Modelling the evolution of supraglacial debris and feedbacks with glacier mass change at Khumbu Glacier, Nepal Himalaya

The feedbacks between mass balance, ice flow and debris transport dramatically modify the response to climate change of debris-covered glaciers in comparison with climatically equivalent clean-ice glaciers. Although thick debris mantles have sustained glaciers at relatively low elevations as the climate warms, supraglacial debris promotes the development of ice cliffs and supraglacial ponds that become hotspots of ablation. As a result, debris-covered glaciers are rapidly losing mass in response to ongoing climate change. Thick debris mantles also alter the dynamic behaviour of mountain glaciers, enhancing mass loss in the upper ablation area and resulting in stagnation and then detachment of the debris-covered tongue from the accumulation area.We developed the higher-order ice flow model iSOSIA to include the feedbacks with mass balance and ice flow that result from the accumulation of supraglacial debris. We investigated the evolution of Khumbu Glacier in the Nepal Himalaya over the last 2,000 years and under projected climate change through 2200 CE. Simulations were evaluated against field and remote sensing data, including englacial borehole observations from the EverDrill project. Our results show that the thick debris mantling Khumbu Glacier no longer reduces mass loss compared to a climatically equivalent clean-ice glacier, and that dynamic detachment likely initiated during the early 20th Century. Projections of future mass change contain large uncertainties due to the complex feedbacks operating on debris-covered glaciers. Our simulations suggest that climate warming during this century will force Khumbu Glacier past dynamic thresholds that lead to sustained and substantial mass loss.
The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)