Avalanche Thermodynamics

Some days, if there's just the right resonance, you can, just for a little while, be better than you really are - like an electron quantum tunneling through an energy barrier it can't climb over, you can tunnel through the personality barrier, even if only for one day.

Friday late afternoon 9th April, there wasn't a breath of wind on lake Wanaka. I checked - through squinting intensely peering eyes in the twilight I observe the tops of the tallest poplar trees : the most flimsy autumn nearly-fallen, most delicate leaves on the very tallest tips do not move a millimetre. Stillness in a vast space like that has a kind of re-scaling effect - the lake becomes an intimate pond, everything seems within reach. (Wind is like a 5th dimension, another degree of separation between things - between people so they can't hear each other; making journeys longer, harder, rougher, bumpier. And usually scaling along with the other dimensions (big things like lakes have big winds, small things like glasses of water have tiny winds) - so everything seems oddly sort of closer together, in a big space, when there is no wind).

What luck ! - a big golden delicious friendly autumn anti-cyclone over the whole country - blue and gold skies, no wind. And the autumn sun never heats things up enough to kick off the huge convections and sea breeze fronts of summer, so the wind doesn't blow up strong and annoying in the late morning and afternoon like it does in the heat of January, in central Otago.

Adele and I had been quietly scheming for months to walk up the Rob Roy glacier track, from the Matukituki valley, just the two of us, the first time out and about without children for 18 years ! - thanks to a relative's visit and a little bit of begging (for three days children-and-house-sitting) and the miracle of my being organised enough to successfully apply for an annual leave day for the Friday (application made two whole days before the trip) ! That track has been a family tradition for nearly ten years but....Adele had never quite made it onto any of the various permutations of kids, grandmother and myself that had previously walked it (in retrospect...mistakes were made...) - so time to make amends. The first time I went up there was in 2000, with my daughter than aged 6 and I had no idea that at the end of the track was a stunning hanging glacier, above a beautiful alpine valley - I had just chosen that wiggly line off the map as it was about the right length and gradient for us - and not *too* wiggly. About an hour into the walk we became alarmed by rumbling sounds - almost making us turn back. After pausing for awhile to see what events these rumbles might presage - avalanches in our general direction ? time portals opening ? volcanoes erupting ? - and observing nothing, we continued on to the end and were stunned to find the cause - a deep blue hanging glacier far above us and the valley, large bits of which were falling off and crashing down into the valley's base, every 20 minutes or so.

So the plan was - drive up from Dunedin on Friday, walk the walk Saturday, drive back Sunday.

We left as early as we could on Friday morning - about 10:00am. There's nothing quite as good as setting sail on the first day of (what one feels, rightly or wrongly, is a deserved) holiday, with a holiday-beginner's determination and confidence that no stone of relishment, small delight or amusement will be left unturned - no opportunity for a laugh or potential point of interest will be overlooked. So first stop was Milton -we never ever usually stop there, but this was now an official road-trip and diversions were our business - for a take-away coffee on the sun-drenched terraces of the war memorial and a chat to a friendly local who said gidday - turns out she was raised on the slopes of Sandymount on the Otago peninsula, when there was a school still there, and she and Adele talked about "The White Masai" and other books they both had read, and she corrected us on a point of local history - Larnach of Larnach's castle fame did not benefit from the estate of his wife's family as much as we had thought, since it seems her step-father siphoned most of it off. And a look through the antique shops - Adele recognised the proprietor of one of them as a regular at the auctions in Dunedin. I guess, buy in town and retail from low-rent premises in small towns on the main highways North and South from Dunedin, with lots of wheel-traffic (the small towns just to the North of Dunedin also boast well appointed antique retailers - Milton is on the road south). (Thats something that always starts to unsettle me on a holiday - seeing the ingenuity with which other people are making a living, and contrasting it with my own plodding, and so the charter of my holiday starts to unravel and existential anxiety returns...but not today, I'm tunneling the barrier...)

So then on , turn right , and to Lawrence - we *do* always stop there, but usually just for the donut from the corner store. This time we stroll as well.

