Patterns Of Glacial Erosion Research Articles

Assessing the relative efficiency of fluvial and glacial erosion through simulation of fluvial landscapes

The relative rates of erosion by rivers and glaciers, and the topographic effects of these two different styles of erosion, remain outstanding problems in geomorphology. We use a quantitative description of local fluvial landscapes to estimate how glaciated landscapes might look now had glaciers not developed. This indicates the landscape modification attributable to glacial erosion. We present examples from the Sierra Nevada, California and the Sangre de Cristo Range, Colorado. In smaller drainage basins, glacial modification is focussed above the mean Quaternary equilibrium line altitude (ELA), where both ridgelines and valley floors have been lowered as a consequence of glaciation. At lower elevations, small glaciers have apparently widened valleys without incising the valley floor beyond what a river would have. This may reflect the short residence time of the glaciers at their full extent, or differences in the subglacial drainage network between the glacier margins and the thalweg. In larger drainage basins, the pattern of glacial erosion is dramatically different. Here, the glaciers have modified longitudinal profiles, as well as valley cross sections, far below the mean Quaternary ELA. Possible causes of this difference in the larger basins include the larger accumulation area, greater shading of the valley floor, longer residence times for ice at its full extent, and the influence of the shallower valley slope prior to glaciation on the subsequent glacier and subglacial drainage conditions.

Spatial Patterns of Glacial Erosion at a Valley Scale Derived From Terrestrial Cosmogenic 10Be and 26Al Concentrations in Rock

The fundamentally geographic issue of the amounts and spatial patterns of erosion necessary to produce classic glacial landforms such as U-shaped valleys has been debated by scientists for over a century. Terrestrial cosmogenic nuclide (TCN) measurements in glacially abraded bedrock were used to determine patterns of glacial erosion and to quantify the amount of rock removed during the last glaciation along valley-side transects in Sinks Canyon, Wind River Range, Wyoming, and the South Yuba River, Sierra Nevada, California. Surface exposure ages from bedrock and erratic samples obtained during this study indicate last deglaciation between 13–18 ka in the South Yuba River and 15–17 ka in Sinks Canyon. These ages are in agreement with previously published glacial chronologies. In both areas, samples from valley cross sections revealed a pattern of erosion during the last glaciation that decreased toward the lateral limit of ice extent, as predicted by numerical models, while transects further upstream recorded >1.4 meters of bedrock removal throughout. The effects of varying interglacial erosion and surface exposure histories on modeled glacial erosion depths were tested, validating the methodology used. The results demonstrate that the TCN technique, applied at the valley scale, provides useful insight into the spatial pattern of glacial erosion. Extensive sampling in areas with limited erosional loss may provide detailed records of erosion patterns with which to test predictions generated by models of ice dynamics and erosion processes.

Age of Sirius Group on Mount Feather, McMurdo Dry Valleys, Antarctica, based on glaciological inferences from the overridden mountain range of Scandinavia

A striking difference in the geomorphology of the ice-sheet overridden lowlands and ranges in Scandinavia and the Wilkes Basin–Transantarctic Mountains region in Antarctica is the occurrence of basal till sequences (of the Sirius Group) on summits and interfluves in the Transantarctic Mountains and the lack of basal tills on corresponding surfaces in Scandinavia. From the pattern of glacially eroded surfaces and preserved preglacial surfaces in northern Sweden, we infer altitudinal and lateral patterns of glacial erosion and deposition governed by topography-dependent basal thermal regimes. Furthermore, summits and interfluves in northern Sweden are often remnants of preglacial surfaces. Consequently, these preglacial surface remnants were preserved underneath patches of cold-based ice. We conclude that the subglacial thermal zonation of ice sheets overriding peripheral mountain ranges is self-sustained by topography; i.e., cold-based ice relates to topographic highs and warm-based ice to topographic lows. We use these inferences to explore the glaciological implications for the Sirius Group sequence on Mount Feather, McMurdo Dry Valleys. A glaciologically plausible explanation for this deposit and similar Sirius Group sequences on dissected summit and interfluve surfaces in the Transantarctic Mountains is that deposition occurred before the bulk of the relief formed. The present relief in the Mount Feather vicinity is at least 11 Ma old. Consequently, the Sirius Group at Mount Feather is at least of middle Miocene age.

