Die Karren

Von Dr. G. Greim

photography — Fig. 1. Erosionsformen im Karrenterrain. (Aus **Friedrich Simonys** Dachsteinwerk. — Verlag von Ed. Hölzel in Wien.). Public Domain.

Year after year, many tourists and pleasure-seekers roam the high mountains and every other area of scenic interest, partly to relax in the open air or to broaden their view by learning something new. Even the highest peaks are not safe from them, and yet some areas are literally avoided by their foot. These include above all the barrow fields, which sometimes cover large areas, and it is easy to understand why someone avoids such a wasteland as they offer, and seeks out lovelier areas elsewhere. Hence it is that almost most travellers to the Alps have seen practically nothing of karren, unless they have stood admiringly before the surface of the karren on the Axenstein, which has been freed from its superficial covering, and have of course been misled by the erroneous inscriptions about its formation, as if one were dealing with a glacier effect. Scientifically educated men, on the other hand, have often paid due attention to the barrows and therefore we have become very familiar with them through Heim, Cvijic and others, while the work of Simony Dachstein, in praise of which it is actually superfluous to say anything else after the recognition it has received everywhere, has provided us with the illustrations in a way that the enclosed illustrations can show better than many words. better than many words.

As is well known, there is no rock in nature that is completely identical throughout its entire mass. This is particularly evident in the weathering of rocks, i.e. in the action of external agents, the most important of which for us is water. Even in a thoroughly uniform-looking limestone there are parts which, even if not externally visible, differ from the neighbouring ones by their composition, especially admixtures of siliceous or clayey substance or otherwise, and thus offer greater or less resistance to weathering than the latter. Thus the surface will weather unequally, depressions and elevations will develop, the latter "weathering out", as is particularly evident in the petrefacts of some fossiliferous limestones. The differences between the adjacent parts increase more and more, the ridges between the depressions become more and more burr-like, and thus the "karren" or "Schratten", called "lapiez" or "lapiaz" in French, gradually develop on bare limestone fields.

If you look at a larger barrow field from a distance, the flat undulating rock plateau usually shows little articulation. It appears quite different when you get closer. One notices a large number of ridges and humps, separated by narrow, deeply cut trenches and depressions, which divide the whole in the most detailed way. There is usually no flowing water in the depressions, as thefelbe quickly seeps into the underlying limestone, and one must therefore often search far and wide for it in the Karrenfeld, while it often bursts forth again as a spring at the lower edge of thefelbe. Characteristic of all the forms that occur in the karren is therefore a peculiar sharpness, which also essentially distinguishes them from those formed by the effects of flowing water.

The depth of the trenches is usually a few decimetres, but can also rise up to 5 and even 10 metres. At the bottom they are often connected by holes that break through the separating ridges at the bottom, so that it is then possible to slip from one trench into the other. The ribs between them are usually rough and sharp-edged, and may even taper into a razor-sharp edge at the top, which cuts the boot leather and easily causes injuries. If the ribs are wide, they are furrowed again in the small, by a mass of small grooves running approximately radially downwards from the highest point and separated by very narrow extraordinarily sharp small ribs, which are sometimes replaced by a large number of completely needle-shaped points. In the small, the furrows are usually wider than the ribs, while in the larger forms this ratio is reversed. The finest details of this arrangement can be clearly traced in the accompanying illustrations (Fig. 1), which, taken from the atlas of Simonys Dachstein area, show a number of photographs of hand pieces of limestone collected in limestone pavementss, all from the Dachstein area from altitudes of 1900 to 2500 m.

