| Description |
Modern mountain landscapes are inhabited by a wide spectrum of glacial landforms, ranging from clean-ice glaciers to heavily debris-covered glaciers to rock glaciers. Today, anthropogenic climate change is resulting in the rapid deglaciation of most alpine environments, causing the cryosphere to change at an unprecedented pace. One such response to a warming environment is the transformation of clean-ice glaciers into fully debris-covered rock glaciers (Anderson et al., 2018). This transformation takes place below the equilibrium line altitude (ELA) as a thickening layer of debris builds in the ablation zone. Once in place, the lower portion of a glacier is shielded from ablation by the mantle of supraglacial debris, thus facilitating the glacier's extension to lower elevations down valley and rendering the form more resilient to climatic warming than typical clean-ice glaciers. Isolated instances of glacier-to-rock glacier transformation have been recorded in various mountain ranges including the Chilean Andes (Monnier and Kinnard, 2015), the Austrian Alps (Krainer and Mostler, 2014), and the Nepalese Himalayas (Jones et al., 2018). However, there do not exist large-scale regional studies that assess the frequency at which glacier-rock glacier transformation has occurred or is unfolding. Here, we manually examine 11,648 Randolph Glacier Inventory (version 6) outlines along the northern extent of the Tibetan Plateau using remote sensing imagery in Google Earth Pro. We inspected the terminus of each glacier for morphological indicators of rock glacier development, including complete surface debris coverage, ridge and furrow topography, and an over-steepened front. 455 glaciers (3.91%) met morphological criteria and were thus classified as rock-glacier-terminating-glaciers (RGTGs). RGTG mean elevation (5157 m.a.s.l.) was found to be 236 meters lower than that of all other glaciers in the study area (5393 m.a.s.l.). Moreover, the median length of RGTGs (1473 m) was more than double that of the non-rock-glacier terminating glacier population (710 m). This supports the notion that high surface debris coverage facilitates the extension and persistence of glacier ice at lower altitudes. This study highlights that the glacier-rock glacier continuum as described in Monnier and Kinnard (2015) is currently unraveling in northern Tibet. Understanding the distribution of RGTGs has implications for understanding the geomorphological response of the cryosphere under future climate warming. |
