The Hunga-Tonga Hunga-Ha’apai underwater volcano is still surprisingly intact. The discovery was made by the New Zealand-led team of experts who set out to map the flanks of the mountain, which were believed to have been severely damaged after last January’s eruption that produced the largest atmospheric explosion recorded on the Land in the last century.
The eruption caused tsunamis that hit the Fiji Islands, Tonga and the American Samoa Islands, causing alarm on the coasts of half the world. Now geologists from New Zealand’s National Institute for Water and Atmospheric (Niwa) have managed to get closer to the area to map the vulva after the eruption and the surrounding seabed. And they could see that structurally Hunga-Tonga Hunga-Ha’apai hasn’t changed much.
Although there has been a lot of ash deposition and sediment movement, the volcano continues to remain high. “Given the violence of the January 15 eruption, I expected the structure to have collapsed or blown up, and it didn’t,” he explained to the Bbc the leader of the expedition, the Niwa marine geologist Kevin Mackay. “While the volcano appeared intact, the sea floor showed some dramatic effects of the eruption. There is fine sandy mud and deep ash ripples up to 50km from the volcano, with carved valleys and huge mounds of sediment.”
From its survey of 22,000 sq km, the Tangaroa team calculates that around 6-7 cubic km of material has been added to the sea floor. These are ash and rock that were initially ejected from the volcano into the air, but then fell back into the water and descended from the sides of the seamount to run to the ocean floor. These density flows, or pyroclastics, were the main factor in generating the tsunami waves that flooded the local islands, Mackay told Bbc News.