Hawaii's Kama'ehuakanaloa Seamount, a.k.a. Lō'ihi

Kamaʻehuakanaloa Seamount is an active submarine volcano about 22 mi off the coast of the Big Island

Today's selection -- from The Underworld by Susan Casey. The monumental violence of underwater volcanoes:

“In 1996, the seafloor around Hawaii rattled with a swarm of four thousand earthquakes, the largest seismic event ever recorded in Hawaii. ‘Nobody had any idea what was happening,’ Kerby recalled, raising his eyebrows for emphasis. ‘It just sounded like something major was going on.’ A Pisces expedition was quickly mounted. Descending into a deep-sea eruption is not on the average person's to-do list, but this was an event scientists couldn't afford to miss. That didn't mean it wasn't wildly dangerous.

“Submarine volcanoes don't always present themselves politely. During one notorious tantrum in September 1952, the U.S. Navy's deep-sea hydrophones detected a series of loud explosions in the Pacific Ocean, 230 miles south of Tokyo. It was a known spot for frisky tectonics, part of a longer arc at the seam where two oceanic plates collide. Active volcanoes had been charted on the nearby seafloor.

“Over the next week the blasts continued, becoming so convulsive they generated multiple tsunamis. Often these outbursts were accompanied by thunder and lightning that lasted for hours. ‘Great sparks rose into the sky,’ one fisherman noted. Someone else called in a ‘pillar of fire.’ Marine observers watched a two-hundred-foot dome of water swell up on the surface like a colossal bubble, its edges running with waterfalls. They heard roaring and moaning noises that seemed to come from the ocean itself, which had turned a sickly green color and was puking up dead fish. When U.S. Air Force pilots flew over the site, they saw spiky black rocks emerge in a boil of whitewater, and then sink back into the depths.

“For marine geologists this was blockbuster stuff, so when the explosions stopped—momentarily, as it turned out—a group of thirty-one Japanese scientists and crew motored out on a research ship, the Kaiyo Maru 5, to document the action firsthand. We'll never know what they witnessed that day, for the ship was never seen again. A few days later, scraps of it were found floating nearby. The wreckage was shot through with lava shrapnel.

Ocean bottom observatory (OBO) at Pele's Vents

“It's hard to imagine the force that's needed to propel hundreds of tons of volcanic mayhem upward through a mile of water, but it's safe to say that you don't want to be near it in a submersible. And the Hawaiian Islands have hosted a lot of turbulent rocks. On a wall outside Kerby's office, I'd noticed a bathymetric map of Hawaii that revealed vast debris fields on the seafloor. Rocks the size of bungalows, buildings, and city blocks had, at some point, careened across thirty-eight thousand square miles of submarine real estate, an area five times larger than the combined landmass of the islands.

“I felt humbled by the sight of the map because I knew what it meant: monumental violence had occurred here in the past, when the volcanoes rose to a point where they shuddered and partially collapsed, generating mighty submarine landslides. (Some of the slides would have caused mega-tsunamis, which explains why coral fragments have been found high on the slopes of the Big Island.) During a massive earthquake swarm, anyone familiar with this submerged carnage would've instantly wondered: Was Lō'ihi shifting and sliding and shedding its skin in that same way now?

"'It was nerve-racking,’ Kerby confirmed. ‘We got out to the site and there was still activity coming off the bottom. The ship was getting hit with these shock waves, just—BANG. I was supposed to go down there to see what was going on.’ He laughed. ‘I never would have done a dive like that if I hadn't been exploring that volcano for nine years already.’”

The Underworld: Journeys to the Depths of the Ocean
author: Susan Casey  
title: The Underworld: Journeys to the Depths of the Ocean  
publisher: Doubleday