Detection technology: unlocking data from vulcanian activity

While current global thunderstorm networks have demonstrated their capability to detect volcanic lightning during major eruptions, the scattered geographical distribution of the sensors has led to reduced sensitivity and delayed or no detection for a relatively high number of explosive episodes.

Lightning mapping array sensors have proved to identify electrical discharges in relatively small explosive eruptions with high precision, but they are expensive and data-intensive. 

What is a vulcanian eruption?

Vulcanian eruptions are short, violent and relatively small explosions of viscous magma, creating columns of ash, gas and occasional pyroclastic flows. 

They are created as a result of the fragmentation and eruption of a plug of lava in a volcanic conduit. These explosions can even push material out at tremendous speeds, in some cases faster than 350 metres per second (800mph). They may be repetitive and could go on for days, months or even years. 

Currently, ongoing vulcanian activity is at Sakurajima in Japan and at the Tavurvur volcano in Papua New Guinea. 

Are they dangerous?

Any volcanic eruption can be dangerous to the surrounding environment. Vulcanian deposits contain large fragments, the bulk of these deposits are dominated by ash, which can pose a significant risk to air traffic.

Volcanic ash consists mostly of sharp-edged, hard glass particles and pulverized rock. It is very abrasive and, being largely composed of siliceous materials, has a melting temperature below the operating temperature of modern turbine engines at cruise thrust. 

An ash cloud may be accompanied by gases such as sulphur dioxide, which when combined with water, creates sulphuric acid, and chlorine, which creates hydrochloric acid when mixed with water. These chemicals are corrosive to the airframe and hazardous to health, so any volcanic ash in the atmosphere may pose a serious hazard to aircraft in flight. 

While many airlines actively avoid flight paths over active volcanoes, such as Sakurajima, eruptions can be spontaneous and arrive without warning. So the ability to use equipment to proactively monitor the potential threat of an ash cloud eruption will enable scientists to predict when one is likely to take place.

How technology is helping

Research from Caron Vossen and her team focused on the long-term observation of electrical discharges during persistent vulcanian activity at Sakurajima, near Kagoshima on the island of Kyushu.

In reporting their findings, they presented a long-term method to monitor relatively small ash-rich eruptions at active volcanoes, using Biral’s BTD-200 Lightning Warning System. The software has a proven track record of detecting volcanic activity and getting data for imminent eruptions, and uses a professional-grade-quasi-electrostatic detection system to provide advance warnings of overhead lightning.

BTD-200 is also supported by the ‘Lightning Works Messenger’ application, which works to send out emails and SMS text messages to site managers and remote staff in real-time. As the most active volcano in Japan, continual monitoring of Sakurajima is important, especially given its close proximity to densely populated areas. In the event of an eruption where a town or city needs to be evacuated, early detection is essential.

How Biral’s BTD-200 played its part

Biral’s BTD-200 Lightning Warning System has played a key role in Vossen and her team’s research.

In order to detect electrical discharges, they placed two sensors in the volcano. One was installed 4km east from the centre of Minamidake crater and another placed 2.8km northwest. Together, they successfully detected in situ electrical discharges during 511 out of 724 events. This was compared to only one or two events detected by the Earth Networks Total Lightning Network (ENTLN) and World Wide Lightning Location Network (WWLLN).

These results show the BTD-200’s ability in pinpointing the start of electrified explosive episodes in near real-time. This also helps to provide indications on the magnitude of these explosions, making them a cost and data-efficient method to monitor ash emissions at active volcanoes.

Commenting on Biral’s technology, world renowned volcanologist Professor Sir Stephen Sparks CBE FRS, said: “Sudden volcanic explosions can happen without warning and are a significant hazard.

"These new instruments to detect explosions through electric discharges offer an opportunity to give early warning at active volcanoes and to better understand the significance of the spectacular lightning induced by volcanic eruptions.”