In the theatrical stage mud avalanches are likewise common. To produce them there must be a great supply of loose debris on steep rocks at a high level and much rapidly melting snow about them, whose water drains into gullies and unites in larger gullies, all with banks of rotten and crumbling rock. On a suitable day in early summer, when the sky is clear and the sun hot, the stones will fall in such numbers that they will plug some gully and dam back the water. It will collect and burst the dam, and a flow of stones, dust, and water will begin. At other neighbouring spots the same thing will happen, and the elements of the avalanche will flow together, block a larger gully, and presently burst that block also. So it will go on till a great mass of mud, water, and rocks collects somewhere and finally bursts loose in an avalanche which sweeps all before it.
Such an avalanche I saw from close at hand on 8th July 1892, in the mountains of Nagar. We were walking up the right bank of a great glacier river, and were forced at intervals to cross its tributaries which came rushing down the hillside on our left. Approaching the mouth of one of these side gullies we heard a noise like thunder and beheld a vast black wave bulging down it. It passed before we arrived and there was silence for a few minutes. Presently the sounds of another were heard aloft, and it soon heaved into view--a terrific sight. The weight of the mud rolled masses of rock down the gully, turning them over and over like so many pebbles. They restrained the muddy torrent and kept it moving slowly with accumulating volume. Each big rock in the vanguard of the avalanche weighed many tons; some were about 10-foot cubes. The stuff behind them filled the gully some 15 feet deep by 40 wide. The thing travelled perhaps at the rate of seven miles an hour. Sometimes a bigger rock than usual barred the way till the mud, piling up behind it, swept it on. The avalanche ate into the sides of the gully and carried away huge undermined masses that fell into it. We saw three enormous avalanches of this sort pass down the same gully in rapid succession, and, after we had gone by, others followed. All the neighbouring similar gullies discharged such groups of mud avalanches during that period of the year. They are one of the chief agents used by nature to pull down mountains during this, the dramatic stage of their existence. The roaring torrential river below carries off the mud and receives the boulders in its bed, where they are rolled along and in time ground to powder.
