Allalin Glacier

Allalin Glacier flows 6.2 km from the north-east face of the Allalinhorn (4,027 m) to a present terminus at ~2,150 m. GLAMOS surveys show the glacier retreated 1,260 m between 1880 and 2022 and its surface area fell from 9.9 km2 (1973) to 7.3 km2 in 2019. Long-term mass-balance series record a cumulative loss of greater than 33 m water equivalent since 1960, with exceptionally negative years in 2003, 2022 and 2023 when large parts of the ablation zone became snow-free by early July. ==Ice avalanches and Mattmark disaster==

On 30 August 1965 approximately two million cubic metres of ice detached from the steep tongue during an "active phase" of enhanced basal slip and swept 800 m downvalley, burying construction barracks at the Mattmark dam site and killing 88 workers—the deadliest glacier accident ever recorded in Switzerland. Detailed post-event mapping and photogrammetry revealed that the active phases recur every 1–3 years, driven by seasonal melt-water pressurisation of a thin basal till layer beneath the cold, hanging tongue. A smaller break-off of about 100,000 cubic metres occurred in July 2000 but was successfully forecast days in advance thanks to surface-velocity and icequake monitoring, prompting evacuations along the avalanche path. ==Monitoring and modelling==

Because of its repeat instabilities Allalin has become a test-bed for early-warning technology. Continuous GPS, radar interferometry and automatic seismic arrays installed since 1998 detect precursory acceleration patterns, log-periodic displacement oscillations and rising icequake rates that typically precede break-off by 2–10 days. Numerical models constrained by these data reproduce the gravity-driven rupture as a transition from distributed creep to localised shear along a temperate–cold ice interface, improving time-to-failure forecasts that are now issued by cantonal authorities whenever sliding speed exceeds 40 cm per day. The glacier is thus one of only a few worldwide where real-time hazard bulletins are routinely disseminated to construction sites, alpine huts and ski lifts in the Saas Valley. ==References==