Preglacial surface remnants and Quaternary glacial regimes in northwestern Sweden

We present a detailed map of the distribution of preglacial surface remnants in the Kebnekaise region of northwestern Sweden. In this mountain area we discern four important large-scale geomorphological units, each representing a specific set of erosional agents and formative conditions. These are: (i) intact preglacial surface remnants, characterized by gentle slopes, round summits, wide shallow valleys, and an absence of rock basins; (ii) preglacial surface remnants showing signs of minor glacial erosion and deposition; (iii) glacially scoured surfaces, including glacial troughs; (iv) deep fluvial valleys cut into the preglacial surface. The pattern of glacial erosion is explained as the result of three specific modes of glaciation known to have existed during the last 120,000 years, and inferred to have repeatedly prevailed during the last 2.75 million years: cirque glaciation, mountain ice sheets, and Fennoscandian ice sheets. A deep-ocean oxygen-isotope record of foraminifera from the North Atlantic (DSDP 607) was used to infer the temporal extent of these modes of glaciation during the last 2.75 million years. We interpret the preglacial landscape preservation and the pattern of glacial erosion in terms of the configuration, the basal thermal regime, and the duration of such glaciation events. The average subglacial thermal regime of both ice sheet types was frozen on the uplands and melting in the main valleys, where outlet glaciers and ice-streams formed. The pre-glacial landscape is best preserved at intermediate elevations, low enough not to have been covered by cirque glaciers, and apparently high enough not to have experienced melted-bed conditions and subglacial erosion during ice sheet overriding events. In a narrow high-relief zone along the elevation axis, interglacial fluvial erosion was morphologically important. The absence of glacial erosion on uplands in this zone allowed fluvial erosion to commence on the same locations during each ice-free interval. In contrast, no persistent fluvial valley pattern could develop in zones subjected to repeated glacial scouring and hence, derangement of fluvial patterns.

Patterns of glacial erosion and deposition in Prydz Bay and the past behaviour of the Lambert Glacier

Styles of glacial sedimentation and erosion in Prydz Bay respond to glacial and interglacial cycles and fall into three zones; an inner zone of net erosion, a middle zone of subglacially eroded and deformed transitional glacial marine deposits and an outer zone of subglacial till deposition and shelf progradation. The inner zone is the region of maximum basal shear stress and inner-shelf deep formation by enhanced erosion in areas where tributary glaciers converge with the extended Lambert Glacier. The middle zone is underlain by sediments deposited near the ice-grounding zone during retreat, both as blanket like deposits and as grounding-line moraines. This material is then deformed into elongate subglacial bedforms (megaflures or drumlins), a process that probably involves some erosion. Deforming subglacial bed conditions extend to the shelf edge within a valley crossing the shelf on the western side of Prydz Bay. The outer zone is a zone of net deposition of compact subglacial till and prograding continental slope deposits formed during full glacial conditions and glacial marine sediment formed during ice retreat. The inferred build up of ice on the Ingrid Christensen Coast may have been responsible for the development of the western ice stream that flowed in Prydz Channel. The geometry of seismic sequences in Prydz Channel suggests that this ice stream and its associated trough mouth fan developed after a major episode of shelf and slope erosion during the Pliocene.

Application of a general sliding law to simulating flow in a glacier cross-section

AbstractObservations at Athabasca Glacier and elsewhere suggest that basal sliding can account for a very significant part of total glacier motion, and that sliding rates vary significantly across a glacier section. The ability to model such spatial variations in basal velocities is important in understanding flow in valley glaciers, as well as in predicting spatial patterns of glacial erosion that drive land-form development models. With a sliding law in which the basal velocity is dependent on the basal shear stress and inversely dependent on the effective pressure at the bed, it is possible to predict an overall flow pattern that is consistent with the empirical data, if it is assumed that friction increases close to the margin of a glacier.

Application of a general sliding law to simulating flow in a glacier cross-section

AbstractObservations at Athabasca Glacier and elsewhere suggest that basal sliding can account for a very significant part of total glacier motion, and that sliding rates vary significantly across a glacier section. The ability to model such spatial variations in basal velocities is important in understanding flow in valley glaciers, as well as in predicting spatial patterns of glacial erosion that drive land-form development models. With a sliding law in which the basal velocity is dependent on the basal shear stress and inversely dependent on the effective pressure at the bed, it is possible to predict an overall flow pattern that is consistent with the empirical data, if it is assumed that friction increases close to the margin of a glacier.

