Glacially folded outwash near Lago Llanquihue, southern Lake District, Chile

Folded outwash occurs in four distinct clusters in an arcuate arrangement j ust west of the terminal Llanquihue moraines deposited by the Lago Llanquih ue piedmont ice lobe at the last glacial maximum. These clusters are physic ally connected along the eastern side to the Llanquihue terminal moraines, and along the western side to the Llanquihue outwash plain. Each cluster co nsists of three to eleven elongated ridges. The maximum height of individua l ridges varies from cluster to cluster beween 18 and 28 m; the maximum len gth of individual ridges is between 93 and 1074 m. The average orientation of the ridges ranges over a 60 degrees sector relative to former ice-flow d irection. The folded outwash sediments are cut by two distinct internal fau lt systems with only a faint surface expression below the Holocene top soil . The folded outwash ridges are interpreted as a push moraine system produced by the same mechanical forces that act in a critically tapered wedge. The folded sediment is a sandy gravel with an angle of friction on the order of phi = 40 degrees. Interpretations of structural data and of mechanical com parisons point to a basal thrust plane in a sand unit with phi, between 24 degrees and 30 degrees and with a pore water pressure index of lambda = 0.7 . It is very unlikely that the observed and analyzed features were formed und er permafrost conditions.