The glacial landsystem of Fjallsjökull, Iceland: Spatial and temporal evolution of process-form regimes at an active temperate glacier

Abstract

This study assesses the spatial and temporal evolution of the glacial landsystem signature at Fjallsjökull, southeast Iceland, using (a) mapping of the glacial geomorphology and surficial geology and (b) repeat uncrewed aerial vehicle (UAV) surveys. A small-scale (1: 15,000 scale) landsystem map has been compiled using LiDAR data (2011−2012) and historical aerial photographs (1945–1998), along with a large-scale (1: 2000 scale) map based on UAV imagery from May 2019. From our mapping and UAV surveys, we identify sediment-landform assemblages that are typical of active temperate glacial landsystems, including recessional push/squeeze moraines and intervening flutings, overridden moraine arcs, proglacial outwash (sandur) fans and linear/ribbon sandar. We recognize three landform zones that are defined by changes in moraine morphology and the nature of proglacial outwash deposition: (1) the outer foreland is characterized by proglacial outwash fans, overridden moraine arcs and broadly linear recessional moraines; (2) the middle foreland contains sawtooth moraines and linear sandar; and (3) the innermost zone comprises extremely sawtooth and hairpin moraines as well as associated crevasse-squeeze ridge limbs. This landform zonation reflects spatio-temporal changes in moraine-forming processes and outwash deposition as determined by changes in snout morphology and proglacial drainage characteristics. Within this general tripartite zonation, we also identify localized (azonal/intrazonal) sediment-landform assemblages that are not typically found at active temperate glaciers, including ice-cored/hummocky terrain and localized kame and kettle topography. Repeat UAV surveying in 2016–2019 has allowed us to capture and quantify recent intrazonal landsystem change at the southern glacier margin. We identify a switch from moraine formation to the development of ice-cored terrain and an ice-cored esker complex in association with the uncovering of a depositional overdeepening. Our study demonstrates the important role that variations in local boundary conditions (e.g. topography) can play in the process-form response of individual active temperate outlet glaciers, contributing to the expanding database on modern glacial landsystems.