Scott Base pressure ridge

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.

 

 

 

 

 

 

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