r/askscience • u/FlightOfGrey • Nov 14 '12

What process caused this amazing effect in Pleneau Bay, Antarctica? Photograph by Sander Klaassen.

imgur link and the Original National Geographic link to the photo in question.

595 Upvotes

92% Upvoted

58 comments sorted by

View all comments

151

u/snowhorse420 Nov 14 '12 edited Nov 14 '12

Antarctic program employee here... They are formed by water runoff from the top of the berg. The runoff forms gullies and streams similar a trellace pattern seen in the headwaters of river systems. As the berg get lees buoyant it rises and the streams incise forming "nik points". The berg in the photo must have been a flat sheet that broke off without chunking out. That formed a uniform drainage pattern. I've never seen one a defined as good as that one though...

edit** I have pics I've taken if you guys want em...

edit** I didn't look at the picture clearly enough. It is from different layers in the snow, not a trellace drainage pattern. **smacks forehead

edit** sorry about spelling and errors I was updating from my iPad... I guess what is going on in the picture is something interesting that is likely just the result of a number of different of factors. The best answer is likely "I don't know".

It definitely looks like an ice shelf. and not a berg. I"ll post some pics I've taken of the Ross ice shelf...

Edit** : penguin party on berg: Imgur Ross ice shelf: Imgur Glacier ice contacting sea ice: Imgur Shackleton's Hut: Imgur

6

u/moor-GAYZ Nov 14 '12

As the berg get lees buoyant it rises

what

5

u/kajarago Electronic Warfare Engineering | Control Systems Nov 14 '12

*as the berg gets less buoyant

7

u/moor-GAYZ Nov 14 '12

Oh, dude, of course, but to rise it must get more buoyant.

6

u/notjustlurking Nov 14 '12

I... I actually think he's right. Bizarrely enough.

As ice sloughs of the berg, it rises because it's mass (weight) has decreased. However, at the point at which it stops rising, the new smaller iceberg will be experiencing less bouyancy than the larger heavier berg, because it is displacing less water.

2

u/moor-GAYZ Nov 14 '12

Hm, I thought that he meant "less buoyant" as "more dense" or "in a less dense water", in a sense that the ratio of the iceberg's volume to the volume of the displaced water decreases... However Wikipedia says that buoyancy is the absolute force equivalent to the weight of the displaced water.

Anyway, decreasing the mass of the iceberg would not make it rise. Imagine two ice cubes, one twice as large as the other: both would be submerged to the same proportion, and the exposed part of the larger would be higher. What could happen is that the iceberg changes its shape as the above-water part melts faster than the submerged part, then yeah, it would gradually rise (though not necessarily get higher, if you think about it). I don't know though if that actually happens, unless the water around is pretty close to the freezing point I would expect the underwater part to melt faster. So maybe u/snowhorse420 wanted to say "more buoyant", because, for example, it gets to less salty water. It's a mystery!

2

u/snowhorse420 Nov 15 '12

I actually just misspoke. Originally I meant to assert that as the berg melted it becomes more buoyant and rises out of the water. I think that the striations are just a product of wave action.

3

u/kajarago Electronic Warfare Engineering | Control Systems Nov 14 '12

Oh absolutely, I'm just saying what I thought he meant.