Transport Direction of Peoria Loess in Nebraska and Implications for Loess Sources on the Central Great Plains

2001 ◽  
Vol 56 (1) ◽  
pp. 79-86 ◽  
Author(s):  
Joseph A. Mason
Keyword(s):  
Climatic Change ◽  
Great Plains ◽  
Source Region ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Secondary Sources ◽  
River Floodplains ◽  
Transport Direction ◽  
Loess Deposition ◽  
Ice Sheet Dynamics

AbstractIn the midwestern United States, large rivers draining the Laurentide Ice Sheet (LIS) were the most important sources of Peoria Loess, deposited during the last glaciation. Loess deposition near those rivers may have responded primarily to ice-sheet dynamics rather than direct effects of climatic change. In contrast, it has been proposed that thick Peoria Loess on the central Great Plains was derived mainly from unglaciated landscapes northwest of the main loess deposits. In this study, transport directions inferred from more than 600 measurements of Peoria Loess thickness in Nebraska are used to test the hypothesis that much of the Peoria Loess on the Great Plains is nonglaciogenic. A strong northwest to southeast thickness trend indicates that most Peoria Loess in Nebraska was transported from one or more unglaciated northwestern source areas rather than from glacially influenced river floodplains. The Missouri River (draining the LIS), the Platte River (draining alpine glaciers), and the Elkhorn River (unglaciated basin) were secondary sources. Their contribution is not detectable beyond a distance of 40–60 km. Peoria Loess deposition on the central Great Plains was largely a direct response to climatic change in the unglaciated source region.

scholarly journals LGM Summer Climate on the Southern Margin of the Laurentide Ice Sheet: Wet or Dry?*

2005 ◽  
Vol 18 (16) ◽  
pp. 3317-3338 ◽  
Author(s):  
David H. Bromwich ◽  
E. Richard Toracinta ◽  
Robert J. Oglesby ◽  
James L. Fastook ◽  
Terence J. Hughes
Keyword(s):  
Boundary Conditions ◽  
Great Plains ◽  
Land Surface ◽  
Thermal Gradient ◽  
Mesoscale Model ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Low Level ◽  
Summer Climate ◽  
Southern Margin

Abstract Regional climate simulations are conducted using the Polar fifth-generation Pennsylvania State University (PSU)–NCAR Mesoscale Model (MM5) with a 60-km horizontal resolution domain over North America to explore the summer climate of the Last Glacial Maximum (LGM: 21 000 calendar years ago), when much of the continent was covered by the Laurentide Ice Sheet (LIS). Output from a tailored NCAR Community Climate Model version 3 (CCM3) simulation of the LGM climate is used to provide the initial and lateral boundary conditions for Polar MM5. LGM boundary conditions include continental ice sheets, appropriate orbital forcing, reduced CO2 concentration, paleovegetation, modified sea surface temperatures, and lowered sea level. The simulated LGM summer climate is characterized by a pronounced low-level thermal gradient along the southern margin of the LIS resulting from the juxtaposition of the cold ice sheet and adjacent warm ice-free land surface. This sharp thermal gradient anchors the midtropospheric jet stream and facilitates the development of synoptic cyclones that track over the ice sheet, some of which produce copious liquid precipitation along and south of the LIS terminus. Precipitation on the southern margin is orographically enhanced as moist southerly low-level flow (resembling a contemporary Great Plains low-level jet configuration) in advance of the cyclone is drawn up the ice sheet slope. Composites of wet and dry periods on the LIS southern margin illustrate two distinctly different atmospheric flow regimes. Given the episodic nature of the summer rain events, it may be possible to reconcile the model depiction of wet conditions on the LIS southern margin during the LGM summer with the widely accepted interpretation of aridity across the Great Plains based on geological proxy evidence.

Age of the Berlin moraine complex, New Hampshire, USA, and implications for ice sheet dynamics and climate during Termination 1

2019 ◽  
Vol 94 ◽  
pp. 80-93
Author(s):  
Gordon R.M. Bromley ◽  
Brenda L. Hall ◽  
Woodrow B. Thompson ◽  
Thomas V. Lowell
Keyword(s):  
New England ◽  
New Hampshire ◽  
Global Climate ◽  
Ice Sheet ◽  
Atmospheric Temperature ◽  
Laurentide Ice Sheet ◽  
White Mountains ◽  
Southern New England ◽  
Ice Sheet Dynamics ◽  
St Lawrence River