Subglacial Morphology in Northern Palmer Land, Antarctic Peninsula

Ice-thickness and surface-elevation data gathered from radio echo flights over the Antarctic Peninsula are presented as profiles for five major outlet glaciers in northern Palmer Land and as contour maps for an area of 8 000 km2 to the east of George VI Sound. Glacier profiles appear to be closely related to ice discharge especially to convergent and divergent flow. Comparison of subglacial topography with geological evidence of faulting suggests that the area around George VI Sound is a region where structure is an important influence on the pattern of glacial erosion.

Ice-Sheet Erosion—A Result of Maximum Conditions?

AbstractUnderstanding the relationship between the morphology of former ice-sheet beds and glaciological processes is handicapped by the difficulty of establishing which stage of a cycle of ice-sheet growth and decay is responsible for most erosion. Discussions at this conference and in the literature display a variety of opinions, some favouring periods of ice-sheet build up, others periods of fluctuations, and still others steady-state maximum conditions. Here it is suggested that there is geomorphological evidence which points to the dominance of maximum conditions.Along the eastern margins of the Laurentide and Greenland ice sheets there is a sharp discontinuity between Alpine relief which stood above the ice-sheet surface at the maximum and plateau scenery which was covered by the ice sheet. Often the two types of relief are adjacent and yet separated by an altitudinal difference of only 100–200 m. The existence of an abrupt rather than gradual transition from one relief type to the other suggests that most glacial sculpture must have taken place while the ice sheet was at its maximum extent. In other geomorphological situations where high mountains were submerged by ice sheets, the major erosional landforms are frequently found to relate to ice sheets rather than to local mountain glaciers, again suggesting the dominance of erosion during full ice-sheet conditions. Finally, the identification of patterns of glacial erosion on an ice-sheet scale in North America and Greenland points to erosion when the ice sheets were fully expanded, rather than to the variable flow conditions associated with growth or decay.If ice-sheet erosion is accepted as being a result of maximum conditions, then it places certain constraints on glacial theory, for example the need to develop theories of glacial erosion which apply beneath ice thicknesses of several thousand metres. It also suggests that the use of steady-state models of ice sheets is likely to be a profitable way of relating glaciological processes to the morphology of former ice-sheet beds.

Ice-Sheet Erosion—A Result of Maximum Conditions?

Abstract Understanding the relationship between the morphology of former ice-sheet beds and glaciological processes is handicapped by the difficulty of establishing which stage of a cycle of ice-sheet growth and decay is responsible for most erosion. Discussions at this conference and in the literature display a variety of opinions, some favouring periods of ice-sheet build up, others periods of fluctuations, and still others steady-state maximum conditions. Here it is suggested that there is geomorphological evidence which points to the dominance of maximum conditions. Along the eastern margins of the Laurentide and Greenland ice sheets there is a sharp discontinuity between Alpine relief which stood above the ice-sheet surface at the maximum and plateau scenery which was covered by the ice sheet. Often the two types of relief are adjacent and yet separated by an altitudinal difference of only 100–200 m. The existence of an abrupt rather than gradual transition from one relief type to the other suggests that most glacial sculpture must have taken place while the ice sheet was at its maximum extent. In other geomorphological situations where high mountains were submerged by ice sheets, the major erosional landforms are frequently found to relate to ice sheets rather than to local mountain glaciers, again suggesting the dominance of erosion during full ice-sheet conditions. Finally, the identification of patterns of glacial erosion on an ice-sheet scale in North America and Greenland points to erosion when the ice sheets were fully expanded, rather than to the variable flow conditions associated with growth or decay. If ice-sheet erosion is accepted as being a result of maximum conditions, then it places certain constraints on glacial theory, for example the need to develop theories of glacial erosion which apply beneath ice thicknesses of several thousand metres. It also suggests that the use of steady-state models of ice sheets is likely to be a profitable way of relating glaciological processes to the morphology of former ice-sheet beds.

