Continued high winds are kicking up lots of snow over the surface.  And the winds combined with some colder temperatures (roughly -20 C or around 0 F), the wind chill is down around -30C.  So we have another tent day today.  I’ll use this blog to talk a bit about why Antarctic ice fields in general, and Davis-Ward in particular, are particularly good places to search for meteorites.

Antarctica is the windiest continent in the world (as we have been experiencing over the last several days…!).  The katabatic winds are particularly strong (up to 70 or 80 mph in the Antarctic winter) and result when cold dense air flows down from the Antarctic platea around the South Pole. (These extreme wintertime katabatic winds are not the winds we’re experiencing right now, thankfully!  The summer time winds are strong, but only ~30 mph.)  Antarctica also holds roughly 90% of the Earth’s ice.  The Antarctic ice sheet reaches thicknesses of approximately 4000m near the center of the continent.  These two elements — ice and wind — combine to concentrate meteorites on the surface.  Here’s how the concentration mechanism works:

The tremendous weight of the Antarctic ice sheet causes the ice to flow from higher to elevations, so generally outward from the interior of the continent.  The moving ice acts as a natural conveyor belt for any material — like meteorites — that falls on the ice.  The Antarctic ice sheet is very roughly 5 million years old in its current configuration, so has been receiving meteorites for rather a long time.

When meteorites fall on the ice, they become buried.  Meteorites within kilometers of ice wouldn’t be very accessible, to say the least.  But when the flowing ice encounters an obstacle, such as mountain or nunatak (a rocky protrusion sticking up above the ice), the ice is deflected upward toward the surface.  This deflection is particularly effective when the ice enters a cul-de-sac and has no where else to flow up upward.

In some locations where the ice is deflected upward, the ice sheet is scoured by the very strong (wintertime) katabatic winds.  This scouring removes the ice — here at Davis-Ward, 5 – 10 cm per year is scoured away — and leaves behind on the surface the meteorites that were previously buried within the ice.

Now the glaciers carry other rocks besides meteorites, and when all those rocks are deposited by the glaciers, they create the moraines referred to in some previous blogs.  So the profusion of rocks — including other black-ish, rounded rocks like basalt and coal — can make spotting the black-ish, rounded meteorites tricky (see the images of ‘can you find the meteorite?’ from previous blogs).

Nonetheless, the combination of ice flow and wind ablation acts to concentrate meteorites for us on the surface.  And out on the blue ice fields, the bright background even helps to set off the rocks for us to see.

Here at Davis-Ward, we have the Daivs Nunataks and Mt Ward, which form small cul-de-sacs, in conjunction with katabatic winds — just the elements we need to get a concentration of meteorites!  Now, if we could only get a little less wind, we could get out there and find them!

-written by Devon Burr and Shannon Walker, Davis-Ward, Jan 12, 2015