A note on the water budget of temperate glaciers

ABSTRACT. The ablation areas of debris-covered glaciers typically consist of a complex mosaic of surface features with contrasting processes and rates of mass loss. This greatly complicates glacier response to climate change, and increases the uncertainty of predictive models. In this paper we present a series of high-resolution DEMs and repeat lake bathymetric surveys on Ngozumpa Glacier, Nepal, to study processes and patterns of mass loss on a Himalayan debris-covered glacier in unprecedented detail. Most mass loss occurs by melt below supraglacial debris, and melt and calving of ice cliffs (backwasting). Although ice cliffs cover only ∼5% of the area of the lower tongue, they account for 40% of the ablation. The surface debris layer is subject to frequent re-distribution by slope processes, resulting in large spatial and temporal differences in debris-layer thickness, enhancing or inhibiting local ablation rates and encouraging continuous topographic inversion. A moraine-dammed lake on the lower glacier tongue (Spillway Lake) underwent a period of rapid expansion from 2001 to 2009, but later experienced a reduction of area and volume as a result of lake level lowering and sediment redistribution. Rapid lake growth will likely resume in the near future, and may eventually become up to 7 km long.

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“…Oerlemans, 2013). Taking the annual mass losses for 2012-2015, this yields an annual internal melt volume of ∼115 000 m 3 .…”

Section: Internal Ablationmentioning

confidence: 99%

Stagnation and mass loss on a Himalayan debris-covered glacier: processes, patterns and rates

Thompson¹,

Benn

Mertes³

et al. 2016

J. Glaciol.

136

251

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“…However, direct evidence for this theory does not exist. Oerlemans (2013) has suggested that the steady accumulation of dissipative meltwater in the accumulation zone plays an important role. In recent years geometric changes caused by surging have been documented extensively (e.g.…”

Section: Introductionmentioning

confidence: 99%

A model study of Abrahamsenbreen, a surging glacier in northern Spitsbergen

Oerlemans

Pelt

2015

The Cryosphere

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Abstract. The climate sensitivity of Abrahamsenbreen, a 20 km long surge-type glacier in northern Spitsbergen, is studied with a simple glacier model. A scheme to describe the surges is included, which makes it possible to account for the effect of surges on the total mass budget of the glacier. A climate reconstruction back to AD 1300, based on icecore data from Lomonosovfonna and climate records from Longyearbyen, is used to drive the model. The model is calibrated by requesting that it produce the correct Little Ice Age maximum glacier length and simulate the observed magnitude of the 1978 surge.Abrahamsenbreen is strongly out of balance with the current climate. If climatic conditions remain as they were for the period 1989-2010, the glacier will ultimately shrink to a length of about 4 km (but this will take hundreds of years). For a climate change scenario involving a 2 m year −1 rise of the equilibrium line from now onwards, we predict that in the year 2100 Abrahamsenbreen will be about 12 km long.The main effect of a surge is to lower the mean surface elevation and thereby to increase the ablation area, causing a negative perturbation of the mass budget. We found that the occurrence of surges leads to a faster retreat of the glacier in a warming climate.Because of the very small bed slope, Abrahamsenbreen is sensitive to small perturbations in the equilibrium-line altitude. If the equilibrium line were lowered by only 160 m, the glacier would steadily grow into Woodfjorddalen until, after 2000 years, it would reach Woodfjord and calving would slow down the advance.The bed topography of Abrahamsenbreen is not known and was therefore inferred from the slope and length of the glacier. The value of the plasticity parameter needed to do this was varied by +20 and −20 %. After recalibration the same climate change experiments were performed, showing that a thinner glacier (higher bedrock in this case) in a warming climate retreats somewhat faster.

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“…This parameterisation for S could be incorporated in models for subglacial hydrology such as Hewitt (2011), Bartholomaus andothers (2011) or Werder andothers (2013). These models could then be coupled with an ice flow model to capture switches in subglacial drainage and surge initiation (Fowler, 1987;Björnsson, 1998;Oerlemans, 2013).…”

Section: Resultsmentioning

confidence: 99%

Effects of ice deformation on Röthlisberger channels and implications for transitions in subglacial hydrology

et al. 2016

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ABSTRACT. Along the base of glaciers and ice sheets, the sliding of ice over till depends critically on water drainage. In locations where drainage occurs through Röthlisberger channels, the effective pressure along the base of the ice increases and can lead to a strengthening of the bed, which reduces glacier sliding. The formation of Röthlisberger channels depends on two competing effects: (1) melting from turbulent dissipation opens the channel walls and (2) creep flow driven by the weight of the overlying ice closes the channels radially inward. Variation in downstream ice velocity along the channel axis, referred to as an antiplane shear strain rate, decreases the effective viscosity. The softening of the ice increases creep closure velocities. In this way, even a modest addition of antiplane shear can double the size of the Röthlisberger channels for a fixed water pressure or allow channels of a fixed radius to operate at lower effective pressure, potentially decreasing the strength of the surrounding bed. Furthermore, we show that Röthlisberger channels can be deformed away from a circular cross section under applied antiplane shear. These results can have broad impacts on sliding velocities and potentially affect the total ice flux out of glaciers and ice streams.

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A note on the water budget of temperate glaciers

Cited by 19 publications

References 22 publications

Stagnation and mass loss on a Himalayan debris-covered glacier: processes, patterns and rates

Stagnation and mass loss on a Himalayan debris-covered glacier: processes, patterns and rates

A model study of Abrahamsenbreen, a surging glacier in northern Spitsbergen

Effects of ice deformation on Röthlisberger channels and implications for transitions in subglacial hydrology

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