What am I doing here VII – The Ground Penetrating Radar

Though this project isn’t really part of my work portfolio, I couldn’t go by without mentioning it. Mostly because its not a project by itself but mainly a survival issue.

Let’s get the context right first: not all is sunshine and rainbow colored unicorns around this ice shelf. When they assembled the modules around here in 2012, one of the touristic attractions of the area was the Gatekeeper chasm. It demanded a mandatory visit. There’s no acronym or antarctic term here. Its exactly that, a big crack in the ice shelf all the way to the ocean bellow. I need to lower the expectations at this point: its not a hole in the shelf with water in it. The ocean’s surface on the bottom of it freezes quite fast and form a thin ice layer by itself. But on the bottom of it its not hard to find salt water…

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In other words, it seems that the shelf is breaking up. And it is. But, as with all things at this scale, its happening really slowly. At least it was. Until two years ago…

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These types of cracks in ice shelves is not common, but it isn’t rare either. Actually, around here it isn’t the only one. The crack that I’m talking about is quite close to the base, about 5 or 6 km away (in a good sunny day you can see its overlapping flaps in the south side of the modules) but about 20 or 30 km down south we have another smaller one. These cracks are formed by the enormous forces that tons upon tons of ice are subjected while they expand toward the ocean but with one side still stuck to the continent at the same time. Eventually these forces can separate a big chunk of it and throw a huge block of ice into the water. If its a relatively “small” (just a few hundred tons of ice…) bit of ice then, voilà, a baby iceberg is born. But sometimes the birth can be catastrophic and the iceberg suffers from gigantism.

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It has happened in the past and it would certainly happen in the future. That’s how nature works. But, these phenomenons are extraordinarily slow and, as such, in 2012 it wasn’t worth to be all worried about something that may need another 100 or 200 years to develop. But once again, Antarctica showed us wrong.

It was actually one of my projects that set of the alarm. In 2014, two stations from the Lifetime of Halley project (the one that tracks the flow of the ice shelf with the GPS receivers), each in one of the sides of the crack, registered an abnormally large drift during that year. A few visits to that crack confirmed everyone’s suspicion: this one was growing quite fast and was threatening to isolate Halley from the rest of the ice shelf, or even cast it on top of a gigantic iceberg.

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Well, threatening may be a bit of an exaggeration. It will still going to take a couple of years until the crack can cross the rest of the shelf and separate us completely. The problem is that nothing can guarantee us that this one is not going to accelerate further and with that, each passing day decreases the available routes to move the station to a secure place.

So then BAS had to put in place a project that has never been done before in this planet – next Summer we are going to move Halley station about 20 km to the Northeast of its current position, in a very, very slow run to “escape” this crack.

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Though the station is divided in individual modules and these are on top of skis, the moving is not going to be trivial. Its going to be a logistical operation of epic proportions, that is going to involve about 100 people at a certain point. It is necessary to separate each module from the others, tow it for more than 20 km and then reassemble everything back in place again. It would be easy if each module didn’t weight 200 tons and took a whole day to move it. And then there’s the problem of them not being small and the base is ridden with cables, towers and containers that need to be moved away before attempting anything. Halley VI is supposed to be the first movable antarctic station. Lets put that to the test then.

And so where do I fit in this story? The plan to move Halley was put on the drawing board the minute that someone realized that one day the station could wake up floating in the frozen ocean. But an operation in such a scale needed careful planing before attempting anything at all. During this planning and preparation phase, pretty much all the time up to the beginning of the 16-17 summer, we needed to monitor any developments in the progression of the crack, just in case it decided to throw us another curve ball. Specifically, there were two new Lifetime Of Halley GPS monitoring stations installed near the tip of the crack last Summer and BAS invested in a piece of equipment that has been proved very useful: a surface radar or GPR (Ground Penetrating Radar). Has the name implies, its one more radar. But this one is pointed to the ground instead.

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The working principle is exactly the same as the other ones: we send a light pulse in a certain direction and then we analise the reflections to determine the state of the ice shelf in this case. With this instrument it is possible to determine, almost with a millimetric precision, where the tip of the crack really is. The shelf that we call home is about 40 meters thick around these parts. And the crack its not moving in a uniform way, i.e, we can be looking at an area where apparently nothing is happening and yet, 10 meters bellow the snow surface, there’s a big hole in the making.

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Lets look at the situation again: last March we were “abandoned to our own luck”, left babysitting a 50 million pounds station on top of an ice shelf that is slowly breaking apart. In whatever scale adventures are measured, this one tops a lot of charts.

“Abandoned” is an harsh adjective really. There are loads of survival and rescue plans in stand by obviously. And there are two other facts to take into account:

1 – We aren’t the first ones to spend a Winter in this situation.

