Blockfields and Blockstreams in the Ligurian Alps (Mount Beigua, Italy)

Abstract

The landscape around the summit of the Monte Beigua Massif (1.287 m a.s.l.) is characterised by the accumulation of large blocks without any source rock faces at their head and by some relict rocky relief. The aims of the present paper are to analyse systematically these landforms, to provide an explanation of their genesis, and to reconstruct the paleoclimatic evolution of this area. Eleven block accumulations have been analysed from a morphological, morphometrical and sedimentological point of view. The block accumulations are all characterised by open work texture at least in the upper 1.5 m, their angular or subangular shape, their frequent vertical dipping, the none or little vegetation in contrast to the woodland coverage just outside the landforms. All these morphological characteristics, and above all, the surface flow structures and pattern blocks, suggest that solifluction, gelifluction or frost creep or a combination of these can be considered responsible for the downvalley movement of these accumulations. To understand whether the periglacial conditions are still present in the area or not, two dataloggers, each one with 4 external thermistors, were installed in January 2003. The subsurface temperature (2 cm) has a range between –13°C and 30°C with very strong diurnal oscillations that, during late winter, can reach 35°C. During the early winter there are very frequent daily freezing-thawing cycles that decrease at the end of the winter and the onset of the spring. The relatively high frost penetration measured now and the usually low winter snow cover suggest a very effective frost action in the past, especially during the Wurm, when the MAAT reached 10-15°C less than in modern times (Clark, 1972) and in this case could be calculated around –2°-0°C. The formation of blockstreams is tentatively attributed to cryotic conditions during the Wurm.