A close-up of the “stormy ocean frozen in eternity” pinnacles.
Juliane in front of the pinnacle ice field. The white areas are the snow covered crevasses.
Yesterday afternoon the winds died down a bit and we were able to head out to our “achondrite orchard” ice field to pull the flags. We had A LOT of flag on that ice field. And achondrite orchard gave us one last good-bye present: 6 more meteorites including another achondrite!! Back in camp we had to dig out our tents again but this morning we woke up to total quietness. Very little wind and no blowing snow! Awesome! That meant we could go out again. This time we went to the Mt. Emily ice fields to pull the flags that we had left there. We got all the flags off the ice and visited the pinnacles. The pinnacles are tension features on the ice where the ice gets pushed up. It really looks like a stormy ocean with angry waves that froze in eternity. It is a beautiful display of nature’s strength and totally breathtaking. Unfortunately, these areas are also full of crevasses. But our trusted and careful mountaineer Brian lead us safely through the beginning of the pinnacle field. In this area the crevasses were not large enough to swallow a skidoo, but large enough to swallow a foot or leg if carelessly placed. Thus, we were extra careful where to step. We had a great time looking down into the crevasses snd fishing out the beautiful and large vapor deposited ice crystals. And the trip was worthwhile, we found 5 more meteorites including another (!) achondrite!! We are ecstatic! That brings out total to 211 meteorites! Once we were back in camp we started to prepare once more for the pull out tomorrow (fingers crossed). Another meteorite inventory, packing and sorting, getting the skidoos ready for the flight, and 35 minutes of digging and shoveling our tent out of the snow. Here is hoping for the wind to stay down so our tent won’t drift over again overnight. Packing and organizing personal bags and cooking dinner (I’m so freakin hungry!) are on the list now and if the weather cooperates we will send our next blog from Shackleton Glacier Camp.
Juliane, Mt. Cecily, Jan. 14th, at 7pm, Antarctica
Editors note: Juliane’s short description of the pinnacles “triggers me ” in the modern parlance, so I think I should add to it a bit. The first thing to note is that I’m not sure anyone knows exactly why or how they form, and I certainly am no expert, but having lived around these things for decades, I am happy to tell you a little more about them and share my utterly reasonable and deeply insightful hypothesis (smirk).
The pinnacles are meter-scale mounds (big ones may be 8 m long and 3 m high) almost always found in localized groups (tens to several hundreds) at and near the crest of domes or ridges on the blue icefields. They are aligned with and centered on the extensional crevasses that cross these highpoints in the flowing ice, and there’s usually a significant 3D shear (rotational) component to the ice’s movement too as demonstrated by the sigmoidal distortion of the crevasses. Individual pinnacles are usually centered on a crevasse, elongated along it and partially snow-filled, but also partially open- usually you can poke through the snow covering and see a contorted opening down into the ice. Usually the biggest pinnacles are right at the crest of the ridge or dome.
My humble opinion is that these pinnacles are places on “ordinary” crevasse that have become slightly more resistant to ablation (through both abrasion and sublimation of the ice). Crevasses are fractures expressing the inelastic (brittle) behavior of surface ice as glaciers move across irregularities in their beds; and the more intricate that bed surface is in 3D, the more directions of differential motion will be expressed by the crevasses that result. What makes the pinnacles different is that they’re on very slow-moving blue ice in a high-wind, high-ablation area (that’s also the tie to meteorite concentrations). These crevasses are opening and distorting much more slowly than those out in the middle of a faster glacier, and when they fill with snow it has time to convert to firn (tough, recrystallized networks of ice crystals rather than loose flakes). Firn is relatively resistant to wind erosion and much more resistant to sublimation than the blue ice around it, and so where a localized spot on the crevasse can host slightly more firn it also becomes more resistant to ablation than its immediate surrounding. Over time these spots become high points through less surface loss, and a field of pinnacles can be the result (and by time I’m suggesting hundreds or even thousands of years, based on heights of several meters and localized ablation that’s a few cm/year). With continued motion of the ice some pinnacles gape open and erode faster, others close or distort, and over time some pinnacles go away and other new ones arise. I would guess that there’s a maximum allowable height for each site based on altitude (a proxy for local climate), ice and wind velocities (a tall pinnacle sees wind speeds that probably counter any increased resistant to motion, and pinnacles in faster ice get structurally destabilized before they can build very high). I’m sure we could model this with some careful assumptions- but I hate modelling because….. assumptions. It would be much more fun to make measurements. Write a proposal, someone, and I’ll collaborate.