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John J Clague - One of the best experts on this subject based on the ideXlab platform.
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The Cordilleran Ice Sheet
2015Co-Authors: Kathy Goetz Roost, John J Clague, Richard B. WaittAbstract:The Cordilleran Ice Sheet, the smaller of two great continen-tal Ice Sheets that covered North America during Quaternary glacial periods, extended from the mountains of coastal south and southeast Alaska, along the Coast Mountains of Britis
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retreat pattern of the Cordilleran Ice Sheet in central british columbia at the end of the last glaciation reconstructed from glacial meltwater landforms
Boreas, 2013Co-Authors: Martin Margold, K. N. Jansson, A. P. Stroeven, Johan Kleman, John J ClagueAbstract:The Cordilleran Ice Sheet (CIS) covered much of the mountainous northwestern part of North America at least several times during the Pleistocene. The pattern and timing of its growth and decay are, however, poorly understood. Here, we present a reconstruction of the pattern of Ice-Sheet retreat in central British Columbia at the end of the last glaciation based on a palaeoglaciological interpretation of Ice-marginal meltwater channels, eskers and deltas mapped from satellite imagery and digital elevation models. A consistent spatial pattern of high-elevation (1600–2400 m a.s.l.), Ice-marginal meltwater channels is evident across central British Columbia. These landforms indicate the presence of Ice domes over the Skeena Mountains and the central Coast Mountains early during deglaciation. Ice sourced in the Coast Mountains remained dominant over the southern and east-central parts of the Interior Plateau during deglaciation. Our reconstruction shows a successive westward retreat of the Ice margin from the western foot of the Rocky Mountains, accompanied by the formation and rapid evolution of a glacial lake in the upper Fraser River basin. The final stage of deglaciation is characterized by the frontal retreat of Ice lobes through the valleys of the Skeena and Omineca Mountains and by the formation of large esker systems in the most prominent topographic lows of the Interior Plateau. We conclude that the CIS underwent a large-scale reconfiguration early during deglaciation and was subsequently diminished by thinning and complex frontal retreat towards the Coast Mountains.
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pre younger dryas resurgence of the southwestern margin of the Cordilleran Ice Sheet british columbia canada
Boreas, 2008Co-Authors: John J Clague, Rolf W. Mathewes, Ian Hutchinson, Jeanpierre Guilbault, B D RickettsAbstract:Clague, J. J., Mathewes, R. W., Guilbault, J.-P., Hutchinson, I. & Ricketts, B. D. 1997 (September): Pre-Younger Dryas resurgence of the southwestern margin of the Cordilleran Ice Sheet, British Columbia, Canada. Boreas, Vol. 26, pp. 261–278. Oslo. ISSN 0300–9483. A lobe of the Cordilleran Ice Sheet readvanced into the central Fvaser Lowland, southwestern British Columbia, Canada, on at least two occasions near the end of the last glaciation. This Ice also flowed into the previously deglaciated, lower reaches of mountain valleys adjacent to the Fraser Lowland and into Washington state. The first of these advances occurred before about 11900 BP and ended with glacier retreat and the establishment of lodgepole pine forest on newly deglaciated terrain. Parts of this forest were overridden by Ice during a second advance, shortly after 11300 BP. The younger advance is most likely older than the Younger Dryas Chronozone (11000–10000 BP) and may correlate with an intra-Allerad cooling event (the Killarney-Gerzensee oscillation). The older advance may have occurred during the Oldest Dryas or Older Dryas cold period. Non-climatic factors could also be involved, as emergence of the Fraser Lowland before the older advance greatly reduced or eliminated calving at the glacier margin and thus altered the mass balance of the Ice lobe.
