Ambiguous "Glacial" Striae Formed Near Waterbodies

1971 ◽  
Vol 8 (4) ◽  
pp. 477-479 ◽  
Author(s):  
A. G. McLellan
Keyword(s):  
Ice Sheets ◽  
Lake Ice ◽  
Direction Of Movement ◽  
Continental Ice Sheets

Striations indistinguishable from glacial striations are formed by boulders pushed shore-wards by lake ice. Thus striations alone do not provide unequivocal evidence for the direction of movement of continental ice sheets.

scholarly journals Last Glacial Maximum and Holocene Climate in CCSM3

2006 ◽  
Vol 19 (11) ◽  
pp. 2526-2544 ◽  
Author(s):  
Bette L. Otto-Bliesner ◽  
Esther C. Brady ◽  
Gabriel Clauzet ◽  
Robert Tomas ◽  
Samuel Levis ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Ice Sheets ◽  
Ocean Model ◽  
Arctic Sea Ice ◽  
Glacial Maximum ◽  
Climate System Model ◽  
Last Glacial ◽  
Global Cooling ◽  
Climate Forcings ◽  
Continental Ice Sheets

Abstract The climate sensitivity of the Community Climate System Model version 3 (CCSM3) is studied for two past climate forcings, the Last Glacial Maximum (LGM) and the mid-Holocene. The LGM, approximately 21 000 yr ago, is a glacial period with large changes in the greenhouse gases, sea level, and ice sheets. The mid-Holocene, approximately 6000 yr ago, occurred during the current interglacial with primary changes in the seasonal solar irradiance. The LGM CCSM3 simulation has a global cooling of 4.5°C compared to preindustrial (PI) conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at LGM. Tropical sea surface temperature (SST) cools by 1.7°C and tropical land temperature cools by 2.6°C on average. Simulations with the CCSM3 slab ocean model suggest that about half of the global cooling is explained by the reduced LGM concentration of atmospheric CO2 (∼50% of present-day concentrations). There is an increase in the Antarctic Circumpolar Current and Antarctic Bottom Water formation, and with increased ocean stratification, somewhat weaker and much shallower North Atlantic Deep Water. The mid-Holocene CCSM3 simulation has a global, annual cooling of less than 0.1°C compared to the PI simulation. Much larger and significant changes occur regionally and seasonally, including a more intense northern African summer monsoon, reduced Arctic sea ice in all months, and weaker ENSO variability.

scholarly journals Source, Transportation and Deposition of Debris on Arapaho Glacier, Front Range, Colorado, U.S.A.

1975 ◽  
Vol 14 (72) ◽  
pp. 407-420 ◽  
Author(s):  
Marith Jean Reheis
Keyword(s):  
Ice Sheets ◽  
Front Range ◽  
Denudation Rate ◽  
The Past ◽  
Glacier Front ◽  
Till Fabric ◽  
Continental Ice Sheets

This study was undertaken to determine the sources of debris and methods of transportation and deposition in and on a small cirque glacier. Data were collected on the amount of debris, stone roundness, the presence of striations and polish, and till fabric. Lichenometry gave relative ages of the tills, and suggests that the Gannett Peak till is of at least three ages and probably overlies Audubon till.Debris originating from subglacial erosion can be differentiated from that from rockfall or avalanches on stone roundness, polish and striations. A maximum of 70% of the present glacial load derives from subglacial erosion, as compared to 88% during the Gannett Peak stade. Rockfall rates are 35-50 m3/year at present and were 290–485 m3/year during the Gannett Peak stade. Data on present-day processes and on the volume and age of Gannett Peak moraines can be used to make comparisons on present and past rates of denudation. The denudation rate in the cirque at present is 95–165 mm/1 000 year; in the past it was 4 920-8 160 mm/ 1 000 year. The denudation rate and the glacial effects on debris are comparable to rates from other glacial areas and effects on debris carried by valley glaciers and continental ice sheets.

scholarly journals Erosion by Continental Ice Sheets

1979 ◽  
Vol 23 (89) ◽  
pp. 401-402
Author(s):  
I. M. Whillans
Keyword(s):  
Mass Balance ◽  
Short Distance ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Present Theory ◽  
Frictional Heat ◽  
Break Up ◽  
Basal Melting ◽  
Continental Ice Sheets

