The Volcanic Lightning Research Project

A collaborative study by New Mexico Tech and the Alaska Volcano Observatory

Sponsored by the U.S. National Science Foundation and the Alaska Volcano Observatory of the University of Alaska

This is a research project by New Mexico Tech and the Alaska Volcano Observatory (AVO) at the University of Alaska, sponsored by the U.S. National Science Foundation. It is an extension of our research studies of thunderstorms. The principal investigators at New Mexico Tech are Ronald Thomas, Paul Krehbiel, and William Rison. The principal investigator at the University of Alaska is Stephen McNutt.

It has long been known that volcanic eruptions can produce spectacular lightning. However, very little has otherwise been known about volcanic lightning, and few scientific studies have been conducted of this very interesting phenomena. It is logistically difficult and dangerous to study active volcanoes, and scientific equipment for documenting and investigating volcanic lightning in remote locations has only recently been developed. Studies of volcanic lightning have both scientific and practical interest. The scientific issues include the questions of how volcanic plumes and clouds become electrified and the similarities and differences with the incidence of lightning in thunderstorms. The measurement techniques we use detect lightning and electrical activity remotely, both inside the volcanic cloud and in inclement weather conditions when visual observations are not possible. Thus the occurrence of an eruption could be confirmed in remote locations and in poor weather conditions. Locating the lightning in the drifting plume can show the location of the ash plume. Measurement of lightning and electrical activity can be another tool to help understand the processes occurring during an eruption. Volcanic lightning is also an additional, often unexpected hazard of eruptions.

How we detect and locate the lightning and electrical activity

We use simple radio receivers to listen for the static that can often be heard on a car radio during a thunderstorm. The static hiss from a single lightning flash consists of many thousands of impulses generated by the lightning. Modern technology allows us to accurately measure the time each impulse arrives at a measurement station. From the arrival times at several stations we can determine the locations of the radio impulses. We use this technology to map out the structure and extent of the complete lightning activity in thunderstorms and are now applying it to the study of volcanic lightning. The systems we have developed for doing this are called Lightning Mapping Arrays (LMAs) and utilize specially designed electronics and GPS receivers to record the arrival times and signal strength at each station. The different stations of a network passively listen for the radio signals in a locally unused VHF televison channel, most often Channel 3. The stations are lightweight and portable, enabling them to be transported and set up relatively rapidly for field studies.

The Redoubt Network

Redoubt started to re-awaken on Sunday January 25, 2009. Having been alerted to the onset of seismic activity by AVO, and starting with a list of possible measurement sites previously scouted out by AVO, we quickly moved to transport and deploy four lightning mapping stations along the Kenai coast on the opposite site of Cook Inlet from Redoubt. By the following Saturday four stations were set up and recording data. The last eruption of Redoubt was in 1989/1990 and began within 24 hours of becoming seismically active. This time Redoubt provided 2 months advance notice, giving us time to finalize the network and to set up internet connections for monitoring its operation. The stations are set up at Ninilchik, Clam Gulch, on Kalifornsky Beach (K-Beach) south of Kenai/Soldotna, and at Nikiski. The spread of the stations enable us to obtain good locations of the lightning activity. All stations have a good view of Redoubt. At three of the four stations, the VHF radio antenna is situated on the edge of the high coastal bluff overlooking Cook Inlet. These stations receive each lightning signal both by direct line of sight and by being reflected from the water surface of Cook Inlet. The interference effects between the direct and reflected signals will enable us to better measure the altitude of the lightning activity. A similar network and and measurment approach was set up in the Homer/Anchor Point area in January 2006 in a successful study of the Mt. Saint Augustine eruption.

To begin with, we are looking primarily at the received signal amplitudes and widths versus time. From the previous Augustine study, this tells us quite a bit about what the volcano is doing electrically. Complete processing of the four-station data to obtain the locations and structure of the lightning discharges will follow.

Other Volcanoes

We have obtained measurements of several other volcanic eruptions. Our first measurements were of the 2006 eruption of Mt. Saint Augustine, an island volcano on the far south side of Cook Inlet. We set up two stations near Homer and in Anchor Point in time for the final explosive eruptions on January 28, 2006. The first of these eruptions produced substantial lightning and was the subject of a Brevia article in Science magazine. Two additional stations were subsequently added on the opposite side of Cook Inlet, closer to Augustine, but the volcano had quieted down by that time. The Augustine deployments provided excellent data and experience for our subsequent studies.

In May and June of 2008 Ron Thomas, Bill Rison and vulcanologist Jeff Johnson of New Mexico Tech deployed four lightning mapping stations and related instruments off the mainland coast of Southern Chile to observe the electrical activity of the major Chaiten volcanic eruption. The stations were set up about a month after the initial, huge and completely unexpected explosion of Chaiten. We thus missed the spectacular lightning associated with the volcano's initial and Chaiten's early activity. However, even a month afterward the volcano continued to have electrical activity, producing occasional, smaller lightning discharges. In December 2007 vulcanologist colleagues Bill McIntosh and Nelia Dunbar and students from NM Tech deployed two LMA stations at 13,000 feet altitude on the rim overlooking the active lava lake of the Mt. Erebus volcano in Antarctica. These measurements detected small sparks being produced during explosive gas eruptions at the surface of the lava lake .

Results So Far

The Redoubt observations are very similar to those seen from Augustine. Essentially continuous sparking and electrical activity is observed during the explosive phase of the eruption, followed after a few minute delay by the onset of discrete lightning discharges in the cloud and downwind plume from the explosion. The plume activity often continues for several tens of minutes or longer, initially being extremely active and then increasingly intermittent with time before finally dying out. The plume discharges are as large and energetic as those seen in large, fully-developed thunderstorms. The difference between Redoubt and Augustine is that the Redoubt explosions have been much more numerous and long-lived, and also have produced substantially more lightning. In addition we have been capturing the complete sequence of eruptive activity, from the very initial explosive eruption sequence to the subsequent, longer-duration eruptions. We should also see the electrical activity from pyroclastic flows, dome-building/collapse events, through the eventual decay of the eruption. The most recent previous eruption of Redoubt was in 1989-90 and lasted 5 months!