The Potential Generation of a Mega-Tsunami
Published By Mikayla Kauinana
– Featured image by Gabrielle Cox
When you think of the word “tsunami”, what do you think of? Do you think of the most recent tsunami from the Tongan explosion of January 14th that impacted the shores of Santa Cruz? Or do you automatically think “Big Wave Incoming, Need to Move Away!”? A tsunami is defined as a series of waves in an ocean due to the displacement of water by a large event. They can be generated due to tectonic plate movement, such as volcanic eruptions, meteor impacts, earthquakes, seaquakes, and so on. A common misconception is that tsunamis can only be generated by tectonic plate movement, which is false. Massive flank collapses of volcanoes can generate tsunamis, which is when the top parts of volcanoes fail to stay on the slope and fall to the water below. From past and current research, it has been theorized that a mega-tsunami can be generated by a large flank collapse. A mega-tsunami has been defined as a tsunami that exceeds all published tsunami scales before it and can have a large scale of destructive effects. The term has been used by the media to gain a fear response towards a possible event like this. We currently don’t know for sure if a mega-tsunami will occur in the near future or if there is one that already happened according to the geological timescale. Recent studies have shown that conclusions about when and how a mega-tsunami could occur could have been based on false data. This makes sense as the majority of the past research hypothesized on the possibility of mega-tsunami generation based on a lack of observational or instrumental data and an incomplete geological record of such events. Since observational and experimental tools were limited in the past, it led to the inaccurate data collection of tsunami and mega-tsunami generation that negatively affected our tsunami forecasting capabilities. Focusing on tsunami generation is important so that we can improve current tsunami forecasting and confirm the actual likelihood of a mega-tsunami occurring, so that people can know the facts and not just speculations.
Currently, our tsunami forecasting depends on an incomplete geological timeline, which isn’t very great since we use our geological timeline to predict earthquakes and volcanic eruptions based on the amount of time passed between the last geological hazard. Improving our forecasting abilities is quite important to detect potential causes for mega-tsunamis and other massive hazards that have a destructive potential towards people, the environment, and the geography it impacts. For example, a tsunami can result in death, disease, and the destruction of at most a city or two, while a mega-tsunami has the potential to drown at least half of California! Known tectonic hazards are being monitored closely for threat level, but non-tectonic hazards, such as the sudden failure of volcanic sides to stay together aren’t high on their list. The importance of monitoring an event like this can be seen by looking at past tsunami accounts generated by these flank collapses, focusing on the elevated marine deposits that have been found as evidence of a past mega-tsunami, and being reminded of the potential destruction level. If there is a strong connection between volcanic flank collapses and the generation of mega-tsunamis, then this would mean that non-tectonic activity could lead to geological hazards as tectonic related hazards do. Taking into account past and current events, we can look at other possible locations that have the potential to generate a mega-tsunami and to uncover if some have already occurred through evidence found on islands. Focusing on the Hawaiian Islands, the Canary and Cape Verde Islands (Atlantic Ocean), and the Mauritius Island (Indian Ocean) we look towards the flank collapses and the elevated marine deposits located there. From the study done by Carayannis in the year 2002, it was found that sudden, catastrophic, flank collapses of ocean island volcanoes have the greatest potential for the generation of a mega-tsunami. The aftermath of island volcanic collapses has been identified by the debris-avalanche deposits and collapse scars that one can see both onshore and offshore, implying large volumes of mass displacing water. As said before, there are some gaps in the catalog of mega-tsunamis and general tsunamis generated by volcano flank collapses, not only for ocean island volcanoes. Due to the small amount of data on the mechanism of these flank collapses that can cause the generation of a mega-tsunami, it has led to models in regard to a mega-tsunami hazard assessment severely lacking in applicable data.1
To the point that we don’t exactly know if a mega-tsunami has occurred in the past, if it will occur in the future, and the range of damage it could result in. Interestingly, marine deposits found at unusually high elevations on the flanks of different ocean islands have been considered as evidence of mega-tsunami occurrences. Islands such as Hawaii, the Cape Verde Islands, and the Canary Islands have been interpreted as the geological record of mega-tsunamis generated by island volcanic flank collapses. There were elevated marine deposits found in Hawaii from the island Lāna’i that have been used as evidence of a mega-tsunami occurrence. The elevated marine deposits of the Canary Islands have been found to be connected with a tsunami generated by a collapse dated to 860–830 kyrs on the eastern flank of Tenerife Island (Güímar collapse) that resulted in deposition of marine sediments at high elevations. However, the potential impact of mega-tsunamis triggered by flank collapses of the Canary Islands has been debated based on incomplete information and simulations generated from that misinformation. The identification of mega-tsunami deposits in Hawaii and the Canary Islands even led to the search for similar evidence found in the Cape Verde Islands!
