After a steep descent through the forest, we finally reach the river. We’re in the southwestern part of Switzerland’s Entlebuch biosphere reserve, not far from the remote wilderness of the Chessiloch gorge – and right at the heart of Maira Coray’s field area. The ETH Zurich geology student is drawing a geological profile along the riverbed for her Bachelor’s thesis, recording the details of all the rock strata over a stretch of several hundred metres. This is Maira’s third visit to the area. This time she is accompanied by her supervisors, Lukas Nibourel and Stefan Heuberger, from the Georesources Switzerland Group in the Department of Earth Sciences, and by Stephan Wohlwend, a scientist from the Climate Geology group, who advises Maira on the interpretation of her field samples. Together, these three experienced geologists give her the expert support she needs and help her collect samples for more lab analyses.
This project is Maira’s first step towards becoming a fully fledged geologist. As well as learning valuable lessons on examining rocks in situ and documenting her findings, she quickly realises that there is a huge difference between constructing geological profiles in theory and recording them in the field.
High demand
Lukas and Stefan have good reasons for sending Maira into this rugged and inaccessible gorge. Switzerland is likely to face a shortage of the hard rock aggregate which is used as ballast to support railway tracks. On the face of it, Switzerland has plenty of hard rock to spare – but very little of it is up to this particular challenge. Not only must hard rock ballast be tough and weather-resistant; the broken stones also need to be irregular and angular in shape so as to ensure they interlock properly in the trackbed. Finding the right rock to meet these criteria isn’t easy: granite from the Aar massif doesn’t come up to scratch, nor does Jurassic limestone – and still less so the platy gneisses from southern Switzerland.
Yet with track ballast being replaced about once every 30 years – on a tight schedule designed to minimise disruption to busy railway timetables – demand is high. A large part of the old ballast can be reused, while much of the rest is repurposed as aggregate for road construction. A steady supply of new ballast material is therefore essential. Yet simply extracting unlimited quantities of rock from existing sites is no longer an option, since quarrying is often incompatible with other interests. Protected landscapes, conservation areas, housing developments and tourist activities all limit the amount of rock that can be taken – a dilemma that also hampers the extraction of other resources like gravel and marly limestones for cement production.
Here in the Chessiloch gorge, the geologists want to study a rock formation that has not yet been exploited. “Most rock ballast is made from siliceous limestone,” says Lukas. “But the Hohgant sandstone in this riverbed might also fit the bill.” However, quarrying near the Chessiloch gorge is out of the question: not only is it a protected biosphere reserve; it is also far too remote, with no roads or railways to transport the rocks. Nevertheless, this spot is of great interest to the geologists. “What we have here is an uninterrupted rock formation that we can record in its entirety,” says Stefan. “It’s a great model to help us determine which sections of the formation would be worth quarrying at other sites where this sandstone occurs.”
