The 2006 Eruption of Augustine Volcano, Alaska Power, J.A., Coombs, M.L., and Freymueller, J.T., editors U.S. Geological Survey Professional Paper 1769 Chapter 25 Lightning and Electrical Activity during the 2006 Eruption of Augustine Volcano By Ronald J. Thomas 1 , Stephen R. McNutt 2 , Paul R. Krehbiel 3 , William Rison 1 , Grayden Aulich 3 , Harald E. Edens 3 , Guy Tytgat 4 , and Edward Clark 2 1 Electrical Engineering Department, New Mexico Tech, Socorro, NM 87801. 2 Alaska Volcano Observatory, Geophysical Institute, University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775. 3 Lagmuir Laboratory, New Mexico Tech, Socorro, NM 87601. 4 IRIS Passcal Instrument Center, New Mexcio Tech, 100 East Road, Socorro, NM 87801. Abstract Lightning and other electrical activity were measured during the 2006 eruption of Augustine Volcano. We found two phases of the activity, the explosive phase corresponding to the explosive eruptions and the plume phase. We classifed the lightning into three types, vent discharges, near-vent lightning, and plume lightning. Vent discharges are small, 10 to 100 m sparks, that occur at rate as great as 10,000 s -1 at the mouth of the volcano during the energetic explosive eruptions. The vent discharges were observed six different times. Near-vent lightning appears to develop upward from the volcanic cone into the developing column during explosions. This lightning is small, in the range of 1 to 7 km, and short, 0.01 to 0.1 s. The behavior of the near-vent lightning indicates an overall positive charge in the ejecta. The plume lightning resembled intracloud thunderstorm lightning. Often it was branched, spanned more than 10 km, and lasted more than 0.5 s. Introduction Throughout recorded history, spectacular lightning discharges have been observed in and from the ash clouds produced by large volcanic eruptions. Lightning has also been observed and photographed during much smaller eruptive activity. Early investigations of volcanic lightning were made during the Surtsey and Heimay eruptions in Iceland in 1963 and 1973 (Anderson and others, 1965, Brook and others, 1974). Lightning associated with eruption of Redoubt in 1989–90 (Hoblitt, 1994) and Spurr 1992 (McNutt and Davis, 2000) occurred in the ash cloud beginning 5 or more minutes after the explosion onsets. (This appears to represent only one type of volcanic lightning, referred to below as plume lightning.) The worldwide observations of volcanic lightning have recently been tabulated, encompassing more than 200 cases associated with 74 volcanoes (Mather and Harrison, 2006; McNutt and Williams, unpublished data), showing that lightning occurs for volcanoes with a wide variety of magma compositions, eruption types, and ash column heights. However, despite increasing interest and additional studies in recent years (reviewed in Mather and Harrison, 2006), volca- nic lightning continues to be poorly understood. Volcanic lightning is at the same time spectacular, dan- gerous, and interesting. It presents danger that most people close to the eruption will not be expecting. Its interests to sci- ence include its roll in the origin of life, similarities and dif- ference to thunderstorms, and why the plume becomes electri- fed. Observing and monitoring lightning during an eruption opens many possibilities. First it could show where there may be danger to people and where fres could be started. The measurement techniques that we present, can detect light- ning at a safe distance even when there is bad weather and visual observations are not possible. Thus, the occurrence of an eruption could be confrmed in remote locations or poor conditions if lightning signals were detected. The location of lightning in the drifting plume would show the location of the ash plume. Measurement of lightning and electrical activity can be another tool to help understand the processes occurring during the eruption. Here we report observations of lightning during the 2006 eruption of Augustine Volcano, Alaska (Thomas and others, 2007), that have provided a much more detailed picture of volcanic lightning than heretofore available. The observations were obtained with a portable lightning mapping system that was recently developed at New Mexico Tech (NMT),