Approximately half a day after the eruption of a submarine volcano in Tonga, it was found that satellites were catching ripples as waves propagated around the volcano.
Experts analyzed that it captured the sea level fluctuations that occurred due to the eruption, and found that "the wave cycle is significantly different from the tsunami caused by the earthquake, which leads to an understanding of the entire phenomenon. Isn't it? "
Earth observation satellites in Europe passed near Tonga on the early morning of 16th Japan time, which is about 13 hours after the eruption, and acquired data.
The "Synthetic Aperture Radar" mounted on this satellite can grasp detailed topographical changes and changes in sea level, and the images show how ripples like waves spread.
Near the center is Tofua Island, about 100 km north of the erupted submarine volcano of Tonga, and semi-circular waves can be seen for several tens of kilometers around it.
Professor Nobuhito Mori of the Kyoto University Disaster Prevention Research Institute, who is familiar with the mechanisms of tsunamis and high waves, analyzes this data as capturing sea level fluctuations that occurred after the eruption.
In addition, the distance between each wave is several kilometers to five kilometers, which is much narrower than the tsunami caused by an earthquake.
This leads to a shorter "period" of each wave, which is consistent with the tendency seen from the data observed by the tide gauges in each region this time.
Professor Mori said, "It is a very rare observation result, and it is important data that shows how the sea level fluctuated after the eruption." It is probable that waves with a fine cycle fluctuated throughout the Pacific Ocean even after half a day because it was prone to such movements. It may have led to the fact that the wave heights differed greatly from place to place around Japan. I point out.
"The change in sea level this time is a very rare and complicated phenomenon caused by a combination of several factors such as changes in atmospheric pressure due to the eruption. The acquisition of spatial data leads to an understanding of the entire phenomenon. I think. "
Tsunami spreads throughout the globe at almost the speed of sound
Analysis of data captured around the world revealed that the tsunamis that reached various places after the eruption of the submarine volcano in Tonga spread to the entire earth at almost the speed of sound.
It was also found that the tsunami was observed at the same timing as the change in atmospheric pressure due to the eruption, and experts point out that "the data support that the change in atmospheric pressure caused the tsunami in various places."
A research group such as Assistant Professor Masumi Yamada of the Kyoto University Disaster Prevention Research Institute announced on the 15th of this month that after a large-scale eruption at a submarine volcano in Tonga, seismometers, pressure gauges, and seabeds observed in various parts of the world such as Japan and the United States. We analyzed the data of the installed tsunami meter and so on.
As a result, the arrival time of the first wave of the tsunami is about 5:30 pm on the 15th of Japan time, which is about 4 hours after the eruption in Hawaii, which is about 5000 km away from Tonga, and from 8 pm in Japan, which is about 8000 km away. It was observed at about 10:30 pm in Chile, South America, about 10,000 km away, around 9 o'clock, at almost the same timing as the change in pressure.
The tsunami traveled concentrically from Tonga to various parts of the world, and its speed was almost the same as the speed of sound.
Since the tsunami caused by a normal earthquake or the collapse of a volcano is slower than the speed of sound, Assistant Professor Yamada and his colleagues believe that the change in atmospheric pressure generated by the eruption caused the tsunami and spread.
Assistant Professor Yamada said, "The effect of changes in atmospheric pressure on the tsunami has never been captured by modern high-density observations. The detailed mechanism that caused the tsunami is not fully understood. Therefore, we need to investigate further. In the future, researchers around the world may analyze these data to make new discoveries. "