Abstract Some of the problems with earlier theories for erosion and transport by ice sheets are discussed, and it is noted that those theories cannot simply account for the often-reported finding that most till is derived from bedrock only a few tens of kilometers up-glacier. Considerations of the mass balance of debris in transport lead to the conclusion that ice sheets are capable of transporting most debris only a short distance. The theory that the break-up of bedrock is mostly a preglacial process is developed. The advancing ice sheet collects the debris and then deposits it after a short travel. As the ice sheet first advances over the regolith, debris is frozen onto the base and is carried until basal melting due to geothermal and frictional heat causes lodgment till deposition. Most debris is deposited during the advance of the ice sheet and is carried only a short distance. A generally small amount of debris is carried at higher levels and is deposited during ice standstill and retreat as melt-out and ablation tills. The present theory makes many predictions, among them, that most till units are not traceable over long distances, that thick till sequences represent unstable glacier margins and not necessarily long periods of glacier occupation, and that lodgment tills are to be interpreted in terms of ice advances and ablation tills in terms of ice retreats. This paper is published in full in Journal of Geology, Vol. 86, No. 4, 1978, p. 516–24.

Suppression of earthquakes by large continental ice sheets

Nature ◽  
1987 ◽  
Vol 330 (6147) ◽  
pp. 467-469 ◽  
Author(s):  
Arch C. Johnston
Keyword(s):  
Ice Sheets ◽  
Continental Ice Sheets

Asynchronously coupling the cryosphere and atmosphere in an energy-balance climate model

1997 ◽  
Vol 25 ◽  
pp. 159-164
Author(s):  
Robert S. Steen ◽  
Tamara Shapiro Ledley
Keyword(s):  
Energy Balance ◽  
Sea Ice ◽  
Time Scales ◽  
Climate Model ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Final State ◽  
Coupling Parameters ◽  
Continental Ice Sheets ◽  
Ice Model

A major component of the climate system on the 10 000-100 000 year time-scales is continental ice sheets, yet many of the mechanisms involved in the land-sea-ice processes that affect the ice sheets are poorly understood. In order to examine these processes in more detail, we have developed a coupled energy balance climate-thermodynamic sea-ice—continental-ice-sheet model (CCSLI model). This model includes a hydrologic cycle, a detailed surface energy and mass balance, a thermodynamic sea-ice model, and a zonally averaged dynamic ice-flow model with bedrock depression.Because of the variety of space and time-scales inherent in such a model, we have asynchronously coupled the land—ice model to the other components of the model. In this paper the asynchronous coupling is described and sensitivity studies are presented that determine the values of the asynchronous coupling parameters. Model simulations using these values allow the model to run nearly ten times faster with minimal changes in the final state of the ice sheet.

Slope-induced errors in radar altimetry over continental ice sheets

1983 ◽  
Vol 88 (C3) ◽  
pp. 1617 ◽  
Author(s):  
A. C. Brenner ◽  
R. A. Blndschadler ◽  
R. H. Thomas ◽  
H. J. Zwally
Keyword(s):  
Ice Sheets ◽  
Radar Altimetry ◽  
Continental Ice Sheets

Interglacial climates: Advances in our understanding of warm climate episodes

2010 ◽  
Vol 34 (6) ◽  
pp. 845-856 ◽  
Author(s):  
Danielle Schreve ◽  
Ian Candy
Keyword(s):  
Western Europe ◽  
Ice Sheets ◽  
Ice Cores ◽  
Temperate Climate ◽  
Warm Climate ◽  
Climatic Evolution ◽  
Extreme Cold ◽  
New Research ◽  
Continental Ice Sheets ◽  
Shed Light

