[Nmap] Northern Glide Cracks

[Rod Gee]

Folks;
Local glide sites in this coastal area are mostly bare bedrock, not 
soil. It's not unusual to see them release in localized slabs in cold 
(in the minus range) air temp conditions, especially when that cold air 
temp follows close on the heels of significant multi-day precip events.
Glide activity is related to snow temp more than air temp. I believe it 
is also affected by length of time between snowpack accumulation and 
slab formation because that affects snowpack density and strength at 
time of slab formation. It is also influenced by slab thickness and the 
basal and mid-pack snow moisture.
Release is also influenced by the terrain configuration's support of the 
slab.
Mid-winter glide activity in this area is not necessarily related to 
free water at the snow/ground interface. I'd suggest this is also the 
case in isothermal conditions; I know it's often mentioned as a 
requirement for slab failure, but my observations suggest that more 
often than not, free water is not observed at the ground.

In isothermal conditions, the glide rate is often slower than during 
mid-winter events. The time between slab formation may be weeks in the 
former vs days for the latter. The ease of triggering either naturally 
or artificially seems easier in mid-winter. Again, that's strictly my 
personal opinion. I think it's because the spring isothermal snowpack 
has greater strength due to better overall grain bonding. We often see 
surprisingly good slab strength even though the snowpack has been 
theoretically isothermal for quite some time. I look for evidence of 
mid-pack strength loss as an indicator of when X results will be acceptable.
 
I'm still not sure how to explain why spring glide releases often occur 
during the overnight cooling phase, but others have opinions on that topic.
Anyway, two-bits worth from the coast. There's more but I'll stop here.

Rod