Comment on “Subglacial erosion and englacial sediment transport modeled for North American ice sheets” by D.H.D. Hildes, G.K.C. Clarke, G.E. Flowers, S.J. Marshall

Larson, Phillip; Mooers, Howard D.

doi:10.1016/j.quascirev.2004.07.001

Cited by 5 publications

(3 citation statements)

References 3 publications

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“…The occurrence of high-carbonate tills in patches of thick, streamlined drift has been interpreted by Hicock (1988) and Hicock and others (1989) to mean that all surface tills in this region were deposited at the base of a fastflowing ice stream. However, the ice stream model does not explain the widely disparate values in till carbonate occurring over distances of only a few kilometres; we believe a different interpretation explains the same data (Larson and Mooers 2005a). Tills sampled in our limited study area contained virtually none of the Paleozoic carbonate and Proterozoic greywacke clasts characteristic of high-carbonate tills found in the region.…”

contrasting

confidence: 59%

Reply to discussion by P.J. Barnett on "Generation of heavy-mineral glacial indicator dispersal trains from a diabase sill, Nipigon Region, Northwestern Ontario"

Larson

Mooers

2006

Can. J. Earth Sci.

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Larson and Mooers 1753Barnett (2006) poses a number of questions regarding some of the field observations and assumptions we used in our interpretation of a heavy-mineral dispersal train derived from an isolated eastern outlier of diabase of the Nipigon sills in northwestern Ontario (Larson and Mooers 2005b). He also brings attention to some details of the regional glacial geologic setting we did not address in our analysis and interpretation of the dispersal train, and highlights new field data (Barnett and Dyer 2005) relevant to interpretation of past glacial processes acting in the broader Nipigon region. We thank Barnett for his comments, and feel they serve in part to highlight the variety of problems regarding glacial erosion and entrainment and transport to which we believe our conceptual model of glacial indicator dispersal (Larson and Mooers 2004) is able to contribute. Barnett (2006) brings attention to the fact that tills exposed at surface in the Beardmore-Geraldton region contain a wide range (< 1 up to 23%) in carbonate content (Thorleifson and Kristjansson 1993). High carbonate contents in these tills are a clear signal of long-distance transport of carbonate-bearing debris from the Hudson Bay Lowlands. The occurrence of high-carbonate tills in patches of thick, streamlined drift has been interpreted by Hicock (1988) and Hicock and others (1989) to mean that all surface tills in this region were deposited at the base of a fastflowing ice stream. However, the ice stream model does not explain the widely disparate values in till carbonate occurring over distances of only a few kilometres; we believe a different interpretation explains the same data (Larson and Mooers 2005a). Tills sampled in our limited study area contained virtually none of the Paleozoic carbonate and Proterozoic greywacke clasts characteristic of high-carbonate tills found in the region. We believe this observation is inconsistent with an origin of the till-forming material by longdistance transport of debris from the Hudson Bay Lowlands by an ice stream, and rather that it reflects local erosion and entrainment and short-distance transport.However, the origin of the tills we sampled in our study area is not relevant to the interpretations we presented. Determining whether the till in our study area was generated by erosion and entrainment into the englacial basal debris layer of the ice sheet, by erosion and entrainment in a subglacial deforming debris layer, or by another process was beyond the scope of our study. We deliberately made no explicit assertion regarding the processes by which diabase was eroded and entrained, and transported. We did, however, attempt to document the rates at which the erosion and entrainment process worked.The only explicit assumptions we incorporated into our interpretations were of the debris mass per unit bed area (m) and of the velocity at which the basal debris layer was transported (u). These values were used to estimate the erosivity (E) recorded in the till sheet, and indirectly the absolut...

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confidence: 59%

Reply to discussion by P.J. Barnett on "Generation of heavy-mineral glacial indicator dispersal trains from a diabase sill, Nipigon Region, Northwestern Ontario"

Larson

Mooers

2006

Can. J. Earth Sci.

