In-Depth: Hunga Tonga-Hunga Ha’apai Eruption

On January 15 local time, a volcano erupted in the Kingdom of Tonga, causing a damaging and deadly tsunami and cutting off communications.

Beth Johnson
7 min readJan 22, 2022


Cowritten by Kerbal01.

CREDIT: Google Maps via BBC News

Earlier this week, we talked briefly about the volcanic eruptions occurring in the Kingdom of Tonga last weekend, and we promised you an in-depth look at the situation. Scientists are continuing to analyze a wealth of data, with more coming in every day, but here is what we know so far.

Several weeks ago, on December 20, 2021, the submarine volcano Hunga Tonga-Hunga Ha’apai began to erupt. That initial set of eruptions was barely noted in international media, with most of the coverage remaining local because nothing much was going on. The visible portion of the volcano, or rather, the island produced at the surface, grew based on an analysis of satellite images. But the volcano quieted back down, and by January 11, 2022, it had been declared dormant.

And then, at 0420 UTC on Friday, January 14 (5:20 pm local time on Saturday, January 15), a much larger eruption occurred that sent a mushroom cloud of ash, steam, and gas up into the atmosphere to a height of nearly twenty kilometers, although later analysis of sulfur dioxide plumes in the stratosphere suggests the height was closer to thirty kilometers. Geologists observing from an ocean vessel nearby noted that the base of the mushroom cloud was about five kilometers wide.

IMAGE: Satellite imagery of the eruption of Hunga Tonga-Hunga Ha’apai volcano near Tonga on Saturday, January 15, 2021. CREDIT: Japan Meteorological Agency

Incredibly, initial reports on Twitter had people hearing the explosion as far away as Australia, Samoa, and Fiji, but further analysis in the past few days has led to the discovery that the explosion was heard as far away as Anchorage, Alaska. I personally checked in with a colleague to ascertain if the very loud boom we heard here at my house on Friday night could have been the eruption as well, and she confirmed that yes, it absolutely could be and probably was.

Ashfall from the eruption coated the Tongan islands, and a tsunami warning was issued for both the Kingdom of Tonga and much…



Beth Johnson

Planetary scientist, podcast host. Communication specialist for SETI Institute and Planetary Science Institute. Buy me a coffee: