I°4 SCENERY OF SWITZERLAND. 
avalanches fall irregularly, as they depend on a 
variety of circumstances; they cannot therefore be 
foreseen, and do much damage, often killing even 
wild animals. 
Ground avalanches occur generally in spring, when 
the snow is thawing. The water runs off under the 
snow, which thus becomes hollow, only touching the 
ground in places. A slight shock is sufficient to set 
it in motion, and it tears away down to the ground, 
which it leaves exposed. Such avalanches depend 
therefore on the configuration of the surface, and are 
in consequence comparatively regular. In many 
cases they follow the same course year after year. 
In these tiacks, trees cannot grow, but only grass or 
low bushes. 
The front part of the avalanche of course first 
begins to slacken its speed. The part behind then 
presses on it, and often pushes over it. Those who 
have been enveloped in an avalanche all agree, that 
during the motion they could move with comparative 
freedom, then at the moment of stopping came ex- 
treme pressure, and they found themselves suddenly 
encased in solid ice. Pressure had caused the 
particles to freeze suddenly. 
Avalanches are often looked on as isolated and 
exceptional phenomena. This is quite a mistake. 
