Ueber die Karrenfelder

Von Prof. Albert Heim

Jahrbuch des Schweizer Alpenklubs XIII, 1877

Partie aus den Karren an den Twärenen auf Silbern, Die Alpen, SAC, 1877. Public Domain.

There is probably no rock in nature that is completely uniform in mass through and through, even in a block of only cubic feet in size. In the apparently most uniform limestone or gypsum, some parts are somewhat heavier, others somewhat easier to dissolve; a very slight difference in porosity or in an admixture, e.g. of pebble or dolomite or clay, may be the cause of uneven weathering, and very often it is only through weathering that the inequalities in mass become visible. Often the fossilisations, which are enclosed in limestones and are themselves calcified, are more difficult to dissolve in the carbonated rain and snow water than the basic mass of the rock. Thus it happens that on weathered surfaces the petrefacts often protrude far beyond the rock, and on the weathered surfaces a richness of petrification[1] is then revealed, of which one can hardly notice anything on the fresh quarry. Any limestone mass that is exposed to moisture will gradually acquire an uneven surface. The depressions formed become water channels, and the water runs off quickly from the elevations in between. The channels deepen more and more as they dissolve and widen at the bottom, the reefs between the depressions become narrower, sharper, more cutting. The unevenness that has begun increases. This is how the bare, wild, rugged limestone surfaces are formed, which in the Alps are called "Karren", "Schratten", "Lapiaz". Our club area contains the largest karren areas ever known.

Fortunately, the relevant part of the map was redrawn in the summer of 1876 by an engineer on behalf of the Federal Staff Office, who had sufficient geological knowledge to correctly understand and depict the peculiarities of the forms. Thus, the excellent and, as I know, very accurate representation on sheet 400 of the Federal Atlas in i 50,000 by the engineer Fr. Becker from Linththal has become a classic picture of the phenomena of the cirques, which every teacher of geology will gladly use to demonstrate to his students. From the Glattenalp to the Pragelpass and from the Bisithal to the cantonal border of Schwyz and Glarus in this part of our map belonging to the canton of Schwyz, the cirques occupy by far the largest part of the surface. On the whole, they form uniformly undulating, little-structured rock surfaces, but in detail they are infinitely richly structured, chopped up into countless humps and ditches. Actual streams are made completely impossible by the pronounced cart formation. As soon as the streams of the surrounding area, e.g. at the "Karrenalp", pour out against the cirques, they are lost in the countless washed-out holes; they usually disappear completely from the surface and then emerge lower down, where there are no more cirques, as springs. Such large& springs can indeed be found at several points in the Bisithal. One of them, the spring in the "Eigeli", is still on our map. Elsewhere, where large cart fields cover the mountain ridges, the same phenomenon is repeated. The wonderful spring in the Hundsloch and the even stronger one in the Fläschloch in the Hinter-Wäggithal, which supplies 45,000 litres of the purest water per minute, are also located at the foot of the cart-covered Rädertenalpen.

In the area of the formed cirques, the rocks are often deep - 1 to 2 metres, not infrequently even up to 4 and even over 10 metres deep - broken through by irregular gullies and holes that are sometimes narrow, sometimes wide, sometimes round, sometimes cleft-shaped, sometimes open on one side, sometimes closed all around. You can often crawl down into one hole and climb up through another. The ridges, ridges or ridges between the holes and furrows are usually very sharp-edged and rough, often razor-sharp, so that you can easily hurt yourself on them. If they are thick and wide, they are again grooved in a peculiar way in the small. From the highest point, small radial furrows run off in all directions, between which very sharp, cutting little ridges have remained. The shapes are reminiscent of the forms that are created when one places all fingers almost closed firmly on clay and then runs them vigorously down over the clay. From the upper edges of the larger ribs, countless such smaller furrows run off on both sides in the direction of the greatest upper surface gradient. On the large scale, the ribs are usually thicker, the furrows narrower; on the small detailed forms, the ribs are narrow, the furrows wider. The jagged and broken rock mass, however, retains its solid coherence, so that loose debris is rare. The thinned ribs often give a bright sound when struck. When the storm sweeps over the sharp edges behind which the deep holes lie, a hollow howl is heard, the like of which the storm wind can scarcely produce elsewhere.

Crossing cart tracks is often not only tedious, but can even be quite dangerous. You have to balance from one ridge to the other. If you use your hands too often, they soon start to hurt and bleed. A misstep quickly knocks you over, and a fall on one of the sharp edges causes serious injuries. Nowhere is a leg broken so easily and quickly as in the karren. Where boulders are scattered over the karren, which was often caused by the former glaciers or rock falls from nearby rock faces or also by shattering by the frost here and there, they often lie in precarious positions on the cutting edges, so that a small push is enough to cause them to topple over. There are karren which are much more difficult to traverse than the labyrinth of a torn glacier; for here step-cutting is not possible. Some parts, such as certain areas on the south-eastern slope of the Pfannenstock and others are even absolutely impassable unless one is clad in tough leather and armed with leather gloves, ladders, ropes and iron picks to hang on to. As varied as the individual shapes of the karren are, the type of form is also uniform, so that even a very trained sense of place, surprised by the fog, always believes to see the same places in a real cart area and has trouble finding the way out again.

