Digital landscapes of deglaciation: identifying Late Quaternary glacial lake outburst floods using LiDAR

Abstract

High resolution DEMs obtained from LiDAR topographic data have led to improved landform inventories (e.g. landslides and fault scarps) and understanding of geomorphic event frequency. Here we use airborne LiDAR mapping to investigate meltwater pathways associated with the Tweed Valley palaeo ice-stream (UK). In particular we focus on a gorge downstream of Palaeolake Milfield, previously mapped as a sub-glacial meltwater channel, where the identification of abandoned headcut channels, run-up bars, rock-cut terrace surfaces and eddy flow features attest to formation by a sub-aerial glacial lake outburst flood (GLOF) caused by breaching of a sediment dam, likely an esker ridge. Mapping of these landforms combined with analysis of the gorge rim elevations and cross-section variability revealed a two phase event with another breach site downstream following flow blockage by higher elevation drumlin topography. We estimate the magnitude of peak flow to be 1-3 × 10 3 m 3 /s, duration of the event to range from 16-155 days, and a specific sediment yield of 10 7 -10 9 m 3 /km 2 /yr. We identified other outburst pathways in the lower Tweed basin that help delineate an ice margin position of the retreating Tweed Valley ice stream. The results suggest that low magnitude outburst floods are under-represented in Quaternary geomorphological maps. We therefore recommend regional LiDAR mapping of meltwater pathways to identify other GLOFs in order to better quantify the pattern of freshwater and sediment fluxes from melting ice sheets to oceans. Despite the relatively low magnitude of the Till outburst event, it had a significant impact on the landscape development of the lower Tweed Valley through the creation of a new tributary pathway and triggering of rapid knickpoint retreat encouraging new regional models of post-glacial fluvial landscape response.

Reconstructing glacial outburst floods (jökulhlaups) from geomorphology: Challenges, solutions, and an enhanced interpretive framework

“…Accurate studies of some flood features, such as bedrock scour marks, boulder morphology, and sediment stratigraphy, can only happen at a sub-meter scale. Field mapping is also often necessary to assess landform and sediment equifinality and preservation (Thorndycraft et al, 2016).…”

“…Van Vliet-Lanoë et al (2020) Iceland Ice-dammed lake drainage along Hvítá River Tómasson (1993Tómasson ( , 2002 Greenland Ice-dammed marginal lake drainage, Russell Glacier Carrivick et al (2013a); Russell (2009); Russell et al (2011) Greenland Ice-dammed lake drainage, Zackenberg River ; United Kingdom Marginal lake drainage, Palaeolake Milfield, British-Irish Ice Sheet Thorndycraft et al (2016)…”

“…Different landforms are optimally identified and mapped at different spatial scales using a variety of methods. A single landform or depositional sequence can also yield diverse information when interpreted at multiple resolutions; for example, satellite imagery may be used to delineate sandur extent, but field investigation is necessary to study sandur sediment stratigraphy (Chandler et al, 2018; Thorndycraft et al, 2016).…”

Engineering geological mapping using airborne LiDAR datasets – an example from the Vinodol Valley, Croatia

“…Grebby et al, 2010;Notebaert et al, 2009;Paine et al, 2018;Sarala et al, 2015;Webster et al, 2006), identification and mapping of landslides (e.g. Bell et al, 2012;Bernat Gazibara et al, 2019;Chigira et al, 2004;Eeckhaut et al, 2007;Görüm, 2019;Jagodnik et al, 2020a;Petschko et al, 2016;Schulz, 2007), soil erosion processes (Baruch & Filin, 2011;Đomlija et al, 2019a;James et al, 2007), coastal (Biolchi et al, 2016;Sander et al, 2016) and glacial landforms (Smith et al, 2006;Thorndycraft et al, 2016), river valley environments (Jones et al, 2007), and active faults (Chen et al, 2015). However, the literature reveals that there is still a lack of studies that demonstrate the potential of HR LiDAR DTM for preparation of the comprehensive engineering geological maps in a large scale, in geologically and morphologically complex areas covered by dense forest vegetation.…”

Identification and Mapping of Soil Erosion Processes Using the Visual Interpretation of LiDAR Imagery

“…Notebaert et al [33] tested the possibilities for mapping of channel patterns, colluvial hillslopes, and fan deposits. Analysis of airborne LiDAR imagery has also been successfully used for identification and mapping of superficial deposits [34], logjams [35], and late Quaternary glacial lake floods [36]. Within most of the visual analyses, the hillshade map has been commonly used as the basic map e.g., [21,23,37], in some cases as the only map used [31,38], but it has been mostly visually analyzed in combination with the slope map and the contour line map e.g., [23], the curvature maps e.g., [22], and the topographic roughness map e.g., [39].…”