The radical changes caused by glacial masses in the past and still present are accompanied by equally important morphological changes in the previously glaciated areas. A first attempt of quantifying the effects of climate change in the Anthropocene was carried out for the Orco and Lanzo Valleys, through a detailed geomorphological analysis and interpretation of traditional aerial photos and digital orthophotos, available at a variety of scales and for different years. This analysis showed that between 1850 and 2006 the overall number of glaciers in the studied area has decreased by 64% which correspond to a reduction of glaciated area of 78% compared with the glacier extent during the peak of the LIA (58.8 km2) (Lucchesi et al., 2014). The areas of recent deglacialization are currently characterized by the outcropping of new large rock surfaces, by extensive and impressive moraines and till, or by the presence of lakes. Overall 13.5 km2 (corresponding to 28%) of the areas of recent deglacialization are characterized by the outcropping of rock, 33.9 km2 (71%) are covered by glacial deposits (till), fluvioglacial or gravitational sediments (slope debris, landslides) and 0.6 km2 (1.3%) are occupied by lakes in 2006. The environment of recent deglacialization is morphologically very young and dynamic, more exposed than others to extremely fast remodeling processes, especially for the areas covered by glacigenic deposits. For instance, on 24 September 1993, after an intense rainstorm, a large portion (800,000 m3) of the frontal moraine of the Mulinet Glacier was removed by a huge debris flow that traveled 4.5 km downstream. Nevertheless, recently deglaciated areas are in part affected by the presence of a more or less pervasive and continuous permafrost (Mair et al., 2011). The presence of permafrost has a stabilizing effect on rock and debris slopes. Under a warming climate, permafrost degradation can become one of the most relevant factors contributing to the development of instability processes (in particular rock falls and debris flows). For this work, we met the geomorphological information obtained for the deglaciated areas (type and extent of outcropping materials), with the permafrost distribution map realized in the framework of the PermaNet project for the European Alps. As a result, we were able to make a first estimate of debris areas and volumes prone to instability, or ready to be mobilized by surface water runoff.
Recently deglaciated areas, permafrost and natural instability in the Orco and Lanzo valleys (NW Italy)
Chiarle M;Fioraso G;Nigrelli G
2014
Abstract
The radical changes caused by glacial masses in the past and still present are accompanied by equally important morphological changes in the previously glaciated areas. A first attempt of quantifying the effects of climate change in the Anthropocene was carried out for the Orco and Lanzo Valleys, through a detailed geomorphological analysis and interpretation of traditional aerial photos and digital orthophotos, available at a variety of scales and for different years. This analysis showed that between 1850 and 2006 the overall number of glaciers in the studied area has decreased by 64% which correspond to a reduction of glaciated area of 78% compared with the glacier extent during the peak of the LIA (58.8 km2) (Lucchesi et al., 2014). The areas of recent deglacialization are currently characterized by the outcropping of new large rock surfaces, by extensive and impressive moraines and till, or by the presence of lakes. Overall 13.5 km2 (corresponding to 28%) of the areas of recent deglacialization are characterized by the outcropping of rock, 33.9 km2 (71%) are covered by glacial deposits (till), fluvioglacial or gravitational sediments (slope debris, landslides) and 0.6 km2 (1.3%) are occupied by lakes in 2006. The environment of recent deglacialization is morphologically very young and dynamic, more exposed than others to extremely fast remodeling processes, especially for the areas covered by glacigenic deposits. For instance, on 24 September 1993, after an intense rainstorm, a large portion (800,000 m3) of the frontal moraine of the Mulinet Glacier was removed by a huge debris flow that traveled 4.5 km downstream. Nevertheless, recently deglaciated areas are in part affected by the presence of a more or less pervasive and continuous permafrost (Mair et al., 2011). The presence of permafrost has a stabilizing effect on rock and debris slopes. Under a warming climate, permafrost degradation can become one of the most relevant factors contributing to the development of instability processes (in particular rock falls and debris flows). For this work, we met the geomorphological information obtained for the deglaciated areas (type and extent of outcropping materials), with the permafrost distribution map realized in the framework of the PermaNet project for the European Alps. As a result, we were able to make a first estimate of debris areas and volumes prone to instability, or ready to be mobilized by surface water runoff.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
