A recent Smithsonian Magazine article gives some interesting insights to present-day Jökulhlaups (glacial outburst floods) that are but minuscule relatives of the cataclysmic Ice Age Floods.
Iceberg Lake was on the edge of a western tributary of the Tana Glacier, but in 1999 the lake suddenly vanished. Dammed on its southern end by ice, the water, with persistently warming temperatures, had bored a hole under the ice and escaped through tunnels to emerge ten miles away and empty into the Tana River.
The sudden drainage of a glacier-dammed lake is not uncommon. “Some lakes in Wrangell-St. Elias regularly drain,” Loso said. Hidden Creek Lake, for instance, near McCarthy, drains every summer, pouring millions of gallons through channels in the Kennicott Glacier. The water gushes out the terminus of the Kennicott, causing the Kennicott River to flood, an event called a jokulhlaup—an Icelandic word for a glacial-lake outburst flood. “The Hidden Creek jokulhlaup is so reliable,” said Loso, “it has become one of the biggest parties in McCarthy.”
But the disappearance of Iceberg Lake was different, and unexpected. It left an immense trench in the ground, the ghost of a lake, and it never filled up again. The roughly six-square-mile mudhole turned out to be a glaciological gold mine. The mud, in scientific terms, was laminated lacustrine sediment. Each layer represented one year of accumulation: coarse sands and silts, caused by high runoff during the summer months, sandwiched over fine-grained clay that settled during the long winter months when the lake was covered in ice. The mud laminations, called varves, look like tree rings. Using radiocarbon dating, Loso and his colleagues determined that Iceberg Lake existed continuously for over 1,500 years, from at least A.D. 442 to 1998.
“In the fifth century the planet was colder than it is today,” Loso said, “hence the summer melt was minimal and the varves were correspondingly thin.” The varves were thicker during warmer periods, for instance from A.D. 1000 to 1250, which is called the Medieval Warming Period by climatologists. Between 1500 and 1850, during the little ice age, the varves were again thinner—less heat means less runoff and thus less lacustrine deposition. “The varves at Iceberg Lake tell us a very important story,” Loso said. “They’re an archival record that proves there was no catastrophic lake drainage, no jokulhlaup, even during the Medieval Warming Period.” In a scientific paper about the disappearance of Iceberg Lake, Loso was even more emphatic: “Twentieth-century warming is more intense, and accompanied by more extensive glacier retreat, than the Medieval Warming Period or any other time in the last 1,500 years.” Loso scratched his grizzled face. “When Iceberg Lake vanished, it was a big shock. It was a threshold event, not incremental, but sudden. That’s nature at a tipping point.”
One of the most startling, and devastating, consequences of this rapid melting of the ice was the Icy Bay landslide. The Tyndall Glacier, on the southern coast of Alaska, has been retreating so quickly that it is leaving behind steep, unsupported walls of rock and dirt. On October 17, 2015, the largest landslide in North America in 38 years crashed down in the Taan Fjord. The landslide was so enormous it was detected by seismologists at Columbia University in New York. Over 200 million tons of rock slid into the Taan Fjord in about 60 seconds. This, in turn, created a tsunami that was initially 630 feet high and roared down the fjord, obliterating virtually everything in its path even as it diminished to some 50 feet after ten miles.
“Alder trees 500 feet up the hillsides were ripped away,” Anderson says. “Glacial ice is buttressing the mountainsides in Alaska, and when this ice retreats, there is a good chance for catastrophic landslides.” In other ranges, such as the Alps and the Himalaya, he says, the melting of “ground ice,” which sort of glues rock masses to mountainsides, can release enormous landslides into populated valleys, with devastating consequences.
“For most humans, climate change is an abstraction,” Loso says when I meet him in his office, which is down a long, dark, heavily beamed mine building in Kennecott. “It’s moving so slowly as to be basically imperceptible. But not here! Here glaciers tell the story. They’re like the world’s giant, centuries-old thermometers.”
Read the entire article “A Daring Journey Into the Big Unknown of America’s Largest National Park” online at SmithsonianMag.com