Modern measurement methods can predict tsunamis
Published: Wednesday, Nov 13th 2024, 12:30
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Modern measuring methods help researchers to predict natural hazards such as tsunamis. They also provide insights into the formation of a mysterious, ten-kilometer-long underwater chain of 170 stone mounds from the Neolithic period in Lake Constance. Swiss geologist Flavio Anselmetti spoke about its mapping, a "hotspot of interaction between humans, the environment and the climate", in Vienna.
He gave a lecture at the Austrian Academy of Sciences (ÖAW) on Tuesday evening. "The history of today's Lake Constance begins when the great Rhine glacier retreated around 19,000 years ago," said Anselmetti, Professor at the Institute of Geology at the University of Bern
In order to better understand the geological history of the tri-national lake, among other things, the researchers used a so-called multibeam echo sounder to measure the lake bed. With this method, instead of sending out a sound wave and measuring the time it takes for it to be reflected back from the bottom, as is the case with individual echo sounder measurements, a fan of signals is sent out that widens towards the bottom and can quickly generate a large number of measurement points.
The problem with the multibeam echo sounder: It is not possible to measure so efficiently in the shallow water of the lake, as the fan from the ship has no room to increase in size towards the bottom. Together with a company from Innsbruck, laser measurements were therefore taken from an airplane.
Before the map was made publicly available, the large data sets from the two measurement methods had to be combined and drinking water wells had to be concealed due to the risk of poison attacks and archaeologically valuable shipwrecks. "But now, for the first time, you can see the lake as if there was no water," explained the geologist.
Anticipating natural hazards
The practical benefit of the survey now lies in being able to better predict potential natural hazards thanks to the exact representation of the lake bed and further analyses. "For example, in the event of an earthquake or a flood in the Rhine delta area, the sediment masses on the slopes could move spontaneously," said Anselmetti. This has the potential to trigger a tsunami. "We model these tsunamis and want to take a sober look at the danger."
On the southern shore of Lake Constance, 170 "mysterious mounds" were also discovered at a depth of three to five meters during the mapping, said the researcher. Lined up like a string of pearls, the chain is around ten kilometers long. "At the press conference at the time, this caused a real hype about the mounds - we still knew very little about them, which is why wild speculation was circulating in many media outlets," said the geologist.
Purpose of the hills unclear
Many questions have been clarified since the discovery in 2015: the mounds with diameters of 15 to 30 meters are very likely man-made, as they differ significantly from the structure of the underlying mud, among other things. With the help of samples, it was possible to date the construction to around 5500 years ago, i.e. the Neolithic period. "That's around the same time as Ötzi, who walked across the Alps," explained Anselmetti. This would make them the largest known Neolithic structure.
However, a number of uncertainties remain to this day, first and foremost the purpose of the mounds. During the investigation of "Hügeli 5", the only mound so far to have been dredged up step by step under water, no settlement remains were found, but only stones and individual pieces of wood.
Other possible uses include fishing, as burial platforms or calendar systems, and even as shoreline protection, breakwaters or piles of stones for agriculture. "But we simply don't know. So speculation is allowed," said Anselmetti.
©Keystone/SDA
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