Drumlins Research Articles

LITHOSTRATIGRAPHY AND DISTRIBUTION OF TILLS IN THE SAADJÄRVE DRUMLIN FIELD, EAST-CENTRAL ESTONIA

Middle and Upper Pleistocene till beds with stratified glaciofluvial and glaciolacustrine deposits constitute the structure of the drumlins in the Saadjarve Drumlin Field. The only interglacial deposits of the area belong to the Karukula Formation (Holsteinian) at the distal end of the drumlin field. The differences in grain-size distribution, mineralogical and chemical composition are regarded as confirmation of the crucial role of compositional characteristics in determining the stratigraphy of these tills. Analysis shows that the Upper Sangaste (Elsterian) till, the oldest in the area, as well as the Valgjarve (Lower Weichselian) and Vortsjarve (Upper Weichselian) tills have distinct compositional characteristics. The Lower and Upper Ugandi (Saale glaciation) tills have no lithological differences; thus there may be only one Saalian till in the area. The stratigraphy and distribution of tills in the Saadjarve Drumlin Field proves an accretionary origin of these drumlins. They started to form during Saale glaciation and the formation process lasted for several glacial advances.

Morphology, internal structure and genesis of the Burtnieks drumlin field, Northern Vidzeme, Latvia

The Burtnieks drumlin field is one of the largest in the Baltic countries. It occupies a broad and uneven bedrock macrodepression. The uneven distribution of drumlins is related to the relief of the bedrock surface. Needle-shaped drumlinoids occur in the proximal part of the drumlin field, and they gradually merge into typical drumlin forms downglacier. This morphologic change reflects the differences in their genesis as suggested by internal structure. The cores of drumlins consist mainly of glaciotectonically deformed Pleistocene sediment and, in some places, also weakly cemented, dislocated Middle Devonian sandstone. All of them are folded into linear anticlines trending parallel to the crests of drumlins. These anticlines contain the remains of preceding subglacial deformation structures. Superimposed imbricate overthrusts cover the flanks of drumlins. Drumlinoids contain diapiric folds in their cores, trending parallel to their axes. The Burtnieks drumlin field was formed during the last activation of the North Vidzeme tongue and three main phases may be distinguished in the development of its glaciotectonic structures. Two alternative genetic hypotheses are proposed for the formation of this drumlin field, both involving multiphase glaciotectonic deformation.

Drumlin evolution and ice sheet oscillations along the NE Atlantic margin, Donegal Bay, western Ireland

Satellite imagery of Donegal Bay, northwestern Ireland, reveals two streamlined subglacial bedform sets produced during the late Devensian glaciation (ca. 22,000–15,000 yrs B.P.). The first bedform set trends northeast-southwest and records fast ice flow from inland ice domes onto the eastern Atlantic continental shelf. The second bedform set, trending east-west, crosscuts and partially reorientates the first. Morphological and sedimentary evidence show that the second set corresponds to the last phase of fast ice flow (drumlinization) in northwestern Ireland. Morphological characteristics of the Donegal Bay drumlin field, and sedimentary characteristics of the Mullinasole drumlin, Donegal Bay, support a two-stage interpretation of drumlin evolution. These are the following. (1) Deposition of glaciomarine mud and diamict facies at a tidewater glacier margin. Stratified diamicts record debris flow events and sediment reworking. This facies sequence is erosionally truncated. (2) Deposition of subglacial diamict and sand facies recording ice readvance and drumlinization. Drumlinization (sediment streamlining) reflects ice mass-balance destabilization, episodic: fast ice flow and ice-marginal oscillation, and may be correlated with millennial-time scale climate changes in the circum-North Atlantic.

Evidence, from microstructures, of deformable bed conditions within drumlins, Chimney Bluffs, New York State

Discussion on the process of drumlin formation has been ongoing for over a century. At present, two dominant schools of thought prevail, viz. formation by (a) subglacial hydraulic mechanisms, and (b) due to subglacial sediment deformation. The latter mechanism depends on the existence of a subglacial deformable bed. Evidence from part of the large central New York drumlin field reveals evidence of syn-depositional deformation during the emplacement of diamictons that constitute the major portion of drumlins exposed along shore bluffs in Chimney Bluffs State Park. These diamictons cannot be lodgement till facies members but appear to comprise facies indicative of melange-style deposition under subglacial deformable bed conditions. The evidence obtained from microstructures and plasma fabric within these diamictons supports the existence of a deformable bed during diamicton emplacement. It is likely that formation of the drumlins occurred under these same subglacial bed conditions.

