Periglacial map of the Bohemian Massif

Abstract

Article in French.

ORIGINAL TITLE: La carte périglaciaire du Massif Bohémien

The Periglacial Commission undertook the task of compiling the world periglacial map; I have endeavoured to contribute both to the content of this map and to its method of representation by focusing on the cartographic elaboration of periglacial phenomena within a selected natural region.

To develop the global periglacial map, the Bohemian Massif was chosen due to the geological and geomorphological diversity of its terrain. (A brief geological and geomorphological sketch of the area is included.)

It was necessary to select an appropriate topographic map onto which symbols representing cryopedological phenomena could be transferred, in order to best illustrate the relationship between these phenomena and the underlying terrain structure. Since the Quaternary stratigraphy of the Bohemian Massif, which facilitates the classification of periglacial features, is based on the superposition of fluvial terraces and aeolian sediments, the map delineates typical areas for these sediment.

In the Bohemian Massif, fluvial terrace deposits have developed from the Neogene through the Danube stage up to the Late Pleistocene; most of them are morphologically well defined. Aeolian sediments are represented in various facies, ranging from dune sands, through transitional sediments, to loess and fluvioglacial or niveo-aeolian sediments, which exhibit rhythmic stratification. Among the Quaternary sediments, thick colluvial deposits have been identified on the north-eastern (colder) slopes, as well as glacial sediments, which occupy only a small part of the region, since the continental glacier reached the Bohemian Massif only via marginal tongues, and mountain glaciers were of limited extent.

Quaternary sediments are indicated separately. Relief is represented by shading and further emphasised by the river network.

The map simultaneously illustrates the distribution of eoglyptoliths, the southern limit of the continental glacier, glaciotectonic features within the range of the glacier, and other related phenomena.

After field investigations and selection of the appropriate topographic base map, the following cryopedological phenomena were mapped:

1. Cryopedological features caused by congelifraction (e.g., rock fractures in compact outcrops, blockfields, cirques and pseudocirques);
2. Cryopedological features resulting from material differentiation caused by regelation processes (polygonal soils, striped soils, and intermediate forms), along with features induced by vegetation activity;
3. Features mainly observed in stratigraphic sections (especially frequent in the Bohemian Massif): wedge cracks, cryoturbation (including involutions), solifluction structures, cryotectonic phenomena, and features caused by solifluction such as blocky terraces, displaced rock blocks, etc.