Next stop Alexandra (Roxborough is skipped on the way out but we stop for autumn fruit on the way back - peaches, plums, apples) - the road trip is official now, we buy a couple of CD's to play on the CD player (having a car that has one is still a novelty !) : Johnny Cash ; Sinead OConner. Plus a new gold pan (and a small shovel) as I forgot to pack my rusty old pan and on the return journey I want to try a spot I noticed a few weeks back at Beaumont, on the Clutha - a rocky river reef with potholes in it is exposed as the river is low and I wonder if the potholes may tend to trap heavier sediment - e.g. iron and gold (yep - later I do get some very small gold flakes, and lots of black iron sands, from the sediment at the bottom of one of these - after much very patient swirling and eluting and dissecting out the small gold flakes with a sharp pointy kitchen knife back at home). And stroll and admire the cedars and the old black and white photos of the long gone arbor day crowd who planted them, of which even the little kids must all be long gone now.

On again - to Cromwell, another stop to enjoy the autumn sun and then the final leg, skirting along the valley to Wanaka. We finally arrive at 5:00pm - thats a 7 hour journey but apparently some people can do it in 3.5, though I've never done better than 5. But in time to snag a good motel room before the "No Vacancy" sign goes up. We hurry to get down to the lake to walk in the sun just before it dips behind the mountains. Friday late afternoon 9th April, there wasn't a breath of wind on lake Wanaka...

Well Saturday was a Perfect Day, a Perfect-Day-and-I'm-Glad-I-Spent-It-With-You type of Perfect Day, blue sky and gold sun and still still. Away by 9:00am and off up the road to the Matukituki valley, past Mt Roy (thats another really good day walk but a bit of a gut buster - but the view at the top is incredible. Do it on a hot day, take plenty of water, and when you get back to the bottom, put your foot down and get to the lake as fast as you can and dive in before you cool off. Aaahhhhh.), onto the gravel road and through all the fords carefully - its the driest I've ever seen , only one had water flowing to wet the tyres.

I've got some new advanced technology for our walks now - a butane canister and a little shiny metal tripod thing that looks like some small and mischievous critter out of the Transformers movies - after only half an hour on the job of walking up that track we set down on a grassy spot overlooking the river for a totally undeserved rest and I masterfully if not majestically, wrangle the technology and boil the billy, for a cup of coffee - luxury !

There have been some big changes on the Rob Roy glacier track since I was there last - but not where you would expect ! The ridiculously dangerous looking landslides - the ones which look like somebody just pressed "pause" at a particularly exciting and fast moving part of their descent - such as the one with what looks like a completely unsupported whole floor of a large building projecting out into space over your head without any visible means of support - "don't whisper too loud or it will come down" - are exactly as they have been for the past 10 years, presumably protected by some sort of spatio-temporal anomaly.

Yet there are other parts where something very scary indeed has happened to quite small insignificant streams - in one section a torrent of assorted boulders has ripped across the track and through the trees since I was last there - an assortment of all shapes and sizes - from huge down to....large, fairly big, big, sizable, soccer-ball size, tennis-ball size, golf-ball size - and quite a few marbles. And if you pause to look, its not just chaos - there are some intriguing patterns, like the dry-stone-wall we notice by the side of the track. We look carefully and can see what has happened - the wall runs along a line of 4 trees, with a few metres between each tree. The gaps have been large enough to let most of the rocks through - until finally a metres-long boulder got stuck at an angle - still leaving gaps but smaller now, so the filter can now trap metre sized boulders - and the metre boulders leave smaller gaps again, so the wall will start to collect half-metre boulders, etc etc - each new addition caught by this filter further alters the properties of the filter, so stacking up what looks like an orderly straight wall of boulders , size-sorted with the biggest at the bottom. And then the occasional stone placed apparently by hand at the top of the wall, or some other unlikely place, where you feel sure it should have rolled off, or could not have got there by chance in the first place - but you can imagine how these represent the peak of the energy of the flood - these placements have had just the right amount of energy to make it to where they are and no further - and probably at the peak of the flood, so nothing more with that peak energy came through to knock them off. And then also, in such a torrent, the total energy will be distributed thoroughly among the millions of rocks, so that it will be able to explore the unlikeliest destinations and architectural constructions - just because there is almost certainly at least one rock with just the right amount of energy, to end up placed *just so*" at the tippety top of wherever you might care to nominate. In thermodynamic terms, the "temperature" of that rock fall was probably quite high.

