In a recent post we described an unexpected encounter at sea with a submarine in the vicinity of the Tonga Trench, the second deepest point on the planet. Maybe it’s something about Tonga that attracts peculiar things, but Bob encountered an even stranger sight in the same area not long after—a disappearing island!
Stranger than encountering a submarine
The Tongan Island chain lies along the rim of the Tonga Trench, a zone of considerable seismic activity. Tremors are common occurrences among the islands, and a terrible tsunami generated from this area struck Samoa and surrounding island countries in 2012.
When Bob was living in the islands in the late 1960s and early1970s, the old Tongan sea captains told him about an island that appears and disappears. Volcanic Falcon Island, known locally as Fonuafoʻou, lies about fifteen miles northeast of the twin islands of Honga Tonga and Honga Ha’apai. When the volcano erupts just below the surface of the ocean, it spews rock into the air, building up a layer that sometimes rises above sea level. But over time the action of the waves washes it away into the depths, erasing it from sight.
Things that go bump in the night
Bob was sailing in this area one moonless night, just west of the islands of Tonga, when he heard an unusual scraping sound against the hull. He looked over the side, but at first couldn’t see what was causing it. Bob went below to the cabin and returned with a flashlight. The loom of the light punched a hole in the darkness, but it didn’t reflect at all. It was as if the light was being absorbed.
Then Bob shone the light alongside the yacht and could distinguish what appeared to be small lumps on its surface. He went back to the cockpit and retrieved a bucket. He tied the lanyard off to a stanchion and dropped the inverted bucket into the water and quickly pulled up on the lanyard to pull it from the sea.
With his mysterious sample in hand he walked back to the cockpit and shone the light into the bucket. He was amazed at what he saw. Stone! Floating on the surface of the water. Rough, roundish, stone about the size of golf balls. He plucked a handful from the water and judged the weight. It was very light and under the scrutiny of the light he could see that the stones were perforated with tiny holes.
Bob knew that it was pumice rock. He remembered the Tongan captains’ stories, and realized that the volcano responsible for Falcon Island was active.
NOAA has photos to prove it
At first light he looked out at the sea and witnessed the odd spectacle of dull, brown-colored lava rock floating on the surface as far as he could see.
NOAA took this photo of a more recent eruption and the plume of pumice floating on the sea.
NOAA now has a guide for mariners that encounter volcanic eruptions.
On a later trip, Bob took the opportunity to sail to Falcon Island on a relatively calm day, taking care to steer clear of the reef at the southern end. In the transparent tropical water he could see the loose rock twenty to thirty feet down, and became one of the few people in the world who has anchored atop this strange island.