I am learning...but what is the condition to have an ice dams? When the air temperature drops, water channels freeze up and water begins to pool up behind the ice. This creates hydraulic pressure behind the ice. When the ice dam is disturbed, the pooled water breaks out, often with an explosive force."
(I had meant to address this a while ago but I could not find the relevant quote at the time and just happened to come across it recently.)
Look at the reference: it is from the avalanche center and I critic them to have an accademic knowledge of the problem, not a pratical knowledge.
Google the words run off and found as much information as you can on: "The draining away of water (or substances carried in it) from the surface of an area of land"
In a previous thread, I talked about the flow of water, the difference between the day and the night. To show some thing, one guy said that it dosen't exist. If I am wrong, I learned some things that can save my life. Wtih that attitude, I can climb and be safer. If you are wrong, you loose your credibility because you don't talk to help other people, you talk to point out that I am wrong. I know that is a point that pissed a lot of you because it is important what the other think. My goal is to show that we can be safer than yesterday by talking of knowledge. If you confront me with the paper of avy center, I will agree that I was wrong for a part of it.
For the damn, it is like waste water sewer. If there is too much water in the same time (rain exceed the capacity of the sewer) there will be an overflow. Any situation creating an overflow will create a damn. An avalanche for example can stop the run off of water and create a damn if the water is trap under the snow/ice. If the water had a place to go, it will create a damn.
In the particular situation of rain, the run off will be hight for the next day or two. So, much a lot of "pipe" will be open and the water won't be trap. As it began to snow, an isolation of the water inside the snow will occur and the water trap inside the snow will flow away. When the run off will dimished, the pipe will stay there, but they will be free of water. It is only when the run off will become higher than the run off will exceed the capacity of the pipe. That it will be dangerous for the climber. A damn, without water, is not dangerous.
But it is true to say that one way that damn can be form is during a rapid drop of temperature and I was wrong. If you go climbing, look for places where the run off can be stop and where the water begin to emerge from the snow above...and avoid the place. Ex. snow pocket can create a damn.