Swisstopo: 25K Geological profiles
Cross sections can be added as separate layers in the swisstopo online tools. Here a NNW – SSE geological cross section through the 138 Ambrì-Piotta 25k sheet 1252 (at an altitude of around 440 m) illustrates the geological structures surrounding the Gotthard Base Tunnel, which passes under Pizzo dell’Uome. Copyright © swisstopo. All rights reserved.
As Switzerland’s national geodata agency, swisstopo produces many layers of high-quality and remarkably accurate online data, including cartography and geological maps, hillshade, slopes, and aerial photography, most of which are freely available. These data are held in layers grouped into 30 different themes, at least eight of which are of potential interest to Earth scientists. Once selected, contrasting layers can be brought together within the “maps displayed” menu and mixed using different relative transparencies to generate bespoke maps at a wide range of scales. These cartographic images can then be exported as pdfs, for printing or use as potential figures. The layers include a superbly drafted national series of seamless topographic maps published at seven different scales, as well as images derived from data extending beyond Switzerland.
A recent addition to the immense variety of information already contained within swisstopo’s multilingual cartographic online data viewer is the geological cross-sections layer entitled “Geological profiles GA25”. Taken from their 1:25,000 scale geological map series, each profile can now be downloaded separately (together with details, including scale and location map showing other nearby profiles). Clicking on any displayed profile the “3D viewer” option makes them appear semi-translucent, which when switched off reveals the GeoCover digital geological map draped over a 3D model. The “camera configuration” mode allows you to play around with height, angle, and pitch, by zooming in and out.
While profiles from recent sheets have yet to be added (along with panoramas and cross sections from geotechnical reports on world-beating railway base tunnels right under the Alps), the most complex online cross sections illustrate the intricate thrust tectonics, highlighting nappes that are piled together. Where thrust sheets are driven up against the crystalline basement, these sections illustrate deceptively simple structures that include major faults and thrusts with significant displacements. In the Jura Mountains, the sections beautifully illustrate angular anticlinal structures in relation to thrusts roughly 3-km above the basal detachment zone or décollement underlying the region.
The entire territory from Geneva to Lake Constance, which encompasses a Molasse Basin that developed as the Alps started rising and were eroded to produce massive volumes of sediment, has now been analysed in great detail using numerous seismic reflection surveys. Vertical exaggerations on some flatter profiles illustrate the detailed sequences and patches of superficial deposits in relation to the landscape and underlying bedrock. Currently, similar figures from the 25k memoirs are not included. They would make useful additions showing the varied nature of superficial material often filling deep hollows within the local bedrock, and in other places illustrating how they provide hydrological connection between lakes. All these fascinating and extensive resources are well worth browsing.
David Nowell
DETAILS
Resource: swisstopo, the Federal Office of Topography, Switzerland; swisstopo.ch
Further reading
- Allenbach, R. Et al. (2017) GeoMol: Modèle géologique 3D du bassin molassique suisse – rapport final. Rapports du Service géologique national 10. Office fédéral de topographie swisstopo, CH-3084 Wabern, Bern.
- Nowell, D.A.G. (2021) Potential of swisstopo and Swiss Geological Survey websites for Quaternary researchers. Quaternary Newsletter 154, 27-51.
