Pôle Alpin Risques Naturels (PARN) Alpes–Climat–Risques Avec le soutien de la Région Rhône-Alpes (2007-2014)
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Fiche bibliographique


Réf. Ajassa & al. 1997 - A

Référence bibliographique complète

AJASSA, R., BIANCOTTI, A., BIASINI, A., BRANCUCCI, G., CARTON, A., SALVATORE, M.C. 1997. Changes in the numberand area of Italian Alpine glaciers between 1958 and 1989. Geografia Fisica e Dinamica Quaternaria, Vol. 20 (2), 293–297. PDF

Abstract: A comparison is made between the data for the year 1958 shown in the Register of Italian Glaciers and the updated Survey prepared from aerial photos taken in 1989 and published by the Ministry for the Environment in 1993. Variations in the number (+ 118 units) and area (- 2005 hectares) of the glaciers on the Italian side of the Alps are assessed to determine their relation to slope exposure. The conclusion is drawn that exposure provides the main explanation of the fluctuations in the glaciated areas during these 31 years.

Riassunto: Gli autori prendono in considerazione i dari forniti dai Catasto dei ghiacciai italiani redatto nel 1958 e quelli aggiornati per canto del Ministero dell' Ambiente ne! 1993. Viene effettuata un' analisi sulle variazioni numeriche ed areali dei ghiacciai del versante alpino italiano, al fine di individuare le relazioni esistenti tra le variazioni stesse e le esposizioni dei versanti. I dati evidenziano, nei 31 anni di intervalle considerato, differenze si a nell a consistenza numerica ( + 118 unità) sia in quella a reale (- 2.005 ha). L'esposizione appareil carattere che maggiormente influenza le variazioni delle coperture glaciali.

Mots-clés

Glacier fluctuations - Italian Alps

 

Organismes / Contact

Dipartimento di Scienze della Terra, Università degli Studi di Torino
Dipartimento di Scienze della Terra, Università degli Studi di Roma "La Sapienza"

 

(1) - Paramètre(s) atmosphérique(s) modifié(s)

(2) - Elément(s) du milieu impacté(s)

(3) - Type(s) d'aléa impacté(s)

(3) - Sous-type(s) d'aléa

 

 

 

 

 

Pays / Zone

Massif / Secteur

Site(s) d'étude

Exposition

Altitude

Période(s) d'observation

 

 

 

 

 

 

 

(1) - Modifications des paramètres atmosphériques

Reconstitutions

 

Observations

 

Modélisations

 

Hypothèses

 

 

Informations complémentaires (données utilisées, méthode, scénarios, etc.)

 

 

(2) - Effets du changement climatique sur le milieu naturel

Reconstitutions

 

Observations

The results of this preliminary study show that, between 1958 and 1989, the number of glaciers has increased by 118, whereas the total area has shrunk by 2005 hectares.

There were more glaciers on N, NW and NE slopes, and to a lesser extent on the SE, both in 1958 and in 1989, and these covered the greatest areas. As already stated, the total number was higher in 1989, with maximum on the N (+20) and NW (+22) and a minimum on the W (+8). With the exception of the E and to a lesser extent the NE, there was a reduction in area, with maximum on the NW (-748 ha) and N (-564 ha) and a minimum on the S (-29 ha).

The increase in number is related to both the breaking up of some glaciers and the recording of «new glaciers» that were either not detected in 1958 or subsequently reformed after being classed as «extinct». Dismemberment mainly occurred on N and NW slopes, and to some extent on the SE, which had the third largest increase (+16). It is most marked in the Rhaetian Alps (all exposures) and the Graian Alps, and negligible in the Cottian Alps and the Dolomites, where there are fewer glaciers and smaller caver areas.

The increase due to regeneration is much more uniform. There are increases of 3-4 units on all slopes except the SW and NW (7 units). The greatest increase is in the Rhaetian Alps (24 units). The areal changes for each significant alpine sector were also considered. The resulting diagrams show that in each mountainous group, excepted Rhetian and, subordinate, Norian Alps, the glaciers' development follows some preferential expositions. While in the Pennine Alps the glaciers are in the southern sectors, and in the Graian Alps the preferred developing directions are NW-NE, and in the Lepontine Alps N-NE. In the Rhaetian and Norian ones enough wide glaciated surfaces were found in any direction.

The comparison between the covered surfaces in the 1958 and 1989 shows that the main variations chiefly interested all the northward expositions and rarely the SW one (Pennine), E (Lepontine and Rhaetian) and finally SE and S (Norian). Not appreciable variations have founded in the Julian Alps. It is clear, therefore, that there has been an increase in glaciated highland on slopes facing NE, E and SW, and to a lesser extent on those facing S, SE, N, and NW. Regression alone was confined to slopes facing W. [A clearer and more comprehensive illustration of the changes in area in the Alps as a whole is provided in fig. 4.]

