Читать книгу The Snow Tiger - Desmond Bagley, Desmond Bagley - Страница 14

The late afternoon sun poured through the windows of the hall, rendered multi-coloured by the stained glass. Patches of colour lay across the tables; the carafe of water in front of Ballard looked as though it was filled with blood.

Dan Edwards loosened his tie and wished he could have a cold beer. ‘They’ll be adjourning pretty soon,’ he said to Dalwood. ‘I wish old Harrison would get a bloody move on. All this talk of snow doesn’t make me feel any cooler.’

Harrison poured himself a glass of water and sipped. He set down the glass, and said, ‘So you took samples of the snow cover on the western slope in the presence of Mr Ballard. What were your findings?’

McGill unzipped the leather satchel and took out a sheaf of papers. ‘I have written an entire report on the events that occurred at Hukahoronui – from the technical side, of course. I submit the report to the Commission.’ He gave the report to Reed who passed it up to Harrison. ‘Part One consists of my findings on the first series of snow profiles which was submitted to the mine management and, later, to the municipal authorities of Hukahoronui.’

Harrison flipped through the pages and frowned, then he passed the papers to Professor Rolandson. They conferred for a moment in low voices, then Harrison said, ‘This is all very well, Dr McGill; but your report appears to be highly technical and contains more mathematical formulae than the majority of us are accustomed to. After all, this is a public hearing. Could you not describe your findings in a language that can be understood by others apart from yourself and Professor Rolandson?’

‘Of course,’ said McGill. ‘Indeed, I did so to the people in Hukahoronui.’

‘You may proceed; and you may expect to be questioned – in the interests of clarity – by Professor Rolandson.’

McGill clasped his hands in front of him. ‘Snow is not so much a substance as a process; it changes in time. It begins with a snowflake falling to earth and becoming part of the general snow cover. It is a six-sided crystal and not very stable, and sublimation begins – a sort of evaporation. Eventually the crystal becomes a small, rounded granule. This is called destructive metamorphism and results in a higher density because the air is squeezed out. At the same time, because of the evaporative process, there is water vapour in the snow mass and, due to the low temperature, the separate granules tend to bond together by freezing.’

‘This bond is not particularly strong, is it?’ asked Rolandson.

‘The bond is not strong, when compared with other materials.’ Rolandson nodded and McGill went on. ‘The next thing to take into account is the temperature through the snow cover. It’s not constant – it’s warmer at the bottom than the top, thus forming a temperature gradient. If you look at Graph One you will find the temperature gradient of those first five samples.’

Rolandson flipped pages. ‘Not a very steep gradient – not more than two degrees.’

‘It’s enough for the next stage in the process. There is still a lot of air in the snow cover and the relatively warm air at the bottom begins to rise carrying water vapour with it. The vapour precipitates on the colder granules above. There is now a building process at work which is called constructive metamorphism, and a new kind of crystal begins to form – a cup crystal.’

‘Could you describe a cup crystal, Dr McGill?’

‘It’s a conical shape with a hollow in the blunt end – the cup.’

‘And how large is a cup crystal?’

‘A well-developed crystal may run to half an inch long, but you can take a quarter-inch as average.’ McGill paused, and when Rolandson remained silent, he said, ‘Graph Two shows the penetrometer readings – that is the resistance of the snow to stress.’

Rolandson studied it. ‘This is the resistance in kilograms plotted against depth?’

‘Yes, sir.’

‘There’s a discontinuity half way down on all five samples.’

‘Yes, sir; that’s a layer of surface hoar.’

Harrison interrupted. ‘If it is not on the surface how can it be described as surface hoar?’

‘It was on the surface. When the surface of the snow is colder than the air above it then there is more sublimation of water vapour – something like the condensation on the outside of a glass of cold beer.’ (In the Press gallery Dan Edwards sighed in anguish and licked his lips.) ‘In this case I should imagine it happened on a clear and cloudless night when there would be a lot of outgoing radiation. Then the hoar, or frost, would form on the surface producing flat plates of thin ice.’

Again Harrison brought up the objection. ‘But this discontinuity, as Professor Rolandson calls it, is not on the surface.’

‘No,’ agreed McGill. ‘Normally, when the sun hits it in the morning it disappears. In this case, I imagine that clouds came over before sunrise and it began to snow again quite heavily. The layer of hoar was covered and preserved.’

‘With what significance?’ queried Rolandson.

‘Several things could happen. The layer is quite hard, as you can see from the penetrometer readings. It is also quite smooth and could form a sliding surface for the snow above it.’ McGill extended two fingers. ‘Secondly, a layer of hoar is formed of flat plates of ice fused together – that is, it is relatively impermeable to air. This means that the most likely place for cup crystals to form would be just under the hoar layer.’

‘You emphasize cup crystals. In what way are they dangerous?’

‘They are dangerous because of their rounded shape and because there is very little bonding between one crystal and another.’ McGill tugged at his ear. ‘As a very rough analogy I would suggest that it would be very difficult for a man to walk on a floor loosely packed with billiard balls. It’s that kind of instability.’

‘Was there any evidence of cup crystals forming at this time?’

‘They had begun to form in sample one, the highest up the slope. I had reason to believe that the process would continue which would result in a marked decline in stability.’

‘Go on, Dr McGill.’

McGill put up a third finger. ‘Three, the weather forecast at the time indicated more snow – more weight – on that slope.’ He dropped his hand. ‘All things considered I came to the conclusion that the snow cover on the western slope of the valley of Hukahoronui was relatively unstable and thus formed a potential avalanche hazard. I so informed the mine management.’

‘You mean Mr Ballard?’ asked Harrison.

‘Present at the meeting were Mr Ballard; Mr Dobbs, the mine manager; Mr Cameron, the mine engineer; Mr Quentin, the union representative.’

‘And you were present during the whole of that meeting?’

‘Yes, sir.’

‘Then I think we can take your evidence as best evidence of what occurred at the meeting, subject to later appraisal. However, the time has come to adjourn for today. We will gather here at ten in the morning when you, Dr McGill, will again be a witness. The hearing is adjourned.’