The Columbia Glacier descends 10,000 feet from an ice field in the Chugach mountains and terminates at Prince William Sound in SE Alaska. This glacier is known as a tidewater glacier, a mountain glacier that terminates in the ocean. Since 1986, the glacier’s terminus, has retreated 12 miles up an inlet in Prince William Sound, and the glacier also has lost about half its total thickness and volume and this loss continues to this day. Per NASA, "By 2014, the terminus had retreated more than 20 kilometers (12 miles) to the north, moving past Terentiev Lake and Great Nunatak Peak. In some years, the terminus retreated more than a kilometer, though the pace has been uneven. The movement of the terminus stalled between 2000 and 2006, for example, because the Great Nunatak Peak and Kadin Peak (directly to the west) constricted the glacier’s movement and held the ice in place."
July 29, 1986
July 2, 2014
The Landsat images above combine short wave-infrared, near-infrared, and green portions of the electromagnetic spectrum. With this combination of wavelengths, snow and ice appears bright cyan, vegetation is green, clouds are white or light orange, and the open ocean is dark blue. Exposed bedrock is brown, while rocky debris on the glacier’s surface is gray.
Like bulldozers, glaciers lift, carry, and deposit sediment, rock, and other debris from Earth’s surface. This mass accumulates on leading edges in piles called moraines. The Columbia’s moraine created a shallow underwater ridge, or shoal, that prevents the mélange from drifting beyond it.
The structure of Columbia’s moraine played a large role in the stability of the glacier before 1980. Like other tidewater glaciers, the Columbia built up a moraine over time, and the mixture of ice and rock functioned like a dam keeping out the sea. It was supported on one end by the shoreline and by the underwater terminal moraine at the other. When the glacier retreated off the moraine around 1980, the terminus lost a key source of support. Once freed from this anchoring point, the grinding and dragging between the sea floor and the massive block of ice was reduced, increasing the rate at which ice flowed forward and icebergs calved from the glacier.
Between 2007 and 2010, part of the terminus began to float as it passed through deep water between the Great Nunatak Peak and Kadin Peak. This changed the way icebergs calved significantly. When the Columbia was grounded, calving occurred at a fairly steady rate, and the bergs that broke off were small. When the glacier began to float, larger chunks of ice tended to break off, as seen in the image from 2009. The terminus has reached shallower waters and is grounded again, but rapid calving is expected to continue until the terminus reaches the shoreline, a point about 15 kilometers (9 miles) from the current terminus that the Columbia will likely reach by 2030.
The retreat has also changed the way the glacier flows. In the 1980s, there were three main branches. The medial moraine, a line of debris deposited when separate channels of ice merge (seen here as a line in the center of the 1986 image) served as a dividing line between two of the main branches. In 1986, there was a branch to the west of the medial moraine (West Branch), a large branch that flowed to the east of it (Main Branch), and a smaller branch that flowed around the eastern side of Great Nunatak Peak.
As the Columbia lost mass and thinned, the flow in the smallest branch stalled, reversed, and eventually began flowing to the west of Great Nunatak Peak. By 2011, the retreating terminus has essentially split the Columbia into two separate glaciers, with calving now occurring on two distinct fronts. The West Branch, previously thought to be stable, surprised scientists with an unexpected retreat that shows up in the 2013 and 2014 images.
Ted Pleffer expands on the west branch retreat
here.
Columbia Glacier expert Tad Pfeffer of the University of Colorado, Boulder, was equally surprised. The ground below a glacier—the bed—plays an important role in determining how much a glacier will retreat. It turns out, however, that it's not so easy to measure the elevation of the bed. The best information available to scientists had suggested that the bed of the West Branch rose above sea level immediately upstream from the nose, or terminus, which would have slowed the retreat of the branch.
"That's clearly wrong given that the terminus is now 3 kilometers back from its previously 'stable' point," Pfeffer said. "Why it hung in its advanced position for so long and why it started retreating is a mystery."
To better characterize recent changes to the Columbia Glacier, Ryan Casotto (University of New Hampshire) and colleagues used ground-based radar to measure the glacier's speed every three minutes for eight days in early October 2014. Preliminary results show that both the West Branch and the East Branch (which feeds into the Main Branch) are now moving between 5 and 10 meters (16 and 33 feet) per day. That's slow for Columbia, but fast compared to other glaciers.
Meanwhile, the area of the Main Branch hasn't changed much since 2012, but this part of the glacier is changing in other ways. The October 2014 field research found a connection between the motion of the Main Branch and the region's tides.
"That tells me that the glacier has thinned so much now and has very little traction against the bed, so that even the up and down tidal motion changes how the glacier is flowing," O'Neel said.
The tides are affecting the glacier as much as 12 kilometers (7.5 miles) upstream. The tidal effect only dissipates where the glacier bed rises above sea level and the ice-ocean connection is lost.
"This behavior makes us think that the Main Branch is once again unstable and possibly due for an episode of very rapid terminus retreat,” Pfeffer said. “It's hard to say how soon or likely that retreat is, however, and we've been surprised before."
Climate Change is tip toeing right behind us and most people don't even know it. It is because the climate changes are quite slow for a human to observe, so that any new changes in our climate will become a new normal at that time and years later new climate changes will become another new normal and on and on until doomsday. We have a war on our hands with the science denying members of congress, I wish I had an answer to see how we can move past them and their obstruction and downright hostility to addressing this looming catastrophe. I am not feeling optimistic.
I transcribed this interview from the Extreme Ice Survey clip above, any errors are mine.
James Balog:
Now Martin Truffer talks about how the retreat is a combination of the glacier dynamic issue and a climate change issue. Tell us about your perception of the climate change part of that equation.
Dr. Tad Pfeffer:
The connection here between climate and the dynamics is that climate, simple melting, isn't what is making the glacier disappear as fast as it is. But climate pushed it into the state it pushed it into the state where dynamics can take over start moving ice out into the ocean very rapidly. And once it's in that state it can't get out of it. The faster it moves the thinner it gets because of stretching. The really important reason why Columbia is getting small so quickly is not because the ice is melting it's because it is pushing the ice out into sea and breaking it up off as icebergs.
James Balog:
Through the winter of 2008-2009 the glacier flow doesn't keep up at all with the calving rate and it pulls free of those support pointes between Kadin and Nunatak and rapidly goes back about another 1/2 mile maybe 3/4ths of a mile.