Satellite thermal observations of the Bezymianny lava dome 1993–2008: Precursory activity, large explosions, and dome growth

Fifteen years worth of Advanced Very High Resolution Radiometer (AVHRR) data is presented and used to quantitatively assess processes occurring at Bezymianny. This andesitic volcano is one of Kamchatka's most dangerous volcanoes with 16 eruptions in the last decade that have dispersed ash into North Pacific air routes. All known episodes of increased activity for which data were available were detected in band 3 (3.53–3.93 μm) AVHRR thermal data. Twenty‐three peaks can be seen in the data; nineteen peaks correspond to known explosions, while the remaining three peaks correspond to known phases of dome growth that were not believed to have been accompanied by explosive activity. Start and end dates of extrusive phases defined by the thermal data are presented. Repose times between phases of extrusion vary from four months to just over two and half years with an average of just less than a year. Using rank‐order statistics a ‘maximum’ time interval between consecutive explosions of 1288 ± 170 days is determined; this could serve as a cut‐off time for declaring the current dome‐growth activity over. The calculated cumulative erupted volume (0.28 km3) and time‐averaged extrusion rate (0.6 m3 s−1) from 1993 to 2008 corresponds to values found at Bezymianny from 1956 to 1976, showing that the satellite‐based methodology provides a good way of quantitatively assessing dome growth. Three different types of precursors to explosive behavior have been identified at Bezymianny: (1) values that cluster around the mode of the data set prior to explosion, potentially due to endogenous dome growth, (2) upward trends that commence 15–20 days prior to explosion and reach sensor saturation levels are due to significant extrusion, and (3) a gradual upward trend that starts 5 days prior to explosion, probably due to ramping up of extrusion. This work shows that retrospectively analyzing and modeling of a volcano's thermal signal provides increased insight into its characteristic behavior. The methods used in this paper can be used at other dome‐building volcanoes around the world. The insights presented here can be used to improve monitoring capabilities to aid in providing early warnings to large explosions at Bezymianny.