Due to the recession of (all of) the New Zealand glaciers, you can no longer walk onto the Fox glacier (the rapid recession has caused the terminal face to be too unstable). Also the walk to the terminal face is much longer than it was 20 years ago. This walk was actually fairly unpleasant, being crowded with bus-loads of tourists (apologies for the hypocrisy here!), being buzzed by helicopters ferrying the lucky few up onto the glacier, and finishing with a fairly anticlimactical view of a (dirty) wall of ice in the distance.
So for this reason (and because helicopters are awesome), we bought our tickets for a guided heli-hike on the ice! :D
The contrast with the somewhat lacking experience described above made it well worth the ticket cost.. And did I mention that you got to go in a helicopter? (twice!)
Apparently they get 290 wet days a year on the glacier, so we were lucky to get glorious sunshine for at least part of the ice-walk. So we didn't mind too much that the clouds decended later on. The guide assured us that if the weather turned too bad for the helicopters to ferry us back to the village, we would have to sleep up on the ice, but not to worry, as the emergency supplies contained lots of whiskey! (he seemed oddly hopeful for a storm).
Anyway, enough rambling, check out the photos. :-)
The glaciologist in me is very happy. And also making me ignore all the things in the pictures that aren't a) ice or b) mountains. And wanting to try to explain them all. And remembering my Scandinavian helicopter glacier experience, which, because helicopters are, as you rightly point out, cool (though perhaps not so much as the ice...), was very fun.
ReplyDeleteI really need to go to NZ - glaciers and LOTR. Not much more I want....
But yes, looks very impressive - you seem to be having a great time!
Gosh. So what is it that causes that amazing ultramarine blue colour in the ice? And is it related, or not at all, to the similarly striking colour of some glacial lakes? I've always assumed the latter is due to suspension of rock powder at a size suitable for - something. Rayleigh scattering? Probably not. Anyway, it's very pretty isn't it. Oh and... I don't recognise the helicopter. Does it really have three rotor blades? How unusual. Mysteries, all mysteries. Discuss!
ReplyDeleteWe did get a lecture on the different colours.
DeleteThe vivid blue-green lakes and rivers are caused by mica (or rock flour as they called it) that is either in suspension (rivers) or settled on the lake bed (up to 1/2 m thick!)
The blue colour in the ice is because ice is blue. I guess this is the same as water, which gets bluer the deeper you go. The red gets preferentially absorbed.
As for the helicopter. It did have three rotors... And not because one was missing, I hasten to add.
I can indeed confirm glacial lakes are that colour because of the suspended sediment (and also because there are sod all in terms of biological processes going on - they're just too cold).
DeleteThis means glacial lake strata are very useful for palynology (the study of fossil pollen) and various kinds of stratigraphic dating.
The ice is blue because, as Dave says, it is blue. Also because, the deeper you get, the more compressed the ice gets and therefore the denser it becomes. So there's more ice and less air so it's more blue.
And then it all melts.
Mmm. That doesn't quite satisfy the physicist does it. In both cases, why the blue? Ice is simple, chemically. There are electron transitions that do - let's say - copper sulphate. What's going on in yer ice, then? And. Why does rock flour do blue, then? (Am I back to Rayleigh?) And why did I initially misread mica for Micras? I really did. I'm sure they aren't dumping those in the lakes. - sorry, NZ. Questions, all questions.
ReplyDeleteOK, having done a bit of research, here goes: Water preferentially absorbs the red end of the spectrum and reflects the blue, so that’s why that’s blue (the OH bond has three modes of vibration that mainly absorb in the IR spectrum, the harmonics of which lead to a weak visible red absorption). It also tends to reflect the sky (which is blue due to Rayleigh scattering - it also contributes to water's blueness because the blue light just gets scattered more due to this). Ice is made bluer by the fact that internal reflected light has long path lengths.
DeleteRock flour provides a very reflective surface at the top of the water column (it’s mainly carried by suspension and then settles out slowly). The flour itself has a high absorption coefficient for short wavelength light (wasn't able to find out why - presumably something to do with either the minerals involved or the particle sizes, but I'm pretty certain it's nothing to do with copper sulphate), so absorbs mainly blue light. The fact that water’s got rid of all the longer-wavelength light means that you mainly get greeny-blue light reflected (as green is the majority of what's left) and it appears so brilliant because of the reflective nature of the light-coloured flour. The more flour there is, the greener the lake, because more blue gets absorbed.
Hopefully, that makes sense!
Getting there - thank you Samuel. So it's those dangling hydrogen atom twanging about again, like in a microwave oven (but at a very very much shorter wavelength - hmmmm). But the critical step is the one we haven't got yet: "The flour itself has a high absorption coefficient for short wavelength light". I too have run into a brick wall on that one. I have found a chart showing that the absorption and scattering coefficients for particles that start to approach light wavelength - particles smaller than 2 microns - are somewhat higher for shorter wavelengths. For bigger particles, the spectrum is flat white, which seems less surprising. So - why? We still haven't found out why glacial lakes are blue!
DeleteIt must be something intrinsic to particles of that size, because the mineralogy will vary greatly. We need a Professor of Optics!
DeleteCould it just be a lot of food colouring?
ReplyDeleteCould it just be a lot of food colouring?
ReplyDeleteActually everyone. Julia has hit the nail on the head. I phoned up the heli-hike guide (Jake), and he admitted that they seed the neve regions (which is where the snow falls to end up in the glacier) with green food colouring... By helicopter obviously, as the neve is a dangerous place, and also because you need to get the food colouring nice and even! :-)
ReplyDeleteI believe you, of course! But where are the astronomers when you need them... Isn't this exactly the same problem as measuring interstellar dust concentration and dimensions by looking at the reddening of starlight passing through the dust? I vaguely recall - was it Robbie? - telling us about this. If whatever the theory is works up there, it must work in a lake too!
ReplyDeleteIndeed! Sounds as if the mechanism should be the same.
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