In December 2021, when a submarine volcano in the Tongan archipelago called Hunga Tonga–Hunga Ha’apai began to erupt, it was unclear what the extent of the volcanic activity would be. In fact, scientists actually declared the volcano dormant on January 11th, 2022. Suddenly, a massive eruption on January 15th would cover parts of Tonga in ash and trigger tsunami warnings around the world. While the devastation caused by the January eruption could take years to fully understand, it highlighted both the unpredictability and global effects of volcanic activity.
Over the past several decades scientists have sought ways to monitor and potentially forecast future volcanic activity. Fortunately, there are several precursors to a volcanic eruption, some of which can be analyzed. A volcanic fumarole, for instance, often releases gasses (called fumarolic gasses) which contain sulfur compounds.
This blast from the Hunga Tonga–Hunga Ha‘apai volcano occured a day before the main January 15 eruption. Image courtesy of Taaniela Kula/Tonga Geological Services
Historically, the way these gasses were measured was through direct sampling, which typically involves a scientist inserting a tube into a fumarole. Clearly, direct sampling is extremely dangerous because fumaroles can release toxic gasses at any time. Therefore, with the advent of portable and lower-cost avionics technology in recent years, drone-based monitoring solutions have gained traction to help scientists forecast volcanic activity.
Image showing direct sampling of fumarolic gasses in volcanoes. Image courtesy of Oregon State University
UAS Technology Allows Remote Analysis of Volcanic Activity
Although the terms “drone” and unmmanned arial vehicle (UAV) are used interchangably, UAV is the accepted term long used in the aerospace and defense community. In 2005, the US DoD and FAA introduced a new term: unmanned aerial systems (UAS). According to the United States International Trade Administration, unmanned aerial systems is a term that applies to both autonomous and remotely piloted aerial vehicles along with their associated equipment.
As avionics hardware and software capabilities have advanced in recent years, so have UAS capabilities. However, volcanoes are particularly harsh environments to operate a UAS. Therefore, a UAS must be specifically designed to monitor and resolve failures which occur during flight.
One company working with NASA to develop such systems for volcanic monitoring is Black Swift Technologies. The Black Swift SuperSwift XT is an upcoming UAS purpose-built for mountainous environments and extreme conditions. In 2017, NASA announced that it awarded a contract to Black Swift Technologies to develop the XT for use in volcanic ash monitoring missions.
Black Swift Technologies’ SuperSwift XT is specifically designed for volcanic missions. Image courtesy of Black Swift Technologies
The XT is equipped with an atmospheric probe, nephelometer, cameras, and dedicated trace gas sensors to help scientists understand volcanic conditions. A nephelometer is a piece of equipment which allows scientists to understand the concentration of aerosol in the atmosphere. In a volcanic mission, this could provide additional insight into the activity and state of the volcano. Recently, the Department of Energy awarded a contract for the development of a compact nephelometer. The reduced size and weight of the instrument could be very useful in aerial systems.
Fiber Optic Cabling Used for Volcanic Earthquake Monitoring
While drones are incredibly useful for sampling and atmospheric modeling, there are also advances in ground-based volcanic modeling technologies. Volcanic eruptions are associated with increased seismic activity, and scientists have recently used fiber optic cables to determine the hypocenters of volcanic earthquakes. By determining the origin of volcanic earthquakes, scientists can consequently understand the magma system beneath the volcano.
Using a distributed acoustic sensing system and fiber-optic cables, scientists can use certain techniques to extrapolate the location of a volcanic earthquake. One of these techniques involves comparing the arrival time differences of seismic waveforms at various seismometers placed along the length of the cable.
Image showing fiber optic cable in volcano. Image courtesy of Nature.com
Using those technologies, they can look at the amplitude of the seismic waveforms and determine whether the seismic activity was deep underground or closer to the surface. Combining these two pieces of information, researchers can determine the origin of the earthquake.
Arrival time difference and asl techniques combined to determine seismic origin. Image courtesy of Nature.com
Ultra low-latency fiber optic communication enables detection of very small deltas in the seismic waveform arrival times and consequently, a more accurate determination of the origin of the volcanic earthquake. Such technology could be adapted in the future to other types of environments.
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