Ice-Cored Lateral Moraines in Tarfala Valley, Swedish Lapland

Abstract

A morphological study which included detailed mapping and ice fabric studies was conducted on the ice-cored lateral moraines in the Tarfala valley, Lapland, Sweden. This study reveals a close association between the lateral moraines and the adjacent talus tongues. The talus tongues are deflected in their lower portions in the direction of glacier flow. Ridges of talus debris continue down-glacier as distinct features which are here termed talus trails. The talus trails coalesce to form the lateral moraines. These relationships suggest the ice-cored moraines are composed primarily of previously englacial debris and glacier ice. The deflected talus tongues and talus trails represent fossil ice flowlines. The geometry of these flowlines reflects conditions characteristic of an accumulation zone and are thus believed to be a unique class of glacial deposits. These deposits are responsible for the bulk and geometry of the lateral moraines and are also the oldest parts of the moraines. The deflected talus tongues and talus trails are estimated to have been formed between 2400 and 2700 BP. These deposits are used to tentatively infer some aspects of the climatic regime during this period. Reconstruction of local accumulation zones and associated equilibrium lines indicates a mean summer temperature decrease of at least 0.9°C. Morphological considerations indicate an unusually large input of talus debris during this period.