The rate of global glacial melting nearly doubled over twenty years according to a detailed scientific report published in the prestigious journal Nature. What’s shocking to me is that the amount of ice melting in Alaska per year is greater than the amount melting in Greenland and Antarctica per year combined. The rate of glacial mass loss in Alaska is 66.7 gigatonnes per year (English units and spelling) compared to 35.5 Gt per year for Greenland’s ice sheet and 20.9 gt per year for Antarctica. The global rate of ice loss is 267 Gt/yr. One quarter of earth’s total ice loss per year is in Alaska now.
There’s an excellent plain language story at the Guardian with a link that gets around the firewall to the original report. Heating of the ocean and atmosphere caused the rapid increase in melting, but the increase was not uniform, with Alaska’s glacial ice melting the fastest of any region on earth. The Guardian piece looks at the global picture, but the effects on Alaska are the most profound and shocking. I will discuss the extraordinary implications of the rapid melting of Alaskan glaciers based on other recent reports. There is a rapidly increasing threat of enormous landslides and megatsunamis as coastal glaciers rapidly retreat destabilizing the coastal geology. The rate of Alaskan earthquakes and volcanic eruptions may also increase in response to the loss of ice mass.
The Guardian summarized the big picture:
Between 2000 and 2019, glaciers lost 267 gigatonnes (Gt) of ice per year, equivalent to 21% of sea-level rise, reveals a paper published in Nature. The authors said the mass loss was equivalent to submerging the surface of England under 2 metres of water every year.
This was 47% higher than the contribution of the melting ice sheet in Greenland and more than twice that from the ice sheet in Antarctica. As a cause of sea-level rise, glacier loss was second only to thermal expansion, which is prompted by higher ocean temperatures.
The Guardian has a summary figure that’s much clearer than the figures in the original report. Please read the Guardian article to get a full sized image. Dailykos images are degraded.
At this point, the effects of glacial melting are less important to sea level rise than thermal expansion of the ocean caused by the ocean taking up heat. About 93% of the total heating caused by human greenhouse gas emissions, tree cutting and environmental damage goes into the global oceans. That is the primary driver of recent global sea level rise. The melting of the ice caps of Greenland and Antarctica may have a large impact in the future but at the present time they are not having as big a global impact as the melting of Alaskan glaciers. Again, from the Guardian.
The authors found the pace of glacier thinning outside of Greenland and Antarctica picking up from about a third of a metre per year in 2000 to two-thirds in 2019. This is equivalent to an acceleration of 62Gt per year each decade.
The study uses historical Nasa satellite data and new statistical methods to construct three-dimensional topographies going back 20 years and covering 99.9% of the world’s glaciers. The result is the most accurate and comprehensive assessment of the world’s 217,175 glaciers to date.
Global ocean heat uptake has not been uniform. Alaska has been strongly affected by the loss of Arctic sea ice and the summer warming of the Beaufort sea to the north of Alaska. The loss of sea ice in the late fall in the Bering sea has been profound. The loss of reflective sea ice has been a major factor in Alaska being one of the most rapidly warming places on earth. And that has led to Alaska’s world beating glacial melting.
The anticipated impacts of the rapid retreat of Alaskan coastal glaciers are stunning. NASA’s earth observatory tells the story with images from space that show the extreme retreat of the Barry glacier from 2013 to 2019. A coastal mountainside has been destabilized by the rapid glacial retreat. Please click the link to see NASA’s imagery of the glacial retreat. It cannot be shown here.
An artist with an eye for landscapes discovered a landslide that her geologist husband couldn’t see until he got a wider perspective from NASA satellites. The top photo is taken by Val Higman, artist.
While kayaking in Barry Arm fjord in June 2019, Valisa Higman, an artist-in-residence at Alaska’s Chugach National Forest, noticed some odd fractures on a cliff overlooking the fjord. Curious if the slope might be in the process of collapsing, she emailed photos (see one of them below) to her brother, Bretwood Higman. “Hig” is a geologist with Ground Truth Alaska, and he has studied landslides and tsunami deposits for decades.
He was soon inspecting the area using Google Maps, zooming in to the maximum extent possible and searching for signs of slippage. He saw the cracks as well, but nothing about them struck him as strong evidence of a big landslide. “But it turns out I had made a geology 101 error,” he said. “I hadn’t zoomed out enough, and I missed the big picture.” Still, he kept Barry Arm on a list of possible landslides to investigate more someday.
