Ice density in crevasses on the Coleman Glacier

[Wildearth]

Hi I rapped down into a crevasse on the Coleman Glacier, day before yesterday and encountered near  impenetrable ice.

Do let me know your opinion on :

1. Does the density of ice vary in crevasses on the Coleman Glacier? ( A glaciologist I spoke with said it does, but there is no pattern. The deeper the crevasse, the denser the ice, lower down because of flow pressure, but there are many other factors...etc
2. Do monopoints work better on bulletproof  crevasse ice? (I was wearing brand new Grivel G12's and they were barely making a dent!)

I haven't found any answers on  crevasse ice density despite scouring the web and asking amongst  my ice climbing friends. 

Many thanks !

[JasonG]

Monopoints may be the ticket, but I suspect that vertically oriented frontpoints on something like the G14 would also work well.  Most importantly with any crampons, they need to be sharp!

And yes, my experience is that the deeper you go the harder the ice, but your glaciologist would know better.

[Wildearth]

Thanks for the input Jason,will try the Monos next time.

[G-spotter]

Ice density = f (temperature, pressure, porosity, time)

 

[Wildearth]

Many thanks G-Spotter. That's a lovely pic !

[JonNelson]

The role of pressure is to remove the air. Once the air pockets are gone, the ice is solid, then the pressure has essentially no impact on density. 

It should be the same as glaze ice that forms over rock without any air bubbles. Ditto for "black ice" on roads--all will have the same density. But the hardness also depends on temperature, with the colder ice being harder. 

 

[JonNelson]

I would guess (not being an ice climber), that the perception of hardness might also depend on the rugosity (i.e., bumpiness). The fairly flat ice walls of a crevasse would then seem harder to penetrate even if the inherent hardness was the same as a solid piece of ice with corrugations from drips because you could aim your pick between corrugations and get it to stick better. 

[G-spotter]

Well, if you want to get technical, the answer isn't really "density" as much as it is "stress and strain". Which is pressure dependent.

Higher pressure ice is harder and deforms less. This is why crevasses have a maximum depth.

http://www.antarcticglaciers.org/modern-glaciers/glacier-flow-2/glacier-flow-ii-stress-and-strain/

[G-spotter]

However, in practice, glacial ice does change in density with increasing pressure

https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=13&ved=2ahUKEwi3zrrhpNfeAhULwFQKHQG8BdkQFjAMegQIBxAC&url=https%3A%2F%2Fwww.igsoc.org%2Fjournal%2F3%2F27%2Figs_journal_vol03_issue027_pg568-573.pdf&usg=AOvVaw1xN96PcWhXuAEe_YNQByYE

[JonNelson]

Thanks G-spotter for those links. 

I didn't see anything about the higher-pressure ice deforming less or limiting crevasse depth, but it sounds interesting. I'll look into more later. 

In my limited reading of ice, I don't recall any definition of "hardness", but I once learned that the grain structure affects the flow properties. Who knows though how any of that related to the guy swinging his pick.

I'm not even sure what I said about hardness depending on temperature is right, but there is the interesting phenomenon of regulation, where one can (very) slowly pass a wire through ice at temperatures near the melting point. It is not pressure-melting. It does suggest a "softness" of sorts.  

Ice is a fascinating material. 

Edited November 15, 2018 by JonNelson

[G-spotter]

well, it goes from brittle to ductile at a depth of ~50m. you need 50m of ice thickness to flow, and so most crevasses are 50m or less deep because that's the brittle fracture depth.

i don' t think that's what the OP observed though.

[Wildearth]

Many thanks G-spotter and Jon for the insights.Very educational, thank you.

[Wildearth]

G- spotter, the links make for fascinating reading, thank you!