SnowFlurry 3 2019/20 | Early winter single-seater

Profile 1, Kraspesferner, 28.11.2019, 2910 m, N

In the products of Lawinen.report, there have been several references in recent weeks to angular layers near the ground above 2800 m, especially on glaciers. However, these are only slightly pronounced and were hardly relevant for tour planning. That's why they were almost completely overlooked alongside the other information in the avalanche.report.

The Snowstormer has taken a look at a location where these layers are present. It is a glacier basin that slopes only slightly to the north at over 2900 m above sea level. You can recognize three basic weather phases since the beginning of September.

Green

On 08.09. it snowed for the first time with 30 - 50 cm in the Northern Stubai Alps. This snow only remained high up in the Alps and on the shaded side. Especially on the glaciers. Here, too, it lies directly on the glacier ice. This is because the glacier was completely ice-free until the beginning of September. Due to the subsequent warming, as is still normal for early fall, the snow became wet and then encrusted into a massive melt crust (hardness 5, can only be penetrated with a knife!). The lumps of melt are 3 to 5 millimeters in size. Actually, the layer is almost more ice than snow, if you were to classify it in common parlance.

Blue

The snow has been falling here since the end of October. The whole thing is relatively homogeneous and compact. You can see two harder, wind-pressed layers. A potential weak layer of small, angular crystals has also developed (between approx. 110 - 120 cm). However, the result of the extended column test only indicates a partial fracture (ECTN10 in this layer). This confirms the assumption that the weak layer is simply not strong enough to cause fractures to propagate. It is therefore irrelevant for us.

Conclusion on profile 1

Many layers that can be interestingly linked to the weather sequence. But no problems for us. The felt at the very top could provide a weak layer for subsequently overlying drift snow. But that would only be a very, very short-term problem (a few hours to days) and would only lead to a settling noise in this 15° steep terrain if a fracture spreads in the felt and a snow slab lying above it sinks slightly. This is because the slope is not steep enough for the snow slab to slide off.

Profile 2 on the next page -->

Profile 2, Rietzer Grieskogel, 03.12.2019, 2585 m, S

Blue

Since the heavy snowfalls of mid-November, there has been a phase of rather warm and precipitation-free weather. Then again 20 cm of fresh snow. During the warm weather phase, a thin and unsustainable melt crust formed on the surface of the snow on this 32° south-facing slope.

Red

During the radiant nights, the snow beneath the melt crust transformed into small, angular crystals, as the temperature difference between the strongly cooling snow surface (on average 10 to 12°C below the night-time air temperature under a cloudless sky!) and the relatively warm snow directly beneath the surface was very large. The angular crystals thus form a weak layer, but this is highly unlikely to be relevant. The crystals are still relatively small (approx. 1mm) and there is no suitable snow slab above them. But even if a suitable snow slab were present above the weak layer, fractures would probably not propagate. The angular layer is simply too weak. For a stronger formation with larger and softer crystals, it would have required much longer "radiant weather" with cloudless nights.

Overall conclusion

The two profiles provide another piece of the mosaic in the assessment of the current avalanche situation and, together with thousands of other pieces of the mosaic - which do not only consist of snow profiles - form the basis for the current avalanche assessment. In the Northern Stubai Alps, this means: A danger level 1 - low avalanche danger (however, the upper range of danger level 1 due to a slight sliding and drifting snow problem) with plenty of snow for the time of year, powder and sunshine.

Note: Thick snowpack - weak layers mostly near the surface and relevant in the short term. Thin snow cover - weak layers mostly relevant in the long term and more near the ground.