Flying over Antarctica, it’s hard to see what all the fuss is about. Like a gigantic wedding cake, the snow icing on top of the world’s largest icing layer looks smooth and pristine, beautiful and perfectly white. Small swirls of snow dunes cover the surface.
But as you approach the edge of the ice sheet, a sense of tremendous underlying power arises. Cracks appear on the surface, sometimes arranged like a washboard, and sometimes a complete chaos of spirals and ridges, revealing the pale blue crystalline heart of the ice below.
As the plane flies lower, the scale of these breaks steadily grows. Not just cracks, but canyons big enough to swallow a jet plane, or spiers the size of monuments. Cliffs and tears, rips in the white blanket emerge, indicating a force that can hurl blocks of ice from the city like so many wrecked cars in a pileup. It is a twisted, torn and twisted landscape.
A sense of movement also emerges, in a way that no ice-free part of Earth can convey – the whole landscape is in motion and apparently not too happy about it.
Antarctica is a continent made up of several large islands, one of them the size of Australia, all buried under a 10,000-foot-thick layer of ice. The ice contains enough fresh water to raise sea levels by nearly 200 feet.
Its glaciers have always been on the move, but under the ice changes are taking place that are having profound effects on the future of the ice sheet – and the future of coastal communities around the world.
Breaking, diluting, melting, collapsing
Antarctica is where I work. As a polar scientist, I have visited most areas of the ice sheet on more than 20 trips to the mainland, bringing weather sensors and stations, walking across glaciers or measuring the speed, thickness and structure of ice.
I am currently the US coordinating scientist for a major international research effort on Antarctica’s riskiest glacier – more on that soon. I crept cautiously through crevices, carefully stepped onto the hard, windswept blue ice, and drove for days over the most dreary landscape you can imagine.
For most of the last few centuries, the ice sheet has remained stable, as far as polar science can tell. Our ability to track how much ice flows each year and how much snow falls on top goes back just a few decades, but what we see is an ice sheet that was almost in balance in the 1980s.
At first, the changes in the ice happened slowly. The icebergs would break off, but the ice was replaced by a new flow. Total snowfall hasn’t changed much in centuries – this we knew by looking at ice cores – and, in general, ice flow and ice sheet elevation seemed so constant that the main purpose of the first ice surveys in Antarctica was about finding a place, anywhere, that had changed drastically.
But now, as the surrounding air and ocean warms, areas of the Antarctic ice sheet that have been stable for thousands of years are breaking, thinning, melting or, in some cases, collapsing into a pile. As these ice edges react, they send a powerful reminder: if even a small part of the ice sheet were to completely collapse into the sea, the impact on the world’s shores would be severe.
Like many geoscientists, I think about what the Earth looks like below the part we can see. For Antarctica, that means thinking about the landscape beneath the ice. What does the buried continent look like – and how does this rocky basement shape the future of ice in a warming world?
Visualizing the world beneath the ice
Recent efforts to combine data from hundreds of ground and air studies have given us a kind of map of the continent beneath the ice. It reveals two very different landscapes, divided by the Transantarctic Mountains.
In East Antarctica, the part closest to Australia, the continent is rugged and rutted, with several small mountain ranges. Some of them have alpine valleys, cut by the first glaciers that formed in Antarctica 30 million years ago, when its climate resembled that of Alberta or Patagonia. Most of East Antarctica’s bedrock is above sea level. This is where the city-sized Conger Ice Shelf collapsed amid an unusually intense heat wave in March 2022.
In West Antarctica, the bedrock is very different, with parts much deeper. This area was once the ocean floor, a region where the continent was stretched and divided into smaller blocks with a deep sea floor between them. Large islands made of volcanic mountain ranges are linked together by a thick layer of ice. But the ice here is warmer and moving faster.
120,000 years ago, this area was likely an open ocean – and definitely within the last 2 million years. This is important because our climate today is rapidly approaching temperatures like a few million years ago.
The realization that the West Antarctic ice sheet disappeared in the past is a cause of great concern in the age of global warming.
Early stages of a full-scale retreat
Towards the coast of West Antarctica is a large area of ice called the Thwaites Glacier. This is the largest glacier on Earth at 110 kilometers in diameter, draining an area almost as large as Idaho.
Satellite data tells us it is in the early stages of a full-scale withdrawal. The surface height has dropped by up to 3 feet each year. Huge cracks formed on the coast and many large icebergs were left adrift. The glacier is flowing at over a mile a year, and that speed has nearly doubled in the last three decades.
This area was noted early on as a place where ice could lose its grip on the bedrock. The region has been called the “weak underbelly” of the ice sheet.
Some of the first measurements of ice depth, using radio echo sounding, showed that the center of West Antarctica had a bedrock up to a mile and a half below sea level. The coastal area was shallower, with some mountains and some higher ground; but a great gap between the mountains lay near the coast. This is where the Thwaites Glacier meets the sea.
This pattern, with deeper ice piled up near the center of an ice sheet and shallower but still low bedrock near the coast, is a recipe for disaster – albeit a very slow one.
Ice flows under its own weight – something we learned in earth science school, but think about it now. With very high and very deep ice near the center of Antarctica, there is tremendous potential for faster flow. Because it’s shallower near the edges, the flow is held back – grinding up the bedrock as it tries to get out and having a shorter ice column on the shore squeezing it out.
If the ice retreated far enough, the retreating front would shift from “thin” ice — still nearly 3,000 feet thick — to thicker ice toward the center of the continent. At the retreating edge, the ice would flow faster, because the ice is thicker now.
As it flows faster, the glacier pulls the ice behind it, allowing it to float, causing more recoil. This is what is known as a positive feedback loop – retreat leading to thicker ice in front of the glacier, making it flow faster, leading to more retreat.
Hot water: The attack from below
But how would this retreat begin? Until recently, Thwaites hadn’t changed much since it was first mapped in the 1940s. At first, scientists thought a retreat would be a result of warmer air and surface melting. But the cause of the changes in Thwaites seen in satellite data is not so easy to detect from the surface.
Under the ice, however, at the point where the ice sheet rises from the continent and begins to protrude into the ocean like a floating ice shelf, the cause of the retreat becomes evident. Here, ocean water well above the melting point is eroding the base of the ice, erasing it like an ice cube would disappear floating in a glass of water.
Water that is capable of melting up to 50 to 100 feet of ice every year meets the edge of the ice sheet here. This erosion allows the ice to flow faster, pushing against the floating ice shelf.
The ice shelf is one of the restraining forces holding back the ice sheet. But pressure from land ice is slowly breaking up this ice sheet. Like a plate shattering under a lot of weight, it is developing huge cracks. When it gives way — and mapping the fractures and flow velocity suggests that’s just a few years away — will be another step that will allow the ice to flow faster, fueling the feedback loop.
Up to 10 feet of sea level elevation
Looking at the ice-covered continent from our camp this year, it’s a sobering sight. A huge glacier, flowing towards the coast and stretching from horizon to horizon, rises up into the middle of the West Antarctic Ice Sheet. There is a palpable feeling that ice is falling over the shore.
Ice is still ice—it doesn’t move that fast, no matter what is driving it; but this gigantic area called West Antarctica could soon begin a multi-century decline that would rise to 3 meters above sea level. In the process, the rate of sea level rise would increase several times over, presenting major challenges for people participating in coastal cities. Which is pretty much all of us.
Ted Scambos is a senior fellow at the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder. He is also the principal investigator for the Scientific Coordination Office of the Thwaites Glacier International Collaboration.
This comment was originally posted by The Conversation — Ice world: Antarctica’s riskiest glacier is being attacked from below and losing its grip
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