scholarly journals Configuration and Dynamics of the Laurentide Ice Sheet During the Late Wisconsin Maximum

2007 ◽  
Vol 36 (1-2) ◽  
pp. 5-14 ◽  
Author(s):  
Arthur S. Dyke ◽  
Lynda A. Dredge ◽  
Jean-Serge Vincent
Keyword(s):  
Ice Sheet ◽  
Gravity Anomalies ◽  
Late Glacial ◽  
Laurentide Ice Sheet ◽  
Geological Evidence ◽  
Original Proposal ◽  
Field Evidence ◽  
Free Air ◽  
Free Air Gravity ◽  
Basin Region

ABSTRACT Prior to 1943 the Laurentide Ice Sheet was considered to have three major domes centered in Keewatin, Labrador, and Patricia (TYRRELL, 1898 a, b; 1913). FLINT (1943) argued that these centres were of only local and temporary importance and favoured a single-domed ice sheet. Despite the lack of supporting geological evidence, and despite the proposition of a Foxe Dome in the interim (IVES and ANDREWS, 1963), the single-dome concept was not seriously challenged until the late 1970's and, in fact, is still strenuously supported (HUGHES era/., 1977 ; DENTON and HUGHES, 1981). This paper extends and modifies recent conclusions that the Laurentide Ice Sheet had more than one dome at the Late Wisconsin maximum. We propose a model incorporating five domes (M'Clintock, Foxe, Labrador, Hudson, and (?) Caribou) based on the position of ice divides, ice flow patterns, drift composition, late-glacial features, postglacial isostatic recovery and free-air gravity anomalies. Our Labrador and Hudson domes closely correspond to Tyrrell's Labradorean and Patrician ice sheets; our Caribou and M'Clintock domes together with the Franklin Ice Complex over the Queen Elizabeth Islands north of the Laurentide Ice Sheet, correspond to Tyrrell's original Keewatin Ice Sheet. The style of glaciation of the Foxe Basin region was not known to Tyrrell, but our reconstruction of the Foxe Dome is in close agreement with the original proposal of Ives and Andrews. Like Tyrrell, our reconstruction is based on field evidence obtained through extensive mapping; the single dome model continues to be unsupported by geological data.

Isostatic response to loading of the crust in Canada

1970 ◽  
Vol 7 (2) ◽  
pp. 716-727 ◽  
Author(s):  
R. I. Walcott
Keyword(s):  
Close Association ◽  
Ice Sheet ◽  
Ground Surface ◽  
Gravity Anomalies ◽  
A Value ◽  
Free Air ◽  
Ice Loads ◽  
Anomaly Map ◽  
Free Air Gravity ◽  
Free Air Anomaly

A smoothed free air anomaly map of Canada indicates that the central part of the region occupied by the Laurentide Ice Sheet is over-compensated. Due to the close association of the free air gravity, the apparent crustal warping, the time of deglaciation, and the congruence of the gravity anomalies and the Wisconsin Glaciation, it is concluded that the over-compensation is due to incomplete recovery of the lithosphere from the displacement caused by the Pleistocene ice loads. The amplitude of the anomalies, about –50 milligals, suggests that a substantial amount of uplift has yet to occur and that the relaxation time of crustal warping is of the order of 10 000 to 20 000 y.The profile of the ground surface at the edge of a continental ice sheet on an elastic lithosphere is assessed using a value of the flexural parameter of the lithosphere calculated from gravity and deformation studies in the Interior Plains. The conclusions are: (a) a purely elastic forebulge is not likely to reach an amplitude of more than a few tens of meters; (b) the crust will be depressed for a considerable distance beyond the edge of the ice sheet; and (c) for large ice sheets crustal failure will probably occur in a preferential zone several hundred kilometers inside the maximum ice limit.

