Réf. Kääb & al 2004 - P

Référence bibliographique complète
Internationales Symposion INTERPRAEVENT 2004, Riva/Trient. Glacier hazards at Belvedere Glacier and the Monte Rosa East Face, Italian Alps: processes and mitigation. KAAB A., HUGGEL C., BARBERO S., CHIARLE M., CORDOLA M., EPIFANI F., HAEBERLI W., MORTARA G., SEMINO P., TAMBURINI A., VIAZZO G. Bd. 1, p. 67-78.

Abstract: In summer 2001, the Belvedere glacier, Macugnaga, Italian Alps, started a surge-type movement with ice velocities increased by one order of magnitude. A lake of 3 million m3 in volume formed on the glacier during spring 2002. Rapid emergency actions were initiated by the Italian Civil Defense Department. This included evacuation of certain parts of the village of Macugnaga, automatic alarm systems, installation of pumps, and detailed scientific investigations. Significantly reduced melt water input in July 2002, together with naturally developing subglacial drainage, helped to stabilise and then lower the lake level. In spring 2003, however, the lake developed again. In mid-June 2003, the lake burst out within a few days, without causing any damage. Besides, the advancing Belvedere glacier causes extensive rock- and ice-fall activity, overruns tourist installations and destabilises its moraines. In the Monte Rosa east face, enhanced rock-fall activity is observed. A drastic decrease in glaciation of the flank uncovers large rock areas and changes the thermal regime of the wall.

Mots-clés
Belvedere, glacier hazards, hazard management, surge, glacier lake outburst.

Organismes / Contact
Department of Geography, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland. kaeaeb@geo.unizh.ch. Phone: +41 1 635 5146.
ARPA Piemonte, Settore Meteoidrografico e Reti di Monitoraggio, C.so U. Sovietica, 216, IT-10134 Torino, Italy.
CNR-IRPI, Strada delle Cacce 73, IT-10135 Torino, Italy.
Studio Epifani, Via XX Settembre 73, IT-28041 Arona (NO), Italy.
Regione Piemonte - Direzione Opere Pubbliche - Settore decentrato Opere pubbliche e difesa assetto idrogeologico di Verbania, Via Romita 13/b, IT-28845 Domodossola (VB), Italy.
Enel.Hydro, via Pastrengo 9, IT-24068 Seriate (BG), Italy.
Studio Ing. Viazzo, Via Chivasso 27/b, IT-13100 Vercelli (VC), Italy.

(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
  Glaciers Mass movements, Glacial hazards Rock fall, Ice avalanches, Glacial lake outburst flooding, Water pocket outburst

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
Italy Alps, Monte Rosa range Belvedere Glacier and Monte Rosa East Face East 2200-4500 m asl for the East Face 2001-2003

(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
From the mid-1980s until 2001 no unusual situation at Ghiacciaio del Belvedere was encountered. In summer 2001, however, heavy crevassing of the glacier surface, a marked increase in thickness, dirty ponds between the glacier and its lateral moraines, and enhanced ice and rock-fall activity from the glacier margins were observed. The processes were interpreted as indicators for a surge-type glacier movement and the local authorities instructed (Haeberli et al., 2002). In the mid-1980s and during 1995-1999, average surface speeds on the lower part of Ghiacciaio del Belvedere were found in the order of up to 40-45 m a-1, or 35 m a-1, respectively (VAW, 1985; Kääb et al., 2003a; Mazza, 2003). During 1999-2001 average speeds of up to 110 m a-1 and during autumn 2001 of up to 200 m a-1 were observed photogrammetrically. Terrestrial surveying and photogrammetry in summer 2002 yielded speeds of up to 80 m a-1.
Modélisations
 
Hypothèses
 

Sensibilité du milieu à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)

 

(3) - Effets du changement climatique sur l'aléa
Reconstitutions
 
Observations
At least seven outburst floods are known to have originated from the glacier in the past, threatening the village of Macugnaga, damaging infrastructure, and affecting the original moraine geometry (Haeberli et al., 2002):
- August 1868: water pocket outburst and moraine collapse at the left tongue;
- August 1896: moraine breaching after heavy rainfall;
- 1904: water pocket outburst and cutting through the right lateral moraine;
- September 1922: water outburst from the glacier after a rainfall period;
- August 1970, August 1978, July 1979: outburst floods from the Lago delle Locce.

