Encyclopedia of Debris Covered Glaciers

Under construction…

Ablation
Accumulation
Alaskan Debris Covered Glaciers
Albedo
Andean Debris Covered Glaciers (South America)
Base Level Lakes
Calving
Clast
Coupled Margin
Crevasse
Cut-and-Closure
Decoupled Margin
Debris Cover
Downwasting
Driving Stress
Dye Tracing
Energy Balance
Englacial Conduit (cave)
Evolution Regimes
Glacial Lake Outburst Flood (GLOF)
Ground Penetrating Radar (GPR)
Heat Flux
High Relief Mountain Ranges
Himalayan Debris Covered Glaciers
Hummock
Ice Cliff
Icefall
Ice Velocity
Incision Rate (in glacier ice)
Jokulhaups
Lateral Moraine
Marginal Lakes
Mass Balance
Mass Continuity
Medial Moraine
Melt Hotspot
Modeling Efforts
Monsoon
Moraine Lake [see Terminal Lake]
New Zealand Alps Debris Covered Glaciers
Østrem Curve
Photogrammetry (Structure-from-Motion, SfM)
Phreatic Conditions (for englacial conduits)
Roof Suture (feature of englacial conduits)
Sink (topographic)
Stagnation
Subsidence
Supraglacial Lake (Perched Lake)
Supraglacial Channel/Stream
Temperature Gradient
Terminal Lake
Terminal Moraine
Vadose Conditions (for englacial conduits)



Mass Balance

Paragraphs about debris covered glacier mass balance.



Østrem Curve

The Østrem Curve describes the influence of debris cover on glacier ice melt. Debris cover influences the melt rate because it decreases albedo and changes the energy transfer properties of the glacier’s surface. The reduced albedo caused by debris cover causes the surface to absorb more solar radiation. The additional absorbed radiation is then transferred to the local environment in the following ways: (1) Re-emission of longwave radiation, (2) Convective and conductive loss of heat to the atmosphere, (3) Evaporating moisture held within the debris layer, and (4) Melting of glacier ice.

ostrem-curve_Ostrem1959
Ablation rate as a function of debris layer thickness (Østrem, 1959). The peak melt rate was observed beneath debris layers approximately 0.5 cm thick.

Very thin debris layers (less than a few centimeters) accelerate ice melt because the absorbed solar radiation is quickly transferred into the ice. Thick debris layers effectively insulate ice from melt because the energy absorbed from incident solar radiation is unable to reach the ice-debris boundary quickly. Therefore, thickly covered ice regions are subject to melt for fewer hours each day.

Gunnar Østrem conducted an ablation experiment on Isfallsglaciären, near Tarfala, Sweeden. He placed moraine material (sand, gravel, etc.) on 2 meter-square clean ice test plots and compared melt beneath the debris layer to clean-ice melt. He varied the thickness and grain size of the debris layer to better understand the relationship between the debris mantle and glacier ice melt.

Recently, Evatt et al. (2015) showed that the turning point where the melt rate switches from increasing to decreasing is affected by the proportion of the ice that is debris covered and a reduction of evaporative heat loss. As the debris layer thickens from zero to a few centimeters, wind becomes increasingly unable to reach the debris-ice interface. This reduces the quantity of heat lost to evaporation, thus increasing the heat available for ice melt. Further increases in debris layer thickness cause the insulating effects of debris to dominate, thereby reducing the melt rate.

In the figure above, we see the impact humidity within the debris layer has on the melt rate. Decreasing humidity increases evaporative heat flux. As the debris layer thickness increases, evaporative heat flux decreases. The decrease in evaporative heat flux causes the peak seen in the Østrem Curve.

Further Reading:

Evatt, G., Abrahams, I., Heil, M., Mayer, C., Kingslake, J., Mitchell, S., Fowler, A., Clark, C. (2015). Glacial melt under a porous debris layer. Journal of Glaciology, 61(229), 825-836.

Gunnar Østrem (1959). Ice Melting under a Thin Layer of Moraine, and the Existence of Ice Cores in Moraine Ridges, Geografiska Annaler, 41:4, 228-230. 

Nicholson, L. I., McCarthy, M., Pritchard, H. D., and Willis, I. (2018). Supraglacial debris thickness variability: impact on ablation and relation to terrain properties, The Cryosphere, 12, 3719–3734.