Debris‐covered glaciers and rock glaciers in the nanga parbat himalaya, pakistan

Abstract

ABSTRACT. The origin and mobilization of the extensive debris cover associated with the glaciers of the Nanga Parbat Himalaya is complex. In this paper we propose a mechanism by which glaciers can form rock glaciers through inefficiency of sediment transfer from glacier ice to meltwater. Inefficient transfer is caused by various processes that promote plentiful sediment supply and decrease sediment transfer potential. Most debris-covered glaciers on Nanga Parbat with higher velocities of movement and/ or efficient debris transfer mechanisms do not form rock glaciers, perhaps because debris is mobilized quickly and removed from such glacier systems. Those whose ice movement activity is lower and those where inefficient sediment transfer mechanisms allow plentiful debris to accumulate, can form classic rock glaciers.We document here with maps, satellite images, and field observations the probable evolution of part of a slow and inefficient ice glacier into a rock glacier at the margins of Sachen Glacier in c. 50 years, as well as several other examples that formed in a longer period of time. Sachen Glacier receives all of its nourishment from ice and snow avalanches from surrounding areas of high relief, but has low ice velocities and no efficient system of debris removal. Consequently it has a pronounced digitate terminus with four lobes that have moved outward from the lateral moraines as rock glaciers with prounced transverse ridges and furrows and steep fronts at the angle of repose. Raikot Glacier has a velocity five times higher than Sachen Glacier and a thick cover of rock debris at its terminus that is efficienctly removed. During the advance stage of the glacier since 1994, ice cliffs were exposed at the terminus, and an outbreak flood swept away much debris from its margins and terminus. Like the Sachen Glacier that it resembles, Shaigiri Glacier receives all its nourishment from ice and snow avalanches and has an extensive debris cover with steep margins close to the angle of repose. It has a high velocity similar to Raikot Glacier and catastrophic breakout floods have removed debris from its terminus twice in the recent past. In addition, the Shaigiri terminus blocked the Rupal River during the Little Ice Age and is presently being undercut and steepened by the river. With higher velocities and more efficient sediment transfer systems, neither the Raikot nor the Shaigiri form classic rock-glacier morphologies.

Modeling debris-covered glaciers: response to steady debris deposition

“…Debris cover more than a few centimeters thick damps the ablation of underlying ice (e.g., Østrem, 1959;Shroder et al, 2000;Owen et al, 2003). If debris supply to a glacier surface is high, mass balance profiles can be greatly altered, leading to increases in glacier volume and length (e.g., Konrad and Humphrey, 2000;Scherler et al, 2011a, b;Fig.…”

Monitoring tropical debris-covered glacier dynamics from high-resolution unmanned aerial vehicle photogrammetry, Cordillera Blanca, Peru

“…The impact of these variables has been studied extensively in other areas, particularly the Himalaya, where large debris-covered glacier tongues are common Buri et al, 2016;Immerzeel et al, 2014;Scherler et al, 2011;Shroder et al, 2000). However, few detailed studies of these processes have focussed on the Cordillera Blanca.…”

Internal Structure and Current Evolution of Very Small Debris-Covered Glacier Systems Located in Alpine Permafrost Environments

“…Moreover, the height and surface of the latter can be lopsided in comparison with the restricted glacier surface (Maisch et al, 1999;Grunewald and Scheithauer, 2010). Finally, the debris evacuation can be limited because the weak driving stress of these thin ice masses is commonly reduced by the presence of cold ice (Gilbert et al, 2012) and/or large and possibly frozen sediment accumulations in the distal zone, such as moraine dam (sensu Benn et al, 2003), ice-cored moraines or rock glaciers (Shroder et al, 2000;Kirkbride and Deline, 2013;Bosson et al, 2015).…”