22 November--Pressure Ridges and Rollers

This was my day off but I volunteered for the Recreation Department to drive a van over to the pressure ridges by Scott Base.  Waiting at the Scott Base transition area for a tour group to come back off the ice, I had time and a good vantage point to look out over the ridges.  And that evening a group of us went back for our own tour of the ridges with Scott, Shuttle Jen's husband.

So what's a pressure ridge?  A pressure ridge forms where two masses of ice collide, either by winds or ocean currents.  Sort of like the Himalayas crumpling up along the collision line of the Indo-Australian Plate and the Eurasian Plate.  In this case the masses are the massive Ross Ice Shelf (roughly the size of Texas, if I remember correctly) and the annual sea ice.  The Ross Ice Shelf is the seaward extension of a number of glaciers as the empty into the /Ross Sea; in this area it is moving at least 385 feet a year.  Combine the ice movement and the wind, and you've got the makings for pressure ridges.

When the two ice masses come together, they first express the pressure with gentle corrugations that they call rollers.  With more pressure these steepen and ultimately crack and get raised up spectacularly.  The process from roller to ridge can be as short as two weeks.  In places you can visually follow foot prints going up the pressure ridge, likely made when the ridge was flat ice.  In other places there are seal feces way up a nearly vertical ridge.

The color of the ice can be a topaz blue, nothing you'd expect to see as you sit back in your comfortable home.  Eery.  Luminous.  Hypnotic.

We saw 3 seals out on our walk and were able to get within 15 feet of them..  One was a mother and pup and the other was a solitary individual.  There were patches of melt water with slushy ice that they might have used to go down below, but we didn't see any ice holes.

Interesting tidbit: the elevation of the South Pole is 9,300 feet, but the effective altitude is considerably higher, varying between 10,800 and 13,120 feet, depending on barometric pressure.  This is because as the Earth spins, centrifugal force moves more of the atmosphere to the tropical areas and thins out the atmosphere at the poles.  Polies are usually put on Diamoxx for a few days before flying to the South Pole and I'm told there is a sign inside the Scott-Amundsen Station showing the current equivalent pressure altitude.  Because the North Pole is at sea level, none of this is necessary there.