THE GLACIER LAKE OUTBURST FLOOD OF AUGUST 20, 1832 IN THE LEVIONA VALLEY (AOSTA, ITALIAN WESTERN ALPS): GEOMORPHOLOGIC EVIDENCE Historical documents report the damages caused by a catastrophic flood which occurred on August 20, 1832 in the Leviona Valley, a tributary of the Valsavaranche in the Aosta Valley. The flood was attributed to the sudden empting of a glacial lake following a long period without any rain. The flood was also described by Alexandre Dumas, who while travelling the Aosta valley was obliged to rest due to road interruption. In the Leviona Valley, an outwash plain is veneered by a layer of large gneissic rounded blocks, 1-2 m in diameter, locally imbricated, forming large longitudinal bars. The lichen cover and the characters of the surficial weathering are comparable to those present on the blocks of the moraines formed in the first half of the past century and differ clearly from those present on older surfaces. For the origin clearly connected to a sudden catastrophic flood and the location corresponding to the historical description we can therefore attribute the block deposit to the 1832 glacier outburst. Glacier front fluctuations and/or rock glacier obstructions could have dammed a temporary small lake that suddenly emptied. Sudden glacier lake outburst floods are natural events peculiar, although not very frequent, to the alpine environment, where topography allows water retention. The knowledge of previous flood events. from historical sources and from geological evidence, together with the identification of possible damming conditions. are necessary to the emluation of geologic hazard in the alpine areas.
La rotta glaciale del 20 Agosto 1832 nella valle di Leviona (Aosta): evidenze geomorfologiche
BARONI, CARLO;
1998-01-01
Abstract
THE GLACIER LAKE OUTBURST FLOOD OF AUGUST 20, 1832 IN THE LEVIONA VALLEY (AOSTA, ITALIAN WESTERN ALPS): GEOMORPHOLOGIC EVIDENCE Historical documents report the damages caused by a catastrophic flood which occurred on August 20, 1832 in the Leviona Valley, a tributary of the Valsavaranche in the Aosta Valley. The flood was attributed to the sudden empting of a glacial lake following a long period without any rain. The flood was also described by Alexandre Dumas, who while travelling the Aosta valley was obliged to rest due to road interruption. In the Leviona Valley, an outwash plain is veneered by a layer of large gneissic rounded blocks, 1-2 m in diameter, locally imbricated, forming large longitudinal bars. The lichen cover and the characters of the surficial weathering are comparable to those present on the blocks of the moraines formed in the first half of the past century and differ clearly from those present on older surfaces. For the origin clearly connected to a sudden catastrophic flood and the location corresponding to the historical description we can therefore attribute the block deposit to the 1832 glacier outburst. Glacier front fluctuations and/or rock glacier obstructions could have dammed a temporary small lake that suddenly emptied. Sudden glacier lake outburst floods are natural events peculiar, although not very frequent, to the alpine environment, where topography allows water retention. The knowledge of previous flood events. from historical sources and from geological evidence, together with the identification of possible damming conditions. are necessary to the emluation of geologic hazard in the alpine areas.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
