Science

The highest volcanic plume has reached the mesosphere – Science et Avenir

January 15, 2022 underwater volcano The eruption of the Hunga Tonga volcano was accompanied by loud explosions, audible even in Alaska. This was followed by a devastating tsunami that left several dead and thousands homeless. The yield of the eruption was measured by NASA and estimated to be between 5 and 30 megatons, or the amount of energy released is greater than that of the atomic bomb dropped on Hiroshima in 1945! Several satellites have been able to observe the volcano, and new data published in Oxford University’s Science journal confirms that the eruption was indeed exceptional.

into the mesosphere

Anger Hunga Tonga created an impressive column of ash and water reaching the atmosphere. Usually, the height of a volcanic plume can be estimated by measuring the temperature recorded at the summit by infrared satellites and comparing it to a vertical temperature profile that serves as a reference. Indeed, in the troposphere (the first and lowest layer of the Earth’s atmosphere), the temperature decreases with height. But in the event of a major eruption, the column of debris can reach the next layer, the stratosphere, which complicates things a little: due to the ozone layer there, which absorbs the ultraviolet rays of the sun, the temperature begins to rise again. …of course, from above. Thus, the measurements become less accurate.

To overcome this problem, the researchers used a new method based on the parallax effect. It involves measuring the apparent difference in the position of an object when viewed from multiple directions. By measuring this apparent change in position and combining it with the known distance between observers, the distance to the object can be calculated. But the volcano was covered three geostationary meteorological satellites during the eruption, so the researchers were able to apply this method to their aerial photographs. And all the more poignantly, three cars took pictures every ten minutes during the volcanic event, enough to document the evolution of the smoke plume. The results show that at its highest point it reached a height of 57 kilometers. Record.

Recording and new method

Before this eruption it was Mount Pinatubo in the Philippines, which held the record for plume observed at 40 km at its highest point during the 1991 eruption. It was followed by El Chichon in Mexico, where a 31 km plume was measured in 1982. The Hunga Tong eruption is also the first observation of the release of materials from the eruption. right into the mesosphere, which starts about 50 km above the Earth’s surface and is still above the stratosphere. Until recently, this measurement would have been impossible due to the lack of a sufficient number of satellites to calculate the parallax. Today, instruments in orbit provide redundant global coverage.

Oxford researchers are now planning to create an automated system to calculate the height of volcanic plumes. And use the data to better model the dispersion of volcanic ash in the atmosphere.

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