[Back]

E.H. Tentschert, R. Poisel, A. Preh, K. Mair am Tinkhof:
"Bliggspitze: a Landslide?";
in: "Mitteilungen für Ingenieurgeologie und Geomechanik, 6th Colloquium "Rock Mechanics - Theory an Practice" with Vienna Leopold Müller Lecture", E.H. Tentschert, R. Poisel (ed.); issued by: Institut für Geotechnik, FB Ingenieurgeologie; Eigenverlag, Wien, 2013, ISBN: 978-3-9501738-0-2, 81 - 91.

In 2007, on a nice summer day, an unidentified event happened in the cirque in the Wurmetal valley in the southern Ötztal Alps in Tyrol. No details are known; it was said, that only some unattended cows had been disturbed. After checking back a lot of fresh deposited talus was found at the toe of the slope of the Bliggspitze - peak (3545m). During the next weeks several rock mass falls occurred, some mixed with ice of the glacier.
The first estimations of worst case-scenarios identified a maximum volume of 4 Mio m³ at risk of detaching and some people suspected a runout into the reservoir several 100 m deeper in the main valley, causing a tsunami potentially spilling over the dam crest.
Mapping of the rock structure revealed two joint sets with dip direction parallel to the slope dip, one set dipping more gently, one set dipping more steeply than the slope. Thus rock slumping had to be assumed as the possible failure mechanism.
. Neither structures produced by rock slumping nor compression structures in the glacial deposits could be found at the toe of the flank.
. At the "main scarp" slickenslide lineaments not parallel to the dip vector of the joints were found, thus indicating that they belong to a tectonic event, not to a landslide.
. The degree of disintegration of the rock assumed to be a landslide did not turn out to be higher than that of the surrounding rock mass. The degree of disintegration in a landslide is higher than that of the surrounding rock mass.
. The difference model of the DEMs before and after the "event" did not show patterns like those of a landslide. Only small, disconnected areas (partly covered with ice before) showed differences in height.
. No dust clouds were observed immediately after the events described above. Thus most probably the events were ice falls taking with them a lot of debris and moraine material.
Thus, the thesis of a huge landslide endangering the reservoir and the dam was to be discounted.

Landslide, Bliggspitze