Seismic characterization of pyroclastic flow activity at Soufrière Hills Volcano, Montserrat, 8 January 2007

Abstract

Abstract. A partial dome collapse with concurrent pyroclastic flow (PF) activity occurred at Soufrière Hills Volcano (SHV), Montserrat on 8 January 2007. Pyroclastic density currents were observed to propagate from the Northwest and West sectors of the summit dome into the heads of Tyres Ghaut and Gages Valley, respectively. Between 10:00 and 10:15 UTC pyroclastic flows entered Tyres Ghaut and from there descended into the Belham Valley reaching a distance of about 5 km from the source. Pyroclastic flow activity on the Northwest and West side of the edifice continued at high levels over the following 1.5 h, although run-out distances of individual flows did not exceed 1.5 km. Subsequent observations showed that material had been removed from the lower Northwest side of the dome leaving an amphitheatre-like structure cutting through the old crater rim. The seismic waves excited by the propagation of pyroclastic flows were recorded by the Montserrat Volcano Observatory's network of broadband seismometers. The seismic records show the onset of a continuous signal before 09:30 UTC with gradually increasing amplitudes and spectral energy in the 1–8 Hz band. The signal rapidly increased in amplitude and a characteristic spindle-shaped waveform with broadband energy (1–25 Hz) was observed accompanying large PF that descended along the slopes of the volcano. The main phase was followed by a sequence of individual seismic pulses which correlated well with visual observations of PF. PF are a major hazard at SHV and pose significant risk for the population living in the proximity of the volcano. They can occur with little or no warning and have the potential to reach inhabited areas to the Northwest. The study of the seismic activity associated with the generation and propagation of pyroclastic flows can help to identify characteristic precursory seismic sequences providing valuable information to improve the understanding of the hazards posed by the SHV and to allow better warning to be given to the authorities.

Observation of infrasonic and gravity waves at Soufrière Hills Volcano, Montserrat

“…The broadband frequency content (1-10 Hz) of this signal is consistent with previous measurements of PF activity [e.g., De Angelis et al, 2007]. Considering the source-receiver distance of 3500 m, only a time delay of ∼10 seconds can be ascribed to the difference in propagation velocity between seismic and acoustic phases.…”

Volcano Seismology: Detecting Unrest in Wiggly Lines

“…1e, f), whereby there is an initial increasing amplitude of the waveform as the amount of material falling down slope increases. Pyroclastic flow signals are distinguishable from rockfalls since their waveforms are at least an order of magnitude larger and they often occur over a longer duration since larger amounts of material are involved moving down slope (De Angelis et al 2007), however the two are likely to exist on a continuum.…”

“…These signals can be exploited to determine the size and magnitude of such events, their location and their direction of travel (e.g. De Angelis et al 2007). Typically rockfall events (small free falling rock events) form a "cigar shaped'' waveform with an emergent onset (Fig.…”

The seismic signatures of the 2009 Shiaolin landslide in Taiwan

“…Experimental man-made rockfall-induced seismic signals have been studied to detect rockfall size and the locations of the impacts (Vilajosana et al, 2008). The seismic method has also been applied to illustrate the seismic signature of pyroclastic flows (De Angelis et al, 2007), showing that seismology can be useful in characterizing hazardous processes such as landslides.…”