On the whole, according to Heim, two main types of karren can be distinguished, for whose occurrence the inclination of the soil is decisive. If the slope is weak, more irregular deep holes and only short furrows open into them, the bottom of which may not slope in the same direction as the surface of the earth. The so-called "honeycombs" mentioned by Becker, which look like honeycombs, probably also belong here. If, on the other hand, the slope of the surface is steeper, parallel furrows form that are less deep and descend roughly in the direction of the greatest gradient. Steep rock sections may be completely fluted as a result. The latter phenomenon is beautifully shown in the illustration of a karren formation above the hollow between the Tressenstein and the Grimming, taken from Simony (Fig. 2); the picture of a limestone pavements on a large scale is provided by the phototype of the Ochsenwiesalpe (Fig. 3), which also belongs to the atlas of the "Dachstein area". "characteristically illustrates the nature of the high karren of the Dachstein massif, in which those desolate boulders of sometimes greater, sometimes lesser extent begin to take hold, which are preferably frequently encountered in the Dachstein limestone, and which, as limestone pavementss, wherever they occur in greater extension, give the mountains that forbidding physiognomy, that desolate appearance, which does not occur to the same extent in any other rock formation in the wide Alpine region. developed to the same degree. In addition, however, there are also fresh green oases of relatively abundant herb vegetation, which, even if only for a short time of the year, offer usable holding and grazing places for alpine farming, especially in the various trough- or basin-shaped depressions, the bottom of which, similar to most sinkholes in the karst landscapes, is bedded with the leaching products of limestone containing iron oxide and clay, etc.". -

It is easy to see that the crossing of a limestone pavements is not easy and gives rise to significant equilibristic feats. The rock is extraordinarily hard, so that the nails do not grip and even the crossing of a glacier torn apart like a limestone pavements is not easy, because there one has the possibility of cutting steps into the ice. Therefore, slipping on the karren is frequent and great caution and dexterity are necessary when crossing. The sharp prongs and needles tear open the hands, broken legs are nowhere so easy to get as on a limestone pavements, not to mention the damage to clothes. In some places, according to Heim, you can only get on completely in leather and with leather gloves, as the constant use of bare hands makes them sore on the rough surfaces in a short time. In addition, some parts are loosened by frost, and if they are just balanced on the edges, they easily topple over when stepped on. The path is followed partly by crawling, partly by walking, partly by climbing, and many a stretch that seemed small at first sight has to be covered in this way with time-consuming slowness. In doing so, one is easily exposed to getting lost, especially when the fog is falling or night falls, because despite the extraordinarily great variety of forms, the individual parts of the field are also of a uniformity that confuses the sense of orientation. A compass and a good alpenstock will therefore be of great help to the hiker in these deserts.

The distribution of the karren has been proved in more recent times by Cvijic to be fairly general. They were first known from the Alps, where they are found in particular abundance near the snow line. But they are also known from the east coast of the Adriatic Sea, from the calcareous coast of the Peloponnese and the islands lying in front of both; they occur on Ithaca even at sea level; moreover, they are common in the Karst and the surrounding calcareous mountains at all altitudes, whence Cvijic cites them from almost sea level (240 m) up to 2000 m above sea level (observed by Hassert on Durmitor, Montenegro). They have also been found in the Jura, around Toulon, in Lebanon and elsewhere, and will probably be found in many other places where conditions are favourable.

Almost everywhere they are associated with sinkholes, so especially in the karst itself, whence Kraus gives some pretty illustrations in his Höhlenkunde, then in the Salzburg Alps, where Fugger found karren and sinkholes together, and in other places in the karst regions, thus showing that they are an essential part of the karst phenomenon and are to be ascribed to it.

From the occurrence under the most varied conditions, as shown above, it is already evident that karst formation has no limit in the vertical direction and is therefore not, as was formerly thought, bound to the snow line or to the action of the last glaciation. With regard to the latter, there is, of course, also a great deal of direct evidence available. Thus Heim found quite juvenile karren in glacial striations, and the karren at some sinkholes probably also speak against their causal connection with glacial action. The detachment surfaces or debris of very young landslides also show karren formations on their surface, as Penck was able to prove from the slab on the north-eastern slope of the Watzmann-Nordeck and on debris of the slavini di San Marco near Roveredo. On the light-coloured limestones in the quarries at Aix, which were only abandoned in Roman times, Heim was also able to establish genuine karren grooves and thus prove that they must have formed in the last 1800 to 1900 years. Heim rightly points out that karren and glaciers are to a certain extent hostile to each other, and that the latter, by rounding off and covering the forms, not only excludes the formation of karren, but even destroys existing ones.