2 – Even if the crack triples its propagation speed, which is highly improbable, we still have a lot of time left to evacuate the station to a safe place before it starts floating in the ocean.

When Winter started officially around here, that is, when the Shackleton took the last people North, there wasn’t much left to do in this sense except monitor the development of the crack. And there where I came in. Since I’m officially the “radar guy”, it is only natural that I inherited this responsibility. Even if that wasn’t the situation, I would surely aim for that role if possible. I mean, ridding on a skidoo over a crack that threatens to swallow the station in the middle of the Antarctic Winter? That the dream of a career!

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In the beginning of each month, a team of three or four goes out of the base carrying a lot of GPSs, a GPR unit and enough batteries to light up a small village, to investigate if we should start pumping the life  boats or if we can sleep restful for another month.

The process itself is composed in to parts: a GPR survey of the area to determine where the tip of the crack really is and a GPS survey of 10 metal poles, lined up in two rows of 5 in each side of the crack and spaced of 1 kilometer each. These ones tell us how much is the crack spreading sideways.

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Normally I’ll stick with the pole survey. Last summer I did a couple of GPR runs in other jobs but, since I already knew how to operate the GPSs from my other projects, I ended up sticking with this one.

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My part is quite simple: towed to my ski-doo is a big pink plastic sledge with four high precision GPS units. Its four heavy hard plastic cases because, as I mentioned before, these are not the pocket GPSs that we use to find that restaurant that everyone is raving about lately. Besides, to endure with the rigors of an Antarctic Winter, each GPS is fed with a high capacity battery to compensate the lower temperatures.

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The first GPS stays fitted in the first pole of the West side of the crack during the whole thing, working has the reference point of the survey. Then I take my ski-doo and the remaining 3 units and, one by one, I sample the position of each of the remaining 9 poles. Since each unit requires an ideal 15 minutes of continuous sampling to get an accurate position, this job can take a good 3 hours in total, translating in about 30 or 40 kilometers with the ski-doo.

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In the first few Winter months we were able to get a couple of good days to do the job. There was plenty of sunlight still left and the field guide was comfortable enough for me to do this part by myself. But when we start losing a lot of sunlight hours, as a precaution, I started taking someone else with me all the time. In any case we are always reachable by radio and he knows that I will be around the pole lines. I shouldn’t get lost that easily. But in Antarctica a wary man is worth 17 and as such I always take company these days.

While I run around the place setting up GPS antennas in aluminum poles, another team is sampling the ice around the area where the tip of the crack should be. This sampling consists and doing several straight lines in a zig zag pattern between some of the poles whose position I’m taking, using the surface radar to take a bunch of snapshots of the shelf’s insides. In this process, the ski-doos go around tied to each other with a thick rope while each of its drivers is also tied to the ski-doo itself. If by any chance one of them gets swallowed by the crack (it is highly improbable, but then again, wary man… 17…) the other one works as a security anchor. Since the GPR can only sample at a maximum of 15 km/h, this job takes quite some time too. Normally we end up roughly at the same time, though most of the time I’m the later one.

Around the halfway point we always take a break for tea and a peanut butter and strawberry jam sandwich. Its one of those zen moments, all sticky with jam while contemplating the infinite of the Antarctic landscape. When it it started to be really cold (our working limit is -30 ºC. Bellow that the ski-doos complain a lot and the rest of the electronic doesn’t like it either), I ended up trying to chew a frozen sandwich. One hour at -25 ºC is more than enough to solidify any bread. But one day I had an idea that proved to be quite genius: right before leaving the modules, I fill up a plastic bottle with near boiling water and wrap a jacket around it along with the food. The jacket is able to hold the temperature for a few hours and the food stays warm and tasty even after the bottle as cooled down. Perfect!

In the beginning, with still plenty of sunlight left, this job was quite simple. I didn’t used the GPS in the ski-doo to find the poles. On a clear and clean day it is easy to spot them on the white foreground. Besides they always have a pair of black flags by their base, which makes it even easier. But when we had to do this in the middle of the dark months (June, July and August), it was actually curious because it is in these situations that we can perceive how much the ice shelf is moving. Each pole moves about 30 to 40 meters Eastward in just a month! If we follow just last month’s position on the ski-doo’s GPS we end up 40 meters away from them. Well, its the ice where they are stuck that moves, but you know what I mean. Then how do we find them in the darkness? Knowing that they always move to the East is already a big help. Afterwards, all we needed to do is drive to the point where they should be and run a couple of circles in the area. The headlights in our field skidoos are powerful enough and the fact that we were able to find everyone of them proves it.

So far the crack as been well behaved. It slowed down a little in the beginning of Winter but has now picked up the pace ever since, but still under the expected rate. There’s nothing to worry about so far.

It seems that Halley is not going to be upgraded to a ship this year…

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