Géomorphologie des socles. Les limites glaciaires sur les socles cristallins. Quelques enseignements apportés par l'Europe du Nord-Ouest et le Canada

• Published in: Revue Géographique de l'Est
• Format: Article in Journal/Newspaper
• Language: French
• Published: PERSEE 1982
• Subjects: Canada; glacier*
• Online Access: http://www.persee.fr/doc/rgest_0035-3213_1982_num_22_3_1419; https://doi.org/10.3406/rgest.1982.1419

Abstract. — Glacial limits on crystalline areas : a few remarks about N.-W. Europe and Canada. The problem of glacial limite is raised most often from a chronostraugraphic and glaciologic angle but should also be considered in the light of morphostructural pattern. For more than fifteen years as a result of teamwork upon crystalline areas englaced in Pleistocene time various parts of North-Western Europe and North Ameriea have been analysed : ancient shields of high latitudes with regional glaciation (British Isles Scandinavia Canada) massifs with local gradation (French Massif Central) late mountain ranges of basement rocks (Pyrénées-Orientales). These studies on the extent of glaciation confirm the need to use jointly several geomorpholopcal assumptions based on the study of landforms and superficial formations. It is important to take into account the nature of material m the basement rock areas because it controls the framework of landforms and topography of differential erosion inherited from pre- or inter-glacial times. It also exercises a wide control over the degree of holocene alteration to such a point that it sometimes overtops climatic parametres and the effet of the morphoclimatic zonation (weathering zones) then fades away. It is also necessary to consider the dimensions of the observed phenomena. The persistency of the inheritages throughout the scale of time actually depends on the size of the landforms and reliefs and on the importance of the alteration. Starting with the example of the Highlands in North-Western Scotland we see that one can combine old residual sepraglacial reliefs of the «nunatak» type and inehrited «blockmeer» on one hand and landforms of «tor> type and volumes kept of decayed rocks of the sandy regolith group on the other hand. The cartographic essay teach us a lot as it leads to a non-hazardous distribution of the phenomena. Logical distribution of this kind is helpful in the reconstruction of old ice-caps. What we leam from studies of other basement rock areas of high and middle latitudes shows that a fine analysis of detail landforms and microforms and the precise examination of decaying mantle varying in thickness and degree of evolution offer a lot of interest. On the whole the morphostructural method of cartography is still appropriate and gives specific help. It can provide an appropriate setting for Upper Pleistocene englaciation «models». Yet an answer to an important question remains : how can we in such a differing morphostructural and climatic context which necessarily influences the condition of the ice and the glacial dynamic reach such close types of relation at the level of interface ice/rock ? The differences of morphogenic efficiency in glaciers cannot be related simply to the ground temperature of glacial organisons.