On January 15, 2022, the Hunga Tonga-Hunga Ha’apai volcano erupted in a massive explosion that sent sonic shockwaves around the planet. The explosive eruption within the Kingdom of Tonga is almost as far away as you can get from Alaska—nearly 6,000 miles. It produced a record breaking series of atmospheric waves, the largest ever recorded, since the fabled 1883 Krakatau eruption. The explosion was an extraordinary event in the modern instrumental era, giving scientists an unprecedented opportunity to study and analyze seismic activity.
Kenneth Macpherson is a research scientist at University of Alaska Fairbanks Geophysical Institute. He was principal investigator of a research team that crunched the numbers from that data-rich eruption. They leveraged a dense array of 150 co-located barometers, infrasound sensors, and seismometers across Alaska. This workflow placed them to quickly and effectively document the effects of the eruption. This is important research because it shows the effect that volcanism far from the Earth’s tectonic boundaries can have on the architecture of the crust.
The Hunga Tonga-Hunga Ha’apai Eruption
The Hunga Tonga-Hunga Ha’apai eruption was not just a local event. Its impacts were felt widely, with far-reaching consequences spanning across state lines and beyond. The atmospheric waves generated by the explosion traveled to Alaska, where they were strong enough to cause noticeable ground shaking.
The information and data collected from this eruption helped researchers gain a better understanding of Alaska’s geological structure. Researchers discovered that pressure waves from the eruption interacted with the ground, leading to air-to-ground coupling that transferred energy deep into Earth’s interior.
“Hunga Tonga was an unprecedented explosion in the instrument age.”
The innovative use of barometers and sensors allowed researchers to analyze how pressure waves from the eruption contacted the ground. This air-to-ground coupling yielded the most detailed data on Alaska’s upper crust to date. The study’s main focus was at a depth of about five kilometers, which is seldom studied with this technique.
Unique Data Collection Method
This foundational research has real and lasting importance whenever we attempt to better understand and address seismic hazards in the region. Because seismic waves travel at different velocities, impacts on ground motion during earthquakes can be enormous. Getting a better handle on all of this information is key to forecasting and minimizing future hazards.
The study, published in the journal Seismica, highlights how the Hunga Tonga-Hunga Ha’apai eruption serves as an additional tool for seismic hazard analysis. As Macpherson pointed out,
“Just knowing those upper crustal velocities is good for seismic hazard analysis. It’s [also] good for network operators like the Alaska Earthquake Center because they can accurately apply the crustal velocity beneath a particular seismic station to potentially increase earthquake location accuracy.”
Lessons learned from this recent, highly-imaged eruption can improve tomographic imaging methods that seek to study deeper geologic structures. By increasing the accuracy of upper crustal velocity corrections, this research allows scientists to have better constrained models of seismic risk over vast areas.
Implications for Seismic Research
This study demonstrates how even distant volcanic activity can have profound implications for understanding local geology and enhancing seismic safety measures.
“If a propagating wave is in deep material and going fast but suddenly hits a softer material, the conservation of energy says, ‘Well, I’m going slower, but I still have the same energy.’ That means amplitudes get bigger, causing stronger shaking.”
The findings from this eruption can enhance tomographic imaging techniques used to investigate deeper geological structures. By improving upper crustal velocity corrections, researchers can gain more accurate models of seismic risks over extensive areas.
Macpherson remarked on the remarkable nature of this event:
“Those pressure waves shook Alaska, 6,000 miles away, which I just think is so remarkable. And many of those were long-period waves and consequently shook Earth to a great depth.”
This study demonstrates how even distant volcanic activity can have profound implications for understanding local geology and enhancing seismic safety measures.