Calving Ice Sets Off Mini-Tsunamis Daily in Antarctica
The placid demeanor of an Antarctic fjord often conceals a more dangerous reality that lurks just below the surface. Even as Ari Friedlaender led us on a quiet search for minke whales in Andvord Bay on March 15, the fjord was showing a very different face several miles away at Neko Harbor, a low, ice-free ridge on the north side of the fjord where a colony of gentoo penguins nests.
Ted Cheeseman, the naturalist who organized this cruise involving both tourists and scientists aboard the Ortelius, stood on the bare, cobbled beach where several passengers lingered near the Zodiac that they would soon ride back to the ship. A faint crack rang out.
The bystanders turned to see a barrage of ice blocks and snow showering into the water a half mile to the west. One of the dozen or so glaciers that pours into Andvord Bay had just calved a bit of ice. It was the kind of event that happens several times a day in a fjord like this—especially in a warm region of Antarctica like the peninsula, where 87 percent of glaciers are in retreat. Cheeseman sent his passengers farther up the beach just in case the falling ice had triggered a wave that might wash up on the shore and soak them. He walked down to the Zodiac and began pulling it into the water, where it would escape damage on the off chance that a wave did hit the beach.
After a few seconds of tugging the boat into the water, Cheeseman noticed something mildly worrying: Water had started to recede down the beach—just a few inches at first but signaling that a wave of some sort was on its way. He pulled the Zodiac deeper into the water so he could jump in, drop the propeller, and drive over the oncoming wave before it grew tall.
The gentle current that was pulling water away from the beach grew into a voracious suck; cobblestones as large as grapefruit tumbled downhill with the current and penguins ran and squawked in alarm. Cheeseman looked up to see the ocean swell, still a hundred feet away, that was gathering all of this water into a wave that would soon smash into the rocks. He was too late. The wave was too large. He was in trouble.
He gave the boat one more shove, then turned and ran up the beach.
One last glimpse back—the Zodiac was vertical on its side. The wave was heaving it forward like a wall of bricks. He ran. The water reached his legs, he lunged forward to surf it, his arms bent protectively over his head. He expected the boat to slam down over him. He bounced and slid through rocks and freezing water.
Cheeseman found himself sprawled over an outcrop of rounded granite, 30 feet up the beach. The Zodiac lay just inches from his feet, flipped over. Its outboard motor had shattered on the rocks. Its equipment box, made of five-eighths–inch plywood, was torn open.
Glaciers calving into the ocean are known, on some occasions, to trigger miniature tsunamis. The calving of an iceberg can set off an ice quake that’s detectable from seismic stations miles away. Cheeseman points out, humbly, that the calving that triggered this nasty wave appeared small by Antarctic standards.
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“I think most of what made the wave came from under the water,” he speculates—from a much larger block of ice that may have broken free from the glacier unseen, below the water’s surface.
“I was so lucky,” he says. Even a 15-year veteran of the Antarctic Peninsula can be caught off guard. Next time he’ll heed his own advice to his passengers and leave the boat to its own fate.
Writer Douglas Fox and photographer Carolyn Van Houten are spending 15 days aboard the M.V.Ortelius as the ship explores glacial fjords along the Antarctic Peninsula, conducting studies of humpback and minke whales. Follow their story here, then see more about life in Antarctica on the new show Deep Freeze, on the National Geographic Channel in fall 2016.