Variability of tephra in lake and catchment sediments, Svínavatn, Iceland

Lake and catchment sediments of Svínavatn in Húnavatnsýssla, northern Iceland contain a complex sequence of primary airfall and secondary reworked tephra layers. A detailed tephrochronology was constructed by identifying and correlating 95 tephra layers from four lake cores and 12 profiles situated in the lowland peats, hillslopes and delta areas of the catchment. The tephra record from each site was highly variable due to both uneven fallout of tephra following the eruption, and later reworking of the deposits in the lake and catchment. The complete tephrochronology includes Hekla 4 ( 3800 years BP), Hekla 3 ( 2800 years BP), the Landnámslag, or Settlement Layer (Vö AD 900), Hekla 1 (AD 1104) and Hekla AD 1300. Two more unidentified and undated tephra layers are also present (one from the Snaefellsjökull system, and one from the Veidivötn volcanic swarm). The correlation of tephra stratigraphies from lake sediments and catchment profiles indicates periods of increased erosion and redeposition in the catchment shortly after the deposition of Hekla 3 possibly due to deteriorating climate during the Neoglaciation.