Chapter 36 - Iceland: glacial landforms prior to the Last Glacial Maximum

Abstract

Glacial sediments and landforms older than the Late Weichselian are rare in Iceland but alternating sedimentary and volcanic formations in the bedrock stratigraphy indicate earlier glacials and interglacials, even as far back as 5–7 million years. This is particularly prominent in the stratigraphy of the Tjörnes Peninsula, N-Iceland, from around 2.6 million years ago, with five extensive glaciations until the Eemian Interglacial. Within the northern and western volcanic zones, similar climatological cyclicity is revealed by the stratigraphy of different volcanic systems where alternating hyaloclastites and lava flows are formed during glacial and ice-free conditions. Likewise, hyaloclastite ridges and tuyas (table mountains) are indicative of volcanic eruptions under ice as opposed to shield volcanoes and extensive lava flows formed during ice-free conditions. Based on relative ages, it has been speculated that some of these formations represent a cyclicity from Marine Isotope Stage (MIS) 12 (the Elsterian glacial), through the Holsteinian Interglacial (MIS 11) and the Saalian glacial (MIS 6), to the Eemian Interglacial (MIS 5e), but the lack of absolute ages makes this inference only hypothetical. Indications of glacial oscillations during the Early Weichselian occur in the bedrock stratigraphy but are poorly constrained in age. Formations from the Middle Weichselian (MIS 3) are best preserved in Southwest Iceland where they have been studied and dated, suggesting that the ice did not extend onto the southwestern shelf during the latter part of MIS 3.