those that caused the highest waves, by the violent entry of large masses of rock fallen from considerable heights into bays, fjords or lakes.
For the new catalog, each historical event was reviewed and investigated, with references to original sources wherever possible, which resulted in the correction of inaccurate data and ancient erroneous interpretations. In total, more than 300 publications were consulted from 1888 to 2024.
There are few records from the 19th century, although the number increases in the 20th century. Only in the first 20 years of the 21st century have as many been documented as in the previous century, which is related to the advance of scientific and technological knowledge for the detection of these events.
Of the 40 megatsunamis included in the catalogue,Some had extreme heights of over 100 meters. During the research for the catalogue, a new megatsunami that took place before 1786 in Lituya Bay (Alaska) has even been documented, which the authors mention, but do not include in the list due to lack of information on the exact date.
The greatest of all
Precisely in Lituya, the largest ever recorded took place in 1958.. It was caused by a rock avalanche triggered by a magnitude 7.8 earthquake that impacted the waters at the head of the bay. The fall of between 35 and 40 million cubic meters of rocks and ice into the sea, from a height of 600 meters, generated a wave of 524 meters, which devastated 10 square kilometers of forest.
The next recorded took place a few years later, in 1963, in the Vaiont reservoir (Italian Alps)when a landslide that occurred while the infrastructure was being filled caused a wave of about 250 meters and destroyed entire towns.
The last one of similar dimensions was produced in 1980 in Spirit Lake (United States), upon reaching 260 meters. It was a landslide associated with the eruption of the Saint Helena volcano.
global warming
The authors conclude that, currently, in glacial areas the combined effects of steep slopes, fractured rock masses and ice retreat play a crucial role for large landslides and avalanches to occur.
He global warmingwhich leads to an increase in temperatures, impacts the high and cold latitudes of both hemispheres, especially in the frozen regions, causing glacial retreat that generates instability of the slopes, which is why they point out that “it is likely that warming global drive an increase in the frequency of large rock slides.”
After this retreat, the rock walls are exposed to erosion and tension changes, modifying their balance, which can cause large rockfalls and avalanches which, when violently falling into the water in fjords and bays, can trigger enormous waves.
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