Under Pressure Ridges

Scott Base pressure ridges
The Scott Base pressure ridges present an undulating landscape of unending variety. In the center of this photo is a melt pool.

If you’ve been following this blog, you’ve been introduced to the pressure ridges near the Double Curtain Glacier, which is across McMurdo Sound from McMurdo Station in the New Harbor/Explorer’s Cove area of the Dry Valleys. During the seven weeks that I was based at the US Antarctic Program’s McMurdo Station, I also made two trips to visit the extraordinary pressure ridges at Scott Base, which neighbors McMurdo and is operated by New Zealand’s Antarctic program. If you’ve seen Anthony Powell’s excellent documentary film, Antarctica: A Year on the Ice, you may have noticed the Scott Base pressure ridges among the time-lapse photography sequences.

Observation Hill view of Scott Base
From the 754-foot-high summit of Observation Hill at McMurdo Station, you can see an aerial view of the Scott Base pressure ridges, including the undulations in the ice shelf that have helped form them. The little black dots on the ice a little left of center are Weddell seals. (Click on photo to see enlargement.) I also photographed the prominent formation in the center from the ground (next image) and made a 3D file of it (shown further down in this post):
Scott Base pressure ridge
This formation is large enough to stand out even from the top of Observation Hill (see panoramic photo above). I also made a 3D file of it from 53 photographs taken while walking around it (scroll down further below).
Scott Base pressure ridge
Scott Base pressure ridge with Scott Base in the background.

In Antarctica, the interaction of permanent thick ice shelf (that constantly floats atop the sea), sea ice (that is subject to melt cycles, and some years even melts to the point where it breaks up and floats out to the ocean) and the stationary rock of the coastline, can cause the ice near the shore to buckle and push up chunks into formations called pressure ridges. The pressure ridges are dynamic and constantly changing due to the action of the forces described above along with the 24-hour summer sun. Summertime temperatures at McMurdo when I was there mostly stayed in the 15 to 30 degree Fahrenheit range, and only a few times that I recall got into the upper 30s (and once a balmy 43 degrees — a few of the young guys took advantage of that heat wave to walk around in shorts!). But even in below-freezing air temperatures, when the sun beats down on the ice, it softens and sometimes melts. Then there are icicles, large chunks splitting off and falling, or gravity sometimes causes a chunk of snow to bend and flop over like a draped cloth.

Scott Base pressure ridge
By November 30th, long icicles had formed beneath this this sheet of ice.
Scott Base pressure ridge
The underside of this large chunk of ice was a deep blue and decorated with icicles. In the background are the green buildings of Scott Base.
Scott Base pressure ridges
A thick mat of softened ice can bend like a draped cloth (lower right) and form graceful curved shapes.

Because of the ice shelf and sea ice dynamics, there are also cracks in the ice and melt pools on the surface that widen and deepen as the air warms (one of those was prominently featured in my post about Mt. Erebus). So there is a small window of time from November until mid-December when it is safe to walk out on the ice to get close to the pressure ridges. The McMurdo Recreation Department leads evening tours for the workers and others in residence there during that rare period. I went on two such trips, on November 24th and 30th. These photographs are, essentially, documentations of ephemeral formations: even though these photo sessions were only six days apart some of the ice had already changed in that brief time.

Scott Base pressure ridge
Another spot where the snow has drooped over like a towel on a rack (upper center).

Where there is a nice-sized crack in the sea ice near the shore of McMurdo Sound or one of its islands, chances are you’ll find a group of Weddell seals laying out along it. Cracks give them a head start in chewing out a seal-sized hole in the ice where they can haul themselves out of the water for a break from non-stop swimming and foraging for food. I’ve never seen an animal that sleeps more soundly than a Weddell seal! They also give birth and nurse their pups on the ice. At least one of the Scott Base seals had a pup:

Weddell seal and pup at Scott Base pressure ridges
Baby Seal!: A Weddell seal and her pup chill out at the Scott Base pressure ridge.



From the shoreline, the ice formations are flatter and some have straight lines and more angular profiles:

Scott Base pressure ridge
Looking out from the Scott Base shoreline at angular pressure ridge formations. On the horizon is Willy Field, one of the airstrips that serves McMurdo and Scott Base. It’s probably about a 15- to 20-minute drive from that spot, i.e., not as close as it looks! It’s pretty much impossible to judge distances in Antarctica. You learn to not even try.
Scott Base pressure ridge
Planar ice formations close up.

From other angles there were other formations to see, as in the two vertical photos below. I also did a few walk-arounds for photogrammetry captures. I’ve processed one of those files for a potential sculpture (horizontal image below those).

Scott Base pressure ridges
Peering through a crevice at the Scott Base pressure ridges results in a puzzling and ambiguous spatial reading.
Scott Base pressure ridges
Another unexpected sculptural ice formation.
Scott Base pressure ridges
A 3D file made from 53 photographs walking around a portion of the Scott Base pressure ridges. I need to edit out a few extraneous forms, but the capture came through mostly intact, with great detail and very few gaps.

At the end of this post is a photograph of another fascinating phenomenon we saw on the November 30th trip to Scott Base: a type of mirage called a fata morgana. It has nothing to do with pressure ridges, but it does have to do with looking across the wide flat expanse of the sea ice toward a distant shore. A young man in our group noticed it first. In a fata morgana, a strip at the bottom of the land seems to be stretched like Silly Putty. This one was subtle, but unmistakable. There are more dramatic examples online. Just search Google Images for “fata morgana Antarctica” or read this explanation.