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history and isostatic effects of the last Ice Sheet in southern british columbia
Quaternary Science Reviews, 2002Co-Authors: John J Clague, Thomas S. JamesAbstract:Abstract The Late Wisconsinan Cordilleran Ice Sheet covered British Columbia, southern Yukon Territory, and parts of Alaska, Washington, Idaho, and Montana. Its major source areas were the high mountain ranges of the Canadian Cordillera, and flow was strongly controlled by topography. The last Ice Sheet began to develop about 30,000–25,000 14C yr ago, but it did not achieve its maximum extent until 15,000–14,000 14C yr BP. Ice Sheet growth was interrupted locally by stillstands and retreat. Ice Sheet decay was rapid and was characterized by complex frontal retreat at the periphery, accompanied locally by brief readvances, and by downwasting and stagnation. By 10,000 14C yr BP,
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postglacial rebound at the northern cascadia subduction zone
Quaternary Science Reviews, 2000Co-Authors: Thomas S. James, John J Clague, Kelin Wang, Ian HutchinsonAbstract:Postglacial rebound is the response of the Earth to the decay of Ice-Sheets. A postglacial rebound model explains crustal tilting and rapid uplift at the northern Cascadia subduction zone that occurred during retreat of the Cordilleran Ice-Sheet. Observations explained by the model include the shoreline tilts of two proglacial lakes that formed at 13.5}14 ka (14C yr ago) and rapid sea level fall (land uplift) at 12}12.5 ka. Modelled mantle viscosity values range from 5]1018 to 5]1019 Pa s, and are consistent with previous viscosity inferences from observations of crustal deformation following subduction zone earthquakes (1018}1019 Pa s). No lower limit to subduction zone mantle viscosity is apparent from our model, but viscosity values equal to or larger than 1020 Pa s are de"nitely ruled out. Our modelled subduction zone viscosity values are smaller than most upper-mantle viscosity estimates derived from postglacial rebound studies of tectonically less-active regions (1020}1021 Pa s). The rapid observed uplift at 12 ka requires, in addition to a low mantle viscosity, rapid unloading from a sudden collapse of remaining coastal portions of the southern Cordilleran Ice-Sheet. The sudden collapse provides 0.18 m of global eustatic sea level rise, approximately 0.7% of the sea level rise associated with melt-water pulse IA. Predictions of a global postglacial rebound model (Ice-3G) with a 1021 Pa s upper-mantle viscosity were previously applied to geodetic data from this region to isolate signals associated with the earthquake cycle. Owing to the low-viscosity values, and resulting rapid recovery of glacial deformation, our model predicts present-day postglacial rebound uplift rates at least 10 times smaller than Ice-3G (less than about 0.1 mm/yr). As the Ice-3G adjustments were substantial, this indicates the need for re-evaluation of the geodetic data. ( 2000 Elsevier Science Ltd. All rights reserved.
Thomas S. James - One of the best experts on this subject based on the ideXlab platform.
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viscosity of the asthenosphere from glacial isostatic adjustment and subduction dynamics at the northern cascadia subduction zone british columbia canada
Journal of Geophysical Research, 2009Co-Authors: Thomas S. James, Kelin Wang, Evan J Gowan, Ikuko WadaAbstract:[1] Late glacial sea level curves located in the Cascadia subduction zone (CSZ) fore arc in southwestern British Columbia show that glacial isostatic adjustment (GIA) was rapid when the Cordilleran Ice Sheet collapsed in the late Pleistocene. GIA modeling with a linear Maxwell rheology indicates that the observations can be equally well fit across a wide range of asthenospheric thicknesses, provided that the asthenospheric viscosity is varied from 3 × 1018 Pa s for a thin (140 km) asthenosphere to 4 × 1019 Pa s for a thick (380 km) asthenosphere. Present-day vertical crustal motion predicted by the GIA models shows rates of a few tenths of a millimeter per year, consistent with previous analyses. The model viscosities largely pertain to the viscosity of the oceanic mantle beneath the subducting Juan de Fuca slab but include a contribution from the mantle wedge above the slab. For comparison, effective viscosities for the upper mantle due to the tectonic regime (subduction) were computed using the strain rates and temperatures of an independent geodynamic model of the CSZ with a wet olivine power law rheology. The effective viscosities agree well with GIA model viscosities of 1019 Pa s or less, corresponding to an asthenosphere of 100 or 200 km thickness. The agreement suggests a significant role for power law flow in the GIA response. Regardless of the microphysical mechanisms responsible for the GIA response, the viscosity values inferred from GIA can be applied to studies of the megathrust earthquake cycle because both processes take place on comparable time scales.
