hot and cold

Scott, great start to a physics of ice thread and the temperatures that create ice. We are now a week into a cold snap, that by old timer standards was pretty frequent. Obviously it is a blessing for ice climbers, yet in a bigger sense it is very important for the Yellowstone and northern Rockies eco system.

The bark beetle, which affects pine trees and leads to great swaths of dead trees, which in turn become a greater fire hazard, which in turn burn leasd to a warmer climate are afected by the -20 temperatures of the past week. Not being a forester (chip in those of you who study our trees) we need a couple of weeks of these temperatures to kill the larvea in the tree. Warm winters and the bark beetles go nuts (the insect shag fest); cold winters and the beetles are not as fruitful. So it is good.

Water, the essential part of our bodies, life and communities is present in vapor, liquid and solid states. The solid state is what ice cimbers seek - the drips that form are a transitory manifestation of water. Timing climbs in between when they form to the point when the ice topples over is part of the challenge. Reading the ice for climbers is akin to reading a river for kayakers. Know your medium and you'll have fun and be safe.

The fattening agent for ice is dependant upon flow and temperatures. Flows can be spring or creek based (Palisade Falls) or a result of freeze / thaw cycles of snow (Smears for Fears). To grow they (our silly little hamster wheels) need really cold temperatures. Water is at it's densist at 39 F. That is the weight to volumne ratio. To go from 33 F to a solid state the latent heat that is present in water needs to be dispersed outward. This can be the atmosphere, rock, an ice screw, roof or skin. The normal amount of energy needed to lower one gram (.0035 ounce) one degree celius ( 1.8 F) is one calorie. Water, peculiar as it is, needs an extra nudge to make the transition from liquid to solid or liquid to vapor. It amounts to 80 calories for the same drop on one degree celcius, for the freezing equation.

You're probably familiar with "the watched water never boils" adage. It is this last bit of energy that is required to make the transition. Fort the vapor equation, water requires an additonal 500 calories to make the transition to vapor.  This is a result of the latent energy stored in water. So when we get the gnar gnar -20 temps the cold is pulling energy from the latent heat at an accelerted rate. Which is good.

But why does it creak and snap when it is cold? The hard brittle ice that we are ever so wary of is 0.1% more compact at 14 F than at 32 F. As the mass hanging from a cliff is under a vast amount of gravitational pull, the creaking is part of the equation. The gap that forms on pillars is the most obvious example of ice shrinking. If the pillar is growing there will be a connection between the base and the pillar. If is shrinking there will be no ice in the gap. So, as they say in the Tube in London, "Mind the Gap"!

A quick way to gauge the growth rete of ice is to observe the creek on the drive up - provided you are the passenger - don't immerse your Subaru in the creek for "close inspection". If you see steam (vapor) rising from the creek and a build up of ice dams and shelfs things are growing fast.  On a lake it takes over an hour to form a third of an inch of ice on 32 F water with ambient air temperatures of 23 F (9 degrees belwo freezing). When it it is -22 F the same third of an inch forms in 10 to 12 minutes, depending on humidity. So when it is super chilly, the ice gets fat. But it is also brittle.

From a climber's anectdotal standpoint, a few days of warm weather will allow the ice to expand and become less brittle. This we know. Plus our precious little fingers don't go through the screaming barfies. My own 2 cents for good Hyalite ice is tempartures in the 20s in town with puddles from ice and snow exposed to the sun. This equates to sticky hero ice!

sublimation - the process of a solid turning to vapor with out passing through the liquid stage.

Most of the information in this post is from "Ice", by Mariana Gosnell.

If you are an expert on ice, water & physics please add to this discussion. I'm a lay person and am interested in learning more.