Science

How satellites have revolutionized the study of volcanoes

Advances in satellite technology over the last 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 are also helping volcanologists keep an eye on Earth’s more common (if less conspicuous) outbursts.

The last time a volcano erupted as violently as Hunga Tonga-Hunga Ha’apai was 30 years ago. At that time, the satellites that monitored the Earth were few and far between. Those who watched the planet’s surface 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, the Remote Sensing Satellite-1 (ERS-1). The cubesats that have since become the cornerstone of commercial Earth observation constellations, such as those of the US company Planet, had not yet been invented.

Still, Mount Pinatubo’s 1991 eruption was the most explosive volcanic event detected by satellites at the time, having been imaged by a Japanese weather satellite located 22,000 miles (36,000 kilometers) above Earth and a spacecraft from the US National Oceanic and Atmospheric Organization that orbited the planet in polar orbit.

Related: Ash From Tonga Volcano Eruption Reaches Record Altitude, But Climate Is Unlikely To Cool

In real time

But the detectors and cameras on satellites in the 1990s weren’t as capable as those that fly around Earth today. And so the amount of data was not as detailed as that produced by the Hunga Tonga-Hunga Ha’apai eruption.

“In a sense, we are very 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. “This is something that even five years ago we wouldn’t have had.”

Proud was one of hundreds of researchers around the world wowed by data coming from orbiting sensor networks after the Hunga Tonga-Hunga Ha’apai eruption spread across the southern Pacific Ocean on Saturday (January 15). ). First was the nuclear-type explosion that has since been described as 500 times more powerful than the Hiroshima bomb. Then came the shock wave that circumnavigated the globe, confounding weather forecast models everywhere, and the cloud of ash thrown so high into the atmosphere that it had never been seen before.

That volcanic cloud was of particular interest to Proud. Since then, he found that it reached record altitudes of more than 30 miles (50 km).

“Our latest data says that the main volcanic ‘umbrella’ reached 35 km [22 miles] altitude, but some points may have reached 55 km [34 miles] altitude!” Proud said on Twitter, adding that the “shocking altitudes… show how violent this eruption was.”

However, he warns that this record is due in part to the availability of measurement technology.

“We think Pinatubo probably got that high too, but we missed it with the technology we had,” he said. “What’s really interesting from a scientific perspective about this event is how high it went and in the coming days and weeks how it will interact with the atmosphere up there.”

Scientists already know that the Hunga Tonga-Hunga Ha’apai volcanic cloud contained a relatively low amount of sulfur dioxide, compared, for example, to the Mount Pinatubo eruption. Sulfur dioxide is of great interest as it can reflect sunlight as it scatters in the atmosphere, thus changing the amount of heat the planet traps. Due to its sulfur dioxide content, the Mount Pinatubo eruption cooled the planet by 1 degree Fahrenheit (0.6 degrees Celsius) in a measurable way for two years. However, current estimates 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.

The cloud of sulfur dioxide emitted by the Hunga Tonga-Hunga Ha'apai has reached the Indian Ocean.

The cloud of sulfur dioxide emitted by the Hunga Tonga-Hunga Ha’apai has reached the Indian Ocean. (Image credit: Copernicus)

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.

“That 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 the eruption of Mount Pinatubo 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 Rim, the so-called ‘Ring of Fire,’ where the Pacific Ocean fills in beneath the surrounding lithospheric plates. It’s a process that drives most of the volcanism in our planet”.

The water that mixes with the magma triggers chemical reactions that are not present in volcanoes that erupt on land. The water mixes with the molten rock, creating gas bubbles. The high temperature in the volcanic chimney pressurizes the mixture like a bottle of champagne. At some point, the pressure is high enough to dislodge the “cork” in that volcanic champagne bottle. How long the volcanic “cork” stays in place and how ferociously it flies depends on the water column above, Karson said.

“If there’s a lot of pressure in the system, in other words the water is relatively deep, then the caps stay in that system and the gases leak out pretty slowly,” Karson said. “If you’re close to the surface, there’s no water pressure to keep the lid off the system and those gases come out catastrophically.”

