Preliminary Measurements of Growth of Nonsorted Polygons, Victoria Land, Antarctica1
- J. C. F. Tedrow
Published Online: 14 MAR 2013
Copyright © 1966 by the American Geophysical Union.
Antarctic Soils and Soil Forming Processes
How to Cite
Berg, T. E. and Black, R. F. (2013) Preliminary Measurements of Growth of Nonsorted Polygons, Victoria Land, Antarctica1 , in Antarctic Soils and Soil Forming Processes (ed J. C. F. Tedrow), American Geophysical Union, Washington, D. C.. doi: 10.1029/AR008p0061
- Published Online: 14 MAR 2013
- Published Print: 1 JAN 1966
Print ISBN: 9781118655801
Online ISBN: 9781118668719
- Beacon and Taylor Valley;
- Cape Evans;
- Contraction sites;
- Hobbs Glacier;
- Nonsorted polygons;
- Victoria Land;
- Wedges types;
- Wright Valley
Nonsorted polygons are common in Victoria Land, Antarctica. Polygons are usually 10–30 meters in diameter and have associated wedges 20–1000 cm in width. The most common wedge filling is a composite of ice, sand, or rubble. In very dry areas with abundant free-running quartz sand, sand wedges are present. In areas of high moisture where cementation of the active layer by ice occurs, ice wedges are found. The wedges go through a predictable sequence of growth, which is reflected at the surface. Youthful wedges less than 75 cm in width are reflected at the surface by troughs as wide as the wedge. Wedges 75–200 cm in width are outlined by double raised-rims bordering troughs that may reach 50–75 cm above the surface. Double raised-rims are usually masked in areas of ice-cored moraine, due to slumping and sublimation of exposed glacial ice. Double raised-rims reach a maximum height of 1.5 meters in Victoria Valley, where wedges 3–10 meters in width are present. Very mature wedges result in a ‘pimple' surface consisting of small mounds 1–5 meters in diameter and 1–2 meters high separated by troughs over 4 meters in width. Polygons are also developed in thin-bedded Beacon sandstone.
Preliminary measurements of growth rates of 0.5 to 3.8 mm per year for wedges in Victoria Land permit dating of various geomorphic surfaces. Results for recent surfaces appear to be good and in agreement with dates derived from lichen studies, but they vary markedly from carbon-14 dates. Preliminary results indicate: (1) that Hut Point Peninsula was submerged or under ice about 1000 years ago; (2) that water filled Taylor Valley to a depth of 300 meters as recently as 1500 years ago; (3) increasing aridity in Wright Valley since the last glaciation, as evidenced by retreat of some alpine glaciers 700 years ago, retreat of snowfields 250 years ago, and distinct drying out of surficial material on ice-cored moraines. That the last glaciation is more recent than previously thought is evidenced by a date of 500 years for moraine in front of the Hobbs Glacier and 1300 years for a terrace in Wright Valley.
Although dating by polygonal ground is still subject to uncertainties, owing to an inadequate time base and uncertainties regarding the physical environment of growth, results to date do permit the determination of ages of glacial events of an order of magnitude. Where polygons are present, surfaces are less than 10,000 years old; where polygons are absent and the thickness of the surface dry zone is greater than 1 meter, surfaces may be older.