The recent volcanic eruption in Tonga was significant- the explosion was heard along coastal Alaska. But for all the devastation that it caused, it wasn’t actually that big an eruption, compared to those of the last century. And it was a trifling eruption compared to Alaska’s Novarupta, which in 1912 was so large that it actually destroyed another mountain over six miles away.
“It drained the magma deposits that were beneath mount Katmai and mount Katmai imploded– this massive volcano, which for a long time was thought to be the origin of the eruption and other volcanoes in the area too, were impacted,” said Katie Ringsmuth, Alaska state historian.
She says the Novarupta eruption turned day to night around the Gulf of Alaska, and the noise from the explosion reached Juneau, nearly 750 miles to the east.
While much is still unknown about the Tonga eruption, there are a few facts beginning to emerge. For starters, the explosion likely was exacerbated by the fact that it was a shallow undersea volcano, explains Michelle Coombs, scientist-in-charge at the Alaska Volcano Observatory in Anchorage.
“The presence of seawater could have added explosive fuel to the eruption and made it relatively much more explosive,” Coombs said.
As water makes contact with the hot magma, it vaporizes and expands rapidly. If this happens quickly enough, there can be a steam-based explosion. It’s happened in Alaska before, at Bogoslof Island in the Aleutian chain. A series of eruptions there in 2016 and 2017 created oversized explosions, shooting ash and debris high into the clouds.
It’s not easy to compare the blasts of the two volcanoes- the Tonga eruption can be studied with the most modern satellite and weather monitoring systems. When Novarupta erupted the wireless radio was still new technology and it would be several years before the U.S. would have commercial broadcasts.
One thing that can be compared is the amount of magma and ash ejected by the two volcanoes- and by that metric, Novarupta was much more significant.
3.1 cubic miles of magma flowed out of Novarupta, filling valleys like soup bowls. More than a foot of ash accumulated in the surrounding area. Kodiak Island buildings had roofs collapse under the weight of it.
The pyroclastic flow from the volcano killed all vegetation in a part of the Ukak River Valley now known as “The Valley of Ten Thousand Smokes.” Riverbeds were vaporized, and they steamed out of the ground from uncountantable fumaroles on the ashy plain.
To this day, the area is almost totally bare. With no vegetation to protect the soil, the ash is picked up by winds and blown across the Shelikof Strait back on to Kodiak- as the ash once was over 100 years ago. Fortunately, Novarupta’s eruption had no known deaths, due to its remote location.
Alaska’s most violent volcanic eruptions seem to be behind it- at least in this lifetime.
“I don’t think folks should lose any sleep over it. And, you know, rest assured that volcanoes, especially large eruptions from volcanoes do provide some warning, and so no need to lose sleep. These things happen pretty rarely in the big scheme of things,” Coombs said.
Alaska still sees a substantial amount of volcanic activity, especially around the Aleutian Islands. While there are a handful of undersea volcanoes in the waters around the state, only the land volcanoes here get to the largest sizes- thankfully, they’re mostly dormant.
Unfortunately, it’s not a foregone conclusion that this eruption in Tonga will be the last from this year- scientists still have more work to do before they can reach that determination.