Snowpack Evolution On Permafrost, Non-Permafrost Soils And Glacier In The Monte Rosa Massif (NW Alps, )

M. Freppaz1* , M. Maggioni1 , S.Gandino2 , E. Zanini1

1Di.Va.P.R.A. - LNSA, Università di Torino, Grugliasco (TO), Italy 2Esercito Italiano - Truppe Alpine - Servizio Meteomont, , Italy

*Corresponding Author: [email protected]

Snow cover evolution is governed by several variables, such as meteorological factors, local topography and snow characteristics. Different types of substrata might present different surface temperatures, influencing therefore the temperature gradient within the snowpack and its evolution. In non-permafrost soils, a thick early winter snow cover maintains soil temperature close to 0 °C, independently from air temperature. In permafrost soils, beneath at least a 1m cover of snow, the ground temperature during February and March is below - 2 to - 3 °C. For glaciers, less literature exist, with some researches that reported an interface temperature between snow and ice of about - 5 °C.

The aim of this study is to follow the evolution of the snow cover on three different substrata (permafrost, non-permafrost soils and glacier) in the Monte Rosa Massif on the Italian NW Alps. Study area The three study sites are located in the area of the Monte Rosa Massif in the North-Western Italian Alps. The permafrost site is at an elevation of 2910 m asl on a North- Glacier West oriented slope of about 10° of inclination; the non- permafrost site is placed at an elevation of 2900 m asl, on horizontal terrain; the glacier site is located on the Indren Non- glacier at an elevation of 3400 m asl, with a South-West permafrost soil Permafrost soil aspect and about 10° of inclination. Nivometeorological data Snow pits were dug periodically, according to the accessibility of the sites, from December 2006 to July 2007: 9 surveys at the permafrost site, 8 surveys at the non-permafrost site, and 6 at the glacier one. Snow temperature was measured every 10 cm with 10-cm long dial stem thermometers. Snow density measurements were made using a 0.5-L stainless steel core in each layer of the snowpack, where also grain type and dimension were recorded. Continuous measurements of the temperature at the interface between snow and the three different substrata have been made through data-loggers (UTL-1).

The characteristics of the snow cover above the three different substrata are summarized Meteorological data in the area, such as wind speed and direction, air temperature and humidity, were registered by an in the Table below. automatic station of the Italian (-Servizio Meteomont) located at 2901 m asl near the three Table Snow cover characteristics for the three sites. Except for snow depth and the sites. snow/substratum interface temperature, the other parameters are average values computed 5,0 160 10,0 140 NON - PERMAFROST 150 on data from manual snow profiles (N = 8 at non-permafrost site, N = 9 at permafrost site, N = 142 GLACIER 125 125 140 140 5,0 120 6 at glacier site). 0,0 120120 104 112 0,0 100 100 -5,0 Parameter Non-permafrost Permafrost Glacier 100 -5,0 80 80 75

°C -10,0 80 cm °C cm Max snow depth cm 180 230 125 73 70 -10,0 60 60 60 Grain type in bottom 5a, 4a 5a, 4a, 3a 4c -15,0 -15,0 40 layer of snowpack 40

-20,0 Maximum grain size mm 2.4 1.8 1.7 20 -20,0 20 in bottom layer -25,0 0 -25,0 0 Hand hardness index 1.8 2.2 5.0 interface t 09/04/2007 14/04/2007 19/04/2007 24/04/2007 29/04/2007 04/05/2007 09/05/2007 11/03/2007 19/03/2007 27/03/2007 04/04/2007 12/04/2007 20/04/2007 28/04/2007 06/05/2007 14/05/2007 22/05/2007 30/05/2007 07/06/2007 01/07/2007 09/07/2007 17/07/2007 25/07/2007 20/12/2006 25/12/2006 30/12/2006 04/01/2007 09/01/2007 14/01/2007 19/01/2007 24/01/2007 29/01/2007 03/02/2007 08/02/2007 13/02/2007 18/02/2007 23/02/2007 28/02/2007 05/03/2007 10/03/2007 15/03/2007 20/03/2007 25/03/2007 30/03/2007 04/04/2007 in bottom layer air t 29/12/2006 06/01/2007 14/01/2007 22/01/2007 30/01/2007 07/02/2007 15/02/2007 23/02/2007 03/03/2007 15/06/2007 23/06/2007 5,00 250 Snow/substratum °C - 0.9 - 5.1 - 4.8 snow depth PERMAFROST 230 Non-permafrost site interface 0,00 200 temperature* The 75% of the snow profiles were weak-based, with a 173 -5,00 bottom layer of faceted and depth hoar crystals. 158 Temperature gradient °C/m - 6.5 - 7.4 - 2.1 150 °C Permafrost site within the snowpack -10,00 cm 110 The 56% of the snow profiles were characterized by faceted 3 100 Density Mg/m 0.305 0.273 0.389 90 95 -15,00 and depth hoar crystals, due to the high temperature gradient

53 50 (recorded especially during March). But the 22% of the snow Effective heat W/mK 0.131 0.116 0.257 -20,00 40 35 35 profiles were also characterized by small rounded crystals, conductivity -25,00 0 typical of an equi-temperature gradient, revealing how the * average values computed on data recorded by data-loggers (12/29/2006 – 04/20/2007). lower ground temperature may induce a lower temperature 15/01/2007 21/01/2007 27/01/2007 02/02/2007 08/02/2007 14/02/2007 20/02/2007 26/02/2007 04/03/2007 10/03/2007 16/03/2007 22/03/2007 28/03/2007 21/04/2007 27/04/2007 03/05/2007 09/05/2007 16/11/2006 22/11/2006 28/11/2006 04/12/2006 10/12/2006 16/12/2006 22/12/2006 28/12/2006 03/01/2007 09/01/2007 03/04/2007 09/04/2007 15/04/2007 gradient (Keller & Gubler, 1993). Our results shows that the main differences in the evolution of the snow cover on permafrost, non-permafrost and glacier substrata are related to hand Glacier site hardness in the bottom layer (higher on glacier), snow/substrata interface temperature (higher on non-permafrost soil) and temperature gradient (lower on Except for the last snow profile, the snow cover was glacier). Moreover, an important out-coming of this work is that the temperature at the snow/substrata interface remains constant around certain values, characterized by a bottom layer of faceted crystals, often well when enough snow covers the substrata, showing the important insulating effect of the snow. bonded together. The snow hardness was very high (level 5),

Acknowledgments higher than in the other sites. Fot the technical support we thank MonterosaSki, Roberto Cilenti, Corpo Guide Alpine di Alagna Valsesia, Regione Autonoma Valle d’-Ufficio Neve e Valanghe, Hervè Jaccond, Emil Squinobal and Antoine Brulport.