Scientific Theme: Advanced Modeling and Observing Systems

Complementary Research: Faculty Fellows Research
Greenland Ice Sheet Moulins – The Link to Increased Ice Velocity
Konrad Steffen
With Russell Huff, Alberto Behar 1 , and graduate students
Funding: NASA Cryospheric Sciences
1 Collaboration: NASA Jet Propulsion Laboratory, Pasadena, CA
Purpose and Objectives
Understanding the flow of water through the body of a glacier or ice sheet is important because
the spatial distribution of water and the rate of infiltration to the glacier bottom is one control
on water storage and pressure, glacier sliding and surging. According to the prevailing
hypothesis, this water flow takes place in a network of tubular conduits.
The prevailing view of englacial water flow through tubular conduits is supported by observations of caves on the
margins of glaciers and explorations into moulins (a vertical shaft in a glacier). Whether such features are unique to
the margin and to moulins is unclear. We carried out two field expeditions along the margin of the Greenland ice
sheet in summer 2006 and 2007 to measure the volume of
moulins using a rotating laser scanner and video equipment.
Further, we lowered an instrument package into the ice sheet
along a 500-m long string measuring environmental
parameters with HD video recording.
Moulin on the Greenland ice sheet along the
western slope of the Greenland ice sheet. There are
45 moulin in an 10 km x 10 km are in the lower
ablation region of the ice sheet, and they each
drain approximately 4.5 10 6 m 3 water during one
melt season.
Accomplishment
The surface velocity of the Greenland ice sheet varies
significantly on both seasonal and shorter time-scales.
Seasonal variations reflect the penetration of supraglacial
water to the glacier bed through significant thicknesses of
cold ice. There, velocity fluctuations were recorded with our
GPS network (eight permanent Trimble stations) which has
been operational in this region since 1995. Shorter-term
events are associated with periods of rapidly increasing water
inputs to the subglacial drainage system. Early-season shortterm
events immediately follow the establishment of a
drainage connection between glacier surface and glacier bed,
and coincide with the onset of subglacial outflow at the
terminus. A mid-season short-term event occurred as surface
melting resumed following cold weather, and may have been
facilitated by partial closure of subglacial channels during
this cold period. There is a close association between the
timing and spatial distribution of horizontal and vertical
velocity anomalies, the temporal pattern of surface water
input to the glacier, and the formation, seasonal evolution,
and distribution of subglacial drainage pathways. These
factors presumably control the occurrence of high-waterpressure
events and water storage at the glacier bed. The
observed coupling between surface water inputs and glacier
velocity may allow predominantly cold polythermal glaciers
to respond rapidly to climate-induced changes in surface
melting.
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