Posts Tagged ‘cracks’

Complex Scientific Equipment

March 29, 2011

Original audio post. Thanks to Lori for the transcription!

Hey! Well, this morning’s weather was pretty unpleasant, although we weren’t sure why it seemed quite so bad. It goes to show how much your points of reference have changed when you find yourself saying “It’s only -15 Celsius with 10-knot winds. Why does it seem so cold?”

So, anyway, we stuck close to camp. Martin and I put together a very sophisticated scientific instrument, which might appear to the uninitiated to be a cardboard box with a hole cut in the bottom.

I transport the device to the field as Ruschle looks on. Photo by Martin.

This allowed us to take photographs of the cracks in the blue ice without the picture being washed out by bright sunlight. Upending the box box on the ice and taking pictures through the hole gave us images in deep translucent blue with a delicate tracery of dark cracks. We’ll use these pictures to try and quantify the effects of cracks on the amount of reflective light.

The cracks as seen under the box.

The weather improved in the afternoon, enough for us to go out and identify sites to measure. I don’t think I mentioned yesterday exactly what we’re looking for. As the ice flows, it moves into the region where wind can scour away the upper layers. So as you walk along the line of flow, you start in an area where the surface is still snow. Then you reach an area where the surface snow has been scoured away by the wind to expose dense old snow from years past (which, as you may recall, is called firn.) Walking further, you reach bubbly ice, and finally dense old blue ice. We are trying to measure along that same line of flow to get measurements from each type of snow and ice.

So, we marked the lines with the bamboo flags that are ubiquitous around McMurdo, and perhaps we’ll get to go back tomorrow and actually measure.

I’ve been concentrating a lot on the science we’re doing here because it’s pretty exciting. But I haven’t talked much about day to day life in camp. The Scott tents alone are worth a whole post, so I’ll try to talk more about that in coming days.

Oh, and we saw a skua!

A different skua, circling over Icestock hoping someone will drop their sandwich.

Skuas are the local scavenger birds. They look like a big brown seagull and like to dive-bomb people carrying food. This one was probably a bit lost. There’s not much to eat out here. But, it was the first living thing besides ourselves we’ve seen in days, so it was pretty interesting. Anyway, until tomorrow, cheers.

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Repost: Cracks and Bubbles

February 8, 2011

Original post, called in on January 13, 2011. Thanks once again to Jonathan Beall for the transcription!

“Hi. Today was a quiet day. Well, in terms of activity. It was a quiet day in terms of activity because it was a noisy day in terms of wind. We had a good day of spirited scientific discussions in the tent instead. We were mostly discussing bubbles and their contribution to the amount of light reflected from ice, or its albedo.

Bubbles are awesome.

Ice is very transparent. Light can travel a long way before it gets absorbed. If there are no bubbles in the ice, most light will just travel straight through, and the albedo will be low. If there are bubbles, though, light can hit the bubbles and bounce away in a different direction. A lot of the light that goes into the ice will end up bouncing right back out, which is why bubbly ice has a higher albedo than clear ice. Ice in glaciers and on ice sheets, like where we are, has lots of bubbles because it’s formed from compressed snow. The spaces between snowflakes at the surface will turn into bubbles as the snow is squeezed into ice and a small amount of the air remains behind as bubbles form.



Complex bubble shapes are partly a result of the complex shapes in the snow crystals that formed them.

We also talked about cracks in the ice, which can increase the albedo just like bubbles do. The blue ice here has lots of cracks in it, mostly quite thin. We think they form partly because the ice is cracking as it moves, and partly because, as the top of the ice erodes away from the constant wind, the ice lower down is no longer under as much pressure, and it expands creating more cracks.

Cracks in the ice (picture taken using the Crack Box, an invention I'll explain in a later post)

We actually put on our parkas and went out to look at the ice near camp to see how the cracks behaved and to figure how we might account for them in our measurements. We probably looked a little silly lying face down on the ice and wriggling along the ice like seals, but then science is frequently a little silly; that’s one of the reasons I like it.

Another incident of science being silly.

Cheers!”