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Notes from the Field

A Peek Inside the Weathering Crust

July 27th, 2016 by Clem Miege

Hi there!

Our team got out of the field a few days ago after a successful field campaign with a lot of great data to analyze! For the coming blog posts, we will be sharing with you the different kind of measurements we made during our stay at the ice camp and but also describe the wide range of instrumentation being used.

For this blog entry, I am going to talk about the surveys we did with a ground-penetrating radar (also known by its acronym: GPR) and the shallow ice cores we collected to help calibrating the radar data by identify the depths of subsurface features. The main of goal of this radar data is to quantify spatial changes in the weathering crust. This crust corresponds to a relatively thin layer (1-2 meters thick) of ice and water starting from the ice surface. It is strongly influenced and shaped by weather variations (sunny days vs. cloudy days, air temperature, melt intensity…)

But before going in those details, here is a photo of our camp in relation to the supra-glacial lake and river to get you situated.

General view of our ice camp with a close up on Rio Behar at the bottom of the photo. Photo by Clem Miege.

General view of our ice camp with a close up on Rio Behar at the bottom of the photo. Photo by Clem Miege.

For the ground-penetrating radar measurements, we brought to the ice camp a radar designed by GSSI, a company specialized into geophysical measurements. The radar basically acts as our eyes to explore the features located in the ice, below the surface. With a 400 MHz antenna, we are limited to look at the first 50m of the ice thickness with a vertical resolution of about 10-20 cm. Any changes in the ice density, stratigraphy or changes in its dielectric properties create internal reflections. We then follow and trace those continuous reflections (also called internal layers) and look at their spatial distribution. In addition, the presence of water within the ice generates a sharp and bright radar reflection because of the significant dielectric contrast between the solid and the liquid phase of the water molecule.

The radar system is made of an antenna and a control unit. It is relatively light and portable, making it possible to use with only one person. To geolocate the radar scans in relation to the ice surface, we carry a precise GPS.

The radar setup with the GPS antenna. Photo by Charlie Kershner.

The radar setup with the GPS antenna. Photo by Charlie Kershner.

 

The radar in action. Photo by Lincoln Pitcher.

The radar in action. Photo by Lincoln Pitcher.

In addition to the GPR work, we have been drilling 10 boreholes from the ice surface. Big thanks to Bob Hawley at Dartmouth for letting us borrow his coring drill. We extracted 75-mm-width ice cores in the top part of the ice column (1 to 2 meters depth) which reveal the ice stratigraphy and densities below the surface. We also measured the height of the water in the borehole (if any) which will be helpful to establish an accurate depth profile for the radar data.

Asa is operating the coring drill from the surface to retrieve ice cores. Photo by Clem Miege.

Asa is operating the coring drill from the surface to retrieve ice cores. Photo by Clem Miege.

 

Clem is processing the first meter of the ice cores, logging mainly stratigraphy and densities. Photo by Matt Cooper.

Clem is processing the first meter of the ice cores, logging mainly stratigraphy and densities. Photo by Matt Cooper.

Back at the office, we will have quite a bit of work to process all the data collected and connect the ice-core data with the radar data.  This dataset will become very helpful to understand the formation of the weathering crust as well as the water being stored in it.

That is it for this post! Thanks for following us and there will be more blog entries soon so you can learn about the other instruments deployed on the ice.

All the best,

Clem

7 Responses to “A Peek Inside the Weathering Crust”

  1. Paul Moertl says:

    Is this on Greenland or elsewhere? I don’t see anything in the article about where you are. (I could be blind, too….)

    • r chase says:

      From a previous posting on earth observatory:To do this work, we will be located in the ablation zone of Greenland ice sheet, at about 80 km from Kangerlussuaq (the closest town) and 1200 m elevation. Our study site is located right next to a lake and a river called the Rio Behar. As you can see from the photo above, this part of the ice sheet is covered by lakes and rivers that are transporting meltwater away from the ice sheet throughout this connected system.

    • Clem says:

      Yes Paul, this fieldwork was accomplished on the Greenland ice sheet, about 70 km East of the little town of Kangerlussuaq.

  2. Melchor says:

    Aquí en la piedad Michoacán México ha cambiado drásticamente el clima. No llovió en mayo.. Los felicitó por el gran esfuerzo. Que hacen . Crearnos conciencia.
    Melchor Gc.

  3. Melchor says:

    Los felicitó y agradezco profundamente. Su esfuerzo.BTY4B

  4. Trey Harpham says:

    The surface of the Moon does not experience significant changes to its features like the surface of the Earth does, so it has a very old surface. Actually, it appears that the Moon is geologically dead. This is because there does not appear to be any current volcanism and there has been very little change in the crust for some time. Evidence from the recent It took about 10 years before we decided to again check out the Moon in detail and at this time there have been several missions looking for water on the Moon. Amongst these are the