Since August 2019, a large accumulation of pumice has drifted in the Southwest Pacific to Australia.
Researchers at the GEOMAR Helmholtz Center for Ocean Research Kiel and colleagues from Canada and Australia, have now identified the origin of the pumice raft. It is a hitherto unnamed underwater volcano in the waters of the Tonga Archipelago.
Various underwater volcanoes were discussed at the time as a potential source. But direct proof of the exact origin of the pumice stone has so far been lacking.
It concerns an underwater volcano just 50 kilometers northwest of the island of Vava'u in the Tonga archipelago. In the international scientific literature, it appears so far only under the number 243091 or under the name of Volcano "F", explains Dr. Philipp Brandl of GEOMAR, first author of the study.
"The team found what they were looking for on freely accessible satellite images. On an image of the ESA Copernicus Sentinel-2 satellite taken on August 6, 2019, clear traces of an active underwater eruption may be Since the images are exactly georeferenced, they could be compared to the corresponding bathymetric maps of the seabed ", collected in January by the Archimedes expedition / research vessel Sonne. "The eruption traces correspond exactly to volcano F", says Dr. Brandl.
To be sure, the researchers also compared this position with information from stations in the global seismic network that recorded the eruption signals. Despite their low number in this region, their data are consistent with the "F" volcano as its origin.
Pumice can form during volcanic eruptions when viscous lava is "turned into foam" by volcanic gases such as water vapor and carbon dioxide. This creates so many pores in the cooling rock that its density is less than that of water. "During an underwater eruption, the probability of generating pumice is particularly high", says Dr. Brandl.
Path and positions of the pumice raft, reconstructed in the study, between August 8 and August 14, 2019 - Graphic Philipp Brandl
Using additional satellite images, the team traced the drift and dispersion of pumice raft until mid-August (map above). It slowly drifted west and reached an area of up to 167 square kilometers. The team was also able to determine the extent of the underwater eruption. It would correspond to a volcanic eruption index of 2 or 3.
With the current direction and speed, pumice raft should touch the Great Barrier Reef off the east coast of Australia in late January or early February. Biologists, in particular, are eagerly awaiting this event as pumice rafts can play an important role in the dispersal of wildlife in the vastness of the Pacific Ocean. The Kiel team of geologists would like to examine pumice samples to more precisely determine the geochemistry of volcano F.
- Geomar - Vulkan „F“ ist der Ursprung der schwimmenden Steine - Forscher veröffentlichen Studie zum Bimssteinfloß im Südwestpazifik - link
- The study was published online in the international journal Journal of Volcanology and Geothermal Research: The 6–8 Aug 2019 eruption of ‘Volcano F’ in the Tofua Arc, Tonga - Philipp A.Brandt & al. - link
- Schmidt Ocean Institute - Traces of an underwater volcano - 11.12.2019 - link