Sea Ice training
Our FSTP instructor, Dan Mahon, did an incredible job of giving us a really great day out on the sea ice. I learned so much! Here's a little bit of what it was like to spend a day with Dan and the rest of the sea ice training group.
Our dependable ride for the day, the FSTP Hagglund.
The back of a Hagglund is cozy! (Photo courtesy of Orin Bakal-Molnar)
Liz riding in the back of the Hagglund. (Photo courtesy of Elizabeth Mockbee)
Nikki and Paul having a great time in the back of the Hagglund. It was a great group! (Photo courtesy of Elizabeth Mockbee)
Sea Ice Science
Our day began with some sea ice science. I had no idea there was so much to learn. I was thinking, "It's cold. The water freezes. What else is there to know?" Oh, I had so much to learn. Dan's idea was that you have to know a little sea ice science before you can travel safely on it.
Cold temperatures are just the beginning
The sea freezes because it's in contact with the colder air. The heat transfers from the water to the air until the water reaches its freezing point. Then, the sea ice goes through the stages we discussed yesterday (Frazzle Ice, Pancake Ice, etc). Once it becomes a solid flat sheet, it will continue to thicken under the surface. In many places we are traveling, it has been cold enough to freeze the water under the ice for six feet!
The ice is stronger the colder it gets. Scientists and engineers rate the ice, based on its temperature. Here are the ratings:
- Period 1 Ice: Temperature = Less than 14˚F (strongest ice)
- Period 2 Ice: Temperature = 14 - 23˚F
- Period 3 Ice: Temperature = 23-27˚F
- Period 4 Ice: Temperature = 27-28˚F (weakest ice)
The scientists and workers at McMurdo Station care about strong ice, because they want to work on it. That involves driving big heavy equipment, like snow machines, a Pisten Bully, a bulldozer, or even a C-17 airplane. You really have to understand the ice to make this all work safely!
Every two weeks, the sea ice group issues the McMurdo Sea Ice report. This details everything that we currently understand about the sea ice.
Stresses
The other problem with this big sheet of sea ice is that there are a lot of forces acting upon it. For example, the wind blows and transfers kinetic energy (moving energy) to the ice. The tide tries to rise and fall and pushes up on the sea ice. Glaciers and the ice shelf are advancing, pushing on the sea ice.
As the sea ice tries to move, it encounters points of resistance. Places where it can't move because it hits the land, a glacier, or an ice shelf. What do you think happens at these places?
CRACKS!
As the sea ice is pulled apart and pushed together, our nice flat sheet begins to crack, opening gaps to the water below. In some places, it is pushed together causing ridges, called pressure ridges. In short, it creates problem spots for scientists and workers.
Watch the part in the middle, the ice is very thin!
You can see where the sea ice has been pulled apart by the forces acting on it.
This 8 foot sea ice crack prevented us from getting any closer to Cape Evans and Mount Erebus.
Sea Ice Cracks
Well, we don't want to fall in - do we? So, we need to learn how to identify cracks and figure out which ones are safe to cross and which ones are not. We call this profiling a crack. Basically, it involves three steps.
Our instructor, Dan Mahon, talks about how to profile a sea ice crack while sitting on the ice. (Photo courtesy of Elizabeth Mockbee)
Step 1
Shovel off the snow across the crack.
Step 1: Remove the snow and drill a hole through the sea ice. (Photo courtesy of Elizabeth Mockbee)
Step 2
Drill holes through the sea ice in different spots along the crack.
Mike and Liz work to profile the sea ice crack by drilling through the ice and measuring thickness. (Photo courtesy of Orin Bakal-Molnar)
Step 3
Use a measuring tape with a flat piece of metal at the end. You lower it in to the hole. Get it to stick at the bottom of the hole, and pull up on the measuring tape. The number is the ice thickness.
To perform this task, you need to work as a group. I made a lot of new friends who were learning about sea ice. It was such a great group to work with!
We saw a lot of cracks out in the sea ice farther out from McMurdo Station. We got lots of practice profiling sea ice cracks.
Safe crossing
The rule of thumb is that each vehicle type requires a certain amount of sea ice to travel safely. This depends on the weight of the vehicle and how it spreads that weight over the sea ice. For example, our Pisten Bully weighs a lot, but its weight is spread out over the 9 feet of track length. So, for our Pisten Bully, we need 30" of sea ice. That's almost three feet. If we find a crack that is less than 30" of ice, we can still cross it, as long as the crack is no more than 36" wide.
Funny story
I met a lot of really neat people on this trip. One of my new friends, Orin, was poking around in a sea ice crack with a shovel. He was testing the thickness of the ice. Look who showed up!
This curious seal surprised us all!
Summary
At the end of the day, I saw some amazing things out on the sea ice. I learned a lot about sea ice safety and how to travel safely to and from our new potential dive sites. I made a lot of new friends. All in all, it was a great day to be here in Antarctica!
Frost flowers forming around a sea ice crack.
Lounging around on the sea ice, during a break. (Photo courtesy of Paul Stewart)