Lastly, counts were made of the number of «glaciers» (area of 5 or more hectares) that have shrunk to glacieret (ice-covered snowfields; less than 5 hectares) according to the terminology recently adopted in the World Glaciers Inventory. Comparison shows that downgradings were more numerous on slopes facing N. This is very clear in the diagram for the Alps as a whole [fig. 6] here again it is clear that glaciers facing N are more vulnerable to shrinkage.

The reason why slopes with a lower average temperature, and threefore theoretically are best able to ensure the continuous existence of a glacier, are apparently the most vulnerable can best be sought through two (or perhaps more) kinds of survey:

  • detailed surveys concentrating on the climate at high altitudes, with particular reference to the types of weather and the passage of atmospheric disturbances over the Alps;
  • detailed surveys of the relations between glacier form and valley morphology, including such parameters as the axes of the main valleys, the ratio between valley slopes and height, and the ratio between the theoretical and actua! radiation on the ice masses. Investigations of this kind may lead to a better understanding of glacial dynamics and the elaboration of forecasting models.

Modélisations

 

Hypothèses

 

 

Sensibilité du milieu à des paramètres climatiques

Informations complémentaires (données utilisées, méthode, scénarios, etc.)

 

The Italian Glaciological Committee (Cgi) has recently completed a survey of Italian ice bodies on behalf of the Ministry for the Environment (Ajassa & Brancucci, 1993; Ajassa & alii, 1994). This survey was based on the «Volo ltalia 1988-89» aerial photographie coverage of the country. Its main purpose was to update the register of Italian Glaciers prepared in 1958 and published by the Italian National Research Center and the Comitato Glaciologico Italiano in 1961.
Use has now been made of the register and the survey, together with the observations in the annual reports of glaciological campaigns conducted by Cgi operators in the Alps, to assess variations in the number and area of the glaciers on the Italian side of the Alps. It should be noted, however, that the superior features of the aerial photographie coverage (Biasini, 1995) have meant that the ensuing survey gave rise to operating standards which are considerably different from those behind the register, and may in sorne cases influence the results suggested below. Identification of the limits of ice bodies, in fact, in the 1989 survey, has always been based on air photos and bence, by examining ali its points on the picture, with the same perspective, irrespective of a glacier's altitude.
The method employed for the survey, on the other hand, gives more precise results than «expeditious» surveying, since the coordinates of these limits are determined by means of digital photogrammetry in the Utm system and related to known points on the Italian Military Geography Institute's 1:25,000 maps. Another advantage is that the same points can be used to plot the corresponding limits derived from earlier or future aerial photos and thus very quickly obtain highly accurate area comparisons via computer (Biasini & Salvatore, 1993 ).
This paper takes a doser look at the relations between the areas covered by ice and the exposure of their slopes by reviewing the entirety of the data with geographical exposure as the common analysis factor. A comparison is made between the numbcr of individual «active» glaciers in the Register and the Survey. An assessment is also made of those that have broken up and those that were classed as «extinct» on the register, or not detected, and now appear as «new glaciers» in the Survey (Ajassa & alii, 1993). Differenees in area are considered and the data for single ranges of the Italian Alps are examined to see whether the fluctuations in number and area that have occurred are related to the location of a glacier as weil as its exposure.
The number and area of the glaciers (divided by Alpine range and exposure) are illustrated in tables and compared in figs. for the two dates (Register and Survey). Synoptic data for the single ranges are also provided as a basis for further investigation.

 

(3) - Effets du changement climatique sur l'aléa

Reconstitutions

 

Observations

 

Modélisations

 

Hypothèses

 

 

Paramètre de l'aléa

Sensibilité des paramètres de l'aléa à des paramètres climatiques

Informations complémentaires (données utilisées, méthode, scénarios, etc.)

 

 

 

 

(4) - Remarques générales

 

 

(5) - Syntèses et préconisations

 

Références citées :

AJASSA R. & BRANCUCCI G. (1993) - Il catasto dei Ghiacciai italiani. Cgi, Torino.

AJASSA R., BIANCOTTI A., BRANCUCCI G., MASSAGLIA L., MOTTA L., MOTTA M. & SATTA E. (1994) - Nuove ricerche sui ghiacciai italiani. Atti Ace. Sc. Torino, 128 (5-6), 147-156.

AJASSA R., BIASINI A., BRANCUCCI G., CAPUTO C., PUGLIESE F. & SALVATORE M.C. (1993) - Il Catasto dei Ghiacciai Italiani: primo confronta tra i dati del 1958 e 1989. Atti del Convegno «Una nuova geologia per l'ambiente», Genova, Giugno 1993.

BIASINI A. (1995) - Caratteristiche e impieghi delle fotografie aeree da alta quota dell' Italia. Atti del IV Workshop del Progetto Strategico Cnr «Clima, ambiente e territorio nel Mezzogiorno», Potenza, 26-29.11.1990.

BIASINI A. & SALVATORE M.C. (1993) - Fotogrammetria digitale e cartografia glaciologica. Atti Ticinensi Sc. Terra, 52, 113-119.

COMITATO GLACIOLOGICO ITALIANO (1961) - Catasto dei ghiacciai italiani. 4 voll., Cnr, Torino. 

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