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history and isostatic effects of the last Ice Sheet in southern british columbia
Quaternary Science Reviews, 2002Co-Authors: John J Clague, Thomas S. JamesAbstract:Abstract The Late Wisconsinan Cordilleran Ice Sheet covered British Columbia, southern Yukon Territory, and parts of Alaska, Washington, Idaho, and Montana. Its major source areas were the high mountain ranges of the Canadian Cordillera, and flow was strongly controlled by topography. The last Ice Sheet began to develop about 30,000–25,000 14C yr ago, but it did not achieve its maximum extent until 15,000–14,000 14C yr BP. Ice Sheet growth was interrupted locally by stillstands and retreat. Ice Sheet decay was rapid and was characterized by complex frontal retreat at the periphery, accompanied locally by brief readvances, and by downwasting and stagnation. By 10,000 14C yr BP,
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postglacial rebound at the northern cascadia subduction zone
Quaternary Science Reviews, 2000Co-Authors: Thomas S. James, John J Clague, Kelin Wang, Ian HutchinsonAbstract:Postglacial rebound is the response of the Earth to the decay of Ice-Sheets. A postglacial rebound model explains crustal tilting and rapid uplift at the northern Cascadia subduction zone that occurred during retreat of the Cordilleran Ice-Sheet. Observations explained by the model include the shoreline tilts of two proglacial lakes that formed at 13.5}14 ka (14C yr ago) and rapid sea level fall (land uplift) at 12}12.5 ka. Modelled mantle viscosity values range from 5]1018 to 5]1019 Pa s, and are consistent with previous viscosity inferences from observations of crustal deformation following subduction zone earthquakes (1018}1019 Pa s). No lower limit to subduction zone mantle viscosity is apparent from our model, but viscosity values equal to or larger than 1020 Pa s are de"nitely ruled out. Our modelled subduction zone viscosity values are smaller than most upper-mantle viscosity estimates derived from postglacial rebound studies of tectonically less-active regions (1020}1021 Pa s). The rapid observed uplift at 12 ka requires, in addition to a low mantle viscosity, rapid unloading from a sudden collapse of remaining coastal portions of the southern Cordilleran Ice-Sheet. The sudden collapse provides 0.18 m of global eustatic sea level rise, approximately 0.7% of the sea level rise associated with melt-water pulse IA. Predictions of a global postglacial rebound model (Ice-3G) with a 1021 Pa s upper-mantle viscosity were previously applied to geodetic data from this region to isolate signals associated with the earthquake cycle. Owing to the low-viscosity values, and resulting rapid recovery of glacial deformation, our model predicts present-day postglacial rebound uplift rates at least 10 times smaller than Ice-3G (less than about 0.1 mm/yr). As the Ice-3G adjustments were substantial, this indicates the need for re-evaluation of the geodetic data. ( 2000 Elsevier Science Ltd. All rights reserved.