AbstractAt its late Pleistocene maximum, the Laurentide Ice Sheet was the largest ice mass on Earth and a key player in the modulation of global climate and sea level. At the same time, this temperate ice sheet was itself sensitive to climate, and high-magnitude fluctuations in ice extent, reconstructed from relict glacial deposits, reflect past changes in atmospheric temperature. Here, we present a cosmogenic 10Be surface-exposure chronology for the Berlin moraines in the White Mountains of northern New Hampshire, USA, which supports the model that deglaciation of New England was interrupted by a pronounced advance of ice during the Bølling-Allerød. Together with recalculated 10Be ages from the southern New England coast, the expanded White Mountains moraine chronology also brackets the timing of ice sheet retreat in this sector of the Laurentide. In conjunction with existing chronological data, the moraine ages presented here suggest that deglaciation was widespread during Heinrich Stadial 1 event (~18–14.7 ka) despite apparently cold marine conditions in the adjacent North Atlantic. As part of the White Mountains moraine system, the Berlin chronology also places a new terrestrial constraint on the former glacial configuration during the marine incursion of the St. Lawrence River valley north of the White Mountains.

scholarly journals Modeling the Influence of Till Rheology on the Flow and Profile of the Lake Michigan Lobe, Southern Laurentide Ice Sheet, U.S.A.

1986 ◽  
Vol 32 (111) ◽  
pp. 235-241 ◽  
Author(s):  
James E. Beget
Keyword(s):  
Yield Strength ◽  
Great Plains ◽  
Lake Michigan ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Plastic Behavior ◽  
Mackenzie Delta ◽  
Western Great Plains ◽  
Basal Till ◽  
Lake Michigan Lobe

AbstractThe late Wisconsin Shelbyville till was deposited in southern Illinoisc. 20 000–21 000 year B.P. and records the maximum southern advance of the Lake Michigan lobe of the Laurentide ice sheet. The yield strength calculated for a representative till debris flow found just south of the ice margin is 8 kPa (0.08 bar), and probably approximates yield strength of basal Shelbyville till. An ice-profile model assuming plastic behavior in basal till suggests the southern Lake Michigan lobe may have been unusually thin. Reconstructed Laurentide glacier profiles from the south-west and western Great Plains (South Dakota, Alberta, Minnesota, and Montana), and the MacKenzie Delta, N.W.T., are similar to those inferred for the southern Great Lakes area, and much thinner than those of most modern ice sheets. The Pleistocene Laurentide ice sheet may have been asymmetric: thicker in the east than in the west. Glaciers resting on weak sediments can move both by subglacial sediment deformation (creep) and sliding at the sediment–ice interface. Till rheology is complex; shearing of till by over-riding glaciers would increase porosity and further reduce yield strength.

Surface exposure dating of the Pierre Sublobe of the James Lobe, Laurentide Ice Sheet

2020 ◽  
Vol 97 ◽  
pp. 88-98
Author(s):  
Stephanie L. Heath ◽  
Thomas V. Lowell ◽  
Brenda L. Hall
Keyword(s):  
Late Quaternary ◽  
Ice Sheet ◽  
Age Dating ◽  
Laurentide Ice Sheet ◽  
Des Moines Lobe ◽  
Exposure Dating ◽  
Des Moines ◽  
Contrast Exposure ◽  
Ice Sheet Dynamics ◽  
Exposure Ages

AbstractThe Laurentide Ice Sheet of the last glacial period terminated in several lobes along its southern margin. The timing of maximum extent may have varied among the terminal lobes owing to internal ice sheet dynamics and spatially variable external controls. Some terminal ice lobes, such as the westernmost James Lobe, remain poorly dated. To determine the timing of maximum ice extent in this key location, we have mapped glacial deposits left by the Pierre Sublobe in South Dakota and applied 10Be surface exposure age dating on boulders on moraine ridges associated with three distinct late Quaternary glacial drifts. The oldest and most extensive “Tazewell” drift produced variable 10Be surface exposure ages spanning 20–7 ka; the large range is likely attributable to moraine degradation and subsequent boulder exhumation. The oldest ages of about 20 ka are probably limiting minimum ages for the Tazewell moraine surfaces. By contrast, exposure ages of the youngest “Mankato” drift of the easternmost Pierre Sublobe tightly cluster at about 16 ka. This age for the Pierre Sublobe is consistent with the nearby Des Moines Lobe, suggesting both acted together.

