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- Chandler, Benjamin M. P., et al.
(författare)
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Sub‐annual moraine formation at an active temperate Icelandic glacier
- 2020
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Ingår i: Earth Surface Processes and Landforms. - : Wiley. - 0197-9337 .- 1096-9837. ; 45:7, s. 1622-1643
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents detailed geomorphological and sedimentological investigations of small recessional moraines at Fjallsjökull, an active temperate outlet of Öræfajökull, southeast Iceland. The moraines are characterised by striking sawtooth or hairpin planforms, which are locally superimposed, giving rise to a complex spatial pattern. We recognise two distinct populations of moraines, namely a group of relatively prominent moraine ridges (mean height ~1.2 m) and a group of comparatively low‐relief moraines (mean height ~0.4 m). These two groups often occur in sets/systems, comprising one pronounced outer ridge and several inset smaller moraines. Using a representative subsample of the moraines, we establish that they form by either (i) submarginal deformation and squeezing of subglacial till or (ii) pushing of extruded tills. Locally, proglacial (glaciofluvial) sediments are also incorporated within the moraines during pushing. For the first time, to our knowledge, we demonstrate categorically that these moraines formed sub‐annually using repeat uncrewed aerial vehicle (UAV) imagery. We present a conceptual model for sub‐annual moraine formation at Fjallsjökull that proposes the sawtooth moraine sequence comprises (i) sets of small squeeze moraines formed during melt‐driven squeeze events and (ii) larger push moraines formed during winter re‐advances. We suggest the development of this process‐form regime is linked to a combination of elevated temperatures, high surface meltwater fluxes to the bed, and emerging basal topography (a depositional overdeepening). These factors result in highly saturated subglacial sediments and high porewater pressures, which induces submarginal deformation and ice‐marginal squeezing during the melt season. Strong glacier recession during the summer, driven by elevated temperatures, allows several squeeze moraines to be emplaced. This process‐form regime may be characteristic of active temperate glaciers receding into overdeepenings during phases of elevated temperatures, especially where their englacial drainage systems allow efficient transfer of surface meltwater to the glacier bed near the snout margin.
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| 2. |
- Chandler, Benjamin M. P., et al.
(författare)
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The glacial landsystem of Fjallsjökull, Iceland : Spatial and temporal evolution of process-form regimes at an active temperate glacier
- 2020
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 361
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Tidskriftsartikel (refereegranskat)abstract
- This study assesses the spatial and temporal evolution of the glacial landsystem signature at Fjallsjiikull, 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 moraineforming processes and outwash deposition as determined by changes in snout morphology arid proglacial drainage characteristics. Within this general tripartite zonation, we also identify localized (atonal/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.
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