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postglacial rebound at the northern cascadia subduction zone
Quaternary Science Reviews, 2000Co-Authors: Thomas S. James, John J Clague, Kelin Wang, Ian HutchinsonAbstract:Postglacial rebound is the response of the Earth to the decay of Ice-Sheets. A postglacial rebound model explains crustal tilting and rapid uplift at the northern Cascadia subduction zone that occurred during retreat of the Cordilleran Ice-Sheet. Observations explained by the model include the shoreline tilts of two proglacial lakes that formed at 13.5}14 ka (14C yr ago) and rapid sea level fall (land uplift) at 12}12.5 ka. Modelled mantle viscosity values range from 5]1018 to 5]1019 Pa s, and are consistent with previous viscosity inferences from observations of crustal deformation following subduction zone earthquakes (1018}1019 Pa s). No lower limit to subduction zone mantle viscosity is apparent from our model, but viscosity values equal to or larger than 1020 Pa s are de"nitely ruled out. Our modelled subduction zone viscosity values are smaller than most upper-mantle viscosity estimates derived from postglacial rebound studies of tectonically less-active regions (1020}1021 Pa s). The rapid observed uplift at 12 ka requires, in addition to a low mantle viscosity, rapid unloading from a sudden collapse of remaining coastal portions of the southern Cordilleran Ice-Sheet. The sudden collapse provides 0.18 m of global eustatic sea level rise, approximately 0.7% of the sea level rise associated with melt-water pulse IA. Predictions of a global postglacial rebound model (Ice-3G) with a 1021 Pa s upper-mantle viscosity were previously applied to geodetic data from this region to isolate signals associated with the earthquake cycle. Owing to the low-viscosity values, and resulting rapid recovery of glacial deformation, our model predicts present-day postglacial rebound uplift rates at least 10 times smaller than Ice-3G (less than about 0.1 mm/yr). As the Ice-3G adjustments were substantial, this indicates the need for re-evaluation of the geodetic data. ( 2000 Elsevier Science Ltd. All rights reserved.
Martin Margold - One of the best experts on this subject based on the ideXlab platform.
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Glacial geomorphology of the central sector of the Cordilleran Ice Sheet, Northern British Columbia, Canada
'Informa UK Limited', 2021Co-Authors: Helen E. Dulfer, Martin MargoldAbstract:Northern British Columbia was repeatedly covered by the Cordilleran Ice Sheet (CIS) during the glacial periods. However, its mountainous terrain and remote location have thus far impeded our understanding of the central sector of the Ice Sheet. The improved resolution of remotely sensed data provides new opportunities to unravel the glacial history of this inaccessible location. Here, we present a comprehensive map of glacial landforms for the central sector of the CIS (55° to 60° N). Seven landform categories were mapped: Ice flow parallel lineations, moraines (CIS outlet glacier moraines, Late Glacial moraines and moraines of unknown origin), meltwater channels (lateral and submarginal, subglacial, proglacial, and meltwater channels of unknown origin), kame terraces, eskers (single ridges and esker complexes), perched deltas and subglacial ribs. Collectively, these landforms provide a record of the extent, thickness and behaviour of the CIS, the direction of its movement and pattern of Ice retreat
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beryllium 10 dating of the foothills erratics train in alberta canada indicates detachment of the laurentide Ice Sheet from the rocky mountains at 15 ka
Quaternary Research, 2019Co-Authors: Martin Margold, John C Gosse, Alan J Hidy, Robin Woywitka, Joseph M Young, Duane G. FroeseAbstract:The Foothills Erratics Train consists of large quartzite blocks of Rocky Mountains origin deposited on the eastern slopes of the Rocky Mountain Foothills in Alberta between ~53.5°N and 49°N. The blocks were deposited in their present locations when the western margin of the Laurentide Ice Sheet (LIS) detached from the local Ice masses of the Rocky Mountains, which initiated the opening of the southern end of the Ice-free corridor between the Cordilleran Ice Sheet and the LIS. We use 10 Be exposure dating to constrain the beginning of this decoupling. Based on a group of 12 samples well-clustered in time, we date the detachment of the western LIS margin from the Rocky Mountain front to ~14.9 ± 0.9 ka. This is ~1000 years later than previously assumed, but a lack of a latitudinal trend in the ages over a distance of ~500 km is consistent with the rapid opening of a long wedge of unglaciated terrain portrayed in existing Ice-retreat reconstructions. A later separation of the western LIS margin from the mountain front implies higher Ice margin–retreat rates in order to meet the Younger Dryas Ice margin position near the boundary of the Canadian Shield ~2000 years later.