scholarly journals Palaeo-ice streams in the northern Keewatin sector of the Laurentide ice sheet

2005 ◽  
Vol 42 ◽  
pp. 135-144 ◽  
Author(s):  
Hernán De Angelis ◽  
Johan Kleman
Keyword(s):  
Potential Role ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Baffin Island ◽  
Ice Streams ◽  
Relative Age ◽  
Ice Stream ◽  
Deep Interior ◽  
Ice Sheet Dynamics ◽  
Streaming Flow

AbstractEvidence for ice streams in the Laurentide ice sheet is widespread. In the region of northern Keewatin and the Boothia Peninsula, Nunavut, Canada, palaeo-ice streams have been recognized, but their location, size and potential role in ice-sheet dynamics are poorly constrained. Based on the interpretation of satellite imagery, we produce a palaeo-ice-stream map of this region. Glacial directional landforms, eskers and moraines were mapped and integrated into landform assemblages using a glacial geological inversion model. Palaeo-frozen bed areas were also identified. Relative age of the geomorphic swarms was assessed by cross-cutting relationships and radiocarbon ages where available. Using this information we obtained a glaciologically plausible picture of ice-stream evolution within the northernmost Laurentide ice sheet. On the M’Clintock Channel corridor, three generations of pure ice streams are found. On Baffin Island and the Gulf of Boothia, glaciation was dominated by frozen-bed zones located on high plateaus and ice streams running along the troughs, i.e. topographic ice streams. A massive convergent pattern at the head of Committee Bay drained ice from both the Keewatin and Foxe sectors and was probably one of the main deglaciation channels of the Laurentide ice sheet. Finally, our results indicate that streaming flow was present in the deep interior of the Laurentide ice sheet, as recently shown for the Greenland and Antarctic ice sheets.

scholarly journals The horned crag-and-tails of the Ungava Bay landform swarm, Quebec–Labrador, Canada

1999 ◽  
Vol 28 ◽  
pp. 168-174 ◽  
Author(s):  
Krister N. Jansson ◽  
Johan Kleman
Keyword(s):  
Spatial Distribution ◽  
Ice Sheet ◽  
Thermal Conditions ◽  
Unique Sequence ◽  
Laurentide Ice Sheet ◽  
Basal Sliding ◽  
Ice Sheet Dynamics ◽  
Basal Melting

AbstractTill lineations are widespread throughout the interior of Quebec—Labrador, Canada. We discuss a previously unrecognized lineation type, horned crag-and- tails, characterized by two till ridges at the lateral flanks of a bedrock crag. This lineation type appears to occur exclusively in the Ungava Bay lineation swarm and has not been reported from other glaciated shield areas. The morphology and spatial distribution of these peculiar landforms are analyzed in the context of Laurentide ice sheet dynamics in central Quebec—Labrador. We propose that a horned crag-and-tail ridge forms when the ice sheet is frozen to the summit of the crag, but basal melting occurs lower down on the crag. The lack of basal sliding at the summit of the crag inhibits till transport across the crag and prevents the accumulation of till in a direct lee-side position. The last phase of the formation is fossilization by basal freezing of the horned crag-and-tail system. This scenario requires that the ice sheet undergoes a transition from frozen-bed conditions to basal melting with frozen patches on topographical highs, and back to fully frozen-bed conditions. Horned crag-and-tails may thus indicate a unique sequence of basal thermal conditions over large areas of Quebec-Labrador.

scholarly journals Geomorphology and sedimentology of surging glaciers: a land-systems approach

1999 ◽  
Vol 28 ◽  
pp. 75-82 ◽  
Author(s):  
David J.A. Evans ◽  
Brice R. Rea
Keyword(s):  
Systems Approach ◽  
Ice Sheet ◽  
System Model ◽  
Laurentide Ice Sheet ◽  
Ice Streams ◽  
Sedimentary Sequences ◽  
Land System ◽  
Land Systems ◽  
Ice Sheet Dynamics ◽  
Diagnostic Criterion

