Derived bedrock elevations, strain rates and stresses from measured surface elevations and velocities: Jakobshavns Isbræ, Greenland
Abstract Jakobshavns Isbræ (69 °10′ N, 49 °59′ W) drains about 6.5% of the Greenland ice sheet and is the fastest ice stream known. The Jakobshavns Isbræ basin of about 10 000 km 2 was mapped photogrammetrically from four sets of aerial photography, two taken in July 1985 and two in July 1986. Posit...
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Language: | English |
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Cambridge University Press (CUP)
1995
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Online Access: | http://dx.doi.org/10.1017/s0022143000017858 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000017858 |
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crcambridgeupr:10.1017/s0022143000017858 2024-03-03T08:45:00+00:00 Derived bedrock elevations, strain rates and stresses from measured surface elevations and velocities: Jakobshavns Isbræ, Greenland Fastook, James L. Brecher, Henry H. Hughes, Terence J. 1995 http://dx.doi.org/10.1017/s0022143000017858 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000017858 en eng Cambridge University Press (CUP) Journal of Glaciology volume 41, issue 137, page 161-173 ISSN 0022-1430 1727-5652 Earth-Surface Processes journal-article 1995 crcambridgeupr https://doi.org/10.1017/s0022143000017858 2024-02-08T08:36:15Z Abstract Jakobshavns Isbræ (69 °10′ N, 49 °59′ W) drains about 6.5% of the Greenland ice sheet and is the fastest ice stream known. The Jakobshavns Isbræ basin of about 10 000 km 2 was mapped photogrammetrically from four sets of aerial photography, two taken in July 1985 and two in July 1986. Positions and elevations of several hundred natural features on the ice surface were determined for each epoch by photogrammetric block aerial triangulation, and surface velocity vectors were computed from the positions. The two flights in 1985 yielded the best results and provided most common points (716) for velocity determinations and are therefore used in the modeling studies. The data from these irregularly spaced points were used to calculate ice elevations and velocity vectors at uniformly spaced grid points 3 km apart by interpolation. The field of surface strain rates was then calculated from these gridded data and used to compute the field of surface deviatoric stresses, using the flow law of ice, for rectilinear coordinates, X, Y pointing eastward and northward, and curvilinear coordinates. L, Τ pointing longitudinally and transversely to the changing ice-flow direction, Ice-surface elevations and slopes were then used to calculate ice thicknesses and the fraction of the ice velocity due to basal sliding. Our calculated ice thicknesses are in fair agreement with an ice-thickness map based on seismic sounding and supplied to us by K. Echelmeyer. Ice thicknesses were subtracted from measured ice-surface elevations to map bed topography. Our calculation shows that basal sliding is significant only in the 10–15 km before Jakobshavns Isbræ becomes afloat in Jakobshavns Isfjord. Article in Journal/Newspaper Greenland Ice Sheet Journal of Glaciology Cambridge University Press Greenland Isfjord ENVELOPE(-26.917,-26.917,73.333,73.333) Journal of Glaciology 41 137 161 173 |
institution |
Open Polar |
collection |
Cambridge University Press |
op_collection_id |
crcambridgeupr |
language |
English |
topic |
Earth-Surface Processes |
spellingShingle |
Earth-Surface Processes Fastook, James L. Brecher, Henry H. Hughes, Terence J. Derived bedrock elevations, strain rates and stresses from measured surface elevations and velocities: Jakobshavns Isbræ, Greenland |
topic_facet |
Earth-Surface Processes |
description |
Abstract Jakobshavns Isbræ (69 °10′ N, 49 °59′ W) drains about 6.5% of the Greenland ice sheet and is the fastest ice stream known. The Jakobshavns Isbræ basin of about 10 000 km 2 was mapped photogrammetrically from four sets of aerial photography, two taken in July 1985 and two in July 1986. Positions and elevations of several hundred natural features on the ice surface were determined for each epoch by photogrammetric block aerial triangulation, and surface velocity vectors were computed from the positions. The two flights in 1985 yielded the best results and provided most common points (716) for velocity determinations and are therefore used in the modeling studies. The data from these irregularly spaced points were used to calculate ice elevations and velocity vectors at uniformly spaced grid points 3 km apart by interpolation. The field of surface strain rates was then calculated from these gridded data and used to compute the field of surface deviatoric stresses, using the flow law of ice, for rectilinear coordinates, X, Y pointing eastward and northward, and curvilinear coordinates. L, Τ pointing longitudinally and transversely to the changing ice-flow direction, Ice-surface elevations and slopes were then used to calculate ice thicknesses and the fraction of the ice velocity due to basal sliding. Our calculated ice thicknesses are in fair agreement with an ice-thickness map based on seismic sounding and supplied to us by K. Echelmeyer. Ice thicknesses were subtracted from measured ice-surface elevations to map bed topography. Our calculation shows that basal sliding is significant only in the 10–15 km before Jakobshavns Isbræ becomes afloat in Jakobshavns Isfjord. |
format |
Article in Journal/Newspaper |
author |
Fastook, James L. Brecher, Henry H. Hughes, Terence J. |
author_facet |
Fastook, James L. Brecher, Henry H. Hughes, Terence J. |
author_sort |
Fastook, James L. |
title |
Derived bedrock elevations, strain rates and stresses from measured surface elevations and velocities: Jakobshavns Isbræ, Greenland |
title_short |
Derived bedrock elevations, strain rates and stresses from measured surface elevations and velocities: Jakobshavns Isbræ, Greenland |
title_full |
Derived bedrock elevations, strain rates and stresses from measured surface elevations and velocities: Jakobshavns Isbræ, Greenland |
title_fullStr |
Derived bedrock elevations, strain rates and stresses from measured surface elevations and velocities: Jakobshavns Isbræ, Greenland |
title_full_unstemmed |
Derived bedrock elevations, strain rates and stresses from measured surface elevations and velocities: Jakobshavns Isbræ, Greenland |
title_sort |
derived bedrock elevations, strain rates and stresses from measured surface elevations and velocities: jakobshavns isbræ, greenland |
publisher |
Cambridge University Press (CUP) |
publishDate |
1995 |
url |
http://dx.doi.org/10.1017/s0022143000017858 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000017858 |
long_lat |
ENVELOPE(-26.917,-26.917,73.333,73.333) |
geographic |
Greenland Isfjord |
geographic_facet |
Greenland Isfjord |
genre |
Greenland Ice Sheet Journal of Glaciology |
genre_facet |
Greenland Ice Sheet Journal of Glaciology |
op_source |
Journal of Glaciology volume 41, issue 137, page 161-173 ISSN 0022-1430 1727-5652 |
op_doi |
https://doi.org/10.1017/s0022143000017858 |
container_title |
Journal of Glaciology |
container_volume |
41 |
container_issue |
137 |
container_start_page |
161 |
op_container_end_page |
173 |
_version_ |
1792500515635986432 |