Ablation of debris‐covered ice: some effects of the 25 September 2007 Mt Ruapehu eruption

Abstract

Abstract Melt rates of ice surfaces are strongly influenced by the existence of debris‐cover. Dependent on thickness, climate and physical properties of debris, a debris layer can enhance or reduce ablation, compared to bare ice conditions. Ice ablation on bare ice and under varying thicknesses of tephra was measured using a network of 12 ablation stakes drilled into the Summit Plateau ice field, Mt Ruapehu, from 17 January to 2 February 2008 in order to study how tephra from the 25 September 2007 eruption was affecting ablation. Observation of air temperature allowed the application of a simple positive‐degree‐day approach to the calculation of ablation rate factors, which for bare ice was 7.8 mm d −1 °C −1 , with a rate of 6.0 mm d −1 °C −1 mm for ice under 10 cm of tephra. Mean daily ablation rates varied from 116 mm d −1 on bare ice to 78 mm d −1 under tephra cover. Debris covers thicker than 70 mm reduced ablation.