Possibly as a consequence of enhanced englacial water pressure or other processes related to the surge-type movement, a supra-glacial lake developed in September 2001 on the Belvedere glacier. During winter 2001/2002 the corresponding depression enlarged presumably due to strongly extending ice flow. The first control visit in mid-June 2002 encountered an exceptionally large lake of nearly 150 000 m 2 with a volume of 3 million m 3 . A cold spell in early July 2002 significantly reduced melt water input, and together with pumping and naturally occurring sub-glacial drainage, helped to stabilise and then lower the lake level slowly. In spring 2003, the large depression at the location of the lake rapidly refilled with melt water reaching a volume similar to the one found in end of June 2002. Between 18 and 20 June 2003 the lake burst out.

Hazards related to the enhanced glacier speed and mass transport include increased rock- and ice-fall activity at its margins and destabilisation of moraines. At some locations the glacier overran its moraines producing frequent ice- and rock-falls over the outer moraine slope. In some places well visible, the enhanced lateral pressure from the surging and advancing glacier led to weakening or even first cutting through the moraines. As potential moraine breaks, such situations are of major concern in view of enhanced runoff or glacier floods running between the glacier and the moraine.

Recently, especially heavy ice- and rock-fall activity originates from two zones situated below and above a hanging glacier, which itself undergoes rapid geometric changes and frequently releases ice-falls. Since summer 2002, its front has largely diminished, and the glacier shows heavy crevassing and mass loss. Already in 2000, a steep glacier covering the lower of the presently active rock-fall source areas disappeared. Mass wasting from the lower rock-fall zone is not only by single rock-fall events but frequently also by debris flows, which are presumably triggered by melt water. The continuation of rock-fall activity during the winter-months points to a substantial change in glacier and rock conditions rather than to seasonal melt effects alone.
Modélisations
 
Hypothèses
The lake outburst of 2003 clearly showed that a supra-glacial lake on the Belvedere glacier has a potential for a catastrophic flood. From a volume of 3 million m3 a maximum outburst discharge in the order of up to 100-200 m3 s-1 can be expected in case of a hydraulic ice dam break. Especially the orographic right glacier stream (Torrente Pedriola) carries an amount of erodable debris, which is apparently large enough for a debris flow to be triggered by a glacier flood. The near to medium-term future of the Monte Rosa east face and the Belvedere glacier will most likely be characterised by drastic and rapid changes in glacier and permafrost conditions. The drastic loss in ice cover on the Monta Rosa east face will cause mechanical and thermal adjustments of ice and rock, on and in the wall. High rock- and ice-fall activity will, therefore, most likely continue. Large events cannot be excluded. Even after the surge-type movement of the Belvedere glacier has come to an end, some individual ice masses will independently continue to deform and slide. In addition to mechanical destabilisation of moraines, weakening by infiltration of meltwater from melt of the accumulated ice masses might take place.

Paramètres de l'aléa
Sensibilité du paramètre de l'aléa à des paramètres climatiques et du milieu
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
 
Belvedere glacier is a humid-temperate glacier with a flat, heavily debris-covered tongue and fed by steep glaciers, ice and snow avalanches as well as rock falls from the large east face of Monte Rosa. It is known as a classic example of a glacier with an elevated sediment bed.

(4) - Remarques générales
 

(5) - Préconisations et recomandations
 

Références citées :

Haeberli, W., Kääb, A., Paul, F., Chiarle, M., Mortara, G., Mazza, A. and Richardson, S. (2002): A surge-type movement at Ghiacciaio del Belvedere and a developing slope instability in the east face of Monte Rosa, Macugnaga, Italian Alps. Norwegian Journal of Geography, 56(2), 104-111.

Kääb, A., Huggel, C., Haeberli, W., Mortara, G., Chiarle, M. and Epifani, F. (2003a): Studio sui problemi connessi alla recente evoluzione dei fenomeni di instabilità riguardanti il Ghiacciaio del Belvedere e la parete orientale del Monte Rosa, Department of Geography, University of Zurich, and CNR-IRPI, Torino.

Mazza, A. (2003): The kinematics wave theory: a possible application to "Ghiacciaio del Belvedere" (Valle Anzasca, Italian Alps). Preliminary hypothesis. Terra glacialis, 6, 23-36.

VAW (1985): Studii sul comportamento del Ghicacciaio del Belvedere, Macugnaga, Italia. Relazione, Versuchsanstalt für Wasserbau, Hydrologie und Glaziologie der ETH Zürich, 97(3), 157.