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The Rigakubu News

Disclaimer: machine translated by DeepL which may contain errors.

The Rigakubu News
Published in The Rigakubu News November 2024
Advancing Science >

~ Message from a Graduate Student~.
Giant Tsunami in the Pacific Ocean ~From Science to Mythology and Archaeology

 


Koki Nakata
Department of Earth and Planetary Science
1st Year Doctoral Student
Birthplace
Chiba, Japan
High School
Kaisei High School
Faculty
The University of Tokyo Faculty of Science

 

A huge rock (see figure), several times as tall as a person, standing alone on a plain. Its weight is estimated to be about 1,600 tons. Its presence is unique and even divine. This huge rock is located on the island of Tongatapu in the Kingdom of Tonga in the South Pacific and is locally called "Maui Rock."

Where did this rock come from? I will not go into details, but it has been pointed out that the rock may be a so-called "tsunami rock" carried by past giant tsunamis from near the coast. In fact, Tonga is at high risk of tsunamis due to the existence of ocean trenches and undersea volcanoes in the vicinity of the island. Most recently, in 2022, Tonga was hit by a tsunami with a maximum run-up height of 20 meters due to the eruption of the Hunga-Tonga-Haapai volcano.

Although it is quite possible that Tonga has been hit by huge tsunamis in the past, the history and scale of such tsunamis are still unknown. Therefore, I am currently conducting research to clarify the actual situation of past tsunamis in Tonga.

Because of the lack of historical records in Tonga, it is necessary to search for geological traces formed by tsunamis in order to clarify the actual situation of past tsunamis. In addition to the aforementioned tsunami stones, sheet-like deposits (tsunami deposits) preserved in the strata are known as geological traces of tsunamis. We conducted field surveys on Tongatapu Island in November 2023 and July 2024 to search for these traces. As a result, we found several tsunami deposits at several sites on Tongatapu Island.

Incidentally, this was my first overseas survey. While there were some difficulties, such as the unfamiliar environment and food, it was interesting to interact with the local people, and it was a valuable experience for me. For example, during the July survey, I was invited to a kava party by the local people. Kava is a common drink in Polynesia, made by adding water to the powder of the root of a pepper tree and straining it. It looks like muddy water, and when drunk, it causes a mild numbing sensation on the tongue and mild intoxication. At a kava party, everyone drinks buckets full of it. The taste was something I had never experienced before in my life, and my head was getting light-headed. It was a precious cross-cultural experience.

Returning to the topic of my research, it is very important to clarify the history of past tsunamis not only as a science but also for tsunami disaster prevention. In fact, I started this research because I wanted to contribute to disaster prevention.

However, that is not the only interesting aspect of this research. For example, there is a myth in Tonga that Maui, a demigod and half-human, threw this rock out of the sea to kill a man-eating bird (this is the origin of the name Maui Rock). In fact, there is a theory that this man-eating bird may refer to a tsunami. Archaeological studies also show that around the 15th century, the South Pacific islands, including Tonga, experienced an almost simultaneous shift of bases inland, an increase in conflicts, and the cessation of inter-island long-distance trade. Some researchers have suggested that this social transformation may have been related to the giant tsunami.


A "Maui Rock" on Tongatapu Island, Kingdom of Tonga. B Field survey. A trench was dug to discover tsunami deposits left in the strata.

Thus, although historical records are scarce in Tonga, there is a possibility that records of past giant tsunamis remain as myths and archaeological traces. It is a very romantic story, isn't it?