We can distinguish two main types of barrows, depending on whether the surface of the limestone rock is more inclined or more horizontal. In the former case, numerous but less deep parallel long furrows prevail in the direction of the greatest inclination, in the latter quite irregular deeper holes and shorter furrows.

On steep walls, the karren often create a vertical striation or canalisation, which is obvious even from a great distance. Escher compared this structure to the view offered by the pipes of an organ. Such organ pipes are beautifully formed on the southern walls of the Ortstock and the Lägernstöcke, as well as on the Scheibenwand and on the Tödi in the Sandalpkessel.

The irregularity of the cirque forms already shows that no mechanical processes can have formed them, but that chemical dissolution of the limestone is the cause of this striking phenomenon. The cirque holes are by no means in the shape of swirl holes, like those in the glacier garden of Lucerne, near Bex, near Sion, near Bern or at the bottom of the waterfalls; they are not expulsions, produced by swirling movements of water with bedload. At the bottom of the furrows and holes we find no rolling stones that could have acted as files. The bottom is bare limestone rock. In general, there are no crevices at the bottom of the furrows. The karren are only formed in relatively pure limestones, which as such are gradually completely soluble in water, even if a little unevenly. In impure limestones, e.g. in limestones rich in clay or siliceous limestones, however, rough surfaces are formed - the siliceous and clayey parts gradually protrude over the more calcareous ones, but the characteristic karren structure does not occur despite the roughness of the forms. The frost then gains clues in the more porous, insoluble, remaining parts and breaks them apart into rubble blocks. The characteristic forms of mechanical weathering are found, with slight modifications, in purer and impure limestones and in most other rocks; the characteristic forms of chemical dissolution, however, are bound to the chemical nature of the rock. We only find karren where the rock as such is soluble and where the chemical dissolution of the rock is far in advance of any mechanical weathering. The more exclusively the chemical dissolution of the rock acts, the purer the limestone, the purer the karren formation occurs.

The formation of the karren is therefore based on the purity of the limestone on the one hand, and on the small non-uniformities in solubility that are nevertheless always present on the other.

In the years 1840 to 1850, geologists mistook the individual erosion basins ( strudellöcher ), which were observed here and there on old glacial soils, for the karren. Others, who had no observations of their own at their disposal, copied the confusion, and so to this day one often finds the cirques listed in geological textbooks as an effect of the glaciers, although Studer in his Physical. Geogr. und Geol. Bd. I, p. 340, already in 1847, their mode of formation, though very briefly, was nevertheless correctly stated. When karren appear at the lower end of retreating glaciers, this is only due to the fact that the ground had already been weathered karstic before the glacier covered it. In general, however, cirques and glaciers are hostile to each other: the advancing glacier soon grinds away the cirque ridges, and old glacial striations in limestone, if they are not protected by debris cover, are soon so furrowed by cirque gullies that only their general shape remains recognisable, while the glacial polish and the glacial striations disappear completely. This can be observed very well, for example, in the valley above the Oberkäsern Alp on the southern slopes of the Windgällen etc., and proves that the formation of cirques has made significant progress since the Ice Age. On the other hand, erratic boulders with cart shapes can be found here and there, but their ridges have been flattened by the characteristic glacial erosion. Such blocks are also preserved in the Glacier Garden in Lucerne, for example. They prove that the formation of karren was already present in the Alps before the Ice Age. Prof. Mousson in Zurich first observed that in the quarries of light-coloured limestone near Aix (Savoy), which have been abandoned since Roman times, many small cart tracks have formed on the surfaces left behind by the Romans and freshly quarried at that time. They are the work of disintegration in about 1800 to 1900 years. The formation of barrows began long, long ago and is always continuing in certain regions.

In the Alps, we find the karren best formed in the limestones of the middle Cretaceous formation, the Schrattenkalk. Studer named this rock stratum, which is often repeated in the limestone Alps, after the "Schratten" or "Karren" which it forms on the Schrattenfluh in the Entlebuch. A large part of the karren of the Silbern and Twärenen belong to the Schrattenkalk. Some other layers of the Cretaceous Formation, which also occur in this area, form somewhat less excellent cirques; I highlight the Seewerkalk as such. The clayey and pebbly limestones do not form any real karren. On the other hand, the "high mountain limestone", i.e. the limestones of the upper section of the Jurassic formation, is an excellent material for the formation of karren. Most of the karren in the Karrenalp and on the slopes of the Pfannenstock and the Faulen belong to this group. Weathering bleaches the black-blue organic colouring of the high mountain limestone and also the grey of the Schratten limestone, so that the karren surfaces usually appear completely light grey or even almost white. In gypsum, too, beautiful cirques form easily and quickly, but they never attain the sharpness of the lime cirques, and because of the much easier solubility of the gypsum, they change quickly and quickly perish again. Karren in dolomite are not rare in the Alps, but are absent in our region.

