Wednesday, May 29, 2013

1998 snowcover from Landsat 5

Through calendar year 1998, Quelccaya was exceptionally well documented by Landsat imagery. From January into early November the ice cap is visible in almost every scene, as the satellite passed overhead every 16 days; 4 are entirely cloudless. Inspired by the Earth Observatory images of Quelccaya posted recently, collaborator Carsten Braun compiled and registered 16 scenes to demonstrate the annual cycle of accumulation and ablation at Quelccaya. These are shown below as an animated GIF cycling continuously through the 16 images, with the 1998 date shown in the upper-left hand corner.

In a year with one of the strongest recent El Niño events, the 1998 annual cycle of snowfall likely differs somewhat from a typical year. The total annual amount of snow, for example, was almost certainly below normal - although we do not have measurements from the summit that year. Nonetheless, these images nicely demonstrate the seasonality of precipitation at Quelccaya:
  • In mid-January, when the wet season was well underway, the 1998 transient snowline is generally only 100-200 m higher than the ice cap margin.
  • Two months later when the wet season is typically concluding, most of the glacier appears covered by snow - yet not quite to the margin and not on terrain adjacent to the ice.
  • Two April images depict the greatest spatial extent of wet-season snowcover on the glacier, with thin cover on other high-elevation areas.
  • By mid-May snowcover had decreased considerably, with snow present only on the glacier - and a transient snowline higher than in the mid-January image. (The 10 May image is shown above; registration issues precluded including it in the sequence below.) Snowline moves slightly higher by mid-June.
  • Surprise! 27 June is well into the dry season, yet snowline reaches the lowest elevation for the year (at least to early November 1998). This scene also has the greatest spatial extent of regional snowcover for all of 1998.
  • By the end of July almost all snow was gone from the landscape again. The transient snowline on the glacier rose continuously through July, August, and September. Very little accumulation for 1997-98 remained by the 15 September image.
  • The image of 1 October shows what appears to be thin snowcover entirely blanketing the glacier. Little snow is visible elsewhere, except to the north in this image; the larger, un-cropped scene on this date shows a very different pattern of snow distribution on the landscape than after the winter (dry season) event of 27 June.
  • By early November the next accumulation season appears to have begun, with deeper snow covering the ice cap and extended slightly beyond the margins.

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