| Summary: | The results of a combined geophysical and geomorphological investigation of thermal-contraction-crack polygons in Northern Victoria Land (Antarctica) are reported. An area of ~30,000 m2 characterized by random orthogonal polygons was investigated using 10 GPR and 2 ERT surveys. The terrain consists of Holocene-age raised beaches. The polygons are well developed only on beaches that are >14 m above current sea level. Uplift curves for the region suggest the beaches formed between 4.2 and 6.3 ka BP. Sections were excavated through two of the fissures that form the polygons. There was good correlation between field observations and GPR (250 Mhz) data. It is concluded that the polygons are composite in nature because the shallow linear depressions that outline the polygons are underlain by fissures that can contain both sandy gravel (i.e., sand wedges) and foliated gravelly ice (i.e., ice wedges) in the same polygon network. Generally, the ice infill is less common than the sandy gravel infill. While thermal-contraction-cracking is the principle mechanism for polygon formation, it is suggested that local micro-site conditions, mainly snow distribution, leads to the different type of fissure infill
|
|---|