Torrents and melting snow

Prospekt Gea, Intresting facts

Photo 1. Satellite image of slopes in the Obruč Mountain Cluster on 18 March 2005. (Source: Google Earth)

Tongues of snow in the upper parts of torrential gullies, where snow accumulates and is slow to melt

Almost regularly at the end of winter, elongated tongues of snow and strips of snow – snowdrifts and snow accumulations created, as a rule, by the bora wind in recesses in the terrain – can be found  in the upper parts of torrential gullies on the southern slopes of the Grobnik mountains. Such snowdrifts are also clearly visible as elongated white strips in aerial and satellite images (Photo 1). Typically, the snowdrifts are slow to melt and can still be found up to several weeks after the neighbouring slopes have lost their snow and the awakening of vegetation has begun in the meadows of narrow-leaved moor grass.

Because the snowdrifts and accumulations of snow in the upper parts of torrential gullies melt relatively slowly, they are like springs that feed the downstream segments with water for as long as the snow lasts.

And while the snow on the neighbouring south slopes melts fairly quickly and the soil begins to dry up, the flow of snowmelt from the melting patches of snow keeps the downstream soil moist and helps to create remarkable ecological conditions in places where the snow melts. Although the snowmelt is usually quickly absorbed into the terrain, the soil in recesses and ditches is often clayey and can retain moisture longer. This fact has a direct effect on the distribution of vegetation.

Generally, the water running down gullies rapidly sinks into the karst underground in places where the ground in torrential gullies is shallow or where the rocky substrate breaks through the surface. That is why it is rare to see large volumes of water rushing down the whole length or larger part of torrential gullies, although this can happen after long, heavy rains in the fall (Photo 2) and/or after the sudden melting of large amounts of accumulated snow towards the end of winter, when the soil and karst underground are saturated with water.

M. R.

Photo 2. A torrential stream in the upper part of Zala Stream at the foot of Obruč Mountain (Photo by M. Randić)