Flusso di ghiaccio

Cartina della velocità nell'Antartide. I flussi glaciali possono essere visti con una velocità in aumento (blu-giallo-bianco) che scorrono verso la costa.[1]
Immagine radarsat dei flussi di ghiaccio che scorrono all'interno della barriera di Filchner-Ronne

Un flusso di ghiaccio o flusso glaciale è una regione di un ghiacciaio continentale che si muove significativamente più veloce rispetto al ghiaccio circostante. I flussi di ghiaccio sono tipi di ghiacciaio[2] e sono importanti nell'Antartide dove la loro quantità si aggira intorno al 10% del suo volume complessivo. Larghi fino 50 km e spessi 2 km, possono estendersi per centinaia di chilometri, e rappresentano la maggior parte del ghiaccio rimasto del ghiacciaio continentale.

La velocità di un flusso glaciale può essere di oltre 1 000 metri per anno, un ordine di grandezza più veloce di quello del ghiaccio circostante. Le forze di taglio ai margini del flusso glaciale causano la deformazione e ricristallizzazione del ghiaccio, rendendolo più soffice, e concentrando la deformazioni in bande strette o margini di taglio, laddove si formano in modo particolare i crepacci.

La maggior parte dei flussi di ghiaccio hanno un po' d'acqua alla loro base, che ne lubrifica il flusso. Anche il tipo di roccia in posto è determinante, mentre i sedimenti soffici, deformabili, rendono il flusso più veloce rispetto alla dura roccia.[3]

Antartide

Lo stesso argomento in dettaglio: Lista di flussi glaciali antartici.

L'indlandsis dell'Antartide defluisce verso il mare per mezzo di molti flussi glaciali. Il maggiore nell'Antartide orientale è il ghiacciaio Lambert. Nell'Antartide occidentale, i grandi ghiacciai Pine Island e del Thwaites sono attualmente quelli più in disequilibrio, con una perdita di massa totale netta tra loro, misurata nel 2006, di 85 gigatonnellate per anno.[4]

È stato affermato che la calotta polare antartica stia perdendo massa. Si pensa che il processo di accelerazione passata e quella in corso dei flussi glaciali e dei ghiacciai di sbocco sia una causa importante, se non dominante, di questo squilibrio.[4]

Groenlandia

I flussi di ghiaccio che deflusicono dal ghiacciaio continentale groenlandese al mare comprendono i ghiacciai Helheim, Jakobshavn Isbræ e Kangerdlugssuaq.

Note

  1. ^ (EN) Bamber J.L., Vaughan D.G., Joughin I., Widespread complex flow in the interior of the Antarctic Ice Sheet, in Science, vol. 287, 2000, pp. 1248–1250, DOI:10.1126/science.287.5456.1248, PMID 10678828.
  2. ^ (EN) National Snow and Ice Data Center, Types of Glacier, su nsidc.org (archiviato dall'url originale il 17 aprile 2010).
  3. ^ (EN) British Antarctic Survey, Description of Ice Streams, su antarctica.ac.uk. URL consultato il 26 gennaio 2009 (archiviato dall'url originale l'11 febbraio 2009).
  4. ^ a b (EN) Rignot E., Bamber J.L.; van den Broeke, M.R.; Davis C.; Li Y.; van de Berg W.J.; van Meijgaard E., Recent Antarctic ice mass loss from radar interferometry and regional climate modelling, in Nature Geoscience, vol. 1, 2008, pp. 106–110, DOI:10.1038/ngeo102.

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Collegamenti esterni

Controllo di autoritàLCCN (EN) sh2005020596 · J9U (EN, HE) 987007540057605171
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