SOURCE OF ASH-ZONE-1 IN THE NORTH-ATLANTIC

Geochemical evidence shows that the silicic component of the widesprea d Ash Zone 1 in the North Atlantic is derived from a major ignimbrite- forming eruption which occurred at the Katla caldera in southern Icela nd during the transition from glacial to interglacial conditions in Yo unger Dryas time. Both trace and major element evidence of the rhyolit ic products excludes the Or ae fajokull volcano as a source. The high- Ti basaltic component in the marine ash zone can also be attributed to contemporaneous eruption in the Katla volcanic complex. Dispersal of tephra from this event is primarily attributed to the generation of co -ignimbrite ash columns in the atmosphere, with ash fallout on both se a ice and on the ocean floor north and east of Iceland. Owing to the c hanging ocean circulation characteristics of the glacial regime, inclu ding suppression of the Irminger Current and a stronger North Atlantic Current, tephra was rafted on sea ice south into the central North At lantic and deposited as dispersed Ash Zone 1. Sediments south of Icela nd also show evidence of the formation of ash turbidites, generated ei ther by the entrance of pyroclastic flows into the sea, or during disc harge of jokulhlaups or glacier bursts from this sub-glacial eruption.