On December 9, 2019, a cloud of steam and volcanic gases erupted from Whakaari Volcano, or White Island, New Zealand. In relation to the eruptions of other volcanoes, the explosion was small. But it claimed the lives of 22 people and injured 25 others, many of whom suffered severe burns.
Now, using high-resolution satellite data and computer algorithms, scientists have revealed how the gases released by the volcano changed subtly before, during and after the 2019 eruption. Observers of such small changes using satellites could greatly improve volcano monitoring and help detect the first eruption warnings, researchers report on June 18 in Science Advances.
Volcanologists typically use instruments on the ground to help warn of eruptions, monitoring changes in gases, such as carbon dioxide and sulfur dioxide, that seep silently from volcanoes between explosions. But only about 50 of the world’s volcanoes are monitored this way. Satellites have been used to study the feathers of large volcanoes, but orbiting craft have not been used to detect gases emitted by small eruptions.
Compared to large eruptions, such as the explosion that beheaded Mount St. Helens of Washington in 1980, small-scale eruptions occur more frequently. So they pose a greater threat to people, says volcanologist Mike Burton of the University of Manchester in England.
Krzysztof Belczyński / Flickr (CC BY-SA 2.0)
Coincidentally, the Sentinel-5 Precursor satellite flew over Whakaari about an hour after the 2019 eruption and collected data on the reflected light from the plume of gases ejected from the volcano with its tropospheric monitoring instrument or TROPOMI. “What we realized was that we could use (satellites) to actually see unprecedented small explosions,” Burton says.
From its seat in the sky, TROPOMI was more suitable than earth instruments to gather information about the high plume. And by the time TROPOMI passed through his head, much of the ash and other air particles that can blur the observations on the ground of the erupting gases had fallen or evaporated from the plume.
Burton and colleagues applied a computer algorithm to TROPOMI data to calculate the backward trajectory of the gases in the pen, essentially rewinding the volcanic eruption. This approach allowed researchers to estimate the amount of sulfur dioxide the volcano erupted before, during, and after the eruption.
About 40 minutes before Whakaari exploded, the volcano's sulfur dioxide emissions increased from 10 kilograms per second to 45 kilograms per second – signaling a potential eruption – and sulfur dioxide and other gases began to rise, the researchers found. .
GeoNet, a New Zealand geological hazard control service, warned several weeks before the eruption, after detecting an increase in ground tremor, geysers boiling in the volcano's crater lake and sulfur dioxide emissions using ground-based instruments, though that tourist companies continued to visit the island. But the new study is the first time scientists have used a satellite to detect precursor changes in sulfur dioxide emissions before a small eruption.
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It was surprising that so much information about this small eruption could be gleaned using satellites, Burton says. "That's a really exciting prospect because now we can expect (measure) many more (eruptions) from space"
An seismic station on the island recorded changes in the tremors caused by the eruption and in parallel with the results of the researchers. As sulfur dioxide emissions and plume height began to rise in the minutes before the explosion, tremors also increased.
This work demonstrates that it is now possible to measure pre-eruption gas emissions via satellites, which will complement terrestrial systems and help provide pre-eruption warnings, says Jorge Andres Diaz, a volcanologist at the University of Costa Rica in San Pedro, who was did not participate in the study. "(It could) be your first line of control, especially in very remote places."
But predicting eruptions involves looking at multiple factors together, including those that TROPOMI cannot detect, he says. The tremors are an example (SN: 17/06/19). It is also useful to monitor other emitted gases such as carbon dioxide which, along with measurements of sulfur dioxide, can reveal when new magma flows into the magma chamber of a volcano, which can cause an eruption. Although TROPOMI cannot detect carbon dioxide, some other satellites do.
"I don't mean we can predict explosions perfectly; we can't do that," Burton says. "It simply came to our notice then. It opens a new frontier. "