A few months later, Chunli Dai offered that chance. The Ohio State researcher was working on a NASA-funded project to develop new ways to automatically detect landslides in the Arctic, and she was looking for test sites to check how well the tool was working. Her project makes use of a high-resolution dataset called ArcticDEM and machine learning to automatically search for and flag landslides.
When Dai used her tools to survey the Barry Arm area, she got some eye-popping results—an entire mountainside near Barry Glacier was slowly and subtly shifting. If the giant, slow-moving landslide were to suddenly collapse into the narrow fjord below, it would generate an extremely large tsunami because of the way the fjord's shape would amplify the wave.
When NASA writes about an extremely large tsunami they are talking about a wave higher than anyone has recorded in human history. In 1958 there was an extraordinary landslide and wave in an Alaskan bay that ran 1700 feet up the adjacent mountainside. It was the highest tsunami wave witnessed and recorded in human history. The volume of soil and rock moving in Barry arm is significantly larger than the amount of soil and rock that moved in 1958. The 1958 story is eye popping in its own right. Glacial melting may have triggered an earthquake that led to a landslide and megatsunami in Alaska’s Lituya bay. The University of Alaska, Fairbanks wrote a story in March on recent research that discovered a link between glacial ice mass loss and the earthquake and tsunami at Lituya bay. news.uaf.edu/...
In 1958, a magnitude 7.8 earthquake triggered a rockslide into Southeast Alaska’s Lituya Bay, creating a tsunami that ran 1,700 feet up a mountainside before racing out to sea. Researchers now think the region’s widespread loss of glacier ice helped set the stage for the quake.
In a recently published research article, scientists with the University of Alaska Fairbanks Geophysical Institute found that ice loss near Glacier Bay National Park has influenced the timing and location of earthquakes with a magnitude of 5.0 or greater in the area during the past century ….snip... (please click the link for details.) In the study, researchers link the expanding movement of the mantle with large earthquakes across Southeast Alaska, where glaciers have been melting for over 200 years. More than 1,200 cubic miles of ice have been lost.
Unexpectedly, the greatest amount of stress from ice loss occurred near the exact epicenter of the 1958 quake that caused the Lituya Bay tsunami.
But as extreme as the Lituya bay tsunami was, a Barry arm tsunami could be an order of magnitude larger according to NASA.
“It was hard to believe the numbers at first,” said Dai. “Based on the elevation of the deposit above the water, the volume of land that was slipping, and the angle of the slope, we calculated that a collapse would release sixteen times more debris and eleven times more energy than Alaska’s 1958 Lituya Bay landslide and mega-tsunami.” That event, which was triggered by a 7.8 earthquake, dropped millions of cubic yards of rock about 2,000 feet (600 meters) into a fjord. It produced what is thought to be the tallest wave (1,700 feet) in modern history. In an event that eyewitnesses compared to an atomic bomb explosion, the huge wave washed away soil in a wide ring around the bay and obliterated millions of trees.
There are many fjords in Alaska and many retreating glaciers. Extreme landslides and megatsunamis are possible in many places other than Barry arm and Lituya bay. There is a growing hazard of extreme events triggered by the rapid retreat of Alaska’s glaciers along thousands of miles of coastline. That risk includes volcanism. At the end of the Pleistocene glaciation, glacial retreat may have led to an increase in activity of Alaskan volcanoes. www.researchgate.net/…
Meanwhile, scientists and engineers are doing their best to warn people of the risk of extreme tsunamis in Alaska and they are actively working to quantify the risks better.
Immediately after seeing the Landsat images, Higman was also convinced something serious was happening and alarmed about what it could mean. Since then, he has been reaching out to colleagues and coordinating with state and federal partners to evaluate the risk. In May 2020, a group of 14 scientists published an open letter warning that a landslide-generated tsunami is likely within 20 years and could happen at any time. If a landslide occurs, the resulting tsunami in Barry Arm could produce waves that are hundreds of feet high. Other, more distant bays—such as the more heavily populated Passage Canal (about 30 miles/50 kilometers away)—could see 30-foot (9-meter) waves.
Extreme impacts from climate change are not a far future problem. They could happen at any time.