Rapidly changing subglacial hydrological pathways at a tidewater glacier revealed through simultaneous observations of water pressure, supraglacial lakes, meltwater plumes and surface velocities

Douglas I. Benn,Heïdi Sevestre,Jack Kohler,Nicholas R. J. Hulton,Bryn Hubbard,Penelope How,Katrin Lindbäck,Adrian Luckman,Wim Boot,Ward J. J. van Pelt

doi:10.5194/tc-11-2691-2017

Abstract

Abstract. Subglacial hydrological processes at tidewater glaciers remain poorly understood due to the difficulty in obtaining direct measurements and lack of empirical verification for modelling approaches. Here, we investigate the subglacial hydrology of Kronebreen, a fast-flowing tidewater glacier in Svalbard during the 2014 melt season. We combine observations of borehole water pressure, supraglacial lake drainage, surface velocities and plume activity with modelled run-off and water routing to develop a conceptual model that thoroughly encapsulates subglacial drainage at a tidewater glacier. Simultaneous measurements suggest that an early-season episode of subglacial flushing took place during our observation period, and a stable efficient drainage system effectively transported subglacial water through the northern region of the glacier tongue. Drainage pathways through the central and southern regions of the glacier tongue were disrupted throughout the following melt season. Periodic plume activity at the terminus appears to be a signal for modulated subglacial pulsing, i.e. an internally driven storage and release of subglacial meltwater that operates independently of marine influences. This storage is a key control on ice flow in the 2014 melt season. Evidence from this work and previous studies strongly suggests that long-term changes in ice flow at Kronebreen are controlled by the location of efficient/inefficient drainage and the position of regions where water is stored and released.

Highlights

Subglacial hydrological processes at tidewater glaciers remain poorly understood due to the difficulty in obtaining direct measurements
Subglacial hydrology has been examined at a tidewater glacier in Svalbard using direct measurements of basal water pressure in conjunction with measurements of hydrological components, modelled components and surface velocities derived from TerraSAR-X imagery
Two key events occur at Kronebreen which provide insights into the hydraulic regime during the 2014 melt season: (1) an upglacier-propagating drainage event over a significant region of the glacier tongue, with simultaneous measurements suggesting this was an episode of early-season subglacial flushing which occurred within a 3-day period (25–28 June) over a distance of 5 km; (2) An unusually high-rainfall event in midSeptember which re-activated the subglacial drainage system www.the-cryosphere.net/11/2691/2017/

Summary

Introduction

Subglacial hydrological processes at tidewater glaciers remain poorly understood due to the difficulty in obtaining direct measurements. The presence of subglacial meltwater is understood to govern the basal water pressure at the bed of a glacier (Meier et al, 1994; Bartholomew et al, 2010). Hubbard et al, 1995; Lefeuvre et al, 2015) Temporal variations, such as diurnal oscillations and rapid changes (i.e. changes between 0 and 12 h), have been linked to changes in subglacial hydrology, such as conduit growth, reorganisation of meltwater pathways and pulsing related to episodic ice motion It has been attributed to basal hydraulic systems that do not operate at atmospheric pressure, such as at laketerminating and tidewater glaciers, where there is an inefficient evacuation of meltwater, because the hydraulic gradient is small (e.g. Sugiyama et al, 2011)

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