Original paper
Obergrenze von Frostbodenerscheinungen
[Upper limit of freezing in soils]
Kuhle, Matthias
Zeitschrift für Geomorphologie Volume 22 Issue 3 (1978), p. 350 - 356
1 references
published: Oct 6, 1978
ArtNo. ESP022002203007, Price: 29.00 €
Kurzfassung
Sowohl auf Spitzbergen als auch in Südost-Iranischen Hochgebirgen läßt sich eine Zone optimaler Strukturbodenausprägung und solifluidaler Aktivitäten nachweisen. Oberhalb dieser Optimalzone nimmt die Formenintensität ab und kommt der nahe, die im Bereich der Untergrenzen vorzufinden ist. In den ariden Arealen der Dhaulagiri-Nordabdachung wurde neben einer Optimalausbildungszone auch eine Strukturboden- und Solifluktionsobergrenze um 5600 m angetroffen. Das Vorhandensein einer Obergrenze war zunächst nur aus jener Optimalausbildungszone theoretisch hergeleitet worden. Die empirische Existenz dieser Obergrenze dürfte sich auf die arideren Leelagen des Himalaya- und Transhimalayasystems und trockene Abschnitte der Anden beschränken; also auf Gebiete, die hinreichend hoch sind, um pergelide Verhältnisse zu ermöglichen, und ausreichend arid, um bis in entsprechende Höhen firn- und eisfrei zu bleiben. In den Alpen reicht die Firn- und Eisbedeckung demgegenüber so tief herab, daß sich nicht einmal eine Optimalausbildungszone beobachten läßt. Der Befund solcher Optimalzone und Obergrenze muß als Bestätigung der Frostwechseltheorie verstanden werden.
Abstract
A zone of optimal formation of patterned ground and solifluction activities can be observed in Spitzbergen as well as in the south-east Iranian mountains. Above this optimal zone there is a decrease in the variety of the forms which is comparable to that found near the lower boundary. In the arid region on the northern slope of the Dhaulagiri-Himalaya not only the optimal zone but an upper boundary of patterned ground and solifluction at an altitude of 5600 m too was discovered. Thereby the existence of an upper boundary could be verified which initially had been deduced from the finding of the above described optimal zone. Probably the empirical existence of this upper boundary is limited to the arid leeward side of the Himalayan and Transhimalayan systems and dry sections of the Andes, regions which are high enough to allow pergelid conditions and sufficiently arid to remain free of firn and ice at the altitude in question. In comparison the Alps’ firn and ice cover reach so far down that not even an optimal zone can be observed. Below, as well as above the periglacial level the frost changes that produce the characteristic forms are lacking; below there are no intense freezing processes, above no thawing processes. In arctic latitudes the “frost change potential” and with it the depth of rearrangement of material depends on its seasonal thawing depth; in subtropical mountains, like those in south-east Iran, it is dependent on the depth of frost penetration into the ground. In a mountain range with a patterned ground upper boundary such as the Dhaulagiri-Himalaya, both primary processes occur: thawing in higher and freezing in lower regions. Whether a “frost patterned ground” near the lower boundary or a “thaw patterned ground” near the upper boundary is concerned, it makes no difference as to their formation which is identical, since both variants are “frost change grounds”. The finding of an optimal zone and upper boundary must be understood as evidence of the theory of frost changes being the most important climatic factor for patterned ground.