Holocene eruptions within the Katla volcanic system, south Iceland: Characteristics and environmental impact

Abstract

– Holocene volcanism within the Katla volcanic system is characterized by: 1) explosive (hydromag-matic) basaltic eruptions along volcanic fissures within the Mýrdalsjökull caldera; 2) explosive silicic eruptions from vents associated with the caldera and 3) predominantly effusive basaltic eruptions involving both the cen-tral volcano and the fissure swarm. Typical Katla eruptions are accompanied by basaltic tephra fall, lightning and glacial floods (jökulhlaups) of meltwater, ice and volcanic debris. Twenty eruptions have occurred in the last 11 centuries. The volume of airborne tephra varies by three orders of magnitude, with an estimated vol-ume of 1.5 km of freshly fallen tephra from the largest historical Katla eruption. The length of documented eruptions varies from 2 weeks to over 5 months. The average repose period since 1500 AD is 47 years with maximum deviations of 33 and 34 years. All Katla eruptions during the last 400 years have begun in the spring-fall season. At least 12 silicic Katla eruptions are known from the period ca. 1700 BP and 6600 BP. The silicic magma was most likely erupted by hydromagmatic explosive eruptions. The tephra dispersal axes indicate vent locations within the caldera or along the caldera rim. The volume of airborne silicic tephra varies by orders of magnitude, the largest and most widespread is tephra layer UN with uncompacted tephra volume of 0.3 km