The Hunga Tonga Eruption Altered the Ozone Layer

When the Hunga Tonga-Hunga Ha’apai volcano erupted on January 15, 2022, it sent shockwaves around the globe. While the immediate tsunami and ash clouds were devastating, scientists soon discovered a hidden effect taking place high above the Earth. Studies reveal that this underwater volcano injected unprecedented amounts of water into the stratosphere, an event that ultimately altered the ozone layer in ways researchers had never documented before.

A Submarine Explosion Like No Other

To understand why this eruption was so unusual, you have to look at its location. The Hunga Tonga volcano sits in the South Pacific Ocean. Before the eruption, its caldera was positioned roughly 150 meters below sea level. This specific depth was the perfect recipe for an atmospheric anomaly.

If the volcano had been much deeper, the immense pressure of the ocean would have suppressed the explosive force. If it had been shallower, there would not have been enough seawater to fuel the reaction. Instead, the molten magma violently interacted with the ocean water, creating a steam explosion of historic proportions. The blast was so powerful that it sent a plume of ash, gas, and superheated steam shooting directly into the upper atmosphere.

The Unprecedented Water Vapor Injection

Shortly after the event, researchers at NASA turned to the Aura satellite to analyze the atmospheric fallout. The satellite is equipped with an instrument called the Microwave Limb Sounder, which measures ozone, water vapor, and other atmospheric gases.

The data was staggering. Atmospheric scientists, including Luis Millán from NASA’s Jet Propulsion Laboratory, calculated that the eruption sent roughly 150 million metric tons of water vapor into the stratosphere. To put this massive number in perspective, that is enough water to fill more than 58,000 Olympic-size swimming pools. This single event increased the total amount of global stratospheric water by an estimated 10 to 15 percent.

Most weather events happen in the troposphere, the lowest layer of our atmosphere. The stratosphere sits directly above it, extending from about 10 to 30 miles above the surface of the Earth. Normally, the stratosphere is extremely dry. While powerful thunderstorms can occasionally push small amounts of moisture upward, a volcanic injection of this magnitude had never been recorded in the modern satellite era.

How Water Vapor Impacts Ozone Chemistry

You might wonder how pure water could possibly damage the ozone layer. The answer comes down to atmospheric temperature and complex chemical reactions.

Water vapor in the stratosphere has a strong localized cooling effect. When the atmospheric temperature drops, it changes natural wind and circulation patterns. More importantly, the combination of excess water and volcanic aerosols creates tiny liquid droplets high in the sky.

These liquid droplets provide a physical surface for chemical reactions to occur. Harmless chlorine compounds naturally drift in the atmosphere, many of which are leftover remnants from human-made chlorofluorocarbons banned in the 1980s. When these inactive chlorine compounds interact with the wet aerosol surfaces created by the volcano, they break down. They transform into active chlorine molecules, which aggressively hunt and destroy ozone molecules.

A Temporary but Significant Depletion

Scientists observed the results of these chemical reactions in the weeks following the eruption. Research published in the journal Science documented a rapid depletion of ozone in the tropical stratosphere directly above the South Pacific ocean. In some localized areas, ozone levels dropped by 5 percent in just one week.

While a 5 percent drop might sound small, it is highly unusual for the tropics. Most severe ozone depletion happens over Antarctica, creating the famous ozone hole. This is because Antarctic winters produce extreme cold temperatures that naturally form clouds in the stratosphere, providing the same surfaces for chlorine activation. The immense water vapor from the Hunga Tonga eruption essentially recreated those frigid Antarctic chemical conditions right near the equator.

Comparing Hunga Tonga to Mount Pinatubo

Historically, massive volcanic eruptions are known for cooling the Earth and damaging ozone through a different mechanism: sulfur dioxide.

For example, the 1991 eruption of Mount Pinatubo in the Philippines injected up to 20 million tons of sulfur dioxide gas into the atmosphere. This gas converted into sulfate aerosols, which reflected sunlight away from Earth and cooled the planet by about 1 degree Fahrenheit for over a year. Pinatubo also caused temporary ozone depletion, but that process was driven almost entirely by the massive sulfur clouds.

Hunga Tonga was vastly different. It produced relatively little sulfur. Instead, its plume was dominated by water vapor. Because water vapor is a highly effective greenhouse gas, it traps heat. Scientists predict the massive injection of water from Hunga Tonga could actually cause a slight, temporary warming effect on the Earth’s surface over the next few years. This makes it a totally unique climate scenario compared to any other volcanic eruption studied in recent history.

The Road to Recovery

The good news is that the ozone depletion caused by the underwater volcano is temporary. The stratosphere is constantly producing new ozone as ultraviolet sunlight interacts with oxygen molecules.

The excess water vapor is currently circulating toward the Earth’s poles. Eventually, it will either escape the highest levels of the stratosphere or freeze and fall out as ice crystals. Researchers expect the tropical ozone layer to fully recover to its normal state as the water vapor dissipates, a natural cleansing process that could take up to five years.

Frequently Asked Questions

How much water did the Hunga Tonga eruption release into the sky? Scientists estimate the eruption injected about 150 million metric tons of water vapor into the stratosphere. This increased the total water content of the stratosphere by 10 to 15 percent.

Will the ozone layer permanently suffer from the eruption? No. The ozone depletion observed over the tropical Pacific was a temporary anomaly. As the excess water vapor slowly leaves the stratosphere over the next few years, the ozone levels will naturally replenish.

Did the eruption cause global warming? Unlike standard volcanoes that cool the earth by blocking sunlight with sulfur, the Hunga Tonga volcano injected massive amounts of water vapor, a known greenhouse gas. Researchers believe this could cause a very slight, temporary warming effect on global temperatures for a few years.

How did scientists measure the water vapor from the volcano? Researchers relied on satellite data. Specifically, NASA used the Microwave Limb Sounder instrument on its Aura satellite, which is designed to measure trace gases like ozone and water vapor in the upper atmosphere.