NASA researchers have estimated the power of a massive volcanic eruption that occurred near the island nation of Tonga on Saturday. James Garvin, chief scientist at the agency's Goddard Space Flight Center, told NPR: "The figure we came up with is about equal to the equivalent of 10 megatons of TNT. ”
This means that the explosive power is more than 500 times that of the nuclear bomb dropped on Hiroshima, Japan, at the end of World War II.
Michael Poland, a geophysicist at the U.S. Geological Survey, notes that the explosion, which can be heard as far away as Alaska, could be one of the loudest events happening on Earth in more than a century. "This is probably the loudest eruption since the 1883 (Indonesian volcano) Krakatoa eruption. That massive eruption in the 19th century killed thousands of people and released large amounts of volcanic ash, plunging much of the region into darkness. ”
In the latest incident, Garvin said he believes the worst may be over — at least for now.
"If the precedent of volcanic eruptions in this environment in the past makes any sense, then we will not have such explosions for some time."
Even three days after the explosion, Tonga was largely isolated from the world. Submarine communication cables appear to have been cut and the airport is covered in volcanic ash, which makes it impossible for rescue flights to reach the capital, Nuku'alofa.
The New Zealand government's reconnaissance flight showed that volcanic ash had covered homes and many other structures. New Zealand's Foreign Ministry reported that two deaths had been confirmed and that the tsunami had flooded the west coast of the main island of Tongatapu and caused significant damage. Wire quoted the Tongan government as saying that another person died and the losses on the outlying islands were even greater – including Mango Island, where all the houses were destroyed.
In the years leading up to the explosion, NASA's team had been studying the volcano behind the eruption. According to Garvin, the islands that make up Tonga lie on a subduction zone in which one part of the Earth's crust slopes towards another.
"In this particular case, we don't know when a volcano with a ring of summits with big hills and east-west was formed," Garvin said.
In late 2014 and early 2015, along the rim of that crater, volcanic activity established a platform that rose from the sea and formed a new island. Layers of steam and volcanic ash eventually connected the island, known as Hunga Tonga-Hunga Ha'apai, with two more ancient islands on either side of it.
Dan Slayback, a research scientist at NASA Goddard and Science Systems and Applications, noted that Hunga Tonga-Hunga Ha'apai was completely destroyed by Saturday's explosion. He said the scale of the explosion even appeared to have blown the old islands nearby to pieces. "They're not ashes — they're solid rocks, but they've been blown to pieces. It is quite amazing to see this situation. ”
Garvin said the island's formation could also be the seed of its destruction. When it rises from the sea, the layer of liquid magma fills a network of chambers beneath it. He suspected the explosion was triggered by a sudden change in underground pipes that led to an influx of seawater. "When you put a ton of seawater into a cubic kilometer of liquid rock, things get bad very quickly."
But according to the U.S. Geological Survey's Poland, despite its explosive power, the eruption itself is actually relatively small. Unlike the 1991 eruption of Pinatubo, which spewed ash and smoke for several hours, the Hunga Tonga-Hunga Ha'apai event lasted less than 60 minutes. He doesn't expect this eruption to cause any short-term changes to Earth's climate, as other large eruptions in the past have done.
In fact, Poland believes, the real mystery is how such a relatively small eruption could produce such a large explosion and tsunami. "It has a huge impact, far beyond the area you would expect if it were entirely on the water." That's the headache. ”
Garvin said scientists hope to conduct more investigations into the area around the crater to follow up. Satellite image analysis is already underway, and there may soon be a drone mission. He hopes the volcano will be safe enough for researchers to visit later this year.
Poland said he believes researchers will learn more in the coming days and months as they conduct new surveys of the area. "It's just a terrible event for the Tongans, but it could be a benchmark, watershed event in volcanology."