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Geochemical characterization of supraglacial debris via in situ and optical remote sensing methods: A case study in Khumbu Himalaya, Nepal

Cryosphere (2012) 6(1) 85-100
DOI: 10.5194/tc-6-85-2012
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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. © Author(s) 2012. CC Attribution 3.0 License.

Figures

  • Fig. 1. Spectral and spatial resolution of Hyperion, ALI, Landsat ETM+, ASTER and MODIS sensors shown with respect to visible to thermal infrared atmospheric transmission (revised after (Kääb, 2005)).
  • Table 1. Summary of in situ sample attributes, including location, elevation, as well as data collection date, sample type and sample ID. The locations of the field measurement sites are mapped in Fig. 2 and sample ID’s are also referred to in Table 3.
  • Fig. 2. Landsat TM (31 October 2009) true color composite of the Khumbu Himalaya study area. Ngozumpa glacier (left) and Khumbu glacier (right) in situ measurement locations are labeled as detailed in Table 1. The approximate area presented in the Hyperion Imja and Lhotse Shar glacier analysis is highlighted with a yellow box in the lower right hand corner.
  • Table 2. A listing of the satellite products and scene dates used for the optical remote sensing methods evaluated in this study.
  • Fig. 3. Khumbu glacier snow, ice and debris field collected surface reflectance. Note the reduction in VNIR reflectance with increasing dust and debris compared to clean snow and bare ice signatures, and SWIR dominant schistic supraglacial debris signature. Satellite reflectance (ASTER AST 07XT) is compared with field reflectance for bare ice and schistic debris signatures.
  • Table 3. In situ and satellite comparison of mineralogy and silica abundance at Ngozumpa and Khumbu glacier sample locations. XRDderived minerals are listed in order of greatest abundance per sample, along with XRF measured SiO2 weight percent and ASTER TIR estimated SiO2 weight percent. ASTER TIR SiO2 weight percent is averaged from the nearest two 90 m pixels to the in situ sample site.
  • Fig. 4. Hyperion (13 May 2002) top-of-atmosphere supraglacial debris and ice reflectance plot (left) is displayed with a true color ALI (4 October 2010) 10 m pan-enhanced image of the Imja and Lhotse Shar glaciers. Atmospheric water vapor, oxygen and carbon dioxide absorption features were removed from the reflectance signatures. The locations of the Hyperion derived spectra for debris are indicated by the blue (Imja glacier debris) and red (Lhotse Shar glacier debris) dots and the Lhotse Shar lightly dust covered ice by the black X.
  • Fig. 5. ASTER SWIR radiance based mineral abundance maps of Ngozumpa supraglacial debris, clockwise from the top left, layered silicate, calcite, alunite and hydroxyl bearing. Cyan arrows on the layered silicate index point to evidence of pulse like glacial flow. The location of the transect used to investigate differing mineral abundances with respect to supraglacial temperatures in Fig. 7 are indicated by the white lines across Ngozumpa glacier.

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CITATION STYLE

APA

Casey, K. A., Kääb, A., & Benn, D. I. (2012). Geochemical characterization of supraglacial debris via in situ and optical remote sensing methods: A case study in Khumbu Himalaya, Nepal. Cryosphere, 6(1), 85–100. https://doi.org/10.5194/tc-6-85-2012

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