There was convincing evidence of similar deposits occupying Maio Island, one of the Cape Verde Islands, up to 5 km inland that recorded four different tsunami events during the last 500 thousand years, one of them being around the time with the Fogo Island flank collapse.2 Numerical simulations of flank collapses and tsunamis show that, whatever the nature of the collapse, tsunami waves moved inland as far as the marine deposit locations. These tsunami deposits found on ocean islands could be used for reconstructing the conditions when the tsunami transported the deposits occurred. This means that the marine deposits can give us a good idea of how, when, and why they were transported to where they ended up, although the connections have been widely debated as theories can only rely on incomplete databases and past experiments. Recently, a mega-tsunami has been said to be imminent and is expected to occur during the human lifetime.
By looking at past tsunami accounts on how they were generated and what they left behind, we can find more background on the potential of a future mega-tsunami happening. Past tsunami accounts that have been analyzed were generated from volcanic flank collapses, as they have been theorized to possess the most potential to generate a mega-tsunami. In fact the 1958 tsunami of Lituya Bay, caused by a giant landslide, can be considered the only historical mega-tsunami but the wave rapidly decreased to 10 m from 524 m when moving 12 km from the source.3 After this occurred, the study led to the term ‘mega-tsunami’ as possessing a wave height greater than 100 m at the source. Compared to this, the flank collapse that occurred on the Ritter Island Volcano in 1888 was much larger. Even though this led to a devastating tsunami it was nothing in comparison to the Lituya Bay Tsunami.4 Based on this topic, there is no doubt that some information is needed, and more work needs to be done to further investigate the possible generation of a mega-tsunami. From the current state of knowledge in regard to a potential mega-tsunami event, it is highly important that research regarding this continues. Especially since there isn’t a complete timeline of tsunami accounts caused by volcanic flank collapses that could aid us in studying the potential past occurrences, generation mechanisms, and after-effects of a potential mega-tsunami event. Elevated marine deposits from potential past mega-tsunamis could be analyzed and an accurate volcanic flank collapse simulation could generate an accurate mega-tsunami simulation. Even if a mega-tsunami is found to be highly unlikely to occur anytime soon, focusing on the subject could lead to a complete geological timeline and improved tsunami forecasting capabilities. Most importantly non-tectonic activity such as the potential for flank collapses could be watched more closely as a real threat!
References
- Pararas-Carayannis, G. (2002). Evaluation of the Threat of Mega Tsunami Generation from Postulated Massive Slope Failures of Island Stratovolcanoes on La Palma, Canary Islands, and on the Island of Hawaii. In Natural Sciences of Hazards: The International Journal of the Tsunami Society (5th ed., Vol. 20, pp. 251–277). LANL Research Library.
- Paris, R. (2020, July 31). Mega-tsunami deposits related to Ocean island flank collapses and asteroid impacts. Geological Records of Tsunamis and Other Extreme Waves. Retrieved April 30, 2022, from https://www.sciencedirect.com/science/ article/pii/B9780128156865000250
- Paris, R., Ramalho, R. S., Madeira, J., Ávila, S., May, S. M., Rixhon, G., Engel, M., Brückner, H., Herzog, M., Schukraft, G., Perez-Torrado, F. J., Rodriguez-Gonzalez, A., Carracedo, J. C., & Giachetti, T. (2017, October 13). Mega-tsunami conglomerates and flank collapses of Ocean Island volcanoes. Marine Geology. Retrieved April 30, 2022, from https://www. sciencedirect.com/science/article/pii/S0025322717302475
- Ward, S. N., & Day, S. (2003, September 1). Ritter Island volcano-lateral collapse and the tsunami of 1888. OUP Academic. Retrieved April 30, 2022, from https://academic. oup.com/gji/article/154/3/891/713958?login=true