Le montagne cadono a pezzi!!!

Stefano Rossignoli 1 ottobre 2012

E’ vero! Ma niente panico.

Succede da sempre…

conoide alluvionale e detritica
conoide alluvionale

Guardate questa immagine. La montagna è lassù e si sta smontando pian piano.

E’ il normale ciclo delle montagne.

Siamo sulle Alpi occidentali, precisamente in Val Ferret.

La Val Ferret (sia quella svizzera che quella italiana), come la Val Veny è caratterizzata da due litologie diverse a seconda del versante che consideriamo…

Andate a guardarvi questo articolo per imparare come si definiscono i versanti di una valle

Sulla destra idrografica della Val Ferret svizzera e della Val Veny e sulla sinistra idrografica della Val Ferret italiana si trovano rocce davvero, perdonatemi la definizione, MARCE, quindi molto erodibili dall’acqua, dal gelo, dal vento e dagli agenti esogeni in generale…ad esempio dalla gelivazione, ovvero il congelamento dell’acqua infiltrata che spacca le rocce per il conseguente aumento di volume dell’acqua che diventa ghiaccio e durante il disgelo, il ghiaccio fonde e libera le lastre spaccate precedentemente lasciandole cadere a valle.

In realtà queste rocce ‘MARCE’ sono frammenti di crosta oceanica miste a rocce sedimentarie trasformate da grandi pressioni e temperature a causa dei processi tettonici che hanno formato le Alpi e, soprattutto sono scistate, ovvero trasformate in sottili straterelli laminari che si aprono facilmente, alle volte anche a mani nude…

Tornando alla fotografia in apertura, si nota come alla base della montagna, dopo il canale percorso da un torrente effimero, ci sia quella che viene chiamata una Conoide Alluvionale. (Effimero vuol dire provvisorio, che a volte c’è e a volte non c’è, che si riempie solo durante i temporali, le grandi piogge o durate un importante disgelo primaverile e che spesso cambia strada!).

Sono proprio le piogge, il gelo invernale, il vento a distruggere pian piano la montagna e a far vincere su di essa la GRAVITA’.

Tutto tende a cadere giù e se la roccia non è un gran che in quanto a resistenza meccanica, viene giù prima che altrove dove magari la roccia è un solido granito…come ad esempio sull’altro versante della Val Ferret dove si trovano  montagne vicine ai 4000m e oltre sul livello del mare.

Mont Dolent 3823m S.l.M.
Mont Dolent 3823m S.l.M.

La montagna si forma, cresce, si alza ma, il suo destino è sempre quello d distruggersi con velocità diversa secondo la sua litologia (tipo di roccia) secondo la sua immersione (orientazione degli strati) o secondo il suo chimismo (i componenti chimici che la formano)…nonché secondo il clima (temperatura, umidità, precipitazioni) a cui è soggetta…

Nulla era come è oggi, nulla resta come è e nulla di quel che c’è oggi sarà così domani. Tutto cambia in continuazione, più o meno velocemente o lentamente ma comunque e sempre INESORABILMENTE…

A presto!

 

 

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