Lightning and electrical activity during the 2009 eruptions of Redoubt Volcano

The warning of the impending eruption of Redoubt by the Alaska Volcano Observatory enabled us to set up a 4-station VHF Lightning Mapping Array (LMA) along the Kenai coast in time to capture the complete sequence of eruptions. The network was situated along a 60 km long north-south line, 70-80 km east of Redoubt on the opposite side of Cook Inlet, and accurately measured the arrival times of VHF radiation produced by electrical discharges during the eruptions. Spectacular and often extremely vigorous electrical activity and lightning occurred during most of explosive events between 23 March and 4 April 2009. The mapping network produced detailed plan-position images of the sequence of discharges over and downwind of the volcano during each eruption. The lightning activity was essentially continuous and uncountable during the explosive phase of each eruption, gradually becoming more discrete and larger as the activity occurred in the plume. During most of the eruptions the lightning remained within 10 km relatively close to the volcano, but during the major eruptions of 23:30 UTC 28 March and the final eruption of 14:00 UTC 4 April the lightning-producing plume drifted across Cook Inlet over the populated Kenai peninsula coast. Individual ground strikes and possibly some in-cloud lightning events were also located by two low-frequency sferics location systems. The BLM network used for forest fire information detected 518 strikes over the full course of the eruptions. The more widespread World Wide Lightning Location Network (WWLLN) located 486 strikes using lower frequency radio waves. Most of the eruptions occurred during overcast or stormy weather and could not be seen visually, but during 3 eruptions the weather was clear enough for the lightning to be visually observed and also captured on photos and video. The visual observations were reported to be spectacular. We are working to correlate the lightning in the photos with the LMA and other detections.