Glasgow's drumlins

Glasgow's drumlins

Ice-flow history and glacial dispersal patterns, southeastern Cape Breton Island, Nova Scotia: implications for mineral exploration

Regional till sampling and stratigraphic studies were completed in southeastern Cape Breton Island, Nova Scotia, in 1990 and 1991 to document the directions and distances that successive ice-flow events have dispersed material and to document regional till geochemical patterns to aid mineral exploration in this heavily drift-covered area. Three major Wisconsinan ice-flow events affected the area: an early eastward flow, followed by a northeastward flow, and finally a southward flow. The shape and magnitude of dispersal trains in the area are the net result of the three ice-flow events, which are variable from north to south. In the north, the northeast ice flow was the dominant erosive and depositional event, producing a large northeast-trending drumlin field. Salmon River porphyry clasts and Pb- and Zn-rich till from the Yava Pb mine were dispersed more than 15 km to the northeast. In the south, eastward ice flow was the dominant erosive and depositional event, producing large east-trending till ridges. Dispersal in this area is difficult to detect because exotic red silty till in the giant till ridges masks underlying mineralized bedrock and dilutes the locally derived glacial debris. Many precious and base metal anomalies and dispersal trains were identified in the regional till samples, several of which are related to unknown mineralized sources.

Evidence of ancient continental glaciation in the Martian northern plains

Whorled ridges, spaced about 2–6 km and forming lobate patterns with lobe widths of about 150 km, occur at many locations in the northern plains of Mars, commonly in close association with sinuous troughs that contain medial ridges. These landforms resemble moraines, tunnel channels, and eskers found in terrestrial glacial terrains, such as the midcontinent of North America. Some Martian landscapes may have formed by disintegration of continental glaciers that covered much of the northern plains into the early Amazonian (i.e., late in Martian geologic history). Meltwater processes apparently were important in the collapse of these hypothesized ice sheets; hence, the glaciers apparently were wet based in part. Whereas striking similarities exist among areas of the northern plains and some glaciated Pleistocene terrains on Earth, there are also important differences; notably, drumlin fields, such as those in many glacial landscapes on Earth, are rare, absent, or not yet resolved in images of the Martian northern plains. Another major difference is that postglacial fluvial and other water‐related modifications (especially erosion) of Pleistocene terrains are substantial, but similar modifications are not observed in the northern plains; a virtually complete and sudden decline in the activity of liquid surface water following glaciation in the northern plains seems to be implied. The climatic implications of the hypothesized Martian glaciers and their decline are unclear. We investigate two possibilities, alternatively involving a relatively warm paleoclimate and the modern Martian climate. The hypothesized ice sheets in the basins within the northern plains (generally at elevations lower than −1 km) suggest a relationship of these frozen bodies of water with former regional lakes or seas, which may have formed in response to huge discharges of water from Martian outflow channels. This possible relationship has been modeled. Glaciers may have evolved from seas by their progressive freezing and then grounding and sublimational redistribution of sea ice. The transition to glaciation may have taken several million years if the climate was very cold, comparable to today's, or tens of thousands of years if the climate was as warm as modern Antarctica. A glacierized sea may have involved an extended period of glaciolacustrine and ice shelf processes.

Physical environment of drumlin formation

AbstractReview of published descriptions of drumlin fields suggests that the following conditions are important to drumlin growth: (1) compressive longitudinal and possibly extending transverse strain rates in the ice, (2) thin ice such as occurs near the glacier margin, and (3) high pore-water pressure in the subglacial sediments. Most drumlin fields display all of these, and no fields of well-developed drumlins were found that did not. On the oilier hand, the lithology of drumlin-forming sediment appears not to be important in promoting drumlin growth, since it varied widely, nor are the lithology and large-scale topography of the bed.

Physical environment of drumlin formation

AbstractReview of published descriptions of drumlin fields suggests that the following conditions are important to drumlin growth: (1) compressive longitudinal and possibly extending transverse strain rates in the ice, (2) thin ice such as occurs near the glacier margin, and (3) high pore-water pressure in the subglacial sediments. Most drumlin fields display all of these, and no fields of well-developed drumlins were found that did not. On the oilier hand, the lithology of drumlin-forming sediment appears not to be important in promoting drumlin growth, since it varied widely, nor are the lithology and large-scale topography of the bed.

