Subglacial drumlins and englacial fractures at the surge‐type glacier, Múlajökull, Iceland

Abstract

The interaction between drumlins and overriding glacier ice is not well studied, largely due to the difficulty of identifying and accessing suitable active subglacial environments. The surge‐type glacier Múlajökull, in central Iceland, overlies a known field of actively forming drumlins and therefore provides a rare opportunity to investigate the englacial structures that have developed in association with ice flow over the subglacial drumlins. In this study detailed ground‐penetrating radar surveys are combined with field observations to identify clear sets of up‐glacier and down‐glacier dipping fractures at Múlajökull's margin. These are interpreted as conjugate shear planes or P‐ and R‐type Reidel shears that developed and filled with saturated sediment derived from the glacier bed, during a previous surge. The fracture sets exhibit focused spatial distributions that are influenced by the subglacial topography. In particular, down‐glacier dipping fractures are strongly focused over drumlin stoss slopes. These fractures, although well developed at depth, were mostly unable to transmit basal water and sediment up to the glacier surface during the surge cycle. In contrast, up‐glacier dipping fractures formed over drumlin lee sides and in more gently sloping swales, and more frequently connected to the glacier surface, providing a pathway for the evacuation of basal water and water‐saturated sediment. The study suggests that the subglacial drumlins under Múlajökull's margin have influenced the nature and distribution of englacial fractures, which could potentially contribute to spatial variations in basal water pressure during a surge. BGS © UKRI 2018

Insights into drumlin development from ground-penetrating radar at Múlajökull, Iceland, a surge-type glacier

“…Additionally, the forefield's sediments have been characterized with analyses of lithostratigraphy (Johnson and others, 2010;Benediktsson and others, 2016), morphology (Benediktsson and others, 2016;Hillier and others, 2018) and strain and consolidation (McCracken and others, 2016). One finding of these studies is that the Múlajökull drumlins are small compared to most Pleistocene drumlins but fall within the size ranges of published drumlin datasets (Johnson and others, 2010;Benediktsson and others, 2016;Finlayson and others, 2019). Hence, by studying the formation of the Múlajökull drumlins we can gain insights into how Pleistocene drumlins formed.…”

“…Some drumlins at the margin of Múlajökull are only partially exposed by ice. On-ice radar surveys show that these drumlins extend beneath the ice and are therefore being affected by ongoing modern-day ice motion (Finlayson and others, 2019).…”

“…Múlajökull provides an opportunity to apply geophysical tools to a location where drumlin development is active and the forefield has been studied through a variety of field methods. Drumlins still under the ice (e.g., Lamsters and others, 2016; Finlayson and others, 2019) allow the observation of glaciological conditions that contribute to drumlin development. Additionally, the forefield's sediments have been characterized with analyses of lithostratigraphy (Johnson and others, 2010; Benediktsson and others, 2016), morphology (Benediktsson and others, 2016; Hillier and others, 2018) and strain and consolidation (McCracken and others, 2016).…”

High-Resolution Surface and Bed Topography Mapping of Russell Glacier (Sw Greenland) Using Uav and GPR

“…This approach is shown to be time and cost-effective for usage in Polar Regions where very detailed information about the ice surface and subglacial topography in a small area of interest is needed (e.g. Finlayson et al, 2018;Karušs et al, 2019).…”

Application of Unmanned Aerial Vehicles for Glacier Research in the Arctic and Antarctic

“…Different kinds of sensors and instruments are placed on satellites and aircrafts allowing mapping ice sheets in Greenland and Antarctica. The Randolph Glacier Inventory (RGI) provides a global inventory of glacier outlines [2]. Global Land Ice Measurements from Space project monitors the glaciers over the globe using data from optical satellite instruments [3].…”