Tephrochronological Studies of Holocene Glacier Fluctuations in South Iceland

Abstract

Stratigraphic studies of tephra layers interbedded with soils have been used to date accurately Holocene glacier fluctuations in southern Iceland. 132 sections up to 11 m deep, and containing up to 78 tephra layers, were logged to a resolution of 0.25 cm. The chronological framework was completed with 15 radiocarbon dates, and by examining the association of the tephra stratigraphy with moraines representing former ice margins, a chronology of Holocene glacier fluctuations was constructed. The forelands of five non-surging glaciers were studied: Seljavallajökull, Gigjökull and Steinholtsjökull (outlets of Eyjafjallajökkull) and Sólheimajökull and Klifurárjökull (outlets of Mýjrdalsjökull). This study has shown for the first time that a large ice mass existed in mid-Holocene Iceland, because after 7000 BP and before 4500 BP Sólheimajökull extended up to 5 km beyond its present limits. Major advances also culminated before 3100 BP, and between 1400–1200 BP. In the tenth century AD the glacier was also longer than during the Little Ice Age (1600–1900 AD). In contrast, Klifurárjökull and all the outlets of Eyjafjallajökull reached a maximum Holocene extent during the Little Ice Age. The anomalous behaviour of Sólheimajökull is probably a result of catchment changes caused by the development of the Mýrdalsjökull ice cap over the last 5000 years. This study highlights the great value of apparently anomalous glacier behaviour to studies of climatic change, but it draws attention to the caution that should be used when interpreting the climatic significance of patterns of glacier fluctuations deduced from glacial deposits.