Wikipedia:Reference desk/Archives/Science/2016 July 19

= July 19 =

Why is Antarctica so round and kind of centered?
Just a coincidence? It looks like a cookie with two bays broken off. Sagittarian Milky Way (talk) 06:59, 19 July 2016 (UTC)
 * It would not be a coincidence. Much of the space between the two bays is below sea level, and would make a huge channel if the ice was not there.  So the West Antarctica is a mountain range, and the West Antarctica is a regular continent, and they are joined together by an ice cap that is so many kilometers thick that it has bottomed out on the ocean floor and joined the two big subcontinents together.  So the round shape is due to the shape of the icecap, which is basically a big glacier flowing out from the high points. Graeme Bartlett (talk) 08:02, 19 July 2016 (UTC)


 * Some of this is perhaps in the eye of the beholder. (How round is round?)  However, I would note that the continental block that forms Antarctica (landmass plus continental shelf) is actually pretty round as these things go, and that would simply be a coincidence.   The boundary between continental crust and ocean crust isn't going to care about the presence of an ice sheet, and is simply a legacy of what was left after the break up of Gondwana and the separation of Antarctica from India and Australia.  (Australia is also relatively round I suppose.)  It is worth noting that we have some good illustrations for Antartica.  I've shown two here.  Much of the Antarctic bedrock is below sea level today, but most of west Antarctica would be above sea level if the weight of the ice sheet weren't pushing it down.  Dragons flight (talk) 08:32, 19 July 2016 (UTC)


 * I would say, as small continents go, it is probably about as round as Australia. StuRat (talk) 14:39, 19 July 2016 (UTC)


 * The best answer I can find can be found at articles like Apophenia and Pareidolia. -- Jayron 32 15:44, 19 July 2016 (UTC)
 * {[re|Jayron32}} Nay, it's not just imagination. The Earth has big regions of land or shallow sea and big regions of deep sea, i.e. oceanic crust.  The presence of so much thin crust from midocean ridges overlain by water would seem to imply that land will be drawn into tight areas.  I don't honestly know the geology very well to explain this right, but there's something real to it. Wnt (talk) 17:23, 19 July 2016 (UTC)

No one has addressed the "centered" component of SMW's question. I've wondered about this, too. The South Pole is near the center of a landmass; the North Pole is near the center of an ocean, and both of them are "roughly circular". Could be a coincidence, but it's ... suggestive, at least. Convection in the mantle is very slow, so the Coriolis force has to be really small, but given the amount of material it's acting on, and the time scales available, can we rule it out? --Trovatore (talk) 17:43, 19 July 2016 (UTC)


 * Well, the Antarctic Plate has moved south to its current position and continues to move today. So this is only a temporary phenomenon. Wnt (talk) 19:34, 19 July 2016 (UTC)


 * Except it isn't that close to the center. The south pole is only about 200 miles from the Ross Sea, whereas it's something like 1800 miles to the Davis Sea.  West Antarctica is considerably smaller than East Antarctica.  The Pole of inaccessibility and Geographical center of Antarctica are both considerably far away from the South Pole.  If you slice the continent in half along the prime meridian-180th meridian line, you do NOT get two similar shapes.  The eastern half is almost a semi-circle that fills the space inside the antarctic circle, I'll give you that, but the western half of that "circle" is more sea than land, and has a much more convoluted shape.  Antarctica is neither centered on the south pole nor is it particularly circular.  Apophenia was the most relevent link for two reasons 1) we have exactly 1 piece of information (the location and shape of Antarctica) and trying to find a reason or pattern for it being so is pointless.  There is no discernible reason beyond random dumb luck.  2) While the south pole is in Antarctica, the continent is neither centered on it, nor is it very circular, but our minds WANT it to be so, so we tend to assume that it is.  When you analyze it by any objective measure, neither is true.  One might as well ask why the Americas look like a duck .  -- Jayron 32 20:02, 19 July 2016 (UTC)


 * If you want a legit bizarre polar shape, take a look at Saturn's hexagon. StuRat (talk) 02:01, 20 July 2016 (UTC)