Allan Hills Far Western Icefield
The Allan Hills Far Western Icefield (76º54'S 157º01'E) is a large bare ice area lying approximately 70 kilometers southwest of the Allan Hills (ALH-DAV-Figure 1 - 46 KB JPEG). This sinuous icefield, trending northwest, is nearly 45 kilometers long and up to 8 kilometers across at its widest point. Approximately 100 square kilometers of ice is exposed. The Far Western Icefield is shown in a Landsat image (ALH4-Figure 1 - 44 KB JPEG), along with the locations of three slope profiles. The slope profiles are given in ALH4-Figure 2 (13 KB JPEG) to show the general trend of topography in the area.
The Far Western Icefield was first visited during the 1982-1983 season. Systematic searches were made in selected areas and 45 meteorites were recovered. One meteorite (ALH 82102) was discovered in the process of emerging from the ice as the surface was ablating. A satellite surveying instrument was employed during this season to determine three base station locations used in the meteorite location surveys. These points potentially can be used in the study of ice movement rates. A brief visit was made during the 1983-1984 season, mainly to collect ice samples and begin the survey traverse that connected all the Allan Hills icefields. Systematic searches of virtually the entire blue ice area were made in the following two field seasons. During the 1990-1991 season the southeastern end of the Far Western Icefield was visited for the purpose re-surveying ice motion points using satellite positioning methods. Some of the areas systematically searched in previous seasons were again searched in detail. Nine additional meteorites were recovered. A few hours were spent at the Far Western Icefield during the 1999-2000 season assessing the area for an emergency landing area for aircraft. One specimen was found.
The Far Western Icefield is the area from which the infamous Martian meteorite ALH 84001 was recovered. ALH4-Figure 3 (34 KB) shows the location on a satellite image.
ALH4-Table 1 gives a tabulation of meteorite types recovered from the Far Western icefield
Crude surveying methods were used to determine meteorite positions during the 1982-83 season. In subsequent seasons most of the meteorite locations and the 1982-1983 base stations were surveyed with the theodolite and EDM. Thus, the relative locations between the 1982-1983 specimens and all the others are not precise. The locations of eight meteorites (ALH 82109, ALH 82116, ALH 82137, ALH 83105, ALH 83108, ALH 84221, ALH 85004, and ALH 85012) were determined only very generally,and positions therefore approximate.
In the 1983-1984 season two carbonaceous chondrite scatter fields were found near the southern end of the icefield. In the larger of the two, 56 fragments were recovered. These have been paired, and are named ALH 83100. The location of ALH 83102 was the site of a smaller scatter field consisting of 21 paired fragments. It was located approximately 50 meters from the larger one. Both sets of specimens probably are parts of the same pairing group.
Acknowledgments; We thank William Cassidy, Tony Meunier and Carl Thompson (1982-1983); William Cassidy, Robert Fudali, A.C. Hitch, Kunihiko Nishiizumi, Paul Pellas, Ludolf Schultz, John Schutt, and Paul Sipiera (1983-1984); Catherine King-Frazier, Scott Sandford, Roberta Score, John Schutt, Carl Thompson, and Robert Walker (1984-1985); Ludolf Schultz, John Schutt, Ernst Zinner, and Michael Zolensky (1985-1986); Sue Iveson, Suzanne Traub-Metlay, John Schutt, and Peter Wasilewski for their contributions. John Schutt accompanied the landing site assessment group during the 1999-2000 season. Tony Meunier of the U.S.G.S. provided location data for the 1982-1983 meteorites and satellite positioning-derived base station coordinates.
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