At the end of our first day of fieldwork we covered our snow pit with plywood to protect our hard work from overnight snowdrifts. We were all happy to simply brush some snow aside instead of having to dig another pit from scratch.
The second day was Kaitlin’s day for sampling. She and Gifford are both studying the nature and dynamics of snow layers. Normally, as PhD students, they would each be focused on their own data collection from different pits and at different sites. However, during the trip planning they realized how much their data complement each others’, and they made a new plan to collect samples from the same pit to align their data sets.
The layers record snowfall events, the seasons, and other environmental conditions, like wind. The lighter areas are less dense snow, with bigger snow crystals, and the darker areas are more dense snow, with smaller crystals.
Kaitlin is measuring permeability of the snow from the surface down to 2 meters. Permeability is how easily air, or any other liquid, flows through a material, which in this case is snow. A good example of permeability is rainfall on flat ground: rain that falls in a sandbox will flow below the surface, but rain that falls on concrete will collect and form a puddle. This difference is because sand is permeable and concrete is not permeable at all.
Kaitlin explained why it’s important to measure permeability in snow–permeability helps us understand how gases flow between the air and the snow, and then within the snow layers too. This information helps ice scientists interpret the gases that are found in ice cores, like those taken from the Greenland Ice Sheet.
To measure permeability, Kaitlin is using a permeameter, which was developed by her adviser, Dr. Mary Albert, and Frank Perron at Polar Research Solutions. The measurements have to be made in the field so the instrument is portable, but I can tell you that the gray and orange battery cases are not light!
But what does it all do?? Right in the middle of the setup you can see the white cylinder that holds the snow sample. Tubing connects a pump, in the yellow case, to the sample to control the flow of air through the cylinder. The air flows through the snow sample and then to the black case, where meters measure the rate of flow.
It all seemed a bit confusing at first, but Kaitlin and Mary led us through the sampling techniques. Here’s Laura, our geologist friend, adjusting the knobs that control the flow of air through the sample:
The coolest part was that we saw that permeability was lowest in the snow surface, where it was wind-packed. The deeper samples were more permeable because the lower layers generally have larger crystals which make for larger passageways for the air to flow through.
We also measured density of the snow. Whereas permeability tells us how much space there is for air flow, density tells us the mass of snow in the layers. Two different samples could have the same permeability but, depending on the crystal structure, they could have different densities. Density is a basic measurement that Kaitlin is taking to help characterize the snow layers and compare them with other sites.
To measure density we used a known volume sampler, and then weighed the samples on a portable scale.
What started out as a cloudy day turned into a calm and sparkly one, perfect conditions for what ended up being a 16-hour science marathon. Kaitlin finished the day with some valuable data and I am coming away with a new-found appreciation for the information that is locked up in these delicate, little pieces of frozen water. Snowflake wonder is knowing that no two snow flakes, nor snow layers, are the same.