Fata morgana, McMurdo Sound
Across the sea ice from the Scott Base pressure ridge there was a fata morgana effect that made the bottom strip of the Transantarctic Mountains across McMurdo Sound appear to be stretched into a horizontal band at the bottom. Fata morganas appear in Antarctica when a band of air just above the sea ice is a different temperature than the air above it, causing a temperature inversion and distorted reflection at the horizon. Fun fact: the name comes from the Italian for Morgan Le Fay, half-sister of King Arthur.







The Road to Double Curtain Glacier

Antarctica sea ice
Sea ice pressure ridges looking toward the Ferrar Glacier.
Pair of skuas in Antarctica
What does the skua say?: Haw! Haw! Haw! Haw! Haw!

I’m back from Sam Bowser’s camp — helicopter picked me up at 5 p.m. yesterday. Sam, his wife Laura and the rest of the team were really welcoming and fun to be with, and took me to a couple of fantastic places. I’ve already posted the trip Laura and I made in the previous blog entry.

The next day Sam, Laura and I went by snowmobile to a fascinating scenic spot that doesn’t really have an official name, but unofficially they call it “the road to Double Curtain Glacier.” Comic relief near the beginning of our trip was provided by a pair of nesting skuas standing on a rock. We stopped the snowmobiles and I got out the telephoto lens. They looked at us, and we looked at them, and then another skua flew a few feet above them, to which they responded by cawing loudly, “Haw! Haw! Haw! Haw!” as if to say, “Don’t even THINK about landing here while we’re on this rock.” Then they calmed down, then they started up again. It sounds like someone laughing sarcastically.

Pair of skuas in Antarctica
We must protect this house!
Pressure ridge near Double Curtain Glacier
The “Road” to Double Curtain Glacier has a lengthy section that looks like this, with very high pressure ridges where the sea ice has been pushed up against the coastline.

What we traveled on was not really a road, of course, it’s a flat area of coastline around New Harbor that this time of year is covered with snow and ice, and it looks like someone plowed a flat area of snow for vehicles and left the piles of snow and ice in a very even line on the sea ice side of the lane. What those piles really are is a pressure ridge, which is a ridge of ice pushed up by the movement of the sea ice. I saw such ridges on the McMurdo Sound sea ice when I was doing my training, but they were only a few inches high. I saw them by the New Harbor camp but they were a few feet high. But as we got closer to the Double Curtain Glacier, the lane got narrower and the wall got higher, forming a crazy Baroque facade that I’m guessing was 20 feet high in places! At some point, the road became so narrowed and slanted we parked the snowmobiles and continued on foot.

Scallop shells
Sam was interested in the large numbers of scallop shells that had been carried to the shoreline by the ice.

The ice has begun to melt and form weird shapes of unending variety. You don’t want to walk too close to one of those towers in case it becomes unstable and collapses. The pressure ridges have carried along numerous scallop shells which are scattered in the ice.

Blue wave of ice
One of the odder sights was this blue curving wave of ice. I wanted to get a closer look, but it was hard to tell if the ice was stable enough to walk on, so I dared go no further.
Fang, the ice formation
I named this formation “Fang,” because it looks like a cartoon wolf in profile.

We eventually came to a place totally blocked off with ice. We climbed a little ways up the hill under the Double Curtain Glacier, and saw a mummified seal skeleton and some moss — the first plant life I’ve seen here. 

Ferrar Glacier, seal skeleton and pressure ridge
Mummified seal skeleton on the hillside above the pressure ridge. The Ferrar Glacier is in the distance.
Mummified seal skeleton
Close-up of the seal skeleton. The flipper anatomy is very clear on the right. There is some dried, mummified skin still attached. No telling how long it’s been here; could have been many years.
Double Curtain Glacier
The Double Curtain Glacier emerges from the fog above the seal skeleton. You can see how it has two different leading edges, hence the name “Double Curtain.”
Moss in Antarctica
There was no plant life in evidence except a patch of moss with white salt crystals on top, not far from the seal skeleton. This is a close-up. We took care not to walk on it because it’s very delicate.
Herbertson Glacier
From this elevated spot you get a good look at the Herbertson Glacier beyond the pressure ridge and across the sea ice from the Double Curtain Glacier.

Many of the photos shown here were from that slightly elevated vantage point on the side of the hill. It was a clear day and we could see the Herbertson Glacier (which was directly across the sea ice) and the Ferrar Glacier (to our right from that spot). As we were leaving, we also drove onto the sea ice about halfway between the Herbertson and the Double Curtain and I got another nice photo of the Ferrar.

Ferrar Glacier
The Ferrar Glacier in the distance, as viewed from the sea ice.

I am incredibly fortunate to have been able to visit this place, which one of Sam’s team told me very few people have gotten to see. Unless you are staying at the New Harbor camp, it is relatively inaccessible. I am working right now on processing some of the 3D captures I made there so I can bring back a little bit of the place for others to see. Once I clean up these files I’ll be able to fabricate them as sculptures with a 3D printer or router. I’ve got one capture processed already. Here are a couple of screenshots of it from the 3D file creation program:

3D file of pressure ridge
3D file of part of the pressure ridge, shown with the “texture layer” (the coloration).
3D file, untextured
3D file shown without the texture layer.