The shape of drumlins, their distribution in drumlin fields, and the nature of the sub-ice shaping forces

This paper examines attempts to define and interpret drumlin shape; in particular the Chorley lemniscate and the Reed—Galvin—Miller ellipsoid. It also considers the Koenderink approach to describing shape, which ignores statistically defined shapes and concentrates on arbitrary smooth lumps of three-dimensional space. The basic shape of a drumlin at first sight appears to offer no clue to the rightness of any of the hypotheses or conjectures about drumlin formation. The shape suggests that a flowing fluid erodes the parts of landscape which have a lower shear strength than the adjacent parts. However, by considering whether the fluid is ice (very viscous) or water (less viscous), it is suggested that it is possible to distinguish between a drumlin formed by deformation and a drumlin formed by basal water erosion, by identifying subtle shape differences produced by different flow regimes. We find little indication, either from drumlin shape or disposition of drumlins in fields, that the basal water erosion mechanism causes the formation of drumlins. Observations of the growth and break-up of bubbles rising through a fluid may serve as an appropriate analogy for describing drumlin growth and eventual break-up. This bubble model is useful in suggesting an accretion model for drumlin growth and predicting that the form of a drumlin before break-up is similar to a spherical cap or parabolic drumlin. The bubble model and observation of flow past obstacles at very low Reynolds numbers suggest that a minimum resistance shape is not always a lemniscate. The variation of the critical stress and strength parameters across a drumlin field (essentially perpendicular to the ice-flow direction) suggests that the distribution could be zonal, that across a drumlin field a change in drumlin density should occur. Considering the drumlins as a whole-field phenomenon the “dimpled” surface of the drumlin swarm may actually reduce drag.

Drumlins of the Puget Lowland, Washington State, USA

The last advance of the Puget Lobe, a piedmont glacier that extended southward down the axis of the fjord-like Puget Lowland from the main mass of the Cordilleran Ice Sheet, produced an extensive drumlin field approximately 170 km in length and nearly 100 km wide. The timing of both the advance and retreat of the lobe across the region is well constrained, and took no more than a total of 1500 years. In the southern portion of the field, drumlin axis orientations are more closely perpendicular to recessional ice margin positions than to the reconstructed ice-maximum surface contours. This suggests that the drumlin field was formed in a time-transgressive manner as the ice front retreated from south to north, and that each of the numerous recessional phases was characterised by a narrow drumlin-forming zone that extended no more than a few kilometres back from the margin. This would also indicate that only a few decades were required for the formation of individual drumlins in the Puget Lowland.The drumlin forms are composed of compact till that overlies and truncates a 100 m thick sand and gravel unit. The sand has been interpreted as proglacial outwash, originally formed as a continuous blanket deposited in front (south) of the advancing Puget Lobe. It forms the main component within the lower 10–50% of the drumlin till, while farther-travelled components appear in progressively greater proportion with increasing height above the contact. The drumlins are thus interpreted as being of constructional origin. Evidence of minor subglacial meltwater activity occurs in the form of scattered, discontinuous water-sorted lenses interbedded throughout the till.The entire drumlin field is subdivided into a series of sub-parallel regions separated by deep troughs that extend to depths as great as 850 m below the drumlin-capped upland surface. Regional relationships indicate that the drumlins and the troughs formed contemporaneously, but that both post-date the deposition of the outwash. Thus, drumlin formation (net subglacial deposition) beneath some portions of the Puget Lobe was accompanied by simultaneous selective linear erosion in adjacent regions. This intense erosion may have been due in part to excavation by concentrated subglacial water flow, in contrast to the minor effects of subglacial water beneath the drumlin-forming portions of the ice sheet. Such fluvially enhanced subglacial erosion would be consistent with previous estimates of high sliding velocity and resultant large volume of meltwater production for the short-lived Puget Lobe.

Drumlin location as a response to bedrock topography on the southeastern slope of the Fennoscandian Shield

There are several thousand drumlins in Estonia, northern Latvia and on the bottom of the Gulf of Finland. Drumlins occur most frequently behind bedrock elevations, on the slopes of which they form huge crag-and-tail formations, and in marginal areas of depressions where the monolithic glacier disintegrated into tongues which moved at different velocities. A dense net of boreholes and detailed geophysical measurements showed that even small irregularities of the bedrock topography and slight variations in the resistance of bedrock to glacial erosion exerted remarkable influence upon the location, shape and internal structure of drumlins and drumlin-like forms. This accounts for the occurrence of drumlins with distinctly different structures within the same drumlin field. However, the drumlins were formed in a variety of ways and at different times under the effect of glaciers with different thickness. In most cases they seem to have formed near the ice margin under rather thin glacier ice during its rapid advance when the dynamics of the ice responded to topographical peculiarities.

