On January 15, 2022, a volcano called Hunga Tonga-Hunga Haʻapai erupted with incredible force, sending ash and vapor 35 miles into the sky. Scientists were surprised by the aftermath. Instead of the typical warming effects from volcanic eruptions, this one actually cooled the stratosphere and changed our understanding of volcanic impacts on climate.
The eruption released 146 teragrams of water vapor into the stratosphere. To put that in perspective, that’s about 10% of all the moisture in that layer of the atmosphere. This amount was nearly four times greater than what was released during the 1991 Mount Pinatubo eruption, once considered a benchmark for volcanic impact.
Why Depth Matters
The unique depth of the Hunga Tonga caldera, sitting 490 feet below the ocean’s surface, played a crucial role in its explosive nature. This depth allowed seawater to superheat rapidly, creating steam that fueled the eruption while ocean pressure helped amplify the blast’s strength.
Interestingly, while many eruptions release sulfur dioxide that warms the atmosphere, this one pushed out mostly water vapor. Normally, sulfur particles can trap heat, which was not the case here. As a result, the atmosphere experienced unexpected cooling.
According to a study published in the Journal of Volcanology and Geothermal Research, the eruption’s mechanics involved gas-driven explosions, which shattered rock and vaporized water at an incredible pace.
The Cooling Effect
Scientists discovered that water vapor can actually emit heat into space. This means instead of trapping heat like sulfur does, water vapor pulls energy away from the stratosphere. The Hunga Tonga eruption resulted in a cooling of 0.5 to 1 degrees Celsius in the upper atmosphere, unprecedented compared to previous eruptions. On the surface, the cooling was barely noticeable, shifting temperatures by just 0.05 degrees Celsius.
Professor Amanda Maycock from the University of Leeds confirmed this eruption did not contribute to record-high temperatures in 2023 and 2024. This revelation settled a question many in the climate community had been considering since those temperatures were recorded.
Record-Breaking Eruption
The eruption also established a new record for the tallest volcanic plume at 35.4 miles. It didn’t just affect the stratosphere; it reached into the mesosphere, where meteors burn up upon entry. The force of the explosion generated pressure waves that circled the Earth four times in just six days, impacting sea levels in far-off places like the Mediterranean, where sea levels rose by about a foot—an event termed a meteo tsunami.
Additionally, conventional tsunamis hit the local region, with waves reaching over 50 feet in some areas. This dual occurrence is unmatched in recorded history.
Lasting Effects
Fast forward to late 2025, and the stratosphere still holds more water vapor than usual from the eruption. Dr. Sandip Dhomse of the University of Leeds suggests this elevated moisture could stay for several more years, a longer-lasting effect than sulfur-driven eruptions usually cause. Some ozone changes were also observed in the Southern Hemisphere shortly after the eruption.
Dr. Yunqian Zhu from the University of Colorado Boulder pointed out that the eruption highlighted gaps in how scientists understand water-rich volcanic events. The lingering moisture could influence atmospheric chemistry well into the late 2020s.
In summary, the Hunga Tonga eruption has reshaped our understanding of volcanic eruptions and their interactions with the atmosphere. It has shown that eruptions can have cooling effects, extend their impact longer, and change established climatic norms. This incident serves as a reminder of the Earth’s dynamic systems and their potential surprises.
For more on the eruption’s effects and other volcanic phenomena, check out NASA’s reports and the Geophysical Research Letters study.