AbstractThe identification of surging glaciers and ice streams in glaciated landscapes is of major importance to the understanding of ice-sheet dynamics and for reconstructing ice sheets and climate. No single landform or diagnostic criterion has yet been found with which to identify surging glaciers. A surging-glacier land-system model is constructed using observations and measurements from contemporary surging-glacier snouts in Iceland, Svalbard, U.S.A. and Canada for differentiating ancient surging margins from other non-surging palaeoglaciers. This integrates the suite of landforms, sediments and stratigraphy produced at surging-glacier margins. Landforms produced during surging include thrust moraines, concertina eskers and subglacial crevasse-squeeze ridges. Sedimentary sequences are usually characterized by multiple stacked diamictons and stratified interbeds, which display severe glaciotectonic contortion and faulting. Hummocky moraine, comprising interbedded stratified sediments and mass-flow diamictons, has also been associated with surge margins where large quantities of supraglacial and englacial debris entrained during the surge event have melted out in situ. An example of the application of the land-system model is presented for east-central Alberta, Canada. A surging palaeo-ice stream is identified within this part of the southwestern Laurentide ice sheet, where thrust-block moraines, crevasse-squeeze ridges, flutings, hummocky moraine and glaciotectonized sediments are juxtaposed.

scholarly journals Relict Late Wisconsinan Dune Fields of the Northern Great Plains, Canada*

2006 ◽  
Vol 58 (2-3) ◽  
pp. 323-336 ◽  
Author(s):  
Stephen A. Wolfe ◽  
David J. Huntley ◽  
Jeff Ollerhead
Keyword(s):  
Boreal Forest ◽  
Great Plains ◽  
Sand Dunes ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Northern Great Plains ◽  
The West ◽  
Air Mass ◽  
Late Wisconsinan ◽  
Dune Activity

Abstract Late Wisconsinan dune activity is investigated within the present-day boreal forest and parkland regions of the northern Great Plains, Canada, to extend the understanding of the spatial and temporal eolian record. Optical ages from stabilized sand dunes document the timing of past activity. Eolian activity ranges from about 16 ka in west-central Alberta to 9 ka in northwestern Saskatchewan. Between about 16 and 13 ka, dune activity in central Alberta occurred in an ice-proximal tundra setting along the margins of the Laurentide and Cordilleran ice sheets. Predominant dune-forming winds were from the west and northwest. Dune activity continued in this area between about 13 and 11 ka within parkland and grassland settings as the Laurentide Ice Sheet retreated to the northeast. Winds continued to blow from the west and northwest, and the climate was likely influenced by an increasingly dominant Pacific air mass. Also beginning at about 13 ka, dune-forming winds along the margins of the retreating Laurentide Ice Sheet were influenced by anticyclonic winds from the southeast that were maintained until about 9 ka. As the Laurentide Ice Sheet retreated, these southeasterly anticyclonic winds were successively replaced by winds from the northwest associated with the Pacific air mass. Dune activity across the region terminated in a time-transgressive manner from the southwest, at about 11 ka, to the northeast, at about 9 ka, with the establishment of boreal forest vegetation and reduced wind strength.

scholarly journals PISM-LakeCC: Implementing an adaptive proglacial lake boundary into an ice sheet model

2020 ◽  
Author(s):  
Sebastian Hinck ◽  
Evan J. Gowan ◽  
Xu Zhang ◽  
Gerrit Lohmann
Keyword(s):  
Boundary Conditions ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Hudson Bay ◽  
Ice Streams ◽  
Ice Flow ◽  
Glacial Retreat ◽  
Proglacial Lakes ◽  
Lake Model ◽  
Ice Sheet Dynamics

Abstract. Geological records show that vast proglacial lakes existed along the land terminating margins of palaeo ice sheets in Europe and North America. Proglacial lakes impact ice sheet dynamics by imposing marine-like boundary conditions at the ice margin. These lacustrine boundary conditions include changes in the ice sheet’s geometry, stress balance and frontal ablation and therefore affect the entire ice sheet’s mass balance. This interaction, however, has not been rigorously implemented in ice sheet models. In this study, the implementation of an adaptive lake boundary into the Parallel Ice Sheet Model (PISM) is described and applied to the glacial retreat of the Laurentide Ice Sheet (LIS). The results show that the presence of proglacial lakes locally enhances the ice flow. Along the continental ice margin, ice streams and ice lobes can be observed. Lacustrine terminating ice streams cause immense thinning of the ice sheet’s interior and thus play a significant role in the demise of the LIS. Due to the presence of lakes, a process similar to the marine ice sheet instability causes the collapse of the ice saddle over Hudson Bay, which blocked drainage via the Hudson Strait. In control experiments without a lake model, Hudson Bay is still glaciated at the end of the simulation. Future studies should target the development of parametrizations that better describe the glacial-lacustrine interactions.

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