Magnetic fabrics of drumlins of the Green Bay Lobe, southeastern Wisconsin

Vreeland, Nicholas P.; Iverson, Neal R.; Graesch, Matthew; Hooyer, Thomas S.

doi:10.1016/j.quascirev.2015.01.015

Cited by 23 publications

(39 citation statements)

References 51 publications

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“…A comprehensive review of drumlin properties by Eyles et al (2016) led them to conclude that most drumlins indeed form in erosional regimes, although the process invoked in their analogy-based, conceptual model-abrasion at the base of a deforming layer-differs from the processes proposed here. As noted by many others (e.g., Gravenor, 1953;Menzies, 1979;Stokes et al, 2011;Vreeland et al, 2015), the diverse internal compositions of drumlins are generally more consistent with relief caused by erosion rather than by deposition. Erosional hypotheses, however, need to account for large volumes of sediment evacuated from the bed.…”

Section: Model Strengthssupporting

confidence: 63%

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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Section: Model Strengthssupporting

confidence: 63%

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

et al. 2017

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“…Macrofabrics in the lowermost metre of the diamicton ( Figure 8A) are highly clustered parallel to the long axis of the drumlin. A mean AMS eigenvalue of 0.71 is considered sufficient to reflect ice flow direction (Vreeland et al, 2015) which, similar to the macofabrics, corresponds with the direction of the drumlin's axis. Most clasts dip in the northern (up-ice) direction.…”

Section: Descriptionmentioning

confidence: 99%

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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“…Borradaile & Jackson 2010;Ferre et al 2014). Interestingly, no relationship between these parameters and strain has been demonstrated in ring-shear experiments of till Vreeland et al 2015); however, we still report and explore these metrics as useful descriptors of the individual sample's AMS ellipsoid. Following AMS analysis, a subset of samples from the eight primary fabric sites of the Dalby Till was disaggregated and their grain-size distributions determined.…”

Section: Field Settingmentioning

confidence: 85%

“…; Vreeland et al . ); however, we still report and explore these metrics as useful descriptors of the individual sample's AMS ellipsoid. Following AMS analysis, a subset of samples from the eight primary fabric sites of the Dalby Till was disaggregated and their grain‐size distributions determined.…”

Section: Methodsmentioning

confidence: 99%

“…Methods AMS provides a quantitative, robust and unbiased assessment of the orientation of non-equant magnetic mineral grains, and has been demonstrated to be a useful and reliable method for characterizing till fabric and interpreting ice-flow history and till kinematics in numerous field and laboratory settings (e.g. Hooyer et al 2008;Iverson et al 2008;Shumway & Iverson 2009;Thomason & Iverson 2009;Gentoso et al 2012;Vreeland et al 2015;Hopkins et al 2016). For nonequant grains, AMS can be controlled largely by shape, where the maximum susceptibility lies along the long axis of the grains (Tarling & Hrouda 1993); thus, AMS provides an effective proxy for the measurement of grain orientation.…”

Section: Field Settingmentioning

confidence: 99%

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An anisotropy of magnetic susceptibility (AMS) fabric record of till kinematics within a Late Weichselian low Baltic till, southern Sweden

Hopkins

Klemån

Evenson

et al. 2016

Boreas

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Herein we report on the results of an anisotropy of magnetic susceptibility (AMS) fabric case‐study of two Late Weichselian tills exposed in a bedrock quarry in Dalby, Skåne, southern Sweden. The region possesses a complex glacial history, reflecting alternating and interacting advances of the main body of the Scandinavian Ice Sheet (SIS) and its ice lobes from the Baltic basin, perhaps driven by streaming ice. AMS till fabrics are robust indicators of ice‐flow history and till kinematics, and provide a unique tool to investigate till kinematics within and amongst till units. The till section investigated here contains ~8 m of the Dalby Till – a dark grey silt‐clay rich till deposited during one or more Baltic advance – overlain by ~1.5 m of the regional surface diamicton. AMS fabrics within the lower part of the Dalby Till conform to the regional surface fluting, and reflect sustained flow from the ENE with progressive increases in basal strain. A boulder‐rich horizon approximately 3 m from the base of the till marks a restricted excursion in till fabric direction, fabric strength and style of strain. Ice flow is from the SW and W in the upper section. We interpret these fabrics to record shifting ice flow and bed conditions at the margins of the Young Baltic Advance ice lobe in southern Sweden, prior to a short‐lived re‐advance of the main body of the SIS over mainland Sweden recorded by the surface diamicton.

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Magnetic fabrics of drumlins of the Green Bay Lobe, southeastern Wisconsin

Cited by 23 publications

References 51 publications

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

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

An erosional origin for drumlins of NW Poland

An anisotropy of magnetic susceptibility (AMS) fabric record of till kinematics within a Late Weichselian low Baltic till, southern Sweden

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