The Size of the 2022 eruption of Hunga Tonga Hunga Ha’apai (Patreon)

The major explosive eruption which occurred from the Hunga Tonga Hunga Ha’apai eruption was definitely one for the record books. However, since >99% of its eruptive products were deposited underwater, it will be incredibly difficult to say how large the eruption truly was. Currently, the Smithsonian institute rates the eruption as a VEI 5, citing a figure of ~6.5 km^3 tephra (1980 Mount Saint Helens was ~1.01 km^3 tephra). However, this figure best represents the missing volume from the 4 km wide caldera which is now 750 meters deeper. The scientist who made these observations (prof Cronin) I interviewed. He said the 6.5 km^3 is thus about the size of the DRE or dense rock equivalent (volume of magma erupted). For context, 1 m^3 of magma can produce up to 2.5 m^3 of ash. Thus, the high estimate is the eruption ejected 16.25 km^3. This is an upper bound.

A NIWA survey found 7.0 km^3 of new sediment on the ocean floor. Here is the problem. Much of the ash has since been compacted by water. The original maximum volume of the ash is crucial in determining tephra, not the compacted volume. This survey was also incomplete, meaning distal areas and land ashfall were not accounted for in volume estimates.

In summary…

Extreme lower bound:

6.5 km^3, VEI 5

Lower bound:

7.0 km^3, VEI 5

Mid end, suggested my several interviews:

8.0-10.0 km^3, VEI 6

High end, my estimate:

~14.2 km^3. VEI 6. A similar figure was suggested by a prior research paper.

Maximum possible size:

16.25 km^3. VEI 6

Due to some definition related weirdness, it is completely possible that this eruption will remain classified as a VEI 5, as there may not truly be a way to determine the total volume of tephra ejected.

With this being said, the 1991 eruption of Pinatubo was also initially underestimated. It was first thought to have ejected 5.0-5.5 km^3, but actually emitted 10.0-13.0 km^3.