The Kaituri drumlin and drumlin stratigraphy in the Kangasniemi area, Finland

The Kangasniemi research area is part of the extensive Pieksämäki drumlin field situated in central Finland. The most common drumlin types in the Kangasniemi area are rock-cored drumlinoids, drumlin shields, and till-cored drumlins. These landforms are composed of sandy till showing well-developed fissility, shear planes, and a range of stratified structures. Till fabrics in the drumlins are strongly oriented and indicate changes in ice flow that occurred during drumlin formation. The drumlins were formed in the late phase of the Weichselian glaciation under a quick and strong southeasterly ice flow. The drumlins in the Kangasniemi area are mainly the result of deposition during ice flow. Accumulation of material occurred around rock or till cores. Ice flow erosion had only an effect on the uppermost part of the drumlins. A clear example of the material accumulation is the “onion-shaped” structure of the Kaituri drumlin.

Drumlins in ice sheet reconstructions, with reference to the western Pennines, northern England

Drumlin morphology and distribution can be used to determine the palaeoglaciological conditions under which subglacial bedforms were created by Late Pleistocene ice sheets. Detailed field mapping of part of the large drumlin fields in northern England, in particular the identification of areas of superimposed drumlins, has been shown to be of significance in the delimitation of the ice divide within the area. The overall distribution of the subglacial bedforms has also been used to define the extent of ice streams within this part of the Late Devensian (Dimlington Stadial) ice sheet. Based on the physical principles which underlie the deformational model of drumlin formation and present-day glaciological information on subglacial ice sheet conditions, variations in drumlin morphology have allowed a first attempt at reconstructing areas of high (> 100 kPa) and low (< 20 kPa) basal driving stresses for this part of the ice sheet.

Episodic ice streams and ice shelves during retreat of the northwesternmost sector of the late Wisconsinan Laurentide Ice Sheet over the central Canadian Arctic Archipelago

A complex of glacial landforms on northeastern Victoria Island records diverse flows within the waning late Wisconsinan Laurentide Ice Sheet over an area now divided by marine straits. Resolution of this ice flow pattern shows that dominant streamlined landforms were built by three radically different ice flows between 11,000 and 9000 BP. Subsequent to the glacial maximum, the marine‐based ice front retreated at least 300 km to reach northeast Victoria Island by 10,400 BP. Disequilibration at the rapidly retreating margin induced minor surges on western Storkerson Peninsula (Flow 1). Next, a readvance into Hadley Bay transported 10,300 BP shells, while a major ice stream over eastern Storkerson Peninsula (Flow 2) remoulded till into a drumlin field several hundred kilometres long and at least 80 km wide until flow ceased prior to 9600 BP. The ice stream surged into Parry Channel, covering 20,000 km2 with the Viscount Melville Sound Ice Shelf. Finally, Flow 2 drumlins on the northwest shore of M'Clintock Channel were cross‐cut c. 9300 BP by advance of the grounded margin of a buoyant glacier (Flow 3), possibly an analogue of Flow 2 displaced farther south.

Tunnel channels and associated landforms, south-central Ontario: their implications for ice-sheet hydrology

The Peterborough–Trenton drumlin field and associated meltwater erosion marks (s-forms) were interpreted as the products of erosion by turbulent separated flows within a catastrophically released subglacial meltwater sheet, the Algonquin event. Recent theoretical modelling of ice-sheet hydrology suggests progressive channelization of meltwater during the collapse of such a sheet. Inductive testing of this hypothesis using observations in south-central Ontario forms the crux of this paper. A geometric model of the interaction of rough ice base and bed surfaces gives inferred meltwater flow patterns. Such a rough interactive geometry is suggested as the bed is drumlinized, and flows responsible for drumlins may be expected to have eroded similar forms into the ice base. Three landforms in south-central Ontario; namely tunnel channels, megachannels, and late-stage sheet-flow scours, are described, and interpreted as evidence of progressive channelization and flow diversion processes, governed by the geometric interactions between the recoupling ice base and its bed and thermodynamic feedbacks within an increasingly discontinuous meltwater sheet. Some fields of transverse ridges within tunnel channels may record meltwater deposition towards the end of the Algonquin event. By contrast, eskers within tunnel channels record a return to seasonally driven meltwater drainage. The Dummer Moraine and the Oak Ridges complex are integrated into a new landform–vent sequence for south-central Ontario which provides a framework for further field testing.