Karren are mainly formed where there is no vegetation cover or debris soil protecting the rock, and where there is continuous wetting of the rock with dissolving water. These conditions are best combined near the lower limit of the snow region, where melting snow soaks the bedrock for most of the year. In these regions, it is not uncommon to find the cirques completely bare and freshly formed over long stretches; in their deepest holes, snow often remains all year round. High terraces, wide gentle slopes or the summits of the limestone mountains at an altitude of 1900 to 2500 metres, if they consist of purer limestones, are almost always covered with fresh cirques.

After snowy winters, in cold, wet summers, many wide cirque fields of the limestone Alps never become snow-free. In the lower regions, or in otherwise favourable locations, the warm years help the vegetation to advance victoriously against the barrows. The alpine plants then first settle in the not too deep holes in the barrows. Like in natural flower pots, they are sheltered here and given good protection from the wind. These holes were the first to catch plant seeds and earthy components that the wind blew in and dragged across the surface. From the individual points of attack, the tough alpine plants spread their creeping web of branches over the rocky surfaces in the form of a cushion that can be easily detached, but which is attached in one place by a tough rootstock in a deep furrow. In summer, the colourful flowers shine wonderfully in the midst of the white-grey, bare barrow field. The holes and furrows of the wild rocky surface fill up more and more with humus soil due to the death of the lower plant roots, the branch and root networks of neighbouring colonies interweave, and gradually only the highest ridges of the barrows protrude stonily rough from the ever denser, thicker and more coherent growing plant cover, and finally, with the continuing effect of the conditions favourable to vegetation, these last ridges are also buried under the swelling plant cover. In the deeper regions, where now limestone pavements can no longer develop freshly, old ones can be found in beautiful development in places when the humus soil is dug up. The roots of the plants have usually etched themselves into such karren, which has changed the picture somewhat. The forms have lost their cutting sharpness and roughness. The true ICS cart formation stops under the covering of soil or rubble. The fact that we often find remains of old cirques under the vegetation shows us that the snow line and the upper limit of the vegetation was once much lower than it is now, and is probably the result of the same causes that gave the glaciers such a wide distribution in the Quaternary period. A fine example of old barrows in the area of the present vegetation is covered in the park of the Hôtel Axenstein. The inscription on it erroneously attributes the phenomenon to glacial action. Similar ones can be found on many alps (Kammlialp, Unter-Baumgartenalp etc.). The cirques are quite widespread in the Limestone Alps. Examples are: Schrattenfluh in the Entlebuch, Gemmi, between Seewelialp and Hohe Faulen, Alps on the south side of Riemenstaldenthaies. The Rädertenalp and the magnificent springs along the way are very easy to visit from the Hôtel in the Hinter-Wäggithal. In many places in the Sentis group, especially on the edge of the big snow, partly along the path from Meglisalp to the Sentis, from Klingen towards the Silberblatt etc., there are Karrenfelder. A small, but quite excellent Karrenfeld is found in a hollow to the south-east on the slope of the Graustock or Mattstock, while the steeper slopes of the Mattstock itself are striped with parallel Karrenfurchen. The site can be reached in about l1k hours from the beautifully situated and excellently kept new Gasthaus zum Leistkamm in Amden, closer and easier than most of the other cart fields. Other cirque fields lie between some of the Churfirsten. Richisau is a good starting point for a visit to the Silbern or for the route via Ochsenfeld and Rädertenalp to Wäggithal. You can also descend from Klönthal through Rossmatterthal and Braunälpeli to Karrenalp and the Braunwald mountains and Linththal, or from Linththal via Braunwald, Karrenalp, Mandliegg to the huts in Rätschthal, and on a second day from there over the Silbern to Richisau. With the help of our map, you can find routes that lead through Karren. Karren can also be seen on the ridge of the Glärnisch-Ruchen, at the Jägernstöcken, on the Glatten, to some extent also on the Kistenpass, etc.

In other mountains, karren are still little known. In the Jura they are only weakly developed, better in the mountains near Toulon, on the Karst and in some places in Sicily. They are certainly not lacking in other high mountains.

The cirques are to the limestone mountains what the "block seas" are to the granitic and gneiss mountains. The former are the result of chemical dissolution of the limestone in carbonated seepage water, the latter, on the other hand, are the result of partial chemical decomposition and frost.

Certainly, the large limestone pavements are among the most remarkable phenomena of our club area of 1876-1878.

[1] Vergl. F. Becker. Die Karrenfelder des Excursionsgebietes, pag. 85 u. if.