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Numerical simulations of the Cordilleran Ice Sheet through the last glacial cycle
The Cryosphere, 2016Co-Authors: J. Seguinot, Martin Margold, A. P. Stroeven, Irina Rogozhina, Johan KlemanAbstract:Abstract. After more than a century of geological research, the Cordilleran Ice Sheet of North America remains among the least understood in terms of its former extent, volume, and dynamics. Because of the mountainous topography on which the Ice Sheet formed, geological studies have often had only local or regional relevance and shown such a complexity that Ice-Sheet-wide spatial reconstructions of advance and retreat patterns are lacking. Here we use a numerical Ice Sheet model calibrated against field-based evidence to attempt a quantitative reconstruction of the Cordilleran Ice Sheet history through the last glacial cycle. A series of simulations is driven by time-dependent temperature offsets from six proxy records located around the globe. Although this approach reveals large variations in model response to evolving climate forcing, all simulations produce two major glaciations during marine oxygen isotope stages 4 (62.2–56.9 ka) and 2 (23.2–16.9 ka). The timing of glaciation is better reproduced using temperature reconstructions from Greenland and Antarctic Ice cores than from regional oceanic sediment cores. During most of the last glacial cycle, the modelled Ice cover is discontinuous and restricted to high mountain areas. However, widespread precipitation over the Skeena Mountains favours the persistence of a central Ice dome throughout the glacial cycle. It acts as a nucleation centre before the Last Glacial Maximum and hosts the last remains of Cordilleran Ice until the middle Holocene (6.7 ka).
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retreat pattern of the Cordilleran Ice Sheet in central british columbia at the end of the last glaciation reconstructed from glacial meltwater landforms
Boreas, 2013Co-Authors: Martin Margold, K. N. Jansson, A. P. Stroeven, Johan Kleman, John J ClagueAbstract:The Cordilleran Ice Sheet (CIS) covered much of the mountainous northwestern part of North America at least several times during the Pleistocene. The pattern and timing of its growth and decay are, however, poorly understood. Here, we present a reconstruction of the pattern of Ice-Sheet retreat in central British Columbia at the end of the last glaciation based on a palaeoglaciological interpretation of Ice-marginal meltwater channels, eskers and deltas mapped from satellite imagery and digital elevation models. A consistent spatial pattern of high-elevation (1600–2400 m a.s.l.), Ice-marginal meltwater channels is evident across central British Columbia. These landforms indicate the presence of Ice domes over the Skeena Mountains and the central Coast Mountains early during deglaciation. Ice sourced in the Coast Mountains remained dominant over the southern and east-central parts of the Interior Plateau during deglaciation. Our reconstruction shows a successive westward retreat of the Ice margin from the western foot of the Rocky Mountains, accompanied by the formation and rapid evolution of a glacial lake in the upper Fraser River basin. The final stage of deglaciation is characterized by the frontal retreat of Ice lobes through the valleys of the Skeena and Omineca Mountains and by the formation of large esker systems in the most prominent topographic lows of the Interior Plateau. We conclude that the CIS underwent a large-scale reconfiguration early during deglaciation and was subsequently diminished by thinning and complex frontal retreat towards the Coast Mountains.
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lateglacial Ice dynamics of the Cordilleran Ice Sheet in northern british columbia and southern yukon territory retreat pattern of the liard lobe reconstructed from the glacial landform record
Journal of Quaternary Science, 2013Co-Authors: Martin Margold, K. N. Jansson, Johan Kleman, A. P. StroevenAbstract:The Liard Lobe formed a part of the northeastern sector of the Cordilleran Ice Sheet and drained Ice from accumulation areas in the Selwyn, Pelly, Cassiar and Skeena mountains. This study reconstru ...
