Larsen B collapse animation.

[silverslith]

Anyone have any theories as to why the larsen B broke up so spectacularly mid autumn in a couple of days (last two frames):eek2: . Remember its (was) 200m thick and 100km x 100km. A bit of a pipsqueak compared to ones like the ross.

 

 

MODIS images from NASA's Terra satellite, National Snow and Ice Data Center, University of Colorado, Boulder.

 

 

This is a true color animation of the events of January, February, and March 2002 as recorded by NASA's MODIS satellite sensor. (MODIS stands for Moderate Resolution Imaging Spectrometer, a sensor flying on NASA's Terra satellite.) The images show the Larsen B ice shelf and parts of the Antarctic Peninsula (on left). The first scene from 31 January 2002 shows the shelf in late austral summer with dark bluish melt ponds dotting its surface. In the next two scenes minor retreat takes place, amounting to about 800 km2, during which time several of the melt ponds well away from the ice front drain through new cracks within the shelf. The main collapse is seen in the last two scenes, on 5 March and 7 March, with thousands of sliver icebergs and a large area of very finely divided 'bergy bits' where the shelf formerly lay. Brownish streaks within the floating chunks mark areas where rocks and morainal debris are exposed from the former underside and interior of the shelf. The last phases of the retreat totalled ~2600 km2.Resolution of the original images is 500 m.

[Buffy]

In engineering its called a "cascade failure," and is quite common in complex systems. A rapid increase in the *rate* of melting at the outer edge--which over the long term has remained stable because a slower melting rate allows the outer edge to build up into a stable ice dam--will easily cause the entire shelf to collapse because there's not enough of a build up there to hold it back.

 

I'm sure though that in this case its either aliens or the CIA....we sure know that it would be imposible for NASA to do it.

 

Cool animation though, thanks for posting it!

 

Global warming is a lot of hot air,

Buffy

[silverslith]

The slow collapse of the "toenail clippings" over the first couple of months was a result of meltwater pools forming parallel to the front of the sheet in fracture crevasses. These trickle through and cause failure. Since the cascade failure happened in march when the sun was giving little heat it may be that the melt pools froze, expanded and forced the fracture of the whole sheet. Another explanation that occurs to me is due to large waves formed by the toenail slivers falling into the water. It seems to me that wen a critical density of these had filled the water in front of the shelf the waves from small calving events could have reflected back and caused a runaway feedback of calving and wave buildup. Its amazing the way that the whole lot destructs and spreads up to 500km out to sea in two days- ten kmph. Maybe the bergs were surfing the waves.:cup:

[silverslith]

I kind of think that the meltpools freezing would weld the shelf back together as much or more as splitting it.

Several other shelves have exploded in simular fashion. A storm off Alaska has been linked to waves that broke up major bergs on the Antarctic coast.

[Tormod]

I kind of think that the meltpools freezing would weld the shelf back together as much or more as splitting it.

 

Aren't the meltpools basically on the surface of the ice?

[Tormod]

Here are some nice photos along with an explanation in the first paragraph:

 

EO Newsroom: New Images - Larsen B Ice Shelf Collapse

[silverslith]

Nice work tormod!

Great to see some higher res and stills of the collapse 48hrs.

I'm still thinking my wave feedback hypothesis might be appropriate as the main collapse was front first. I can't see how meltpools at the back caused this or complete fragmentation. Did anyone see the waves from the eeney weeny teenie alpine glacier go over the 20m high viewing platform full of tourists a few weeks ago?

 

Not sure how deep the meltpools went but they are clearly visible in the first few frames of the animation as blue stripes parallel to the shore. They form in fracture crevasses and probably go deep pretty fast.

Tormods Nasa pics:

EO Newsroom: New Images - Larsen B Ice Shelf Collapse

 

 

[Tormod]

I can't see how meltpools at the back caused this or complete fragmentation.

 

No, I don't think the meltpools are *the* cause, but they are definitely a catalyst when meltwater runs down into cracks and freeze (causing expansion as you explained above).

 

I agree with you - there are probably several things happening, like Buffy's mention of a cascade failure. I wonder if also warmer ocean temperature is playing in (just a guess, frankly).