Midway on its 800-kilometer (500-mile) voyage from Auckland to
Raoul Island, New Zealand, the HMNZS Canterbury received an
intriguing report: a maritime patrol aircraft had spotted a vast
area of open ocean covered with floating pumice. Soon after, the
ship was sailing through a mass of buoyant volcanic rocks. Up to
two feet thick, the pumice raft was about half a nautical mile
(1 kilometer) wide, and "extended sideways as far as the eye
could see," wrote Rebecca Priestley, a science writer aboard the
ship. Although the lightweight, gas-filled pumice posed no
threat to the Canterbury, enough got stuck in the water filters
to provide samples for analysis. Though the pumice was spread
over a vast area of the South Pacific, the origin was a mystery
to the crew of the ship. An undersea volcano several hundred
kilometers to the north of the pumice--Monowai--had erupted on
August 3, but an airline pilot reported seeing pumice as early
as August 1. Two data sources provided clues to pinpoint the
volcano: earthquake