The gas can expand a thousand times in volume as it changes from a liquid form, Karson said; a process that happens instantaneously, blasting the rock with explosive force.

The 1991 eruption of Mount Pinatubo in the Philippines injected large amounts of aerosol particles into the Earth's stratosphere, which scattered and reflected sunlight, lowering Earth's average global temperature by about 1 degree Fahrenheit over the next 15 months.  Later, however, temperatures rose again.

The 1991 eruption of Mount Pinatubo in the Philippines injected large amounts of aerosol particles into the Earth’s stratosphere, which scattered and reflected sunlight, lowering Earth’s average global temperature by about 1 degree Fahrenheit over the next 15 months. Later, however, temperatures rose again. (Image credit: Richard Hoblitt/USGS)

Where will the next one explode?

Satellites, Karson admits, played an indispensable role in tracking the Hunga Tonga-Hunga Ha’apai eruption. Volcanologists place sensors on volcanoes that they think might become active. But very little is still known about the processes inside the Earth, and estimates are crude at best.

“We don’t know when the next eruption will take place at a particular volcano, so we put instruments on the ones we think are most active,” Karson said. “But this particular volcano wasn’t instrumented very much at all.”

Despite the technological boom of the last decade, satellites still do not provide as detailed a picture as ground sensors. Still, much can be learned from their data and images about the scale of the impact, the spread of the volcanic cloud, and the changes in the terrain around the volcano.

“There’s a lot that can be done,” Karson said. “For example, you might wonder how much the ground level has changed, and that can also be determined from satellites these days. But gases, for example, disperse in the atmosphere and can end up being diluted and difficult to measure from of those great heights.

A series of images captured by the European satellite Sentinel 2 shows the devastation caused by the Cumbre Vieja volcano on the Spanish island of La Palma a month after the eruption began.

A series of images captured by the European satellite Sentinel 2 shows the devastation caused by the Cumbre Vieja volcano on the Spanish island of La Palma a month after the eruption began. (Image credit: Copernicus)

slow burning destruction

Karson’s main research interests are the more modest, slow-burning volcanoes that spew lava for weeks and months, often causing severe but more predictable damage that people can prepare for. Even those volcanoes benefit from satellite monitoring. For example, the damage caused by the Cumbre Vieja volcano on the Canary Island of La Palma in the Atlantic Ocean last year was assessed in detail almost daily by satellites in the European constellation Copernicus. The analysts were able to count the individual buildings that disappeared in the lava flow and calculate the exact area of ​​land buried by the molten rock.

“Today it’s quite common even in incredibly remote areas to capture [volcanic eruptions] with satellites,” Karson said. “Now there are more and more satellites all the time. They have different systems, so we’re much better positioned to make different kinds of observations.”

Watching the cloud

The scale of the impact of a volcanic eruption may not necessarily be directly proportional to its ferocity, Karson added.

For example, the slow-burning eruption of the Eyjafjallajökull volcano in Iceland in 2010 produced huge amounts of ash that were extremely dangerous to aircraft. Nearly 100,000 flights had to be grounded on busy transatlantic routes as a result of the eruption.

Hunga Tonga-Hunga Ha’apai, on the other hand, dumped its debris in a fairly remote area of ​​the Pacific Ocean that not many flights cross. Scientists, however, continue to carefully monitor the spread of the cloud, which has since crossed Australia and begun spreading across the Indian Ocean.

“The ash cloud will eventually spread very thinly globally,” Proud said. “For the next few weeks it will likely remain in the southern hemisphere, following winds across the southern Indian Ocean and into southern Africa.”

For now, most of the cloud is well above the aircraft’s cruising altitude, he added. Even though the explosion is over, satellites will keep their eyes peeled for Hunga Tonga and the volcanic cloud for weeks to come. Proud said some unexpected insights could come out of the research. For example, due to its altitude, volcanic ash could interact with the ozone layer, something that had never been studied before.

Follow Tereza Pultarova on Twitter @TerezaPultarova. Follow us on Twitter @Spacedotcom and on Facebook.

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