Examining rates of glacial erosion, exhumation, and debris evacuation over a wide range of time scales at Khumbu Basin, Mt. Everest, Nepal

Abstract:

New data from the glaciated Khumbu Basin at the base of Mt. Everest define erosion rates over two time scales: contemporary (decades) and the Holocene (~10⁴ years). The rates are derived by examining the flux of rock debris on and within Khumbu Glacier, the volume of stored debris in Khumbu Basin, and the rate of evacuation of suspended sediment through field studies and remote sensing. We find that contemporary and Holocene basin-averaged erosion rates range from 0.3 to 0.8 mm/yr, suggesting that erosion of Khumbu Basin has, on average, maintained a steady pace over time intervals ranging from 10² to 10⁴ years. Contemporary suspended sediment evacuation is, however, 50 times slower than the Holocene-averaged sediment production indicating that the bulk of the material eroded resides within the basin, consistent with geomorphic evidence of substantial accumulation of debris within the basin. Curiously, the basin-averaged erosion rates are similar to published long-term (O ~ 10⁷ yr) exhumation rates derived from thermochronometric data in the region, which reflect both erosional and tectonic exhumation. This similarity may be a coincidence, and it is surprising in view of likely changes in climate, structural development, and relief evolution. Regardless, these erosion and exhumation data provide valuable clues about the evolution of the highest topography on the planet.