Regional old-snow problem in southern territories. Fatal avalanche accident Laserztörl in Lienz Dolomites

Following the heavy snowfall, a favourable snowpack structure prevails in far-reaching parts of Tirol. Nevertheless, we face an old-snow problem in the Central Stubai Alps region of North Tirol and the East Tirol regions south of the Venediger range: the further south you go, the more striking it becomes.

This was demonstrated by wide-ranging snowpack analysis in recent days, also by avalanches in which persons were involved and naturally triggered avalanches.

The old-snow problem developed in these regions as a consequence of the shallowness of the snowpack, compared to other regions. Frequently, ground-level layers occur beneath a melt-freeze crust which consist of faceted, loosely-bonded crystals, plus some depth hoar. The “slab” which is the prerequisite for slab avalanches formed on top of that during the most recent round of snowfall, often under wind influence.

The melt-freeze crust formed during the period of higher temperatures and solar radiation in the longish phase without precipitation, then again during the period of rain around Christmas. Beneath that, faceted crystals were generated, especially during nocturnal periods of outgoing radiation, as was depth hoar. The melt-freeze crust enhances and amplifies wide-ranging fracture propagation once a weak layer has been triggered.

In foreground, a snow profile of the upper part of the snowpack reveals the mass of fresh snow, beneath that deposited between melt-freeze crusts, very loosely-bonded layers. Stability tests showed a high proneness to triggering. In background, avalanches triggered naturally due to the additional loading of recently accumulated snowdrift masses. Defereggen in East Tirol.  (photo: 19.01.2019)

We currently draw spatial limits around the old-snow problem: starting at about 1600 m up to at least 2400 m. The problem is more noticeable on W/SW to N to E/SE facing slopes and in flat south-facing terrain. Caution is urged especially at the borders of sparsely wooded zones.

As a result of this old-snow problem, a slab avalanche was triggered yesterday, 19.01.2019, below the Laserztörl in the Lienz Dolomites. A person ascending on a slope slightly more than 35 degrees steep was swept along and died as a consequence of the avalanche accident. A second person found some protection behind a large rock and was not injured.

Avalanche accident Laserztörl. The persons were on their ascent in the right part or the avalanche. Major fracture propagation resulted from a melt-freeze crust and weak layer of faceted crystals beneath it.  (photo: 20.01.2019)

Today, on 20.01.2019, we conducted our investigations together with the Alpine Police, using a state government helicopter. The slope faces NE to SE, mostly at an angle of 35 to 40 degrees steep. The fracture depth varies between about 30 cm and (in places near the ridgeline) about 100 cm. The length of the avalanche is estimated at just under 300 m.

A member of the Alpine Police below the Laserztörl in extremely steep terrain adjacent to the ridgeline. The greatest fracture depth was measured here, a result of wind impact. (photo: 20.01.2019)

View from the burial spot towards Laserztörl  (photo: 20.01.2019)

The state government helicopter just before landing. We also discovered the ascent track and the end of the avalanche wedge.  (photo: 20.01.2019)