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“…In addition, soft bed sliding has been implicated in the rapid advance of the Puget lobe of the Cordilleran ice sheet during the late Pleistocene [ Brown et al , 1987] and probably also contributed to the rapid advance of Taku Glacier in the early 20th century [ Motyka and Post , 1995]. Soft sediments and their erosion therefore play a significant role in a glacier's dynamics and need to be taken into account in modeling glacier and ice sheet advances [ Larson and Mooers , 2005]. Once unlithified sediment is totally eroded, bedrock will be reached, substantially reducing proglacial sediment delivery and changing the dynamics of basal motion.…”

Section: Summary and Further Implications Of Findingsmentioning

confidence: 99%

“…Such erosion has not been well quantified, therefore it has not been addressed in models of continental ice sheet expansion [e.g., Hildes et al , 2004] and of advancing tidewater glaciers [e.g., Nick and Oerlemans , 2006], even though. erosion and redistribution of stored sediment may have been an important control on the dynamics of advancing glaciers [ Meier and Post , 1987; Post and Motyka , 1995; Larson and Mooers , 2005].…”

Section: Introductionmentioning

confidence: 99%

Rapid erosion of soft sediments by tidewater glacier advance: Taku Glacier, Alaska, USA

Motyka¹,

Truffer²,

Kuriger³

et al. 2006

Geophysical Research Letters

102

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[1] Taku Glacier in southeast Alaska has advanced 7.5 km over the last 115 years, overriding its own glaciomarine and outwash sediments. We have documented rapid erosion of these sediments by comparing radio echo soundings (RES) along five transects (2003)(2004)(2005) to earlier RES surveys (1989 and 1994) and to early bathymetric surveys of the proglacial fjord. Erosion rates, _ E, reached 3.9 ± 0.8 m a

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Numerical modelling of subglacial erosion and sediment transport and its application to the North American ice sheets over the Last Glacial cycle

Melanson

Bell

Tarasov

2013

Quaternary Science Reviews

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sheet evolut ion. however, glacia l sys te m mod els (GS?lIs) ca nnot a ddl'l'ss thi s whiklackin g pro per re prese nta ti ons of su bg lucia l sod in u-nt production a nd t.rnnsp ort. Toward t h is goa l. I pre sent a co nt.ine ut.al subg lacia l process mod el for sodi nu-nt prod uct.ion , cnt.rain mcnt, tra us port. und dep ositi on . T he model is driven h~' t lu-du t aca libra t ed ?lIVN :3-0 GS;l.1 an d hy a newl y develop ed su bgla ciul hyd rol ogy COIllJ)(}--uent.. Model results ar c com pa red agu iust t he prese nt -day d ist.ribut iou of glacig pIlic sed ime nt ove r Nort h Am er ica und geolog ica l l'sti Iltal<'S of Luurc ut.ido orosiou . C ivon t he mod el's par am etri c sc ns irivity, t he ca lculat ed eros ion depths fall within t.lu-gpo log ica l pst ima tl's of Lau ren ti de eros ion, with t he excep t.ion of Ha llpt' s ubru sio n Inw th a t uud orestim a tos a brasion hy a t leas t all or de r of mugn itu do. Ill. a dd it.ion . t hrmod el overest ima tes se d ime nt cnt.ru iru u cnt a nd t.hus eng luciul t ra nspo rt . whic h pit her sllggests that t he la rge-scale n -pn -scnt at ion of l'l'ge iat ioll iut rusio n is iundcquut e or that t he ba sa l hydrology modul e underesti ruatr -s water pl'l'SSIll'l 'S.

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Comment on “Subglacial erosion and englacial sediment transport modeled for North American ice sheets” by D.H.D. Hildes, G.K.C. Clarke, G.E. Flowers, S.J. Marshall

Cited by 5 publications

References 3 publications

Reply to discussion by P.J. Barnett on "Generation of heavy-mineral glacial indicator dispersal trains from a diabase sill, Nipigon Region, Northwestern Ontario"

Reply to discussion by P.J. Barnett on "Generation of heavy-mineral glacial indicator dispersal trains from a diabase sill, Nipigon Region, Northwestern Ontario"

Rapid erosion of soft sediments by tidewater glacier advance: Taku Glacier, Alaska, USA

Numerical modelling of subglacial erosion and sediment transport and its application to the North American ice sheets over the Last Glacial cycle

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