Progressive formation of modern drumlins at Múlajökull, Iceland: stratigraphical and morphological evidence

Benediktsson, Ívar Örn; Jónsson, Sverrir Aðalsteinn; Schomacker, Anders; Johnson, Mark D.; Inǵólfsson, Ólafur; Zoet, Lucas K.; Iverson, Neal R.; Stötter, Johann

doi:10.1111/bor.12195

Cited by 34 publications

(96 citation statements)

References 52 publications

(174 reference statements)

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“…They occur in fields covering large areas that were previously occupied by ice sheets (Menzies et al, 2018). They have also been observed under contemporary ice streams (Domack et al, 2006;King et al, 2007King et al, , 2009Smith et al, 2007;Smith and Murray, 2009;Spagnolo et al, 2014) and surge-type outlet glaciers (Johnson et al, 2010;Benediktsson et al, 2016;Lamsters et al, 2016). They have also been observed under contemporary ice streams (Domack et al, 2006;King et al, 2007King et al, , 2009Smith et al, 2007;Smith and Murray, 2009;Spagnolo et al, 2014) and surge-type outlet glaciers (Johnson et al, 2010;Benediktsson et al, 2016;Lamsters et al, 2016).…”

Section: Introductionmentioning

confidence: 93%

An erosional origin for drumlins of NW Poland

Hermanowski

Piotrowski

Szuman

2019

Earth Surf Processes Landf

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Drumlins are landforms essential to understanding of ice sheet movement over soft beds, sediment transport along the ice/bed interface, and the formation of a wide range of glacial deposits. Although investigated more than any other glacial landform, the origin of drumlins remains contentious. Using high‐resolution LiDAR imagery and field data, we investigate the geomorphology and internal composition of one of the biggest drumlin fields in the North European Lowland. The Stargard drumlin field consists of over 1300 drumlins and related streamlined subglacial bedforms in a terminal part of a major Weichselian palaeo‐ice stream of the southern Scandinavian Ice Sheet. The drumlins are typically 600‐800 m long, 200‐250 m wide, 3‐6 m high and have axial elongation ratios ~2 but in some cases exceeding 15. Several subzones inferred from drumlin morphometry exist reflecting different ice flow dynamics. The most elongated drumlins occur in areas where ice moved down‐slope and where thick fine‐grained deposits of low hydraulic conductivity occur in the substratum. The largest portion of land occupied by drumlins and the greatest frequency density of drumlins occur where the ice moved up‐slope. Stargard drumlins are composed of a wide variety of glacial deposits including various types of tills and meltwater sediments, which range from undisturbed to heavily deformed. There is no correlation between the deposits in the drumlins and the drumlin forms indicating that the deposits pre‐date the drumlinizing process. It is suggested that the drumlin field was generated by a combination of direct glacial erosion and subglacial meltwater erosion by removing antecedent material from the inter‐drumlin areas and streamlining the resultant bumps. Our data support the search for a unifying theory of drumlin formation and suggest erosion as the most plausible single mechanism generating drumlin landscapes. © 2019 John Wiley & Sons, Ltd.

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Section: Introductionmentioning

confidence: 93%

An erosional origin for drumlins of NW Poland

Hermanowski

Piotrowski

Szuman

2019

Earth Surf Processes Landf

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“…The piedmont, warm‐based glacier, Múlajökull, an outlet glacier of the Hofsjökull ice cap, has surged eight times since 1924, with quiescence periods of 5–30 years (Björnsson et al, ). Evidence of earlier surges in the form of multiple end moraines is ubiquitous, including the glaciotectonic Little Ice Age terminal moraine that formed between 1717 and 1760 (Benediktsson et al, ; Jónsson et al, ). Most of the recent surges have resulted in glacier advances of 200–400 m, each leaving end moraines (Figure b; Benediktsson et al, ; Johnson et al, ).…”

Section: Observations At Múlajökullmentioning

confidence: 99%

“…Most of the recent surges have resulted in glacier advances of 200–400 m, each leaving end moraines (Figure b; Benediktsson et al, ; Johnson et al, ). The most recent surge in 2008 caused only a ~20 m advance but left a prominent glaciotectonic moraine (Benediktsson et al, ). The last major surge in 1992 terminated at approximately the same position as the three previous surges in 1954, 1972, and 1986 (Jónsson et al, ).…”

Section: Observations At Múlajökullmentioning

confidence: 99%

“…The drumlins occur in an arc‐shaped zone within ~1.2 km of the glacier margin (Figure ). More drumlins continue to be exposed as the margin recedes (Benediktsson et al, ; Johnson et al, ; Jónsson et al, ), and ground penetrating radar reveals that drumlins extend upglacier from the margin several hundred meters (Lamsters et al, ). Exposed drumlins were shaped by ice no farther than ~2 km from the former glacier margin at its maximum, as indicated by the position of the Little Ice Age terminal moraine (Figure b; e.g., Benediktsson et al, ; Jónsson et al, ).…”

