La frana del Pizzo Cengalo e le colate detritiche sono state provocate da un effetto domino, da una serie di processi concatenati che si verificano raramente a livello mondiale. Lo rileva uno studio pubblicato venerdì da un gruppo di esperti istituito dal canton Grigioni. Due elementi sono stati centrali: la roccia e il ghiaccio.
Semplificando, gli oltre tre milioni di metri cubi di roccia sono franati sul ghiaccio sottostante, che si è staccato, in parte sciogliendosi. L’acqua che si è creata ha così messo in movimento le masse rocciose franate provocando il flusso di detriti che si è riversato lungo la Val Bondasca. La presenza simultanea di questi eventi è, come detto, una particolarità, eppure, analizzando la situazione geologica del Cengalo, quanto successo potrebbe ripetersi.
Un altro elemento sorprende i ricercatori. Le valanghe rocciose di grandi dimensioni, solitamente, non si verificano all’improvviso, ma sono precedute da crolli di piccole dimensioni. Questo, però, non accadde a Bondo.
sulma
RG 12.00 del 15.12.2017: il servizio di Roberto Scolla
RSI Ticino e Grigioni 15.12.2017, 13:07
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