Controls on Meltwater Production and Lake Level Rise
in the McMurdo Dry Valley
Andrew G. Fountain1, Karen J. Lewis1, and Peter Doran1
Glacial meltwater is the only important source of water to the ephemeral streams and perennially
ice-covered lakes in the McMurdo Dry Valleys. The ecosystems that inhabit the streams and lakes
depend on this water for their habitat and for the distribution of nutrients. Lake levels have been
rising since 1905, indicating that the hydrology of the valleys is not in equilibrium. The cause of the
lake level rise is glacial melt and suggests that the climate of the valleys is changing. Large volumes
of meltwater are generated in the valleys when air temperatures are well above freezing. Meltwater
is also generated when air temperatures are just below freezing because solar radiation penetrates
the glacier surface, raising ice temperatures to the freezing point. During the past few years, typical
summer air temperatures have been below freezing and the flux of meltwater small. In response,
lake levels have been steady or slightly declining. One major factor in the meltwater flux is the
effect of snow. Under current summer conditions, a thin layer of snow (cm) covering the ice can
persist for much of the season and is sufficient to eliminate meltwater production by increasing the
surface albedo. To investigate the effect of snow on ice for meltwater flow, a simple energy balance
model was developed. The model is used to examine the range of atmospheric and surface condi-
tions that enhance or diminish meltwater production. Implications of the results for climatic condi-
tions that create rising lake levels are explored and the relevance to the formation of paleo-Lake
Washburn (13,000 years ago) are discussed.
1
Portland State University Department of Geology, Portland, Oregon 97207-0751, USA
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