Limited glacial erosion during the last glaciation in mid-latitude cirques (Retezat Mts, Southern Carpathians, Romania)

AbstractA large valley, ideally suited for “selective linear erosion” by ice, extends from the Kreiger Mountains to Tanquary Fiord, north–central Ellesmere Island. During the last glaciation, the outlet glacier at the head of the valley advanced 18 km and was at least 250 m thick where it contacted the sea in the lower valley. Erosion of bedrock inside the last ice limit is recorded by an abraded diabase dike, and by crag–and–tail features developed in limestone. During deglaciation (7800 B.P.), melt–water streams along the ice margin incised a large alluvial fan that pre–dates the last glaciation. The fan shows little alteration by the over–riding ice and its final erosion by the melt–water streams incised, but did not remove, its original ice–wedge polygons.The preservation of the fan indicates that the glacier was locally non–erosive and that it probably advanced across the fan by over–riding a protective frontal ice apron. Although it is commonly assumed that such alluvial fans occupying glaciated valleys are of post–glacial age, this need not be the case in permafrost terrain. In fact, at this site, there has been a net increment of alluvium versus glacial erosion or deposition spanning the last glacial cycle. The paper discusses the processes of erosion associated with sub–polar glaciers and questions whether erosion by them or more pervasive ice is responsible for such High Arctic valleys and fiords.

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Inferences on glacial flow from till clast dispersal, Waterford area, New Brunswick

Géographie physique et Quaternaire ◽

10.7202/004773ar ◽

2002 ◽

Vol 51 (1) ◽

pp. 29-39 ◽

Cited By ~ 8

Author(s):

B. E. Broster ◽

M. D. Munn ◽

A. G. Pronk

Keyword(s):

New Brunswick ◽

Secondary Source ◽

Dispersal Patterns ◽

Glacial Erosion ◽

Central Plateau ◽

Ice Flow ◽

Last Glaciation ◽

Flow Directions ◽

Surrounding Areas ◽

Basal Till

Abstract Dispersal patterns for till clasts from the Waterford area, New Brunswick, are compared to source outcrops and used to confirm dominant ice-flow directions in a region reported to show multiple and conflicting striae directions. The results demonstrate that the last glaciation produced elongated south and eastward trending dispersal patterns, indicative of the dominant ice-flow directions. Clasts have been derived locally. Train lengths generally vary from 4 km to about 10 km for material in basal till, but can achieve distances up to 26 km because of transport in englacial positions. Felsic and intermediate metavolcanic and intrusive clasts occur in till at locations north of outcropping plutons on the Central Plateau. The till overlies part of the Carboniferous Basin and has been derived in part, from underlying conglomerate bedrock. Since these conglomerate units contain fragments from the surrounding areas including the Central Plateau, they provided a secondary source for some lithologies during glaciation. Glacial erosion of underlying conglomerate units may account for occurrences of distinctive till clasts found at other areas of the New Brunswick lowlands, previously thought to imply northward glacial transport.

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Fire Lake depression: a glacially eroded feature in southwestern Saskatchewan, Canada

Canadian Journal of Earth Sciences ◽

10.1139/e88-196 ◽

1988 ◽

Vol 25 (12) ◽

pp. 2130-2138 ◽

Cited By ~ 2

Author(s):

E. A. Christiansen ◽

E. K. Sauer

Keyword(s):

Shear Resistance ◽

Glacial Erosion ◽

Last Glaciation ◽

Surface Removal ◽

Physical Dimensions

Fire Lake depression, which is 9 km long, 5 km wide, and about 100 m deep, was formed by surface removal of about 40 m of drift, mainly till, and 60 m of Cretaceous sands, silts, and clays. The depression, which was formed during the last glaciation, was partly filled with hummocky glaciolacustrine sands and silts. The bedrock beneath the depression is slickensided, folded, brecciated, softened, and gouged, typical of structures formed by shear.The physical dimensions, stratigraphy, structure, and age (last glaciation) indicate that the Fire Lake depression was formed by glacial erosion. The folding, faulting, brecciation, gouge, and softening of the bedrock beneath the depression are indicative of shear and suggest glacial thrusting. The process of glacial thrusting was not verified, however, because the sediments excavated from the depression were not found. The fact that the base of the depression corresponds to the uppermost, most clayey bed (least shear resistance) suggests that the depression was formed during one episode of glacial erosion.

