The 1104 AD Plinian eruption of Hekla volcano, Iceland

Plinian eruptions in Iceland have attracted renewed attention due to the global disruption of air traffic in 2010. Hekla is the most active volcano in Europe with this type of activity. It has had 18 historical subplinian-Plinian eruptions, and since 1970 the frequency of such eruptions has increased to one every decade. Hekla is currently inflated to the levels seen prior to the most recent eruptions in 1991 and 2000. A future eruption at the end of the current stage of unrest is likely to pose a hazard to air traffic between North America and Europe because all historical Hekla eruptions, independent of size, have had a violent initial subplinian-Plinian phase that produced a sustained ash plume. We present a detailed study of the largest historical eruption, the so-called H1 eruption in 1104 AD, during which 2.5 km3 tephra was deposited over half of Iceland and beyond. Grain size analysis, componentry, and density/vesicularity were used to characterize the deposit and quantify changes during the course of the eruption. H1 was a relatively steady, dry eruption with a more powerful opening phase followed by a lower intensity waning phase. The juvenile material consists of three types of pumice (white, grey and banded), implying that the H1 magma underwent a complex history of ascent in the conduit. These data will be essential inputs to Volcanic Ash Advisory forecast models for tephra dispersal during the next eruption of Hekla.