Recent studies of Augustine Volcano, funded by other sources, have shown that there are two distinct types of observable electrical activity associated with eruptions. One is a newly discovered continuous radio frequency (RF) radiation at the crater mouth during the main eruption, and the other is large-scale lightning in the volcanic plume several minutes after the main eruption, with characteristics similar to lightning found in thunderstorms. These observations, made using Lightning Mapping Array (LMA) instrumentation developed at the New Mexico Institute of Mining and Technology, were the first detailed, high time resolution observations of such volcanic electrical activity. In this new research program volcano-produced electrical activity will be observed at two permanent sites in Alaska with an array of atmospheric electrical instrumentation including the LMA to make detailed three-dimensional images of the electrical activity; and electric field mills, fast antennas and slow antennas to characterize the polarity of the lightning activity. A low-power version of the LMA sensor will be developed, which will allow for long-term monitoring of volcanic electrical activity in remote locations, and for rapid deployment to sites with no grid power available. The research will involve both scientific studies of volcanic lightning and electrical activity, and continued development and advancement of the instrumentation for making such observations. The intellectual merit of the proposed research will derive from the scientific investigations. One major scientific goal is to use lightning mapping observations to ascertain the electrical structure of volcanic plume clouds. This will help lead to a better understanding of the charging mechanism in the plume. A second major goal is to better characterize the continuous RF activity during the explosive phase. A third major goal is to ascertain the usefulness of monitoring of electrical activity as an additional tool for the determination of the status of active volcanoes.
Broader impacts of the proposed activity will include further development of the lightning mapping technique as a useful technology to study and monitor volcanic eruptions. The system that will be developed could evolve into one that could be used to monitor a volcano and confirm eruptions, even when weather conditions preclude visual observations. It could be used as an additional tool to help volcanologists in their decision-making process for generating warnings to nearby populations, and to aircraft. Tracking of the in-plume lightning can give the direction that the ash cloud is moving. The system will give the volcanologists another tool to study the eruptions with high time resolution. The understanding of charging in the volcanic plume could lead to a better understanding of the charging in thunderstorms. A final aspect of the proposed research will be the development of a set of lightweight, solar-powered, battery-operated mapping stations that can be readily deployed for a variety of experiments and studies that are as yet not easily conducted. The involvement of graduate and undergraduate students both in the scientific and applied aspects of the research has broad implications for their education that can only come from working on real problems. This research will involve a collaboration between atmospheric and earth scientists in a cross-disciplinary environment. Inter-agency and international collaborations will be established as needed to work with groups in areas where it looks reasonable to deploy our instrumentation to study active volcanoes. This interdisciplinary activity has already introduced new techniques that will be used for monitoring active volcanoes in Alaska. The collaborations will become broader as interactions develop with volcanologists and disaster planners in communities near volcanoes around the world.
Lightning commonly occurs in the plumes of explosive volcanic eruptions, but there have not been very many scientific studies to understand why it happens. The purpose of our research was to learn more about the types of lightning that occur in volcanic plumes in order to gain a better understanding of the eruptive and meteorological conditions that give rise to volcanic lightning. We detect lightning in a plume by measuring the radio-frequency emissions that lightning produces as it propagates. Our monitoring instrument, called the Lightning Mapping Array, was previously developed with funding from the National Science Foundation to study thunderstorm lightning and is now used by NASA and meteorologists around the country to help with short-term weather forecasting and advisories. Large volcanic eruptions, such as the 1980 eruption of Mt. St. Helens, can send volcanic ash high into the atmosphere and into the paths of airplanes. Airborne volcanic ash can disrupt jet engines and cause them to shut down, thus early detection of volcanic eruptions is critical to aviation safety. In fact, one of the busiest passenger and cargo airplane routes in the world passes over Alaska's Aleutian islands, which are home to more than 40 active volcanoes. The study of volcanic lightning is important because it can provide a means to detect or confirm volcanic eruptions when cloudy conditions prevent detection by visual or satellite observations. During our project we were able to use the Lightning Mapping Array to study lightning from four major volcanic eruptions: Chaiten, Chile (2008), Redoubt Volcano, Alaska, USA (2009), Eyjafjallajökull, Iceland (2010), and Grimsvotn, Iceland (2011). All four eruptions produced prolific lightning. We have learned that there are two distinct phases or types of lightning activity in a volcanic plume. The first phase occurs at the vent of the volcano while it is actively erupting. During this phase we have observed small discharges, on the order of several hundred feet in length, at rates of up to 5000 per second, which is unlike anything that has ever been observed in a thunderstorm. We call these discharges 'vent discharges,' and they occur because the ash from the volcano is electrically charged during the eruption process. The second phase of lightning occurs throughout the plume and is very similar to lightning that is observed in thunderstorms. We call this type of lightning 'plume lightning.' In a thundercloud, charge is produced through the collisions of ice particles, and we believe this process also occurs in volcanic plumes in addition to the charging on erupted ash. For this reason, volcanic plumes are sometimes called 'dirty thunderstorms.' There are still many interesting questions to pursue in future volcanic lightning studies. Our results from the eruption of Redoubt Volcano have shown that the quantity of lightning that occurs during an eruption -- both vent discharges and plume lightning -- may be linked to the size of the eruption. Therefore, the intensity of lightning activity may be able to indicate how large a plume is and how much ash has been erupted, which could help volcano observatories issue warnings to the public. However, our results from Eyjafjallajoköll, which was a much smaller eruption compared to Redoubt, have shown that plume lightning in smaller eruptions may be strongly influenced by meteorological conditions, specifically ambient air temperature, which can control the production or non-production of ice in a plume. These results imply that if an eruption is big enough, it will make lightning regardless of the meteorological conditions, but if it is smaller than this threshold, meteorology might be important. Determining what is 'big enough' is an important question that needs further research.
