Climate of The Alps - Glacial Region

Glacial Region

On the higher parts of lofty mountains in the Alps more snow falls in each year than melts. A portion of this is carried away by the wind before it is consolidated, but a large portion accumulates in hollows and depressions of the surface and is gradually converted into glacier ice which descends by slowly flowing into the deeper valleys where it help swell perennial streams.

Mountain snow does not lie in beds of uniform thickness and some parts are more exposed to the sun and warm air than others. Beds of snow commonly alternate with exposed slopes covered with brilliant vegetation without an obvious boundary of perpetual snow. A seemingly clear boundary seems visible when a high mountain chain is viewed from a distance: Similar conditions are repeated at many different points, so that the level at which large snow beds show themselves can be seen as approximately horizontal. But this is true only as far as the conditions are similar. On the opposite sides of the same chain the exposure to the sun or to warm winds may cause a wide difference in the level of permanent snow, though the increased fall of snow on the side exposed to moist winds may more than compensate for the sun's rays.

Still, the "line of perpetual snow" is not fixed. The occurrence of favorable meteorological conditions during several successive seasons may and does increase the extent of the snowfields and lower the limit of seemingly permanent snow, while the opposite may cause the limit to rise higher on the flanks of the mountains. Hence all attempts to fix accurately the level of perpetual snow in the Alps are fallacious. At best, local accuracy might be established for a particular district. In some parts of the Alps the limit is about 2400 m (7900 ft) elevation, while in others it cannot be placed much below 2900 m (9500 ft). As very little snow remains on rocks angled more than 60°, this is soon removed by the wind, some steep masses of rock remain bare even near the summits of the highest peaks, but as almost every spot offering the least hold for vegetation is covered with snow, few flowering plants are seen above 3350 m (11,000 ft).

There is reason to think, however, that it is the lack of soil rather than climatic conditions that checks the upward extension of the alpine flora. Increased direct effect of solar radiation compensates for the cold of the nights, and in the few spots where plants have been found flowering up to a height of 3650 m (12,000 ft), nothing has indicated that the processes of vegetation were arrested by the severe cold which they must sometimes endure. The climate of the glacial region has often been compared to that of the polar regions, but they are very different. Here, intense solar radiation by day, which raises the surface when dry to a temperature approaching 27°C (80°F), alternates with severe frost by night. There, the Sun, which never sets is only able to send feeble rays that maintain a low temperature, rarely rising more than a few degrees above the freezing point. Hence the upper region of the Alps sustains a far more varied and brilliant vegetation.