Photogrammetric monitoring of lava dome growth during the 2009 eruption of Redoubt Volcano

Abstract

The 2009 eruption of Redoubt Volcano, Alaska, began with a phreatic explosion on 15 March followed by a series of at least 19 explosive events and growth and destruction of at least two, and likely three, lava domes between 22 March and 4 April. On 4 April explosive activity gave way to continuous lava effusion within the summit crater. We present an analysis of post-4 April lava dome growth using an oblique photogrammetry approach that provides a safe, rapid, and accurate means of measuring dome growth. Photogrammetric analyses of oblique digital images acquired during helicopter observation flights and fixed-wing volcanic gas surveys produced a series of digital elevation models (DEMs) of the lava dome from 16 April to 23 September. The DEMs were used to calculate estimates of volume and time-averaged extrusion rates and to quantify morphological changes during dome growth.Effusion rates ranged from a maximum of 35m3s−1 during the initial two weeks to a low of 2.2m3s−1 in early summer 2009. The average effusion rate from April to July was 9.5m3s−1. Early, rapid dome growth was characterized by extrusion of blocky lava that spread laterally within the summit crater. In mid-to-late April the volume of the dome had reached 36×106m3, roughly half of the total volume, and dome growth within the summit crater began to be limited by confining crater walls to the south, east, and west. Once the dome reached the steep, north-sloping gorge that breaches the crater, growth decreased to the south, but the dome continued to inflate and extend northward down the gorge. Effusion slowed during 16 April–1 May, but in early May the rate increased again. This rate increase was accompanied by a transition to exogenous dome growth. From mid-May to July the effusion rate consistently declined. The decrease is consistent with observations of reduced seismicity, gas emission, and thermal anomalies, as well as declining rates of geodetic deflation or inflation. These trends suggest dome growth ceased by July 2009. The volume of the dome at the end of the 2009 eruption was about 72×106m3, more than twice the estimated volume of the largest dome extruded during the 1989–1990 eruption. In total, the 2009 dome extends over 400m down the glacial gorge on the north end of the crater, with a total length of 1km, width of 500m and an average thickness of 200m.