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Glacial Erosion of a High Arctic Valley

Journal of Glaciology ◽

10.1017/s0022143000006882 ◽

1986 ◽

Vol 32 (110) ◽

pp. 60-64 ◽

Cited By ~ 11

Author(s):

John England

Keyword(s):

High Arctic ◽

Alluvial Fan ◽

Alluvial Fans ◽

Glacial Cycle ◽

Glacial Erosion ◽

Outlet Glacier ◽

North Central ◽

Last Glaciation ◽

Melt Water ◽

Ice Wedge

AbstractA large valley, ideally suited for “selective linear erosion” by ice, extends from the Kreiger Mountains to Tanquary Fiord, north–central Ellesmere Island. During the last glaciation, the outlet glacier at the head of the valley advanced 18 km and was at least 250 m thick where it contacted the sea in the lower valley. Erosion of bedrock inside the last ice limit is recorded by an abraded diabase dike, and by crag–and–tail features developed in limestone. During deglaciation (7800 B.P.), melt–water streams along the ice margin incised a large alluvial fan that pre–dates the last glaciation. The fan shows little alteration by the over–riding ice and its final erosion by the melt–water streams incised, but did not remove, its original ice–wedge polygons.The preservation of the fan indicates that the glacier was locally non–erosive and that it probably advanced across the fan by over–riding a protective frontal ice apron. Although it is commonly assumed that such alluvial fans occupying glaciated valleys are of post–glacial age, this need not be the case in permafrost terrain. In fact, at this site, there has been a net increment of alluvium versus glacial erosion or deposition spanning the last glacial cycle. The paper discusses the processes of erosion associated with sub–polar glaciers and questions whether erosion by them or more pervasive ice is responsible for such High Arctic valleys and fiords.

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Über glaziale Erosion und Übertiefung

E&G Quaternary Science Journal ◽

10.3285/eg.46.1.08 ◽

1996 ◽

Vol 46 (1) ◽

pp. 99-119

Author(s):

Karl-Albert Habbe

Keyword(s):

Positive Mass ◽

Glacial Erosion ◽

Motion Mechanism ◽

Mass Budget ◽

Erosion Processes ◽

Last Glaciation ◽

Feeding Area ◽

Alpine Foreland ◽

Longitudinal Extension ◽

Shear Planes

Abstract. Glacial erosion and overdeepening is - as can be shown by the longitudinal profile of every valley formed by glaciers - not a process active on the whole longitudinal extension of the glacier in the same way, but is characterized by marked discontinuities. The reasons have been discussed for nearly a century, but the problem remained unsolved until now. It can - as H. Louis (1952) has demonstrated - be solved only when the motion mechanism of the glaciers is known. The present paper demonstrates on the base of observations in the area of the Iller glacier of the last glaciation that Pleniglacial glaciers with positive mass budget (advancing glaciers) have moved in another way than present-day glaciers with their - mostly - negative mass budget. Furthermore it is demonstrated that this particular motion mechanism can actually be observed at advancing outlet glaciers of the Vatnajökull in Iceland. It is characterized by a summation of numerous push movements of flat ice-shields on shear-planes over stagnant-ice of preceding advances, all of them of relatively short duration and range. They originated in precipitation-caused mass surpluses in the feeding area. This motion mechanism implies that an impact on the underground is possible only where (and when) the glacier advances beyond its stagnant-ice basement, i. e. immediately behind the front of the advancing glacier. A larger amount of glacial erosion can be expected only when the glacier after the advance remained in the maximum position reached for a longer time and, additionally, (snow)meltwater under hydrostatic pressure could affect the underground. Further observations on meltwater movement within the glacier are presented from Iceland, on meltwater impact on the underground (mainly) from the German Alpine Foreland. To sum up, the discontinuities of glacial erosion and overdeepening can be explained by the motion mechanism of advancing glaciers described, the protective effect of the overridden stagnant-ice basement of preceding advances, and the characteristic movement of (snow)meltwater in, below and along the glacier. Because the erosion processes described take place (mainly) immediately behind the front of the advancing glacier, they are a phenomenon restricted in space as well as in time, but therefore must be of extraordinary intensity.

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