Variations in hydraulic efficiency of the subglacial drainage landsystem control surging and streaming regimes of outlet glaciers

• Published in: Journal of Glaciology
• Main Authors: Édouard Ravier, Thomas Lelandais, Jean Vérité, Olivier Bourgeois
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press 2023
• Subjects: Drainage efficiency; experimental modelling; ice stream; ice surge; palaeoglaciology; Environmental sciences; GE1-350; Meteorology. Climatology; QC851-999; Journal of Glaciology
• Online Access: https://doi.org/10.1017/jog.2022.107; https://doaj.org/article/49b291ac6b6b4f6884e2bda11c064a65

Surging and streaming of glaciers are modulated by meltwater availability and pressure which controls mechanical coupling at their beds. Using laboratory-scale experimental modelling and palaeoglaciological mapping, we explore how subglacial drainage landsystems control meltwater drainage efficiency and ice flow velocities for terrestrial-based ice lobes resting on flat horizontal and permeable beds. Two end-members regimes, surging and streaming, appear in our experiments. The surge regime is characterised by a rapid increase of drainage efficiency through development of tunnel valleys and their tributaries, thus reducing the duration of ice flow speed-up events by lowering water pressures and increasing ice-bed coupling. Tunnel valleys connected to ice lobe margins, submarginal thrust moraines, reduced ice lobe extensions and ephemeral shear margins are the most distinctive characteristics of this regime. The stream regime is characterised by disconnected channels of smaller dimensions unable to evacuate all the meltwater: this prolonged drainage inefficiency leads to sustained high ice flow velocity and steady shear margins. Small and rectilinear meltwater channels devoid of tributaries, often disconnected from ice lobe margins, and lineation swarms are diagnostic of this regime.