Peat and lake sediment cores from Peninsula Muñoz Gamero in the southernmost Main Andean Cordillera, and also Seno Skyring fjord and Peninsula Brunswick in the Andean foothills, have been investigated to refine the local Holocene tephrochronology. New 14C ages, together with calculated peat growth and sedimentation rates, provide age constraints. The thickest (5-15 cm) tephra layer in the cores resulted from an eruption of the Mount Burney volcano at approximately 4254±120 cal. yr BP. Isopach maps for this eruption indicate deposition of approximately 2.5_3 km³ of tephra, mainly in the forested Andean area southeast of the volcano. Mount Burney had another large Plinian eruption between 9009±17 and 9175±111 cal. yr BP, and also four smaller eruptions during the Holocene. Tephra from large explosive eruptions of the Reclus (>15384±578 cal. yr BP), Hudson (between 7707±185 and 7795±131 cal. yr BP) and Aguilera (<3596±230 cal. yr BP) volcanoes also occur in some of the cores as indicated by the characteristic compositions of their tephra glass, which differ both from each other and also from that of tephra derived from Mount Burney. Significant loss of alkali elements during alteration of the volcanic glass in the tephra layers was observed, especially within acid peat soils, and this may be an important factor in the plant nutrient supply.