Implications of Late Pleistocene Glaciation of the Tibetan Plateau for Present-Day Uplift Rates and Gravity Anomalies

1997 ◽  
Vol 48 (3) ◽  
pp. 267-279 ◽  
Author(s):  
Georg Kaufmann ◽  
Kurt Lambeck
Keyword(s):  
Tibetan Plateau ◽  
Late Pleistocene ◽  
Ice Sheet ◽  
Gravity Anomalies ◽  
The Tibetan Plateau ◽  
Pleistocene Glaciation ◽  
Free Air ◽  
Uplift Rates ◽  
Free Air Gravity ◽  
Central Tibet

Minimal and maximal models of Late Pleistocene Glaciation on the Tibetan Plateau are considered. The large ice sheet models indicate that disintegration of the ice sheet could have contributed up to 7 mm/yr of present vertical uplift and 2 mm/yr of horizontal extension. The former value can account for more than 50% of the observed uplift in central Tibet. The peak free-air gravity anomaly arising from the deglaciation would be around −5.4 mGal. In contrast, the smaller ice sheet models do not contribute significantly to the signals of present uplift and gravity anomalies. Modern geodetic measurements therefore have the potential to constrain the Late Pleistocene glaciation of the Tibetan Plateau. Assuming a large ice sheet over the Tibetan Plateau, the disintegration can contribute up to 6 m of eustatic sea-level rise.

5. Gravity and the figure of the Earth

2018 ◽  
pp. 69-91
Author(s):  
William Lowrie
Keyword(s):  
Accurate Determination ◽  
Measurement Techniques ◽  
Gravity Anomalies ◽  
Dynamic Processes ◽  
The Core ◽  
The Earth ◽  
Free Air ◽  
Figure Of The Earth ◽  
Free Air Gravity

‘Gravity and the figure of the Earth’ discusses the measurement of gravity and its variation at the Earth’s surface and with depth. Gravity is about 0.5 per cent stronger at the poles than at the equator and it first increases with depth until the core–mantle boundary and then sinks to zero at the Earth’s centre. Using satellites to carry out geodetic and gravimetric observations has revolutionized geodesy, creating a powerful geophysical tool for observing and measuring dynamic processes on the Earth. The various measurement techniques employed fall in two categories: precise location of a position on the Earth (such as GPS) and accurate determination of the geoid and gravitational field. Bouguer and free-air gravity anomalies and isostasy are explained.

Empirical Determination of the Gravity Anomaly Covariance Function in Mountainous Areas

1980 ◽  
Vol 34 (3) ◽  
pp. 251-264 ◽  
Author(s):  
Gerard Lachapelle ◽  
K. P. Schwarz
Keyword(s):  
Gravity Anomaly ◽  
Covariance Function ◽  
Physical Geodesy ◽  
Gravity Anomalies ◽  
Mountainous Areas ◽  
The North ◽  
Regression Parameters ◽  
Free Air ◽  
Vening Meinesz ◽  
Free Air Gravity

An evaluation of the empirical gravity anomaly covariance function using over 95 000 surface gravity anomalies in the North American Western Cordillera was carried out. A regression analysis of the data exhibits a strong and quasi-linear correlation of free air gravity anomalies with heights. This height correlation is removed from the free air anomalies prior to the numerical evaluation of the gravity anomaly covariance function. This covariance function agrees well with that evaluated previously by the authors for the remainder of Canada. A possible use for such a covariance function of ‘height independent’ gravity anomalies in mountainous areas is described. First, the height independent gravity anomaly at a point of known height is evaluated by least squares prediction using neighboring measured height independent gravity anomalies. Secondly, the part caused by the height correlation is calculated using linear regression parameters estimated previously and added to the predicted height independent gravity anomaly to obtain a predicted standard free air anomaly. This technique can be used to densify the coverage of free air anomalies for subsequent use in integral formulas of physical geodesy, e.g., those of Stokes and Vening Meinesz. This method requires that point topographic heights be given on a grid.

Free air gravity anomalies over the oceans from Seasat and GEOS 3 altimeter data

Eos ◽  
1987 ◽  
Vol 68 (2) ◽  
pp. 17 ◽  
Author(s):  
G. Balmino ◽  
B. Moynot ◽  
M. Sarrailh ◽  
N. Valès
Keyword(s):  
Gravity Anomalies ◽  
Altimeter Data ◽  
Free Air ◽  
Free Air Gravity
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