Documentation and visualization of the morphodynamics of Hinteres Langtalkar rock glacier (Hohe Tauern range, Austrian Alps) based on aerial photographs (1954-2006) and geodetic measurements (1999-2007)

Graz

2010

S. 103-116

Artikel aus einer Zeitschrift

200172695

Hinteres Langtalkar rock glacier (46°59'N, 12°47'E) is located in a glacially shaped cirque situated in the center of the Schober group of the Hohe Tauern range, Austria. This tongue-shaped creep phenomenon of mountain permafrost is approx. 850 m long, 200 to 350 m wide, and stretches vertically between 2455 m and 2725 m altitude. Over the course of time, the snout of the rock glacier has advanced into the uppermost cirque's lip, which is much steeper than the cirque floor behind, causing disintegration of this part of the rock glacier through active sliding processes (since 1994). Consequently, flow velocities behind the frontal slope have significantly increased because of a lack of counterpressure. Maximum horizontal flow velocities reached 2 to 2.5 m a-1. The prevailing high longitudinal strain rates of up to 20x10-3 a-1 (2002-2006) have triggered surface ruptures and crevasse-like openings. In this paper we present quantitative information on the kinematics and surface deformation of the rock glacier based on the photogrammetric evaluation of multi-temporal aerial photographs (10 different epochs between 1954 and 2006) and annual geodetic measurements (1999-2007). Results obtained from recent investigations are highlighted. Based on the available information, covering a time span of 52 years, we analyze the changing kinematic state of Hinteres Langtalkar rock glacier. Special emphasis is put on the more recent situation of the rock glacier, which is characterized by the rapid development of tension cracks and the accelerated disintegration of the permafrost body.The mainfindings of this paper are as follows: (1) There is most probably a persistent climatically-induced permafrost melt in the order of a few centimeters per year. (2) Specific topographic situations (e.g. increasing slope inclination) may cause acceleration of flow/creep of a rock glacier, with the implication of possible surface ruptures in case of high strain rates and insufficient internal cohesion. (3) Interannual changes of flow/creep velocities are most probably due to the thermal conditions of the permafrost body, more or less true irrespective of (2). Furthermore, the authors propose to augment the present monitoring program by a high-resolution airborne laser scanning (ALS) mission which should be repeated (at least once) at a time interval of several years depending on the height accuracy to be achieved and the prevailing permafrost melt.