Assuming equal distribution in all directions, the 2-cm isopach of Hunga Tonga would be similar in area. Note that that was with a strong southerly wind: the ash was almost entirely to the north, with 2 cm thickness out to 150 km away but only in a narrow cone. Hekla in 1108 AD covered about 10,000 km 2 within the 2-cm isopach (contour of ash thickness). That information is not enough information to calculate the total volume of ash! For that you need to know thickness at several distances from the eruption.
Photos suggest something like 1-2 cm of ash on Tonga, 60 km from the epicentre of the blast. The tsunami may have contributed to the lost land, especially if it was much higher than we assumed. The destruction suggests that it was caused by more than the explosion (which would have gone for the steep, high ridges). That includes two small islands that existed 3 kilometers to the south, on the southern caldera rim. The lower lying land, perhaps some tens of meters above sea, is all gone. (Officially it is called Hunga Ha’apai, and Hunga Tonga is the eastern ridge, but this distinction has quickly been lost.) It is interesting that these are the highest ridges of the old caldera rim. Hunga Tonga has been reduced to two small slivers of land, as shown above.
But these pale into insignificance compared to the local damage. The coast is polluted over 1 or 2 kilometers. There is an oil spill in Peru, from a tanker that was pumping out oil as the tsunami rolled in. There is damage further away, boats in harbours in New Zealand and Japan, and some minor coastal damage in the US. Damage at the capital is limited, but other islands have not yet been contacted, and it appears that they have been affected much worse than initial reports suggested. There is extensive damage along the western shores of the Tonga archipelago. The death toll of the tsunami at the moment stands at five, three at Tonga and two in Peru. The cone and ridge before the destructionĪs more information comes in, it is time for a brief update, and for a theory on why the eruption of Hunga Tonga was so destructive for what was, after all, a fairly small volcano.
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