Kelin Wang - One of the best experts on this subject based on the ideXlab platform.
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viscosity of the asthenosphere from glacial isostatic adjustment and subduction dynamics at the northern cascadia subduction zone british columbia canada
Journal of Geophysical Research, 2009Co-Authors: Thomas S. James, Kelin Wang, Evan J Gowan, Ikuko WadaAbstract:[1] Late glacial sea level curves located in the Cascadia subduction zone (CSZ) fore arc in southwestern British Columbia show that glacial isostatic adjustment (GIA) was rapid when the Cordilleran Ice Sheet collapsed in the late Pleistocene. GIA modeling with a linear Maxwell rheology indicates that the observations can be equally well fit across a wide range of asthenospheric thicknesses, provided that the asthenospheric viscosity is varied from 3 × 1018 Pa s for a thin (140 km) asthenosphere to 4 × 1019 Pa s for a thick (380 km) asthenosphere. Present-day vertical crustal motion predicted by the GIA models shows rates of a few tenths of a millimeter per year, consistent with previous analyses. The model viscosities largely pertain to the viscosity of the oceanic mantle beneath the subducting Juan de Fuca slab but include a contribution from the mantle wedge above the slab. For comparison, effective viscosities for the upper mantle due to the tectonic regime (subduction) were computed using the strain rates and temperatures of an independent geodynamic model of the CSZ with a wet olivine power law rheology. The effective viscosities agree well with GIA model viscosities of 1019 Pa s or less, corresponding to an asthenosphere of 100 or 200 km thickness. The agreement suggests a significant role for power law flow in the GIA response. Regardless of the microphysical mechanisms responsible for the GIA response, the viscosity values inferred from GIA can be applied to studies of the megathrust earthquake cycle because both processes take place on comparable time scales.
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postglacial rebound at the northern cascadia subduction zone
Quaternary Science Reviews, 2000Co-Authors: Thomas S. James, John J Clague, Kelin Wang, Ian HutchinsonAbstract:Postglacial rebound is the response of the Earth to the decay of Ice-Sheets. A postglacial rebound model explains crustal tilting and rapid uplift at the northern Cascadia subduction zone that occurred during retreat of the Cordilleran Ice-Sheet. Observations explained by the model include the shoreline tilts of two proglacial lakes that formed at 13.5}14 ka (14C yr ago) and rapid sea level fall (land uplift) at 12}12.5 ka. Modelled mantle viscosity values range from 5]1018 to 5]1019 Pa s, and are consistent with previous viscosity inferences from observations of crustal deformation following subduction zone earthquakes (1018}1019 Pa s). No lower limit to subduction zone mantle viscosity is apparent from our model, but viscosity values equal to or larger than 1020 Pa s are de"nitely ruled out. Our modelled subduction zone viscosity values are smaller than most upper-mantle viscosity estimates derived from postglacial rebound studies of tectonically less-active regions (1020}1021 Pa s). The rapid observed uplift at 12 ka requires, in addition to a low mantle viscosity, rapid unloading from a sudden collapse of remaining coastal portions of the southern Cordilleran Ice-Sheet. The sudden collapse provides 0.18 m of global eustatic sea level rise, approximately 0.7% of the sea level rise associated with melt-water pulse IA. Predictions of a global postglacial rebound model (Ice-3G) with a 1021 Pa s upper-mantle viscosity were previously applied to geodetic data from this region to isolate signals associated with the earthquake cycle. Owing to the low-viscosity values, and resulting rapid recovery of glacial deformation, our model predicts present-day postglacial rebound uplift rates at least 10 times smaller than Ice-3G (less than about 0.1 mm/yr). As the Ice-3G adjustments were substantial, this indicates the need for re-evaluation of the geodetic data. ( 2000 Elsevier Science Ltd. All rights reserved.
