Buried soil cracks in alluvium near Braidwood, NSW

Abstract

Buried soil cracks developed within sandy alluvium are described from the Upper Shoalhaven Valley south-west of Braidwood. The cracks, 10-40 mm wide and filled with an indurated sandy matrix, are about 1 m apart, up to 1.75 m deep, and arranged in a polygonal pattern. Determinations are made of the field and laboratory characteristics of the materials in which the cracks are developed and of the in-fill matrix, and these characteristics are related to possible mechanisms of formation. One possible group of mechanisms is seasonal frost-induced cracking associated with periodic filling in of the cracks by wind- or water-borne debris, then partial truncation of the materials followed by burial under alluvium. The cracks are unlikely to be more than c. 21 000 years old, and may be younger.