Seismic activity related to the 2000 eruption of the Hekla volcano, Iceland

Abstract

The 2000 Hekla eruption took place from February 26 to March 8. Its seismic expressions were a swarm of numerous small earthquakes related to its onset, and low-frequency volcanic tremor that continued throughout the eruption. A swarm of small earthquakes was observed some 80 min before the onset of the eruption, and the size of the events increased with time. Low-frequency volcanic tremor, with a characteristic frequency band of 0.5-1.5 Hz and dominant spectral peak(s) at 0.7-0.9 Hz, became visible at 18:19 GMT on February 26, marking the onset of the eruption. The tremor amplitude rose quickly and was very high in the beginning of the eruption. However, it soon began to decrease after about an hour. In general, the seismic activity related to the 2000 Hekla eruption was very similar to what was observed in the previous eruption in 1991. Based on knowledge gained from seismicity and strain obEditorial responsibility: J Stix servations from 1991, this was the first time that a Hekla eruption was predicted.

The millennium eruption of Hekla in February 2000

“…Eruption tremor has been inferred to be associated with degassing of magma in eruption conduits (McNutt 1994;McNutt et al 1995). An analysis of tremor in the Hekla 2000 eruption indicates that it is of shallow origin (Soosalu et al 2005), consistent with degassing of H 2 O. Exsolution of CO 2 is seemingly less violent as it takes place along the whole height of the conduit and is over at the depth of 3 km. Although the CO 2 concentration was initially high on the basis of modelling , there are indications that magma flowing towards the surface lost CO 2 to its surroundings on its way (Taylor et al 1983;Eichelberger et al 1986;Jaupart and Allegre 1991;Gardner et al 1996).…”

“…Between eruptions, earthquakes are scarce at Hekla. About 1.5 h before the 2000 eruption, intense earthquake activity started, which was thought to mark the onset of magma rise towards the surface (Soosalu et al 2005). Earthquakes accompanying the eruption were initially small and shallow (0-4 km), but after the onset of the eruption, earthquakes extended to depths of 14 km, although they were mostly concentrated between 4 and 9 km (Soosalu et al 2005).…”

“…About 1.5 h before the 2000 eruption, intense earthquake activity started, which was thought to mark the onset of magma rise towards the surface (Soosalu et al 2005). Earthquakes accompanying the eruption were initially small and shallow (0-4 km), but after the onset of the eruption, earthquakes extended to depths of 14 km, although they were mostly concentrated between 4 and 9 km (Soosalu et al 2005). Ground deformation accompanying the eruption in 1980-1981 indicated a magma reservoir at a depth of some 8 km (Kjartansson and Grönvold 1983), but a detailed seismic survey did not support the existence of any substantial magma reservoir under Hekla at any depth between 0 and 14 km prior to or during the 2000 eruption (Soosalu and Einarsson 2004).…”

Precursors to dyke-fed eruptions at basaltic volcanoes: insights from patterns of volcano-tectonic seismicity at Kilauea volcano, Hawaii

“…However, such prolonged accelerations are not ubiquitous and, in particular, basaltic eruptions at volcanoes in extensional stress fields can begin after hours or less of elevated seismicity (Klein 1984;Soosalu et al 2005).…”

Helicopter location and tracking using seismometer recordings

“…The frequency shift along with the angle information deduced from radar (Kalkan & Baykal, 2009) or microphones oriented in different directions (Damarla, 2010) was successfully used to estimate location, heading and altitude of the moving object. Seismologists working on volcanoes usually encounter tremor accompanying eruptions (McNutt, 1992;Soosalu et al, 2005). Time and frequency domain methods are usually applied in order to analyse the temporal evolution of the signal.…”