Vulcanologists initially thought it had come from a seafloor volcano at the Monowai Seamount to the south of Tonga after “rafts” of pumice were first discovered by the New Zealand Defense Force on August 9.
But using satellite images and past seismic records, it was later possible to pinpoint the time and location of the eruption to July 17 at the Havre Seamount, well to the southwest of Monowai.
By July 21, the eruption appeared to have waned, but dense rafts of pumice were left scattered across the ocean’s surface after being spewed from a depth of about 3,600 feet.
The image to the right was captured by NASA’s Aqua satellite on July 28 and shows that thick rafts of the pumice had drifted to the northwest of the underwater eruption site.
The pumice was later split into several twisted segments by prevailing wind and ocean currents, which also carried it to the north and east of the Havre Seamount.
Little had been known about the Havre Seamount before the eruption, and vulcanologists were not even aware that it was an active submarine volcano.
While the coverage of the pumice was expansive in some of the rafts, the material was so light in density that it did not impede maritime traffic and posed no threat to vessels.