A 6500-YEAR-OLD HISTORY OF TEPHRA DEPOSITION RECORDED IN THE SEDIMENTS OF LAKE-TUTIRA, EASTERN NORTH-ISLAND, NEW-ZEALAND

Lake Tutira is a small lake formed as a result of a landslide about 65 00 radiocarbon years BP. It is situated 100 km east, and downwind, of the central North Island volcanoes and has provided a trap for tephras which have erupted since the mid-Holocene. Detailed studies of cores from the lake and adjacent swamps have revealed 23 tephra layers, whic h represent tephra deposition into Lake Tutira every 300 years on aver age. Sixteen of these layers are macroscopic and seven are microscopic , occurring as concentrations of volcanic glass. The tephra layers mar k rhyolitic and andesitic tephra eruptions from Taupo, Okataina, Egmon t, and Tongariro volcanic centres. They were identified using their fe rromagnesian mineralogy, major element compositions of glass shards, a nd their stratigraphic position, particularly with respect to radiocar bon dates. The Lake Tutira tephra record is the most detailed record y et found in eastern North Island, and the detection of microscopic tep hra layers indicates the value of lake sediments and swamps as traps f or distal tephras. Copyright (C) 1996 INQUA/Elsevier Science Ltd