Mudflow – the phenomenon relating to the category of natural disasters; the stream which is suddenly collapsing from mountains consisting of the water mixed with products of destruction of rocks (clay, the earth, sand and stones). The danger of a mudflow consists in its huge destructive force which is combined with a surprise factor.
Mudflow, sil or a mud stream – all this names of the same natural phenomenon in the form of the weight which is promptly overthrown from mountains half consisting of water half – from clay, sand, small and large stones. The mudflow arises suddenly and runs low in 1-3 hours, but for this short time on the way wipes everything off the face of the earth. The destructive force of a mudflow is huge. The water and mud stream pulls out trees with roots, destroys bridges, dams, houses. The mudflow moves with strong noise, the earth shudders from blows of boulders. At the same time the movement of a mudflow is not continuous, but wavy (separate shafts). The mudflow very quickly moves, and from the moment of its origin in mountains to a stream exit to the valley sometimes there pass only 20-30 minutes. Depending on structure the mud streams are subdivided on: • Mud – water mix with the earth and a small amount of stones; • Mud-stone – water mix with the earth, gravel, pebble, medium-sized stones; • Water stone – water mix with large stones and blocks. All area of emergence and action of a mudflow is called the torrential pool. The mudflow in case of coincidence of three conditions is formed: • A congestion of considerable volume of water in mountains; • Existence on hillsides within the torrential pool of enough sand, stones, pebble, gravel, i.e. easily moved masses; • The steepness of hillsides on the area of the torrential pool not less than 10-15 ˚. The following factors can be an incitement for a descent of a mud stream: • Heavy and long downpours in mountains; • Fast thawing of mountain glaciers and snow; • Emissions of volcanoes and earthquake; • The explosive works which are carried out in mountains; • Deforestation on slopes; • Large-scale construction works. The person who is on the way of a descent of a mudflow cannot escape. Rescue – only in preliminary withdrawal from a way of a mud stream. Unfortunately, it is not possible to predict emergence of a mudflow presently. Therefore, having heard noise of a mud stream, it is necessary to rise immediately from a bottom of valley to mountains, from the mass of water rushing down with the earth and stones up and aside. It is necessary to consider also that of a stream large stones and the whole boulders can be thrown out the parties.