Section: Observations At Múlajökullmentioning

confidence: 99%

“…Patterns of basal till movement and effective stress on the bed within and between drumlins are provided by, respectively, 2,200 measurements of till anisotropy of magnetic susceptibility (AMS) calibrated to laboratory ring shear experiments and a similar number of till‐density measurements calibrated to laboratory consolidation tests (McCracken et al, ). Additional guidance and constraints are provided by stratigraphic observations (Benediktsson et al, ; Johnson et al, ), observations and analyses of drumlin shape (Benediktsson et al, ; Jónsson et al, ) and forefield elevation (McCracken et al, ), ground‐penetrating radar data that bear on drumlin structure, and baseline glaciological data from Múlajökull (Björnsson et al, ; Minchew et al, ).…”

Section: Introductionmentioning

confidence: 99%

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A Theoretical Model of Drumlin Formation Based on Observations at Múlajökull, Iceland

et al. 2017

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The drumlin field at the surge‐type glacier, Múlajökull, provides an unusual opportunity to build a model of drumlin formation based on field observations in a modern drumlin‐forming environment. These observations indicate that surges deposit till layers that drape the glacier forefield, conform to drumlin surfaces, and are deposited in shear. Observations also indicate that erosion helps create drumlin relief, effective stresses in subglacial till are highest between drumlins, and during quiescent flow, crevasses on the glacier surface overlie drumlins while subglacial channels occupy intervening swales. In the model, we consider gentle undulations on the bed bounded by subglacial channels at low water pressure. During quiescent flow, slip of temperate ice across these undulations and basal water flow toward bounding channels create an effective stress distribution that maximizes till entrainment in ice on the heads and flanks of drumlins. Crevasses amplify this effect but are not necessary for it. During surges, effective stresses are uniformly low, and the bed shears pervasively. Vigorous basal melting during surges releases debris from ice and deposits it on the bed, with deposition augmented by transport in the deforming bed. As surge cycles progress, drumlins migrate downglacier and grow at increasing rates, due to positive feedbacks that depend on drumlin height. Drumlin growth can be accompanied by either net aggradation or erosion of the bed, and drumlin heights and stratigraphy generally correspond with observations. This model highlights that drumlin growth can reflect instabilities other than those of bed shear instability models, which require heuristic till transport assumptions.

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Using the size and position of drumlins to understand how they grow, interact and evolve

Ely

Clark

Spagnolo

et al. 2017

Earth Surf Processes Landf

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Drumlins are subglacial bedforms streamlined in the direction of ice flow. Common in deglaciated landscapes, they have been widely studied providing rich information on their internal geology, size, shape, and spacing. In contrast with bedform investigations elsewhere in geomorphology (aeolian and fluvial dunes and ripples for example) most drumlin studies derive observations from relict, and thus static features. This has made it difficult to gain information and insights about their evolution over time, which likely hampers our understanding of the process(es) of drumlin formation. Here we take a morphological approach, studying drumlin size and spacing metrics. Unlike previous studies which have focussed on databases derived from entire ice sheet beds, we adopt a space-for-time substitution approach using individual drumlin flow-sets distributed in space as proxies for different development times/periods. Framed and assisted by insights from aeolian and fluvial geomorphology, we use our metric data to explore possible scenarios of drumlin growth, evolution and interaction. We study the metrics of the size and spacing of 36 222 drumlins, distributed amongst 71 flow-sets, left behind by the former British-Irish Ice Sheet, and ask whether behaviour common to other bedform phenomena can be derived through statistical analysis. Through characterizing and analysing the shape of the probability distribution functions of size and spacing metrics for each flow-set we argue that drumlins grow, and potentially migrate, as they evolve leading to pattern coarsening. Furthermore, our findings add support to the notion that no upper limit to drumlin size exists, and to the idea that perpetual coarsening could occur if given sufficient time. We propose that the framework of process and patterning commonly applied to non-glacial bedforms is potentially powerful for understanding drumlin formation and for deciphering glacial landscapes.

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Progressive formation of modern drumlins at Múlajökull, Iceland: stratigraphical and morphological evidence

Cited by 34 publications

References 52 publications

An erosional origin for drumlins of NW Poland

An erosional origin for drumlins of NW Poland

A Theoretical Model of Drumlin Formation Based on Observations at Múlajökull, Iceland

Using the size and position of drumlins to understand how they grow, interact and evolve

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