Formation of murtoos by repeated flooding of ribbed bedforms along subglacial meltwater corridors

Late erosion pulse triggered by rapid melt in the cold‐based interior of the last Fennoscandian Ice Sheet, an example from Rogen

“…The anastomosing pattern and sharp boundaries of widespread hummock tracts and their close association with murtoos suggest large pulses of subglacial meltwater drainage through meltwater corridors (Öhrling et al, 2020;Peterson et al, 2017;Peterson Becher & Johnson, 2018;Rampton, 2000). We interpret the murtoos as a deposition of till (Peterson Becher & Johnson, 2021), reworked from ribbed moraines (Vérité et al, 2022), whereas the isolated mounds are interpreted as partly disintegrated ribbed moraines retaining bouldercovers and an unmoved core. The hummock tracts, corridors and murtoos were formed subglacially after the ribbed moraines and reflect warm-based conditions where the drainage system transitioned from distributed to channelized pathways (Ahokangas et al, 2021;Mäkinen et al, 2017;Ojala et al, 2019Ojala et al, , 2021.…”

“…We interpret the change from undisturbed till to, respectively, sharply defined ribbed moraines, modified ribbed moraines, and, eventually, hummocks and murtoos in given ribbed moraine fields, to be the result of increased meltwater drainage at the bed (e.g., Vérité et al, 2022). The sharp boundary between the ribbed moraines and hummock corridors suggests that the disintegration occurred locally, through liquefaction (Peterson Becher & Johnson, 2021), and possibly in combination with thawing of the core of the ribbed moraine.…”

“…With the increasing influx of meltwater, subglacial drainage pathways in topographic lows developed into meltwater corridors. Along those pathways, ribbed moraines were exposed to larger fluxes of water, and where they became saturated with water, the ridges breached and were reshaped into murtoo-related bedforms and/or hummock tracts (Vérité et al, 2022). During the erosion of ribbed moraines, boulders were redeposited and winnowed and formed local boulder fields directly down-ice (Borgström & Wastenson, 1983).…”

Advances in understanding subglacial meltwater drainage from past ice sheets

“…A recent body of work examining physical processes of and conditions for subglacial fluvial erosion, deposition and sediment mobility is an important step forward others, 2016, 2018;Damsgaard and others, 2017;Hewitt and Creyts, 2019;Kirkham and others, 2022;Stevens and others, 2022;Vérité and others, 2022). These studies build towards an integrated or continuum view of meltwater organization, depending on water supply and sources, basal conditions and substrate properties.…”

Variations in hydraulic efficiency of the subglacial drainage landsystem control surging and streaming regimes of outlet glaciers

“…Recent modelling developments have allowed the evolution of subglacial drainage type (channelized vs distributed) and ice flow dynamics to be experimentally monitored for wet-based and land-terminating outlet glaciers resting on permeable, erodible and deformable sedimentary beds (Lelandais and others, 2018; Vérité and others, 2021). The interplay between the subglacial drainage and ice dynamics have been modelled for unprecedented periods of time (potentially tens to hundreds years) corresponding to the formation and evolution of tunnel valleys (Lelandais and others, 2016), the lifecycle of ice streams (Lelandais and others, 2018) or the development of subglacial bedform fields (Vérité and others, 2021, 2022). The modelling approach is complementary to the morphometric and spatial analysis of exposed subglacial landscapes where tens to hundreds years of meltwater drainage and ice flow dynamics evolution have potentially been fossilised through assemblages of landforms (eskers, tunnels valleys and channels, moraines) and bedforms (streamlined and ribbed bedforms) assemblages (Kehew and others, 1999; Storrar and others, 2014; Lewington and others, 2020; Sharpe and others, 2021).…”