On January 15, 2022, the Hunga Tonga-Hunga Ha’apai exploded in the Pacific – and the Tonga archipelago was again one island poorer; only a few rocky peaks protrude from the sea. But the island arc at the Tonga Trench, on which Tonga and other islands lie, has the highest density of underwater volcanoes on earth. One of them erupted on September 10th and has since created a new island on Home Reef, as NASA has determined using satellite images.
As early as September 11, the volcano broke through the waterline, while at the same time the sea around it turned greenish from the eruption material: sulfur compounds and released acids also ensure that the water here has a very low pH value, at least temporarily. According to estimates by the Tonga Geological Survey, as of September 14, the island already had an area of 4,000 square meters and a height of about ten meters above sea level.
Home Reef lies on the Kermadec-Tonga subduction zone where three tectonic plates meet. Here the Pacific Plate subducts under two other plates, with the fastest subduction known worldwide taking place on the east side of the Tonga Plate: At a rate of 24 centimeters per year, crustal material disappears at depth here; its melt promotes active volcanism in the region. At the same time, the second deepest deep-sea trench on earth is located here, which is up to 10,000 meters deep.
Islands have appeared on Home Reef four times since records began, but most of them were short-lived. In one case on a neighboring volcano, however, the mainland even survived 25 years. The surf often causes the islands to disappear again, as the loose volcanic material can be quickly removed. In other cases, further, destructive eruptions cause the new land to sink back into the sea. So the future of the new island on Home Reef is uncertain – and rather short.