The drumlin fields of the Novaya Zemlya‐Urals region and the Kara Sea center of glaciation

Abstract Assemblages of drumlins, crag‐and‐tail features, giant glacial grooves, and megaflutes—collectively termed “drumlin fields"—are described along the southwestern shorelines of the Kara Sea, i.e., southernmost Novaya Zemlya, Vaygach Island, the Yugorskiy Peninsula, and the Pay‐Khoy ridge. All these landforms were formed during one of the latest stages in glaciation in the Eurasian Arctic, radiocarbon dated at about 8.5 thousand years ago. At that late stage, the ice kept spreading out of the Kara Sea center, which is strongly suggested by the NE‐SW orientation of the landforms. This is consistent with the model of a continuous marine Eurasian ice sheet and contradicts the concepts of “restricted” and “diachronous” glaciation. The Kara center of glaciation turns out to be one of the most stable and long‐lived features of the Northern Hemisphere's glaciation.

Exceptionally long, narrow drumlins formed in subglacial cavities, North Dakota

An array of about 200 exceptionally long and narrow drumlins occurs in north‐central North Dakota. The most prominent of the drumlins is 27 km long, and their average length is between 2 km and 3 km. The drumlin field is closely associated with, and occurs immediately up‐glacier from, an extensive area of ice‐thrust topography. Most of the drumlin ridges have small glacier‐thrust masses at their heads. Internal structures are complex, but typically include large numbers of gravity faults, which dip away from the center of the drumlin ridges. Materials contained in the drumlins were transported from higher pressure areas beneath the glacier, inward toward lower pressure areas (cavities) by flowing, thrusting, squeezing and other processes. The close and systematic association of the long drumlins with nearby areas of ice‐thrust topography indicates a genetic tie; conditions that caused the glacier to form large ice thrusts also contributed to drumlin formation. Major factors involved in the formation of the drumlins were high porewater pressures in interbedded permeable and impermeable materials beneath a thin, swiftly flowing glacier, and the presence of areas of frozen ground near the margin of the glacier.

The 1992 Farrington Lecture: Drumlin Bedforms and Related Ice-Marginal Depositional Systems in Ireland

The Irish drumlin bell comprises a wide morphological range of subglacial bedforms which are best developed in lowland zones located mainly in northern and western sectors of the island. Stratigraphic evidence suggests that drumlinisation occurred around 17ka B.P. in response to fast ice flow from major centres of inland ice dispersion onto the continental shelf. Well-defined moraines and morainal banks bordering the drumlin fields indicate that drumlinisation was accompanied by a high basal debris flux to ice sheet margins which was resedimented in a variety of subaquaeous settings. Field observations indicate that the fast ice flow responsible for streamlining and sediment moulding was closely associated with intense marine downdraw, a decrease in basal effective pressures and a general lowering of ice sheet profiles during deglaciation. Deglacial mechanisms of this type help to explain the very rapid termination of the last glacial cycle because downdraw ice-stream drainage basins must expand in area i...

Glaciomarine facies from the western sector of the last British ice sheet, Malin Beg, County Donegal, Ireland

The coastal margins and mountainous core of County Donegal, Republic of Ireland have been areally scoured and deeply-eroded along structural lineaments by major Late Devensian ice streams which moved generally westwards onto the continental shelf. A raised glaciomarine sequence is selectively preserved along a gully at Malin Beg and comprises mud/muddy diamict, sand and diamict. (1) The mud, which was deposited from suspended sediment plumes, passes upwards into muddy diamict, which reflects an increase in ice-rafting. The muds contain a redeposited foraminiferal assemblage of ice-proximal origin pumped into the water column by jets reworking previously deposited outwash. The presence of Middle Devensian shells have been identified from the mud by amino-acid analysis. This suggests a Late Devensian age for the succession. (2) The overlying sand indicates an increase in traction current activity at the site. (3) There is a sharp planar contact between the sands and the overlying tabular diamict unit. (4) A surficial sheet of coarse-grained breccia is attributed to intense periglacial weathering along the slopes of Leahan mountain. This sequence and those at other sites in western Ireland (e.g. Belderg, Co. Mayo) provide a record of deep isostatic depression and sedimentation in a peripheral trough at the north-western margin of the last British ice sheet. Directional indicators including drumlin fields and major troughs indicate that the north-western sector of the ice sheet was drained by major ice-streams. These ended in calving bays. Ice marginal response to ice wastage depended largely on catchment factors such as the magnitude of the ice reservoirs and the length of flow lines. Ultimately calving led to accelerated ice flow and areal down draw and collapse of the north-western sector of the ice sheet.