The divergent opinions about the cause of the formation of karren seem to have been supported mainly by the fact that other phenomena have been confused with real karren. These include above all the surface forms of limestones produced by fuviatile effects, the swirl holes and others, which on the one hand differ essentially from the sharp forms of the barrows by their rounding, and on the other hand possess evidence of the forces that produced them in the rolling stones found in them, which are never found at the bottom of real barrows. Similarly, the assertions about the existence of barrows on crystalline rocks are probably due to confusion with similar forms of other origin.

From all of these mistakenly understood as karren, real karren differ mainly in the conditions of their formation, which are generally not mechanical but chemical. The most important is the nature of the rock. Carls are only formed in pure limestones, which, although a little uneven, are gradually completely or nearly completely soluble. Bituminous and marly limestones also give rough forms, but no karren, as the limestones in the Moravian Devonian area and the northern European Cretaceous areas show. Only where this rock is soluble as such and chemical weathering has a head start over mechanical weathering does it form true limestone pavementss. In the Alps, for example, the limestones of the middle Cretaceous, the so-called Schratten limestones and those of the upper Jurassic are most suitable for this. In gypsum, too, beautiful karren are formed easily and quickly, but they never reach the sharpness as in the limestones.

Another essential condition is of course the wetting of the limestone with water, which must be as uninterrupted as possible. In this respect, the conditions at the snow line can also have an essential promoting effect on the formation of barrows, in that they can better ensure a constant wetting of the limestone surface, but without thereby moving into the series of essential conditions for the formation of barrows, as the spread of the barrows clearly shows. Another circumstance comes into consideration, to which Simony draws attention in the explanation to Fig. 1, namely that the absorption capacity of carbonic acid in water increases with decreasing temperature, which may well be effective in the cold seepage water of snow, and then represents an essentially promoting moment for the dissolution of the limestone.

Rock structure can also become important for the occurrence of barrows. Flat saddles or horizontal bedding will allow the formation of large barrow fields, while strong folding will only lead to the formation of barrow furrows, as in Figure 2, or, if the rock is too badly shattered, the formation of barrows will be very difficult. Then, on the one hand, the mechanical processes of weathering the rock will take over and the many crevices will allow vegetation to settle easily and be covered by it.

The latter then makes the formation of barrows impossible at all, for they only arise where the surface of the rock comes to light, and debris or decomposition products or vegetation do not spread a covering over it. The vegetation is also able to put an end to the formation process of the barrows. Deeper regions or warmer years help it to advance, the plant seeds tolerated by the wind settle in the barrows and first gain a foothold in the shallower barrow channels and depressions, where they sit protected as in flower pots. As they develop, they extend the branches of the root system further and further and a complete root cushion forms, which is easy to detach and only gets stuck in one or a few places in a crevice. The cushion as well as the accumulating dying parts provide the substrate for new colonies and the colony gradually rises higher until it touches and merges with neighbouring ones. In this way, gradually more and more prominent parts are buried under the plant cover, until finally, if the conditions are permanently favourable, the whole limestone pavements disappears and is withdrawn from the activity of the surface waters, thus setting a goal for its further development. Later, when the humus cover is covered, it is found again, like the one already mentioned in the park of the Axenstein Hotel, but the forms have usually lost some of their sharpness, which is probably due to the corrosive effect of the humus acids.

If the limestone pavementss, e.g. in the Alps, also present the most desolate and lonely parts, they nevertheless offer, as can be seen, a mass of interesting things, and will probably awaken in many a reader the desire not to be satisfied by the masterly illustrations of Simony included, but to take a look at the certainly worth seeing phenomena themselves on occasion[1].

[1] In addition to Simony's Dachstein, the following literature was used:
1. Prof. A. Heim, Über die Karrenfelder im Jahrbuch des Schweizer Alpenklubs XIII.
2. Cvijic, Das Karstphänomen. Geographische Abhandlungen, Band V, Heft 3, wo auch die übrige Litteratur zu finden ist.

from: Globus 70, Vieweg Braunschweig, 1896, S.104-107. urn:nbn:de:kobv:11-d-4729494