Notes from a glacier – What lies beneath (GPR – Ground Penetrating Radar)

The initial phase of work on the glacier has been largely preoccupied with what is under the glacier.  This is an extremely important issue. We’re going to be sticking a few very expensive probes under the ice that the tech team of Glacsweb have been sweating over for the last year. If we mistakenly drop them into a subglacial river and they disappear, they’ll be less than impressed with us!

Thankfully we’ve got a GPR unit (Ground Penetrating Radar) which we’ve borrowed from NERC. Set up in the right manner this gives us an idea of where the bottom of the ice is, and perhaps what is down there.  However, gathering the data is unbelievably tedious.

First of all we make a decision about where we want to image the ice bed. The technique is essentially 2-D, so we draw out a load of lines on our map of the site. We then go and mark out the transects on the ice by putting a stake in the ice every 25 m.  This involves using an hand auger to make a hole in which the bamboo cane and stand, and then sticking a bit of gaffer tape on top to make it visible. It’s very high tech glaciology in practice. In short, this gets hard work by the time you get to your 80th metre deep hole…My shoulders are pretty sore at the moment.

Being candid briefly, I had serious doubts about doing these stake transects when we first started. It seems a bit stupid to go to loads of effort marking out transects. Why not just get a differential GPS (super accurate) and just find the transects as you go? But, I’m now a convert to the cane method. It might be some effort but its actually very helpful to visualise the transects out on the ice when you’re interpreting the data. You also end up using the marker repeatedly when doing tasks later in the expedition and its quite reassuring to have markers all over the glacier when visibility drops to <30 m, which is quite frequent as clouds pass through the area.

Once you’ve set out these transects, which isn’t a quick task, you set about collecting the radar data. This involves dragging the radar sledge across the ice in 0.5 m intervals.  The ice is anything but flat, with about ~1 m of terrain, so this is hard work and quite slow at around 0.3 km/hr. Even worse, because you have one person controlling the sledge movement and another taking the readings, the conversation is limited to ‘yep’ ‘ok’ ‘yep’ ‘ok’ ad infinitum…It’s beyond mind numbing.

Fortunately though, not only are we having beautiful weather here most of the time, the data is also brilliant, and because of that the GPR gets a bit addictive. Each day (more to come on the daily routine) we get back in, have dinner, and then set about seeing what we collected that day.  It’s really satisfying getting to see what’s underneath you all day, and what ambiguous/bizarre landforms appear to be present. Generally it results in debate to some ungodly hour and then a decision to go and collect more data in certain areas the next day.  And coming back to my initial rationale, the subglacial rivers produce very bright reflections on the bed and so we can essentially do a dot-to-dot across all our transects and then avoid placing our probes there.

Other fieldwork ‘shorts’:
– Always carry a trowel.
– H&S don’t trust us to stay upright, so we have to wear helmets. Surely it’s only a matter of time before this is applied to my office back in uni.
– Hot tubs are brilliant, but working until midnight tends to limit their use.
– We may have somewhere between 1 and 6 probes, but don’t ask the question too pressingly as you might force one of the tech team into a nervous breakdown.
– Richard Waller was a class act to have around for the first week of fieldwork. Check him out http://www.keele.ac.uk/gge/people/riw/ and follow him on twitter.

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2 comments

  1. GPR (ground penetrating radar) Is a method of locating underground utilities and other buried systems.
    Ground penetrating radar

  2. Having read this I’m not sure whether to be happy or sad that I wasn’t out there on the ice collecting the GPR data for my M.Sc. thesis. Greenland sounds fun until you set to think about the “beyond mind numbing” part.

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