Snow accumulation at Quelccaya Ice Cap seems to have reached a maximum
in early February this year. Despite a couple minor snowfall events,
snow depth at the summit early in April has already decreased by about
one-third, reaching 29% of the median for 4 April (based on 2005-15).
For perspective, snow depth is now less than half that of the previous
early-April minimum.
The water equivalence (w.e.) of 2015-16 accumulation to date is not
known, and won't be until a density profile is made. Although it is
possible that the snowpack w.e. is not as anomalous as depth, due to
melting and even rain, the correlation between depth and w.e. at
Quelccaya summit is typically strong.
Additional snow accumulation after early April is not likely, as the
conclusion of the wet
season, or the "snow-accumulation decay date" (Hurley et al., 2015)
occurs between by mid-March and mid-May. And even in years when the wet
season continues into May, the rate of accumulation generally decreases
substantially.
The image above illustrates anomalously low snowfall of the 2015-16 El
Niño
year. This is a nearly cloud-free view from 24 March, depicting the
seasonally-green wetlands (bofedales) and the numerous lakes impounded
behind moraines - many of which formed within recent decades. A
transient snowline near the margin delineates old glacier ice of the
ablation zone and this year's accumulation. At least one other snowline
is faintly visible, particularly on the west side, which may represent
ablation-zone ice with a thin cover of 2015-16 snow.
Comparing imagery of snowcover extent from year to year on a fixed date is risky. Only by observing the
minimum
extent of snow cover prior to the next wet season can one assess
accumulation in a simple, meaningful way via satellite. During this important El
Niño year we will continue to monitor snowcover.
In the meantime, fieldwork will be undertaken at Quelccaya during April
and May to assess snowcover depth along transects, measure density, and
obtain samples for comprehensive chemical and isotopic analysis.
Measurements at the AWS and time-lapse images will be recovered which
will help us better understand how this strong El Niño is being recorded
at Quelccaya.
