Nick Barnes said...
The southern half of the glacier front looks to have retreated about 4km since the 2006 line.
July 31, 2009 7:43 PM
Tenney said...
Yes, it looks like the 2006 line is the area of retreat -- wonder why that is.
I am still pretty much of a newbie, so I am still wondering if the tongue breaks up every year.
August 1, 2009 12:58 AM
Nick Barnes said...
Let me share some of my (limited) understanding of this glacier.
The main fjord, up to 10 km wide and maybe 50 km long, contains a lot of bergs from the glacier, with some sea ice between the bergs. The glacier is quite thick - 1-2 km - so the larger bergs are enormous and often ground on the fjord floor (a smaller berg will turn onto its side when it calves). This slows the outflow in the fjord - some bergs can spend years in the fjord - which is why the ice-filled fjord has this unusual look on satellite pictures: an ice finger poking out into Disko Bay and the Davis Strait. But it's important not to confuse this ice-filled fjord with the glacier itself.
Of course, the glacier used to occupy the fjord. It retreated out of most of the fjord in the late 19th and early 20th century. Then the front stayed in about the same place for 40 years, before retreating out of the rest of the fjord since 2000. The calving front continues to retreat (looking at these pictures).
It's important to remember that the glacier flows much more quickly than it retreats. Flow at the calving front is about 10 km/year. The current retreat is something like 1 km/year. Flow of the small bergs in the fjord is much quicker than the glacier flow (however, as noted above, the large bergs can get stuck).
Now the retreat has passed the confluence, where multiple ice streams in the interior of the ice sheet join to make the glacier at the head of the fjord. The confluence is roughly fan-shaped, but the ice sheet isn't homogeneous; roughly speaking here there's a northern ice stream and a southern ice stream, and the ice between them doesn't flow as fast as the streams themselves. The ice streams carve channels for themselves in the bedrock. The flow rates upstream from the confluence are lower, of course.
August 1, 2009 6:31 AM
Nick, that was a really helpful explanation. Please feel free to add to it, and I will post it up. Thanks, Tenney
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The southern half of the glacier front looks to have retreated about 4km since the 2006 line.
Yes, it looks like the 2006 line is the area of retreat -- wonder why that is.
I am still pretty much of a newbie, so I am still wondering if the tongue breaks up every year.
Let me share some of my (limited) understanding of this glacier.
The main fjord, up to 10km wide and maybe 50km long, contains a lot of bergs from the glacier, with some sea ice between the bergs. The glacier is quite thick - 1-2 km - so the larger bergs are enormous and often ground on the fjord floor (a smaller berg will turn onto its side when it calves). This slows the outflow in the fjord - some bergs can spend years in the fjord - which is why the ice-filled fjord has this unusual look on satellite pictures: an ice finger poking out into Disko Bay and the Davis Strait. But it's important not to confuse this ice-filled fjord with the glacier itself.
Of course, the glacier used to occupy the fjord. It retreated out of most of the fjord in the late 19th and early 20th century. Then the front stayed in about the same place for 40 years, before retreating out of the rest of the fjord since 2000. The calving front continues to retreat (looking at these pictures).
It's important to remember that the glacier flows much more quickly than it retreats. Flow at the calving front is about 10 km/year. The current retreat is something like 1 km/year. Flow of the small bergs in the fjord is much quicker than the glacier flow (however, as noted above, the large bergs can get stuck).
Now the retreat has passed the confluence, where multiple ice streams in the interior of the ice sheet join to make the glacier at the head of the fjord. The confluence is roughly fan-shaped, but the ice sheet isn't homogenous; roughly speaking here there's a northern ice stream and a southern ice stream, and the ice between them doesn't flow as fast as the streams themselves. The ice streams carve channels for themselves in the bedrock. The flow rates upstream from the confluence are lower, of course.
Here you can see it in 2007, but only at 500m/pixel - the higher-res pictures have been taken down to save space. It's hard to tell whether it's much different.
http://rapidfire.sci.gsfc.nasa.gov/realtime/single.php?2006213/crefl1_143.A2006213145500-2006213150001.500m.jpg
Thanks Nick,
It is difficult to be sure, but I think I can see where certain ground features are not exposed in the 2006 photo. But, who knows the scale?
Nick, I will be going offline for a while, due to health problems.
You can write at my profile's e-mail address if you want.
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