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Gigantic Iceberg Disintegrates as Concern Grows Over Glacier Stability, Sea Level Rise

The stability of a key Antarctic glacier appears to have taken a turn for the worse as a large iceberg that broke off during September has swiftly shattered. Meanwhile, scientists are concerned that the rate of sea level rise could further accelerate in a world forced to rapidly warm by human fossil fuel burning.

(Iceberg drifting away from the Pine Island Glacier rapidly shatters. Image source: European Space Agency.)

This week, a large iceberg that recently calved from West Antarctica’s Pine Island Glacier rapidly and unexpectedly disintegrated as it drifted away from the frozen continent. The iceberg, which covers 103 square miles, was predicted to drift out into the Southern Ocean before breaking up. But just a little more than two months after calving in September, the massive chunk of ice is already falling apart.

The break-off and disintegration of this large berg has caused Pine Island Glacier’s ice front to significantly retreat. From 1947 up until about 2015, the glacier’s leading edge had remained relatively stable despite significant thinning as warmer water began to cut beneath it. But since 2015, this key West Antarctic glacier has begun to rapidly withdraw. And it now dumps 45 billion tons of ice into the world ocean each year.

(Glaciers like Pine Island balance on a geological razor’s edge. Because they sit on a reverse slope, it only takes a relatively moderate amount of ocean warming to precipitate a rapid collapse. These collapses have happened numerous times in the past when the Earth warmed. Now, human-forced climate change is driving a similar process that is threatening the world’s coastal cities. Image source: Antarctic Glaciers.)

The present rate of melt is enough to raise sea levels by around 1 millimeter per year. That’s not too alarming. But there’s concern that Pine Island Glacier will speed up, dump more ice into the ocean and lift seas by a faster and faster rate.

Pine Island Glacier and its sister glacier Thwaites together contain enough water to raise seas by around 3-7 feet. The glacier sits on a reverse slope that allows more water to flood inland, exposing higher and less stable ice cliffs as the glacier melts inland. If the glacier melts too far back and the ice cliffs grow too high, they could rapidly collapse — spilling a very large volume of ice into the ocean over a rather brief period of time. As a result, scientists are very concerned that Pine Island could swiftly destabilize and push the world’s oceans significantly higher during the coming years and decades.

No one is presently predicting an immediate catastrophe coming from the melt of glaciers like Pine Island. However, though seemingly stable and slow moving, glacial stability can change quite rapidly. Already, sea level rise due to melt from places like Greenland and Antarctica is threatening many low-lying communities and nations around the world. So the issue is one of present and growing crisis. And there is very real risk that the next few decades could see considerable further acceleration of Antarctica’s glaciers as a result of human-forced warming due to fossil fuel burning.

Dr Robert Larter, a marine geophysicist at British Antarctic Survey, who has researched Pine Island Glacier in his work with the Alfred Wegener Institute, recently noted to Phys.org:

“If the ice shelf continues to thin and the ice front continues to retreat, its buttressing effect on PIG will diminish, which is likely to lead to further dynamic thinning and retreat of the glacier. PIG already makes the largest contribution to  of any single Antarctic glacier and the fact that its bed increases in depth upstream for more than 200 km means there is the possibility of runway retreat that would result in an even bigger contribution to sea level.”

CREDITS:

Hat tip to Colorado Bob

Hat tip to Erik Friedrickson

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One By One, the Flood Gates of Antarctica are Breaking Open

“We have still time to avoid the worst of it, but we have already opened a number of flood gates, one in West Antarctica, and several in Greenland.”Dr Eric Rignot.

“This kind of rifting behavior provides another mechanism for rapid retreat of these glaciers, adding to the probability that we may see significant collapse of West Antarctica in our lifetimes.” Ian Howat, Earth Sciences associate Professor at Ohio State University.

“Burning all the world’s coal, oil and gas would melt the entire Antarctic ice-sheet and cause the oceans to rise by over 50m, a transformation unprecedented in human history. The conclusion of a new scientific study shows that, over the course of centuries, land currently inhabited by a billion people would be lost below water.” — The Guardian.

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Massive Rift Forming in Larsen C

Larsen C. It’s the next big ice shelf on the butcher’s block in West Antarctica. And now it appears the shelf may be well on its way to facing the same fate as its companions Larsen A and Larsen B. That fate — disintegration and the ultimate release of glaciers that have been held in check for thousands of years into the world ocean.

It was only about 150 years ago that the Larsen Ice shelves were discovered. And the Larsen shelf system is thought to have been mostly stable throughout the last 12,000 years. But in 1995 Larsen A splintered into a million icebergs. And in 2002 the larger portion of Larsen B broke apart. Warming Ocean waters heated by an atmosphere loaded with greenhouse gasses did the damage. And now the same warm water currents that shattered Larsen A and Larsen B are endangering their larger cousin — Larsen C.

larsen-c-ice-rift

(Ice shelves and sea fronting glaciers serve as the flood gates keeping West Antarctica’s glaciers from spilling into the ocean and raising sea levels by as much as 20 feet. But warm ocean waters are causing these flood gates to melt and crack wide open. The above image shows a massive abyssal rift forming in the Larsen C ice shelf. A similar rift formed in the center of the Pine Island Glacier last year. A signal that the West Antarctic Ice Sheet could undergo a major collapse over the next 100 years. Image source: NASA.)

