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192 M. Marthaler and H. Rougier Fig. 13.5 View of the Zermatt Valley dominated by the Dent Blanche nappe (above the yellow thrust) which groups together the Paleozoic rocks of continental origin of the Matterhorn, Dent Blanche and Ober Gabelhorn. Dominating the village, the sedimentary strata deposited in the Tethys Sea during the Triassic, Jurassic and Cretaceous periods are clearly visible (after Rougier 2002, modified) This nappe forms a large klippe (which also includes other famous summits as the Dent Blanche, the Weisshorn or the Ober Gabelhorn; Fig. 13.5), which floats like a raft on the remains of the disappeared ocean. Argand compared the Dent Blanche nappe to a “sledge crusher” (traîneau écraseur in French), but we know today that it is a small piece of the upper (African) continental plate lying on the remains of the Tethys Sea, which came to be embedded under the plate. At first glance, the geomorphological analysis is rather simple: everything depends on the selective erosion of rocks of varied nature that form the mountain. The major part of the pyramid is carved in gneiss of the Arolla unit, in places more schistose; the innumerable slope changes of the faces and ridges (Fig. 13.3) are an expression of these selective erosion processes. On the other hand, the summit part, called “the roof”, is part of the hard gneiss of the Valpelline series (Fig. 13.6). This upper part is nearly vertical, contrasting with the relatively less inclined lower sectors (especially the Hörnli ridge; Fig. 13.3) where differential dissection domi- nates. Between these two sections of the mountain is a flat area called “the shoulder” (Fig. 13.6). Other flat areas, often very small, are superimposed, e.g. the one that allowed the construction of the Solvay hut, very close to the vertical “Moseley Slab” (Fig. 13.3). The four-face pyramid does not end however by a point: one is not in Giza! The Matterhorn’s summit is a 110 m long ridge gently inclined to the west, so that the Italian summit is slightly lower (one metre!) than its Swiss counterpart (Fig. 13.3). In reality, everything is shared on this ridge, since the border between the two countries faithfully follows 13.3 13.3.1 The Matterhorn, a Geomorphological Monument The Structure: The Building Materials The contact between the Tsaté nappe and the Dent Blanche nappe is revealed by a remarkable morphological contrast. The thrust passes at the base of the Matterhorn pyramid (Figs. 13.4 and 13.5), a hundred metres above the Hörnli hut, 3400 m a.s.l. (Figure 13.3). From this boundary between calcschists and gneiss, no more hiking or skiing is possible: it is the domain of climbers.PDF Image | An Outstanding Mountain The Matterhorn
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