The formation of a palagonite breccia mass beneath a valley glacier in Iceland

Abstract

A mass of palagonite breccia, with associated palagonite tuffs, basalt pillows, and large bodies of columnar basalt, is described from southeastern Iceland. It rests upon a glacially striated surface, with or without a thin intervening tillite layer. The mass is probably of early Pleistocene age and the evidence shows that the basalt which gave rise to it flowed down a valley beneath a valley-glacier. The mass has a present volume of 1.5 km 3 (the original volume must have been several time s this) and the basalt flowed certainly for 22 km, and probably for 35 km, beneath the ice. It is believed to have flowed through a central conduit along the valley bottom, and the breccia and contained pillows mainly developed by escape of the basalt upwards and sideways from this conduit into the glacier or its melt-waters.