Morphometric analysis on the size, shape and areal distribution of glacial cirques in the maritime alps (western french‐italian alps)

Abstract

The morphometry of 432 glacial cirques in the Maritime Alps (Western French‐Italian Alps), studied over several years of fieldwork, was analysed with the use of a geographical information system. Some of the parameters automatically evaluated from digital elevation models required an objective and relatively new definition. In particular, cirque length was measured along a line that, from the threshold midpoint, splits the cirque into two equivalent surfaces; cirque width was automatically drawn as the longest line inscribed in the cirque and perpendicular to the length line. Significant correlations were found among the different factors and parameters analysed. In particular, cirque shape analysis showed that cirques develop allometrically in the three dimensions, i.e. more in length and width than in altitudinal range. Nevertheless cirques of the Maritime Alps have a regular, almost circular shape (mean L/W value = 1.07). The correlations among length, width and area are all very high (r2= 0.8–0.9). In terms of size, cirques show a wide range in area from 0.06 to 5.2 km2 with a mean value of 0.4 km2. The largest cirques are found on SSW‐facing slopes and at high elevations. Small cirques can be found at all altitudes but all those at high elevation are part of compound cirques at the main head valleys. Most cirques (37%) are characterized by a northern aspect; NE and SW are also frequent directions.

ACME, a GIS tool for Automated Cirque Metric Extraction

“…The latter were calculated using a combination of GIS techniques (e.g. Pérez-Peña et al, 2009), some of which use an interface in Italian (Federici and Spagnolo, 2004) and are no longer compatible with recent versions of ArcGIS. Table 1 demonstrates that ACME values are very similar to those published before and the differences between the two are not statistically significant, with the exception of cirque width.…”

A mass movement origin for cirques

“…, and large cirques are some hundreds of metres deep (Kirkbride and Matthews, 1997;Garcia-Ruiz et al, 2000;Federici and Spagnolo, 2004), we derived the value of k in Equation 2 by putting dy/dt = 10 −3 m a −1 and y = 300 m, giving k = 3 × 10 −6 a −1 . If we then assume that glacial erosion begins once a hollow is c. 20 m deep (Benn and Evans, 1998), integration of Equation 2 indicates that it takes approximately 1 million years for a cirque to grow from 20 m to 300 m depth, and the average erosion rate over this time is about 0·3 mm a −1 (Figure 2).…”

“…In fact this is not the case; cirques less than about 80 m deep are rare (Federici and Spagnolo, 2004), and the paucity of small cirques suggests that large cirques may in fact not develop from small ones.…”

“…Evans and Cox, 1974;Evans, 1977Evans, , 1994Evans, , 1996Garcia-Ruiz et al, 2000;Federici and Spagnolo, 2004). Most cirques have lateral dimensions between 200 m and 2500 m, with the great majority being between 400 m and 1000 m wide (De Blasio, 2002) and between 200 and 500 m deep (Federici and Spagnolo, 2004). As Evans (1996) points out: '.…”

The plant endemism in the Maritime and Ligurian Alps

“…The northern part of the MLA is characterised by a temperate climate and it homes a more mesophilous vegetation compared to the southern part (Regione Piemonte 2001, Brunetti et al 2006. In addition, during the Pleistocene, many glacial events affected this area (Ponel et al 2001, Ehlers andGibbard 2004) and repeatedly influenced its geomorphology (Malaroda 2000, Federici andSpagnolo 2004). In this review, we examine the present advances in knowledge about the endemic plants growing in the MLA in order to identify and to describe the evolutionary and biogeographical mechanisms driving the high biodiversity of this area.…”