LONG-DISTANCE MARKER HORIZONS FROM SMALL-SCALE ERUPTIONS - BRITISH TEPHRA DEPOSITS FROM THE AD 1510 ERUPTION OF HEKLA, ICELAND

Icelandic tephras in northwest Europe that have been linked to specifi c eruptions include those from the major Holocene tephras Hekla 4, Hek la 3, Hekla AD 1104 and Oraefajokull AD 1362. Eight other tephras have been identified in the British Isles and Scandinavia, but they have n ot been correlated to specific eruptions. Icelandic tephras with volum es at least an order of magnitude smaller than the major Holocene depo sits are also capable of forming extensive marker horizons, and althou gh in distant parts these tephras may cover areas >1 x 10(3) km(2), th eir distributions are not continuous. In this paper, tephra deposits f rom the British Isles, correlated with deposits from the AD 1510 erupt ion of Hekla (Iceland), are assessed as an example of a distant marker horizon that has been formed by a tephra of a comparatively small vol ume. Important implications are that these types of tephras may have f ormed some, if not all, of the eight currently unattributed horizons k nown in the British Isles, and that extensive tephra horizons are not necessarily associated with environmentally significant eruptions.