The slope of the breached channel controls potential flood volume of moraine-dammed lake outbursts

Glacial lake outburst floods (GLOFs) originating from breaches of moraine-dammed lakes represent serious risk in high mountain regions around the world, as recently exemplified by the 2023 South Lhonak GLOF. Informed disaster risk reduction requires reliable modelling inputs. While computational capacities and modelling tools improved greatly in past years, some of the key input parameters remain poorly addressed. Among these, the estimation of realistic potential flood volume represents a major challenge. To bridge this gap, we compiled a dataset of breached moraine-dammed outbursts and calculated mean slope of the breached channel after the GLOF, as it can be used to approximate breach depth / lake level drop and so volume. The mean slope of the breached channels in the dataset varies from 2.3° (Q0) to 19.5° (Q4), while Q1 is 3.1° and Q3 is 6.6° while the median (Q2) is 5.0° and the mean is 5.5°. We found that a little change in slope of the breached channel changes estimated potential flood volume substantially, especially in cases of rather flat wide dams, suggesting high sensitivity of predictive GLOF modelling studies to this parameter.

EGUsphere preprint: https://doi.org/10.5194/egusphere-2025-4136