The Quaternary is characterized by the alternation of relatively brief periods of temperate climate (interglacials) with episodes of extreme cold, often with the build-up of extensive continental ice sheets. Over the last decade, new research has revealed far greater complexity and diversity in the interglacial record than previously recognized, with temperate-climate episodes of markedly different duration, stability and intensity. These findings not only shed light on the climatic parameters behind changing floras and faunas during the Pleistocene but also aid our understanding of climatic evolution during the Holocene (the current interglacial), in particular the search for the most appropriate past analogues. In this progress report, we review the basis for interglacial complexity, drawing upon the evidence from long continuous terrestrial records in the Mediterranean, Antarctic ice cores and river terrace sequences in western Europe, before using the details of the British Quaternary interglacial record as an example of how marine and terrestrial records can be linked.

scholarly journals Glacier-Bed Landforms of The Prairie Region of North America

1980 ◽  
Vol 25 (93) ◽  
pp. 457-476 ◽  
Author(s):  
S. R. Moran ◽  
Lee Clayton ◽  
R. Leb Hooke ◽  
M.M Fenton ◽  
L.D. Andriashek
Keyword(s):  
United States ◽  
Shear Strength ◽  
North America ◽  
Pore Pressure ◽  
Marginal Zone ◽  
Ice Sheets ◽  
The United States ◽  
A Value ◽  
Basal Sliding ◽  
Continental Ice Sheets

AbstractTwo major types of terrain that formed at or near the bed of Pleistocene continental ice sheets are widespread throughout the prairie region of Canada and the United States. These are (1) glacial-thrust blocks and source depressions, and (2) streamlined terrain.Glacial-thrust terrain formed where the glacier was frozen to the substrate and where elevated pore-pressure decreased the shear strength of the substrate to a value less than that applied by the glacier. The marginal zone of ice sheets consisted of a frozen-bed zone, no more than 2–3 km wide in places, within which glacial-thrust blocks are large and angular. Up-glacier from this zone, the thrust blocks are generally smaller and smoothed. Streamlined terrain begins 2–3 km behind known ice-margin positions and extends tens of kilometres up-glacier Streamlined terrain formed in two ways: (1) erosion of the substrate as a consequence of basal sliding in the sub-marginal thawed-bed zone, and (2) erosional smoothing accompanied by emplacement of till in the lee of thrust blocks where they were deposited and subsequently exposed to thawed-bed conditions as a result of further advance of the glacier.

scholarly journals Sensitivity of Northern Hemispheric continental ice sheets to tropical SST during deglaciation

2004 ◽  
Vol 31 (2) ◽  
Author(s):  
Keith B. Rodgers ◽  
Sylvie Charbit ◽  
Masa Kageyama ◽  
Gwenaëlle Philippon ◽  
Gilles Ramstein ◽  
...  
Keyword(s):  
Ice Sheets ◽  
Northern Hemispheric ◽  
Continental Ice Sheets

scholarly journals Modelled subglacial floods and tunnel valleys control the lifecycle of transitory ice streams

2018 ◽  
Author(s):  
Thomas Lelandais ◽  
Édouard Ravier ◽  
Stéphane Pochat ◽  
Olivier Bourgeois ◽  
Christopher D. Clark ◽  
...  
Keyword(s):  
Ice Sheets ◽  
Drainage System ◽  
Water Drainage ◽  
Ice Streams ◽  
Drainage Systems ◽  
Bed Erosion ◽  
Physical Experiments ◽  
Flow Speeds ◽  
Continental Ice Sheets ◽  
Mass Transfers

Abstract. Ice streams are corridors of fast-flowing ice that control mass transfers from continental ice sheets to oceans. Their flow speeds are known to accelerate and decelerate, their activity to switch on and off, and even their locations to shift entirely. Our analogue physical experiments reveal that a lifecycle incorporating evolving subglacial meltwater routing and bed erosion can govern this complex transitory behaviour. The model ice streams switch on when subglacial water pockets drain as marginal outburst floods. Then they decelerate as basal coupling increases as a consequence of the lubricating water drainage system spontaneously organising itself into channels that erode tunnel valleys. They surge or jump in location when these water drainage systems maintain low discharge but they ultimately switch off when tunnel valleys have expanded to develop efficient drainage systems. Beyond reconciling previously disconnected observations of modern and ancient ice streams into a single lifecycle, the modelling suggests that tunnel valley development may be crucial in stabilising portions of ice sheets during periods of climate change.

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