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postglacial rebound at the northern cascadia subduction zone
Quaternary Science Reviews, 2000Co-Authors: Thomas S. James, John J Clague, Kelin Wang, Ian HutchinsonAbstract:Postglacial rebound is the response of the Earth to the decay of Ice-Sheets. A postglacial rebound model explains crustal tilting and rapid uplift at the northern Cascadia subduction zone that occurred during retreat of the Cordilleran Ice-Sheet. Observations explained by the model include the shoreline tilts of two proglacial lakes that formed at 13.5}14 ka (14C yr ago) and rapid sea level fall (land uplift) at 12}12.5 ka. Modelled mantle viscosity values range from 5]1018 to 5]1019 Pa s, and are consistent with previous viscosity inferences from observations of crustal deformation following subduction zone earthquakes (1018}1019 Pa s). No lower limit to subduction zone mantle viscosity is apparent from our model, but viscosity values equal to or larger than 1020 Pa s are de"nitely ruled out. Our modelled subduction zone viscosity values are smaller than most upper-mantle viscosity estimates derived from postglacial rebound studies of tectonically less-active regions (1020}1021 Pa s). The rapid observed uplift at 12 ka requires, in addition to a low mantle viscosity, rapid unloading from a sudden collapse of remaining coastal portions of the southern Cordilleran Ice-Sheet. The sudden collapse provides 0.18 m of global eustatic sea level rise, approximately 0.7% of the sea level rise associated with melt-water pulse IA. Predictions of a global postglacial rebound model (Ice-3G) with a 1021 Pa s upper-mantle viscosity were previously applied to geodetic data from this region to isolate signals associated with the earthquake cycle. Owing to the low-viscosity values, and resulting rapid recovery of glacial deformation, our model predicts present-day postglacial rebound uplift rates at least 10 times smaller than Ice-3G (less than about 0.1 mm/yr). As the Ice-3G adjustments were substantial, this indicates the need for re-evaluation of the geodetic data. ( 2000 Elsevier Science Ltd. All rights reserved.
Ian Hutchinson - One of the best experts on this subject based on the ideXlab platform.
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pre younger dryas resurgence of the southwestern margin of the Cordilleran Ice Sheet british columbia canada
Boreas, 2008Co-Authors: John J Clague, Rolf W. Mathewes, Ian Hutchinson, Jeanpierre Guilbault, B D RickettsAbstract:Clague, J. J., Mathewes, R. W., Guilbault, J.-P., Hutchinson, I. & Ricketts, B. D. 1997 (September): Pre-Younger Dryas resurgence of the southwestern margin of the Cordilleran Ice Sheet, British Columbia, Canada. Boreas, Vol. 26, pp. 261–278. Oslo. ISSN 0300–9483. A lobe of the Cordilleran Ice Sheet readvanced into the central Fvaser Lowland, southwestern British Columbia, Canada, on at least two occasions near the end of the last glaciation. This Ice also flowed into the previously deglaciated, lower reaches of mountain valleys adjacent to the Fraser Lowland and into Washington state. The first of these advances occurred before about 11900 BP and ended with glacier retreat and the establishment of lodgepole pine forest on newly deglaciated terrain. Parts of this forest were overridden by Ice during a second advance, shortly after 11300 BP. The younger advance is most likely older than the Younger Dryas Chronozone (11000–10000 BP) and may correlate with an intra-Allerad cooling event (the Killarney-Gerzensee oscillation). The older advance may have occurred during the Oldest Dryas or Older Dryas cold period. Non-climatic factors could also be involved, as emergence of the Fraser Lowland before the older advance greatly reduced or eliminated calving at the glacier margin and thus altered the mass balance of the Ice lobe.
