A cross-validated three-dimensional model of an englacial and subglacial drainage system in a High-Arctic glacier

Lena U Hansen,Jan A Piotrowski,Douglas I Benn,Heidi Sevestre

doi:10.1017/jog.2020.1

Abstract

AbstractRecent speleological surveys of meltwater drainage systems in cold and polythermal glaciers have documented dynamic englacial and in some cases subglacial conduits formed by the ‘cut-and-closure’ mechanism. Investigations of the spatial distribution of such conduits often require a combination of different methods. Here, we studied the englacial drainage system in the cold glacier Longyearbreen, Svalbard by combining speleological exploration of a 478 m long meltwater conduit with a high-resolution ground penetrating radar (GPR) survey with two different centre-frequencies (25 and 100 MHz). The results yielded a 3-D documentation of the present englacial drainage system. The study shows that the overall form of englacial conduits can be detected from velocity−depth converted GPR data, and that the 3-D model can facilitate a method to pinpoint the reflections in a radargram corresponding with the englacial drainage system, although fine detail cannot be resolved. Visible reflections approximately parallel to the mapped englacial water drainage system likely result from sediment incorporated in the ice or from abandoned parts of the englacial drainage system.

Highlights

Due to the inaccessibility of the interior of glaciers, fewer studies have been carried out on englacial and subglacial meltwater systems than on supraglacial meltwater systems
The study shows that the overall form of englacial conduits can be detected from velocity−depth converted ground penetrating radar (GPR) data, and that the 3-D model can facilitate a method to pinpoint the reflections in a radargram corresponding with the englacial drainage system, fine detail cannot be resolved
By combining direct speleological exploration with GPR survey, we document a dynamic englacial meltwater drainage system in Longyearbreen formed by the ‘cut-and-closure’ mechanism

Summary

Introduction

Due to the inaccessibility of the interior of glaciers, fewer studies have been carried out on englacial and subglacial meltwater systems than on supraglacial meltwater systems. To address the issue of englacial conduit formation, new theories of routing supraglacial meltwater to the englacial and subglacial system have been proposed, one of them being the ‘cut-and-closure’ mechanism. This was first described by Vatne (2001) and later elaborated by Gulley and others (2009a), who observed that in crevasse-free areas of cold and polythermal glaciers (Longyearbreen, Svalbard and Khumbu Glacier, Himalaya) where sufficient meltwater generates an incision rate greater than the rate of surface ablation, englacial and occasionally subglacial channels can evolve from supraglacial streams that gradually cut through the glacier surface

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Conclusion