The discovery of the periglacial realm

The term periglacial was introduced by the Polish geologist Walery von Lozinsk in 1910 and 1911 to describe the particular mechanical weathering he had observed in sandstones of the Gorgany Range in the southern Carpathian Mountains - today the reactions of the permafrost to changing temperatures is one of the major fields of research. Read more about the periglacial realm on the American Scientific Blog.

Tofane Rock glacier

An active superimpose a relict rock glacier in the Tofane mountain group (South-East Dolomites 46°32``0`N 12°3``0E):

Fig.1

Survey methods for rock glacier creep

The understanding of the movement of rock glaciers is of major interest in periglacial geomorphology, particularly considering the potential response of ongoing climatic warming trends, and changing temperature regime within the ice-rock mixture. Direct observation of the internal deformation with boreholes is time consuming, logistic complex and so expensive.
Anyway the conducted surveys showed that most of horizontal movements are concentrated in spatially delimitated “shear zones”, so the movement of surface is still a good approximation of the internal movement.
Remote sensing methods are nowadays widespread tools for environment and geological research. These methods can survey large areas, providing large data masses at low costs.
Photogrammetry adopted on various, mostly Swiss, rock glaciers, represents the best technology for monitoring the superficial deformation. Within this approach air-photos of different ages are compared and the displacement of single marker points – for example large boulders- traced and mapped.
Differential Synthetic Aperture RADAR Intereferometry (D-InSAR), a satellite based remote sensing, is still to be evaluated and calibrated by ground-based methods. An important historic method was and is the triangulations of points by the use of a theodolite from a fix point.

In the last years the use of the Global Positioning System (GPS) has acquired importance. The development of light, easy to carry and use receivers, the use of a fixed base point that allows high precision measurements, has gathered this method high acceptance and use in difficult terrain.
GPS is based on the distance measurements between several satellites and a receiver. Only one receiver allows an accuracy of few meters, depending of the quality of the satellite signal. The accuracy is strongly improved by the use of a second receiver – the reference- set up at a fixed point, that measuring his position several times and so compensating the “noise”.
During the measurement of the surface the second receiver – the rover- is moved, and comparing his relative position to the reference.

References:

CHESI, G.; KRAINER, K.; WEINOLD, T. & MOSTLER, W. (1999): Bewegungsmessungen am aktiven Blockgletscher Inneres Reichenkar mit der GPS-Methode. X. Int. Geodätische Woche Obergurgl: 223-227
CHESI, G.; GEISSLER, S.; MOSTLER, W.; KRAINER, K. & WEINOLD, T. (2003): 5 Jahre Bewegungsmessungen am aktiven Blockgletscher Inneres Reichenkar (westliche Stubaier Alpen) mit der GPS - Methode.XII. Internationale Geodätische Woche Obergurgl 2003: 201-205
FONTANA, T. (2007): Bewegungsmessung von Blockgletschern mittels GPS. Diplomarbeit,. Fak. Für Bauingenieurwissenschaften, Univ. Innsbruck.
LAMBIEL, C. & DELALOYE, R. (2004): Contribution of real-time kinematic GPS in the study of creeping mountain permafrost: Examples from the Western Swiss Alps. Permafrost and Periglacial Processes 15(3): 229-241

The active rockglacier at Hohe Gaisl - implications on genesis

Active rockglaciers are less common in the mountain ranges composed of carbonatic rocks, such as the Northern Cretaceous Alps ort he Dolomites, even if here more than lithology probably the minor mean elevation plays a role.
Although few active rockglaciers are present in the Dolomites, they have never been studied in detail.
One studied rockglacier is located in the “Gletscherkar (glacier cirque)” on the north-eastern side of the Hohe Gaisl (3146m). The rockglacier lies in a deeply incised cirque, surrounded by steep walls composed of upper Triassic dolomite and limestone.

Fig.1. Air photos and digital terrain modell of the Hohe Gaisl mountain group with two active rockglaciers in the north-eastern cirques (Autonomous Province of Bozen/Bolzano - South Tyrol)

Fig.2. View to west on the Hohe Gaisl mountain group with two active rockglaciers in the north-eastern exposed, deeply incised cirques. The visited rockglacier can be found in the right cirque (north).

Debris of the rockglacier is mainly derived from a prominent, NW-SE-trending fault, along which the bedrock is intensively deformed. The rockglacier is 850m long, 300-550m wide and covers an area of 0,3 square kilometres. The rockglacier extends from an altitude of 2340m at the front to about 2500m. The eastern lobe shows well developed surface topography of transverse ridges and furrows. The surface is coarse grained and varies from place to place, manly constituted of poorly sorted gravel and sand, huge boulders are missing, great blocks exceeding 1m are rare.

Fig.3. View to west on front of the "Gletscherkar" rockglacier.

In the upper part massive ice is exposed during the summer months at several places below a less than 1m thick debris layer. The ice is coarse-grained, banded, and contains thin, fine-grained debris layers parallel to the banding. Rarely larger clasts occur within the ice.
During the melting season small thermokarst lakes may be developed on the upper part of the rockglacier.

Fig.4a. Ice-exposure on the rockglacier (15.09.2007).
Fig.4b. Fine-grained debris layers parallel to the banding in the ice (15.09.2007).

Georadar measurements provided information on the internal structure and thickness of the rockglacier. The data indicate that the rockglacier has a total thickness of approximately 25m. In the lower and middle part the debris layer is 3-5m thick. Below the debris layer numerous, well developed reflectors are visible indicating the presence of shear planes in the frozen body of the rockglacier, which according to ice exposure in the upper part is composed of coarse (glacier) ice with numerous thin debris layers parallel to the banding. A thin sediment layer (?lodgement till) may be present at the base of the rockglacier.

Internal structure and ice exposure clearly indicate that the rockglacier in the Gletscherkar developed from a debris-covered cirque glacier. It is suggested that the glacier has developed from a small cirque glacier during retreat trough inefficiency of sediment transfer from the glacier ice to the meltwater. The presence of a cirque glacier at Gletscherkar is documented in the older literature and on older maps, for example on a topographic map published in 1902 (FREYTAG 1902).

References:

KRAINER, K. & LANG, K. (2007): Active rock glaciers at Hohe Gaisl (eastern Dolomites). Geo.Alp 4, 127-131
LANG, K. (2006): Geologie des Hohe Gaisl Massivs (Pragser- und Ampezzaner Dolomiten) unter besonderer Berücksichtigung der aktiven Blockgletscher. Unveröff. Diplomarbeit, Institut für Geologie und Paläontologie Leopold-Franzens-Universität Innsbruck, 170S.
SHRODER, J.F.; BISHOP, M.P.; COPLAND, L. & SLOAN, V.F. (2000): Debris-covered glaciers
and rock glaciers in the Nanga Parbat Himalya, Pakistan. Geografiska Annaler 82(A):
17 - 31