Abstract
Abstract. Surface glacier debris samples and field spectra were collected from the ablation zones of Nepal Himalaya Ngozumpa and Khumbu glaciers in November and December 2009. Geochemical and mineral compositions of supraglacial debris were determined by X-ray diffraction and X-ray fluorescence spectroscopy. This composition data was used as ground truth in evaluating field spectra and satellite supraglacial debris composition and mapping methods. Satellite remote sensing methods for characterizing glacial surface debris include visible to thermal infrared hyper- and multispectral reflectance and emission signature identification, semi-quantitative mineral abundance indicies and spectral image composites. Satellite derived supraglacial debris mineral maps displayed the predominance of layered silicates, hydroxyl-bearing and calcite minerals on Khumbu Himalayan glaciers. Supraglacial mineral maps compared with satellite thermal data revealed correlations between glacier surface composition and glacier surface temperature. Glacier velocity displacement fields and shortwave, thermal infrared false color composites indicated the magnitude of mass flux at glacier confluences. The supraglacial debris mapping methods presented in this study can be used on a broader scale to improve, supplement and potentially reduce errors associated with glacier debris radiative property, composition, areal extent and mass flux quantifications.
Highlights
Earth observing satellite technology has advanced greatly in recent decades, offering rich spatial, temporal and spectral imaging of Earth’s glaciers
Southern Himalayan glaciers are characterized by extensive debris cover and are losing significant ice mass in recent decades (e.g. Bolch et al, 2011)
Sustained and widespread ice loss in the Himalayas (Berthier et al, 2007) and in other glacierized regions contributes to crustal uplift (Tamisiea et al, 2001; Larsen et al, 2005) and sea-level rise (Meier et al, 2007)
Summary
Many of the world’s glaciers have moderate to significant surface debris. Supraglacial debris is derived from either local rock and ice fall or from atmospheric deposition of particulates. In addition to glacier extent and kinetic studies, Wessels et al (2002) used ASTER data to analyze spectral variability of supraglacial lakes in the Everest region; Kaab (2005) utilized false color ASTER band composites to indicate debris patterns and indication of flow regimes at Hispar glacier in the Karakorum, Pakistan and Unteraar glacier in the Swiss Alps; Suzuki et al (2007) mapped thermal resistance of debris covered glaciers in the Lunana and Khumbu Himalayas; and Mihalcea et al (2008) utilized ASTER data to map glacier debris spatial distribution and thickness. We demonstrate that supraglacial composition can be mapped via spectral satellite data and is relevant to many glaciologic variables, including radiative absorption, ablation, generation of supraglacial melt as well as englacial and supraglacial mass flux. These supraglacial debris composition impacts are applicable to glaciologic understanding at regional and global scales
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