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Studies of the Shrinkage After a Sudden Advance, Blue Bands and Wave Ogives on Glaciar Universidad (Central Chilean Andes)

  • Louis Lliboutry (a1)
Abstract

The recently discovered Glaciar Universidad is the second largest glacier in central Chile. Aerial photographs taken in 1945 show that just before that date it had undergone a “glacier flood” or sudden advance, similar to those suffered by four other great glaciers of central Chile between 1927 and 1947. The cause of these floods is sought. Surface features (firn line, absence of penitentes but presence of “pocket-penitents”, glacier mills, dirt cones, water-filled holes with submerged ice crystals in them) prove that Glaciar Universidad is the most northerly glacier in the Andes of an Alpine type. The disposition of blue bands, crevasses, closed crevasses and shear planes is reported. Wave ogives are studied and an explanation is given of why dark Forbes’ bands form subsequently on these waves. A kind of unstratified esker of a form similar to a deposit observed by Mr. W. H. Ward in Baffin Island, has been studied, as also has the shearing of the frontal cliff along dirt strata; a theory of both phenomena according to which shear transfers material from the bed to the surface is questioned.

Résumé

Ce glacier, récemment découvert, est le deuxième du Chili Central par son étendue. Des vues aériennes de 1945 montrent qu’il venait alors de subir une grande crue, analogue à celles qu’ont eu entre 1927 et 1947 quatre autres grands glaciers du Chili Central. On examine la cause de ces crues. Les aspects superficiels (ligne de névé, absence de pénitents mais présence toutefois de pocket-pénitents, moulins, cônes graveleux, trous pleins d’eau avec cristaux submergés) montrent que le Glaciar Universidad est, en allant vers le sud, le premier glacier de type Alpin des Andes. On signale la disposition des bandes bleues, des crevasses, des crevasses refermées et des cisaillements. On étudie les vagues au pied d’une chute (wave ogives) et l’on explique la formation ultérieure de bandes brunes (chevrons) sur ces vagues. On étudie enfin une sorte d’esker non stratifié semblable à un dépôt observé par Ward à l’île de Baffin, et des cisaillements de la falaise frontale le long de lits de terre. La théorie suivant laquelle le matériau du lit remonte à la surface du glacier grâce à des cisaillements est mise en doute.

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Copyright
References
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1. Lliboutry, L. Nieves y Glaciares de Chile, Fundamentos de Glaciología. Santiago, Ediciones Universidad de Chile, 1956. 471 p.
2,3. Haefeli, R. Some observations on glacier flow, Journal of Glaciology, Vol. 1, No. 9, 1951, p. 49698 and correspondence ibid., No. 10, 1951, p. 580–82.
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15. Cotton, C. A. Climatic Accidents in Landscape-Making. Christchurch, Whitcombe & Tombs, 1947. Plate XVI, Fig 2
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Journal of Glaciology
  • ISSN: 0022-1430
  • EISSN: 1727-5652
  • URL: /core/journals/journal-of-glaciology
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