For today, a huge rift running through the ice shelf is about to break off a Delaware-sized iceberg into the Atlantic Ocean. The rift is broadening, deepening and extending. And it now measures 70 miles long, 300 feet wide, and a third of a mile deep. Once this enormous abyssal crack runs its course and causes about 10 percent of the ice shelf to break off, the big land-grounded glaciers sitting upon mountainous slopes behind the ice shelf will have less protection. They will increase their forward speed and contribute larger volumes of ice outflow to the growing problem of global sea level rise.

In this way, rifts in Antarctica’s sea fronting glaciers and ice shelves can be seen as giant cracks in the flood gates holding back enormous glaciers that, when released, will lift global sea levels by feet and meters.

Big Crack in the Pine Island Glacier

Closer to the center mass of West Antarctica, the Pine Island Glacier serves as one of the most important of these flood gates. In total, the large grounded glaciers in what could best be termed as an ice bottle neck hold back about 10 percent of all of West Antarctica’s interior ice mass. But just last year a huge rift that formed in this glacial buttress during 2013 cracked wide open — causing three massive icebergs totalling ten times the size of Manhattan to break off.

According to a new study, warm ocean water flooded far inland along the underside of the Pine Island Glacier. It ate away at its base and then spilled down-slope to cut out a melting hollow in the glacier’s heart. Ultimately, an enormous crack formed within the glacier 20 miles away from where the ice mass meets the ocean at the surface.

(Massive crack forms in the Pine Island Glacier, then causes three very large icebergs to break off during 2015. A new study finds that the Pine Island Glacier is melting from the inside out and an inland flood of warm ocean water is causing both the melt and the formation of large rifts in the ice. Scientists believe that these could be the first signs of a significant collapse of West Antarctica that could occur without our lifetimes. Video source: Ohio State.)

Then, in 2015, gigantic chunks of ice covering 225 square miles broke off from the Glacier and floated out into the Amundsen Sea. This was the second series of icebergs to break off from the Pine Island Glacier in as many years. And scientists were notably very concerned.

Pine Island Glacier is particularly vulnerable because it sits on a reverse slope. In other words, a below sea level bed slopes lower as you progress toward the center of the Continent. And, in fact, large portions of West Antarctica are below sea level (see topographic image below).

Pine Island Glacier itself rests upon an opening to one of the deepest valleys sloping inland. At the location of the Pine Island glacier a rift between 500 and 2,000 feet below sea level runs down toward a central region of West Antarctica that sits between 2,000 and 6,000 feet below sea level. And within this basin is a pile of glacial ice that from bedrock to its highest point above sea level towers two and a half miles high. The very valid concern for this glacier is that melt and rifting, once started, will tend to accelerate — taking out larger and larger chunks of the inland ice as it is exposed to the warming ocean and heating atmosphere.

The Larger Picture — Glacial Flood Gates are Cracking Open

Larsen C and Pine Island Glacier serve as but two of the many flood gates that run all along the coast of West Antarctica and East Antarctica. But the increasing flows of warm water coming in from the ocean and a related rise in the frequency of events where large masses of ice break off from buttressing glaciers and ice shelves has put West Antarctica in danger of facing a near term collapse.

west-antarctica-below-sea-level

(Islands encased in ice. Much West Antarctica, on the left side of this topographic image, sits between 0 to 6,000 feet below sea level. If the buttressing glaciers and ice shelves like Larsen C and Pine Island are lost, there is little to prevent the warming oceans from flooding inland and setting off a rapid cascade of melt and seaward outflow. Scientists now believe that such a collapse could happen within our lifetimes. Image source: Antarctic Bedrock.)

With information from new glacial stability assessments in hand, Antarctic ice specialists are warning that the western region of this frozen land may collapse in a major melt event that over the next 100 years could raise sea levels by 10 feet. And West Antarctica is but one of three global regions — including Greenland and East Antarctica — capable of contributing significant glacial outbursts during this period.

Links:

West Antarctica Ice Shelf is Melting From the Inside Out

With a Collapsing West Antarctica, Sea Levels Could Rise Twice as High as We Thought

Combustion of Available Fossil Fuel Reserves Sufficient to Eliminate Antarctic Ice Sheet

Burning all Fossil Fuels Will Melt Entire Antarctic Ice Sheet

Rift in Antarctica’s Larsen C Ice Shelf

The Larsen Ice Shelves

NASA Captures Disturbing Images of Antarctica Ice Rift

Antarctic Bedrock

Pine Island Glacier Topography

Hat tip to Colorado Bob

Hat tip to ClimateHawk

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