ablation zone

[dummy]

The first few posts on this thread were a pretty good discussion of the topic, but it's lost in spray.

 

"do you think it is really impossible to garantee safety by climbing something like the sitkum glacier without a rope in the summer?

 

yes, I think it is IMPOSSIBLE to guarantee safety on any glacier when you are not on the ablation zone . It may be IMPROBABLE that you will fall into something on the Sitkum.

 

Can somebody clarify the ablation zone?

[Marmot74]

The ablation zone is the area of the glacier below the firn line that has more snow melt per year then snow that falls on it, therefore resulting in lots of bare ice and rock. It is usually easy to spot crevasses in the ablation zone due to most of the snow being melted opposed to the accumulation zone which is above the firn line and can be totally covered in snow.

Edited March 26, 2005 by Marmot74

[MisterMo]

The firn line and the neve line being one and the same, of course, for those who may bump into one term or the other.

[genepires]

To pick nicks. But the ablation zone can have covered crevasses in them. Right now there are lots of covered crevasses on ablation zones. Maybe I am confused, but with the definition given above, (which is the definition given in most instruction books) the ablation zone and dry portion of the glacier are not the same thing. I suppose they are the same in october but not in june. It seems like some people confuse ablation/accumilation zone with wet/dry glaciers. Dry ablation zones (reduntant I suppose) are good for unroped walking around.

 

I think that the post mentioned by dummy should replace "ablation zone" with "dry glacier".

[Marmot74]

Thats why I said its USUALLY easy to spot crevasses in the ablation zone, I did not say it always is. These are just guidelines and there are always exceptions in everything.

[Alpinfox]

Interesting that the Sitkum Glacier was used as the example of a "safe" glacier to be on unroped. I punched through a snowbridge while descending unroped on the lower Sitkum one hot afternoon. Luckily my backpack stopped me and I only went in up to my waist, but both feet were swinging in free space.

[Fairweather]

That lower lobe of the Sitkum is usually about 50/50 by September. That is, the lower portion is bare ice below the firn line and the upper portion is still covered in neve'. It's similar to the area of ice above Heliotrope Ridge on Baker or Inter Glacier on Rainier....probably best to rope up from the beginning and resist the temptation to 'keep going' in an unsafe manner. The classic unroped bare-ice romp is Blue Glacier on Olympus below Cal-Tech moraine.

[MisterMo]

I think the both the temp and season of the year are as important considerations as anything. Early winter can be sketchy as stuff is drifted over but hasn't undergone enough freeze/thaw cycles to be strong, whereas by March or so snowed over stuff is about as safe as it's going to get...leastwise in the Cascades.

[Mark_Husbands]

My limited understanding:

 

Ablation zone/accumulation zone are defined by net loss/gain of mass over long time scales. this corresponds to the upper limit of bare ice in summer, most of the time, but as others have pointed out, in winter or after snows crevasses can be covered in the ablation zone.