Geografie 1960, 65, 110-121
Potholes in the River Jizera, Northern Bohemia
The article treats of the evorsional phenomena skirting the river bed on the upper and middle course of the Jizera (righthand tributary of the Elbe, Bohemia). On a 50 km long section of this course 700 giant pots have been ascertained. Attention has been paid to their shape, size, height above the surface, position with regard to the stream gradient and the rock structure in the place of their occurrence. As far as the rock structure is concerned evorsional phenomena occur especially in phylites and melaphyres, in other kinds of rock they are comparatively scarce (green shales, metamorphic diabase, migmatitic gneiss, quartzite, erlan, porphyrite granite). They most often occur in the rocky base, few of them were found in the rock debris. They occur in places where the gradient of the stream exceeds 10 %. Most of them are leeside holes, only approximately one third being streamside holes. They occur close to the surface of the stream (approximately 50 cm above it), none have been found higher than 200 cm above the surface. They occur within the reach of the inundation waters which partake most in their formation. They are usually small size phenomena, the majority of them being of a diameter not exceeding 50 cm. Their shape depends upon the rock structure and its jointing. Consequently thier outline is usually irregular, quite often being elliptical, scarcely circular. Approximately one half of them displays the shape of shallow to middle-deep flat-bottomed bowls. A perfect evorsional shape has been ascertained only in approximately one seventh of cases (cylindrical, spherical, cone- and shell-shaped).
