Recent volcanic history of the Veidivötn fissure swarm, southern Iceland — an approach to volcanic risk assessment

Abstract

Abstract The recent volcanic history of the southwestern part of the Veidivotn fissure swarm, southern Iceland, provides a basis for assessment of volcanic risk in an area of large hydropower potential. Local tephrastratigraphy and regional tephrochronology provide relative and absolute dating of individual eruptions as well as information on the volume and distribution of the products formed in each eruption. Three large eruptions took place in this area in ∼ 1480 A.D., ∼ 900 A.D. and ∼ 150 A.D., respectively. Each eruption produced approx. 1 km3 (DRE) of basaltic, and minor amounts of silicic lava and tephra on fissures up to 42 km long. No evidence is found of smaller eruptions during this period. The estimated eruption frequency, one eruption every 600–800 years, implies that this part of the Veidivotn fissure swarm is inactive for long periods between relatively large volcanic events. A change in the mode of eruption from effusive to explosive took place during this period. The hazards posed by this area include far-reaching lava flows, widespread heavy tephra fall with thicknesses in excess of 2 m at distances of 10 km, and damming of a large glacial river with the consequent formation of unstable lakes. A volcano-tectonic model, which explains the observed eruption frequency and provides a basis for a long-term monitoring program, is proposed. Eruptions on the Veidivotn fissure swarm are interpreted as corollaries of rifting episodes initiated in the Bardarbunga central volcano. Volcano-tectonic episodes affect the fissure swarm at an average interval of 100 years. Minor episodes are limited to the central volcano and adjacents parts of the fissure swarm. During the less frequent major episodes, rifting and volcanic activity extends to the extreme southwestern part of the fissure swarm. Seismic monitoring of the Bardarbunga central volcano could provide an early warning of renewed activity on the Veidivotn fissure swarm. A major rifting episode resulting in eruption on its southwestern part can be expected during the next 100 to 300 years.