I located my copy of Liam’s paper, it is too long post. It was presented at a meeting of the AGU in San Francisco, Dec. 91. An excerpt from it follows. “Since a very small portion of the slopes tested with explosives eventually produce “post control” avalanches, it is obvious that most of the time traditional methods of explosives control are effective (he is talking about hand charges). However, even the small number of “post control” avalanches that do occur, verges on the unacceptable.
In the eyes of the victim and the public they can raise doubts as to the effectiveness of even the best run avalanche control program. They might be difficult to defend legally, and if they happen to you, or in your area of responsibility, they can ruin a perfectly good day.”
In my opinion and experience an option to leaving it closed might be to go back with a much larger shot and perhaps different shot placement. This would be more likely to, either release the snow, or prove to that it is stable.
Another way to look at post control releases is when there has been a past problem with post control releases in a starting zone or with a particular snow structure, use 25-50 pounds. Or perhaps 2-3 of them in a simultaneous air burst in different locations in the same starting zone.
Another way to explain post control releases is that they are the infrequent result of the use of charges that are too small.
Snow strength is variable, and the strength in each starting zone is not known exactly every control mission. Ideally, the standard charge size and placement should be more than capable of releasing any possible snow weakness down to a stable base, or the ground.
To take this to extremes: If 2 ounces of explosives were commonly used, I expect there would be a lot more post control releases. If 200 pounds was the standard charge, and plenty of them were used, I expect that post control releases would be extremely rare.
Anyone have thoughts about Post Control Avalanches? This would be good input for Dan Millers research program at MSU.
ReplyDeleteWhat size charges used, snowpack structure and length of time before the post avalanche.
It seems with large shots around 48 hours is aproprate to keep it closed if you suspect potential post control avalanches.
I know there are no peramiters or guideline on this but it would be intresting to see if there is any common ground on this issue.
About 15 years ago Liam Fitzgerald wrote the best article I have seen about Post Control Avalanches. If any one has a copy please post it.
ReplyDeleteI located my copy of Liam’s paper, it is too long post. It was presented at a meeting of the AGU in San Francisco, Dec. 91. An excerpt from it follows. “Since a very small portion of the slopes tested with explosives eventually produce “post control” avalanches, it is obvious that most of the time traditional methods of explosives control are effective (he is talking about hand charges). However, even the small number of “post control” avalanches that do occur, verges on the unacceptable.
ReplyDeleteIn the eyes of the victim and the public they can raise doubts as to the effectiveness of even the best run avalanche control program. They might be difficult to defend legally, and if they happen to you, or in your area of responsibility, they can ruin a perfectly good day.”
In my opinion and experience an option to leaving it closed might be to go back with a much larger shot and perhaps different shot placement. This would be more likely to, either release the snow, or prove to that it is stable.
Another way to look at post control releases is when there has been a past problem with post control releases in a starting zone or with a particular snow structure, use 25-50 pounds. Or perhaps 2-3 of them in a simultaneous air burst in different locations in the same starting zone.
Another way to explain post control releases is that they are the infrequent result of the use of charges that are too small.
Snow strength is variable, and the strength in each starting zone is not known exactly every control mission. Ideally, the standard charge size and placement should be more than capable of releasing any possible snow weakness down to a stable base, or the ground.
To take this to extremes: If 2 ounces of explosives were commonly used, I expect there would be a lot more post control releases. If 200 pounds was the standard charge, and plenty of them were used, I expect that post control releases would be extremely rare.