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196 M. Marthaler and H. Rougier Fig. 13.9 Palaeogeographic map and cross-section, during the middle Cretaceous period, showing how the opening of the North Atlantic caused Iberia to drift off to the Southwest. Separated from Europe, Iberia became a micro-continent whose northeastern part was formed by the Briançonnais peninsula (Marthaler 2005) the Matterhorn area because of postglacial weathering and gravity processes that have destroyed most of erosional glacial landforms such as roches moutonnées. Subglacial erosion by meltwater has been quite important, excavating glacial pots. For example, beautiful examples exist in the Gletschergarten (Glacier Garden) downstream of the Gorner glacier (Fig. 13.1), where the subglacial gorge also remains in perfect condition today. These episodes of strong glacia- tion were interspersed with warm interglacials during which the erosive action was more or less similar as today. A specificity of glacial erosion at the Matterhorn is the contact of several glacial cirques forming a horn. The nature of the bedrock is important in the genesis of cirques, their extent being correlated with the density of fractures (Galibert 1965). This is exactly what happens in the Matterhorn: the “roof” provides blocks from the gelifraction of compact gneiss, but the masses of fragile schistose gneiss underneath are sensitive to glacial abrasion. Thus, through glacial abrasion during glacial periods and through freeze-thaw alternation during interglacial episodes, cirques gradually formed. A perfect example is the gigantic cirque that occu- pies the entire eastern face of the Matterhorn (Figs. 13.3 and 13.9). The situation is similar on the other sides: for this reason the Matterhorn is defined as a “pyramid of cirque intersec- tions”. René Godefroy (1948) wrote: “Les cirques entrent en lutte, leurs arêtes séparatives s’aiguillent en même temps qu’elles s’abaissent. Des pointes s’isolent, culminantes, surtout aux intersections des crêtes, là où se nouent les têtes de vallées glaciaires. Elles ont la forme de corne (all. Horn), comme le Cervin (Matterhorn). Les sommets correspondent aux points culminants de la surface initiale, débarrassée de neige et par conséquent attaquée en dernier lieu par la dissection des cirques” (translation: “Cirques are fighting, their separating edges become sharper at the same time as they lower themselves. Peaks are isolated, culminating, especially at the intersections of the ridges, where the heads of glacial valleys are knotted. They have the shape of horn (German: Horn), like the Matterhorn. The peaks correspond to the highest points of the initial surface, cleared of snowPDF Image | An Outstanding Mountain The Matterhorn
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