Glacial Canons

Previous articleNext article FreeGlacial CanonsW. J. McGeeW. J. McGee Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Volume 2, Number 4May - Jun., 1894 Article DOIhttps://doi.org/10.1086/606974 Views: 56 Citations: 20Citations are reported from Crossref PDF download Crossref reports the following articles citing this article:Wesley Clary, Lindsay Worthington, Louis Scuderi, Sean P.S. Gulick, Elia Scudiero Quantifying the relative influence of ice sheets, faults, and instability on channel and gully cross-profile shapes in the Gulf of Alaska, Marine Geology 435 (May 2021): 106416.https://doi.org/10.1016/j.margeo.2020.106416Olivia Steinemann, Susan Ivy-Ochs, Kristina Hippe, Marcus Christl, Negar Haghipour, Hans-Arno Synal Glacial erosion by the Trift glacier (Switzerland): Deciphering the development of riegels, rock basins and gorges, Geomorphology 375 (Feb 2021): 107533.https://doi.org/10.1016/j.geomorph.2020.107533Valerio Faraoni Natural phenomena described by the same equation, European Journal of Physics 41, no.55 (Aug 2020): 054002.https://doi.org/10.1088/1361-6404/ab9c93Valerio Faraoni Maximizing friction in the erosion of glacial valleys, Journal of Glaciology 125 (Jul 2020): 1–4.https://doi.org/10.1017/jog.2020.47 References, (Oct 2017): 342–383.https://doi.org/10.1002/9781118652541.refsValerio Faraoni, Adriana M. Cardini, Hubert de Guise Analogues of glacial valley profiles in particle mechanics and in cosmology, FACETS 2, no.11 (May 2017): 286–300.https://doi.org/10.1139/facets-2016-0045 References, (Apr 2013): 363–382.https://doi.org/10.1201/b14059-13Simon J. Cook, Darrel A. Swift Subglacial basins: Their origin and importance in glacial systems and landscapes, Earth-Science Reviews 115, no.44 (Dec 2012): 332–372.https://doi.org/10.1016/j.earscirev.2012.09.009Neal R. Iverson Shear resistance and continuity of subglacial till: hydrology rules, Journal of Glaciology 56, no.200200 (Sep 2017): 1104–1114.https://doi.org/10.3189/002214311796406220Yingkui Li, Jon Harbor, Arjen P. Stroeven, Derek Fabel, Johan Kleman, David Fink, Marc Caffee, David Elmore Ice sheet erosion patterns in valley systems in northern Sweden investigated using cosmogenic nuclides, Earth Surface Processes and Landforms 30, no.88 (Jan 2005): 1039–1049.https://doi.org/10.1002/esp.1261Derek Fabel, Jon Harbor, Dennis Dahms, Allan James, David Elmore, Linda Horn, Kelly Daley, Charles Steele Spatial Patterns of Glacial Erosion at a Valley Scale Derived From Terrestrial Cosmogenic 10 Be and 26 Al Concentrations in Rock, Annals of the Association of American Geographers 94, no.22 (Jun 2004): 241–255.https://doi.org/10.1111/j.1467-8306.2004.09402001.xChristopher C. Duncan, Andrew J. Klein, Jeffrey G. Masek, Bryan L. Isacks Comparison of Late Pleistocene and Modern Glacier Extents in Central Nepal Based on Digital Elevation Data and Satellite Imagery, Quaternary Research 49, no.33 (Jan 2017): 241–254.https://doi.org/10.1006/qres.1998.1958Jonathan M. Harbor Development of glacial-valley cross sections under conditions of spatially variable resistance to erosion, Geomorphology 14, no.22 (Nov 1995): 99–107.https://doi.org/10.1016/0169-555X(95)00051-1 References, (Jan 1994): 421–472.https://doi.org/10.1016/B978-0-08-037944-9.50024-8Jonathan M. Harbor Glacial geomorphology: modeling processes and landforms, Geomorphology 7, no.1-31-3 (Jul 1993): 129–140.https://doi.org/10.1016/0169-555X(93)90014-SJonathan M. Harbor Glacial geomorphology: modeling processes and landforms, (Jan 1993): 129–140.https://doi.org/10.1016/B978-0-444-89971-2.50010-9Jonathan M. Harbor, Dennis A. Wheeler On the mathematical description of glaciated valley cross sections, Earth Surface Processes and Landforms 17, no.55 (Aug 1992): 477–485.https://doi.org/10.1002/esp.3290170507Jonathan M. Harbor A discussion of hirano and Aniya's (1988, 1989) explanation of glacial-valley cross profile development, Earth Surface Processes and Landforms 15, no.44 (Jun 1990): 369–377.https://doi.org/10.1002/esp.3290150408Jonathan M. Harbor Early Discoverers XXXVI: W.J. McGee On Glacial Erosion Laws and the Development of Glacial Valleys, Journal of Glaciology 35, no.121121 (Jan 2017): 419–425.https://doi.org/10.3189/S0022143000009357Michael J. Bovis The Interior Mountains and Plateaus, (): 469–515.https://doi.org/10.1130/DNAG-CENT-v2.469