There are a number of hiking and skiing trails around McMurdo Station. Some, like the Arrival Heights track, one can do alone and without giving notice; others, like the Castle Rock Loop, go far enough from the station and through questionable enough terrain that one has to check out, travel with a partner, and take radios in case of emergency.
I have become a great fan of the country walk in the UK. You dive into a beautiful morning on a promising footpath, refuel at a pub, keep walking all afternoon, maybe a quick half at another pub, then fall into bed all topped up on nature and exercise endorphins. Having been shuttled nearly everywhere in Antarctica via a motor vehicle of some sort, I was desperate to stretch my legs and cover some of Antarctica myself. I wanted to visit Castle Rock anyway, and the trip there and back was about the length of a leisurely country walk back home, so it was a natural thing to do once all my planned trips were over. My coordinator's opposite number is an avid hiker so he and I set out one sunny morning to put some miles on our sturdy boots.
The track is scenic and adventurous without being too arduous, so the Castle Rock Loop is a popular hike for the locals, as you can tell by the well-trammelled path in the photo above. Its full extent loops down to Scott Base and around back to McMurdo, but the shoreline down there didn't hold much interest and I'd done the route between Scott Base and McMurdo loads of times, so we just walked to Castle Rock and back.
It was a beautiful day. Much like the day I went up to Arrival Heights, it was calm, sunny, and hovering around freezing, the sort of conditions I insisted on calling 'picnic weather' long after the joke wore off. We also had an amazing low layer of thin cloud, which I unromantically call 'pond scum clouds' in my head, rather an unfair name as not only are they sometimes iridescent but they create wonderful light effects on the ground beneath them. On this day they were penned against Ross Island and cast their dappled shadows over Windless Bight, thereby showing up the perspective and giving everything the suggestion of being underwater.
In far worse conditions, Wilson, Bowers, and Cherry-Garrard walked across this view in June and July, 1911.
Away from Ross Island the sky was clear, and from up here on the spine of the peninsula you could see pretty much everything, including Williams Field, where I'd spent so much time recently:
There's nothing like a pure white background to show you how much pollution our internal combustion engines spew out – that smoke plume is, I believe, from a C-130 which was warming up to take off that day. It's a lot better than coal, but we've got a long way to go yet.
Humans' rudimentary flying machines are not the only thing to have emitted noxious gases into the Antarctic atmosphere. Mt Erebus still puffs away with the occasional mild eruption, but the Hut Point Peninsula is an artefact of a more active volcanic past. Much of the rock is obviously igneous, black or grey and spongy with bubbles, and most of the hills that stand up from the body of the peninsula are old volcanic craters, which spewed that aerated rock in ages past. Castle Rock is similar in origin, but gets its distinctive shape from having been an sub-glacial volcano, rather than a surface cinder cone. It's not exactly a volcanic plug, like the Devil's Tower in Wyoming, where the central chamber of a volcano solidified into a tower of basalt and the softer layers on the outside eroded away. Rather it is the volcano, having melted its way up through thick ice, which held its sides almost vertical while new layers of lava were deposited on top. This stratification, as well as the way the igneous rock has weathered orange-brown, makes it look more like sandstone than basalt to the casual observer, especially one who's spent so much time in the parks of southern Utah.
It feels enormous when you're standing under it – the name 'Castle Rock' is well-deserved – but when compared to other sub-glacial volcanoes (for instance Tuya Butte) it is but a teeny tiny fairy volcano.
This southeast face is the most precipitous; the north side slopes more and there is a climbing trail up it, should one wish to scramble a bit. It was just on the verge of opening for use when we visited, so we didn't climb. We did take as many pictures as we could, staying on marked paths, but before long it was time to turn around and head back again.
We stopped at a small shelter we'd passed on the way up, which you can just see as a little red blob in the photo above. It is officially known as an Apple , but some refer to it as a Tomato, which it more closely resembles if you ask me. It's an emergency shelter, in case you happen to be doing the Castle Rock Loop when a blizzard blows up, and it is actually rather cosy inside.
Further along the trail, the familiar landmarks of McMurdo rose into view.
That's Observation Hill on the left, and Arrival Heights on the right, with the "Golf Ball" under Mt Discovery in the middle.
As you may be able to guess from the above photo, the slope dips more steeply as we approach the base, and because of this it catches the afternoon and evening sun, and gets very icy. We both had good hiking boots but not crampons, so on the way up had tried to climb by the snowier sections. I was looking forward to sliding down on my coat on the return journey but alas it wasn't quite steep or slippery enough for that – the best I could manage was a slow bum-scoot, which was fun but not exactly efficient. However, it got me close to some funny features I'd noticed on the way up.
The whole slope was dotted with these spots of clearer ice, many with a chrysanthemum-like crystal structure. What was going on here? What were these things?
My guide explained that they form when a rock gets blown onto the slope. Being dark, it absorbs a lot more heat from the sun than the surrounding ice does, and so melts its way down through the ice, and keeps going as long as it the sunlight can reach it. When the ice refreezes to fill the hole, it reorganises its crystalline structure from the chaotic granules left over from when it was snow, to something that reflects the container in which it was formed. You can sometimes see this radial pattern in your ice cube tray – this is exactly the same thing.
We had been walking on ice and snow all day, which made for a surprise when I stepped back onto the familiar gravel of McMurdo. I have walked on a lot of snow in my life but I suppose I always went from frozen water to frozen ground or pavement. I have not, apparently, stepped from ice to fine gravel so dry that the pebbles haven't frozen together, and my first impression on doing so was that I had stepped onto cake. It was a very strange sensation that took some minutes to shake, but I can remember it even now.
It had been a very good thing to stretch my legs, and getting out in the fresh(er) air with a walking partner who could make good conversation but also didn't mind silence did me some good, to process the whirlwind of trips I'd made in such a short time. In that sense, my own walk to Castle Rock was much in keeping with those who made the hike when waiting for the sea ice to freeze over in 1911 – it was somewhere to go that was well away from the madding crowd in the Discovery Hut, where one could have a private conversation or just catch a bit of peace and quiet. On its busier days, the route is well-enough travelled that one stands the risk of encountering as many people out there as anywhere else, but we got a quiet weekday when everyone else was working. Being a bright day in midsummer, my imagination will have to add the richer hues of the dying light of autumn, but I'm glad I got to stand there in person at least.
If you want more detailed, expert analysis of the geology of Castle Rock, this is the PDF for you.