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postglacial rebound at the northern cascadia subduction zone
Quaternary Science Reviews, 2000Co-Authors: Thomas S. James, John J Clague, Kelin Wang, Ian HutchinsonAbstract:Postglacial rebound is the response of the Earth to the decay of Ice-Sheets. A postglacial rebound model explains crustal tilting and rapid uplift at the northern Cascadia subduction zone that occurred during retreat of the Cordilleran Ice-Sheet. Observations explained by the model include the shoreline tilts of two proglacial lakes that formed at 13.5}14 ka (14C yr ago) and rapid sea level fall (land uplift) at 12}12.5 ka. Modelled mantle viscosity values range from 5]1018 to 5]1019 Pa s, and are consistent with previous viscosity inferences from observations of crustal deformation following subduction zone earthquakes (1018}1019 Pa s). No lower limit to subduction zone mantle viscosity is apparent from our model, but viscosity values equal to or larger than 1020 Pa s are de"nitely ruled out. Our modelled subduction zone viscosity values are smaller than most upper-mantle viscosity estimates derived from postglacial rebound studies of tectonically less-active regions (1020}1021 Pa s). The rapid observed uplift at 12 ka requires, in addition to a low mantle viscosity, rapid unloading from a sudden collapse of remaining coastal portions of the southern Cordilleran Ice-Sheet. The sudden collapse provides 0.18 m of global eustatic sea level rise, approximately 0.7% of the sea level rise associated with melt-water pulse IA. Predictions of a global postglacial rebound model (Ice-3G) with a 1021 Pa s upper-mantle viscosity were previously applied to geodetic data from this region to isolate signals associated with the earthquake cycle. Owing to the low-viscosity values, and resulting rapid recovery of glacial deformation, our model predicts present-day postglacial rebound uplift rates at least 10 times smaller than Ice-3G (less than about 0.1 mm/yr). As the Ice-3G adjustments were substantial, this indicates the need for re-evaluation of the geodetic data. ( 2000 Elsevier Science Ltd. All rights reserved.
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postglacial rebound at the northern cascadia subduction zone
Quaternary Science Reviews, 2000Co-Authors: Thomas S. James, John J Clague, Kelin Wang, Ian HutchinsonAbstract:Postglacial rebound is the response of the Earth to the decay of Ice-Sheets. A postglacial rebound model explains crustal tilting and rapid uplift at the northern Cascadia subduction zone that occurred during retreat of the Cordilleran Ice-Sheet. Observations explained by the model include the shoreline tilts of two proglacial lakes that formed at 13.5}14 ka (14C yr ago) and rapid sea level fall (land uplift) at 12}12.5 ka. Modelled mantle viscosity values range from 5]1018 to 5]1019 Pa s, and are consistent with previous viscosity inferences from observations of crustal deformation following subduction zone earthquakes (1018}1019 Pa s). No lower limit to subduction zone mantle viscosity is apparent from our model, but viscosity values equal to or larger than 1020 Pa s are de"nitely ruled out. Our modelled subduction zone viscosity values are smaller than most upper-mantle viscosity estimates derived from postglacial rebound studies of tectonically less-active regions (1020}1021 Pa s). The rapid observed uplift at 12 ka requires, in addition to a low mantle viscosity, rapid unloading from a sudden collapse of remaining coastal portions of the southern Cordilleran Ice-Sheet. The sudden collapse provides 0.18 m of global eustatic sea level rise, approximately 0.7% of the sea level rise associated with melt-water pulse IA. Predictions of a global postglacial rebound model (Ice-3G) with a 1021 Pa s upper-mantle viscosity were previously applied to geodetic data from this region to isolate signals associated with the earthquake cycle. Owing to the low-viscosity values, and resulting rapid recovery of glacial deformation, our model predicts present-day postglacial rebound uplift rates at least 10 times smaller than Ice-3G (less than about 0.1 mm/yr). As the Ice-3G adjustments were substantial, this indicates the need for re-evaluation of the geodetic data. ( 2000 Elsevier Science Ltd. All rights reserved.