(Its actually interesting to think about an avalanche like that in thermodynamic terms, and consider defining the "temperature" of the fall, in the sense of the distribution of the energies of all of the millions of rocks coming down. To recap on what "temperature" is - consider your cup of tea - the kinetic energies of all of the tea molecules in there, at any instant of time, ranges from zero for a very few that are stationary (just for that instant, by chance), up through lots in the mid range, on up to a few very energetic molecules moving very fast. And the hotter your cup of tea, the more that the tea molecules spread themselves out to occupy all of the energy levels available. "Temperature" is a parameter that describes the shape of this distribution, of how many tea molecules there are at each level of energy. Applying that to the rock slide, and thinking about the distribution of energy levels of all of the rocks, we must have a similar situation - at any instant there will be a very few rocks temporarily stationary, with zero kinetic energy (e.g. they have just collided and bounced back off another larger rock) ; many in the midrange, on up to (presumably) a very few very energetic rocks. So there should be an "avalanche temperature", in the sense of one or more parameters that describe the shape of this distribution of how many rocks there are at each energy level. Maybe the most interesting (and frightening) prediction of that thermodynamic way of thinking, is that there will be the very occasional extremely energetic boulder, heavy and moving very fast - much faster than the group average velocity of the avalanche as a whole - and the higher the "temperature" of the avalanche, the more of these there will be - though even in a "low temperature" avalanche, very occasionally you will see one. Maybe this accounts for the peculiar danger and almost bizarre unpredictability of mountain floods and avalanches - where people are swept away and killed by apparently docile babbling brooks that suddenly run amok after a bit of rain, in every-day spots you and the kids have been to lots of times : the idea is that we are actually here experiencing the micro-behaviour of large assemblies that usually you have to be the size of a molecule to experience - it is as though we have been shrunk down to the size of a tea molecule and experience directly the energies and collisions and unpredictability of individual tea molecules - rather than the smoothed out average behaviour we see from our large-scale vantage point. Hmmm - the thermodynamics of rocks slides - must look into it...).

Another change on the track is that there's some serious upgrading going on, using a small digger evidently dropped in by helicopter - looks like its become very popular in the last 10 years and all those feet are gradually wearing down the track base leaving a tangle of exposed tree root trip-wires - so its being widened and built back up, and in some places shifted.

Its a pleasant walk - Adele doesn't find it too bad, and I'm tunneling the barrier, being better than I really am - relishing the time, not thinking about work or wishing for something better or remembering something worse...

The most amazing change is up the top at the end of the track. What used to be a wide fairly flat grassy beautiful alpine meadow, is now devastation, like a bomb has gone off in a quarry pit. (We later learn this was all caused by a night's rain only two weeks ago - the Saturday night of the Warbirds-over-Wanaka weekend). We can see how high the water level was via debris caught in the lower branches of bushes, and flattened grasses. Amazingly the long-drop dunny they have up there survived - though apparently they had to dig it out, it was half buried. (Thank goodness it wasn't flushed in the process !).

(I reflect that if I had been caught out up there in the rain and had to pick the safest place to pitch my tent, I would have pitched it up the top in that meadow, right under the bomb. Yet further down where the creek roars and foams and looks ferocious would have been , counter intuitively, much safer. Stay well away from mountains when its raining ! Else you will likely experience thermodynamic rescaling, and what its like to be a tea molecule in a hot cuppa)

On the way back we did a reckless river crossing of the Matukituki river rather than go over the swing bridge, just for the hell of it. It was really a bit too deep, we shouldn't have done that.

It was the best day I've had in years.