Developments in satellite technology over the past decade have allowed the world to witness the devastating Hunga Tonga-Hunga Ha’apai eruption and its aftermath in real time and in unprecedented detail. The findings could shed light on the anatomy of rare explosive volcanic eruptions and their effects on the planet. But satellites also help volcanologists keep tabs on Earth’s more common (though less eye-catching) explosions.
The last time a volcano erupted as violently as Hunga Tonga-Hunga Ha’apai was 30 years ago. At that time, surveillance satellites Earth were few and far between. Those who surveyed the surface of the planet were mostly led by the military. the European Space Agency (ESA), now an Earth observation superpower, was about to launch its first Earth observation mission, Remote Sensing Satellite-1 (ERS-1). The cubesats that have since become the cornerstone of commercial Earth observation constellations, such as those from the US company Planet, had yet to be invented.
Yet the Mount Pinatubo eruption in 1991 was the most explosive volcanic event detected by satellites at the time, having been photographed by a Japanese weather satellite sitting 22,000 miles (36,000 kilometers) above Earth and a spacecraft from the National Oceanic and Atmospheric Organization of the United States that circled the planet in polar orbit.
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In real time
But the satellite sensors and cameras of the 1990s were nowhere near as good as what flies around the Earth today. And so the amount of data was nowhere near as detailed as what the Hunga Tonga-Hunga Ha’apai eruption produced.
“In a way, we’re really lucky to have all these satellites in orbit now,” Simon Proud, a satellite data and meteorology researcher at the University of Oxford, told Space.com. “It’s something we wouldn’t have had five years ago.”
Proud was one of hundreds of researchers around the world captivated by the data pouring in from orbiting sensor arrays after the Hunga Tonga-Hunga Ha’apai eruption crossed the South Pacific Ocean on Saturday January 15. First there was the nuclear-like explosion which has since been described as 500 times more powerful than the Hiroshima bomb. Then came the shock wave that swept around the world, confusing weather forecasting models everywhere, and the ash cloud hurled so high into the atmosphere that it had never been seen before.
This volcanic cloud was of particular interest to Proud. He has since discovered that he has reached record altitudes of over 30 miles (50 km).
“Our latest data indicates that the main volcanic ‘umbrella’ has reached 35 km [22 miles] altitude, but some points may have reached 55 km [34 miles] altitude!” Proud said on Twitteradding that “the shocking altitudes … show just how violent this eruption was”.
However, he warns that this record is partly due to the availability of measurement technology.
“We think Pinatubo probably went that high, but we missed it with the technology we had,” he said. “What’s really interesting from a scientific perspective about this event is both how high it has gone and over the coming days and weeks how it will interact with the atmosphere there. -high.”
Scientists already know that the Hunga Tonga-Hunga Ha’apai volcanic cloud contained a relatively small amount of sulfur dioxide, compared to, for example, the eruption of Mount Pinatubo. Sulfur dioxide is of great interest because it can reflect sunlight when dispersed in the atmosphere, changing the amount of heat the planet retains. Due to its sulfur dioxide content, the eruption of Mount Pinatubo cooled the planet by 1 degree Fahrenheit (0.6 degrees Celsius) in a measurable way for two years. Current estimates, however, suggest that despite its cataclysmic proportions, the Hunga Tonga-Hunga Ha’apai volcanic cloud contained only 2% of Mount Pinatubo’s amount of sulfur dioxide.
Uncorked bottle of champagne
The difference, however, is not due to the size or force of the explosion, volcanologist Jeffrey Karson, of Syracuse University in New York, told Space.com.
“It has to do with the source of the molten rock at depth,” Karson said. “Some volcanic materials have a lot of sulfur, some have very little sulfur. It depends on the source.”
The force of the Hunga Tonga-Hunga Ha’apai explosion, the largest the planet has witnessed since Mount Pinatubo erupted in 1991, was the result of a combination of factors, according to Karson.
“There is nothing geologically unusual about this volcano,” Karson said. “It’s one of thousands of volcanoes around the Pacific, the so-called ‘Ring of Fire,’ where the Pacific Ocean is packed under the surrounding lithospheric plates. It’s a process that drives most volcanism on our planet.”
Water mixing with magma triggers chemical reactions that are not present in volcanoes erupting on land. The water mixes with the molten rock, creating gas bubbles. The high temperature in the volcanic vent pressurizes the mixture like a bottle of champagne. At some point, the pressure is high enough to move the “cork” of this bottle of volcanic champagne. How long the volcanic “plug” stays in place and how fiercely it blows away depends on the water column above it, Karson said.
“If there’s a lot of pressure on the system, in other words, the water is relatively deep, then the lids are held on that system and the gases escape quite slowly,” Karson said. “If it’s close to the surface, there’s no water pressure to hold the lid on the system and those gases come out catastrophically.”
Gas can expand a thousand times in volume when changing from liquid form, Karson said; a process that happens instantly, blasting rock apart with explosive force.
Where will the next one explode?
Satellites, Karson admits, played an indispensable role in monitoring the Hunga Tonga-Hunga Ha’apai eruption. Volcanologists place sensors on volcanoes they believe may become active. But very little is still known about the processes inside the Earth, and the estimates are very crude at best.
“We don’t know when the next eruption will be on a particular volcano, so we put instruments on the ones we think are the most active,” Karson said. “But this particular volcano hasn’t been instrumented much.”
Despite the technological boom of the last decade, satellites still do not provide as detailed an image as ground sensors. Yet, much can be learned from their data and images about the magnitude of the impact, the spread of the volcanic cloud, and changes in the terrain around the volcano.
“There’s a lot to do,” Karson said. “For example, you might wonder how much the ground level has changed, and that can also be determined from satellites nowadays. But gases, for example, disperse in the atmosphere and can end up being diluted and difficult to measure from these great heights.
Slow burning destruction
Karson’s main research interests are smaller, slow-burning volcanoes that spurt lava for weeks and months, frequently causing severe but more predictable damage that people can prepare for. Even these volcanoes benefit from satellite monitoring. For example, damage caused by Cumbre Vieja Volcano on the Canary Island of La Palma in the Atlantic Ocean last year was assessed in detail almost daily by the satellites of the European constellation Copernicus. Analysts were able to count the individual buildings that disappeared into the lava river and calculate the exact area of land buried by the molten rock.
“Nowadays it is quite common, even in incredibly remote areas, to capture [volcanic eruptions] with satellites,” Karson said. “There are more and more satellites all the time now. They have different systems and so we’re in a much better position to make different kinds of observations.”
Keep an eye on the cloud
The magnitude of the impact of a volcanic eruption is not necessarily directly proportional to its ferocity, Karson added.
For example, the 2010 slow-burning eruption of the Eyjafjallajökull volcano in Iceland produced huge amounts of ash which was extremely dangerous for aircraft. Nearly 100,000 flights had to be grounded on busy transatlantic routes following the eruption.
Hunga Tonga-Hunga Ha’apai, on the other hand, dumped its wreckage in a rather remote area of the Pacific Ocean that few flights cross. Scientists, however, are still carefully monitoring the spread of the cloud, which has since crossed Australia and started spreading across the Indian Ocean.
“The ash cloud will eventually spread very thinly around the world,” Proud said. “Over the next few weeks it will likely remain in the southern hemisphere, following winds across the southern Indian Ocean and into the southern part of Africa.”
For now, most clouds are well above the planes cruising altitude, he added. Even though the explosion is over, satellites will keep their eyes on Hunga Tonga and the volcanic cloud for weeks. Proud said unexpected insights may come out of the research. For example, due to its altitude, volcanic ash could interact with the ozone layer, which has never been studied before.