The secret role volcanic ash plays in shaping high-altitude clouds
After a volcanic eruption, ash doesn’t just fall to the ground. According to Texas A&M University research, it begins a ripple effect that prevents heat from getting trapped, cooling the climate.
When volcanoes erupt, they don’t just spew ash into the air. They start a chain reaction that cools the environment.
After volcanic eruptions, volcanic ash plays a largely unseen role in the creation of cirrus clouds. These high-altitude clouds form after water droplets freeze spontaneously in the upper troposphere and lower stratosphere, or if water freezes on small particles like volcanic ash. The former creates lighter and wispier clouds that, due to their extreme cold, trap heat below in the atmosphere. Xiaohong Liu, professor and Reta Haynes Chair in Geosciences in the Department of Atmospheric Sciences at Texas A&M University, said the latter creates cirrus clouds with larger and fewer ice crystals that fall faster, allowing more heat to escape Earth.
Liu and his team used NASA satellite data to measure three volcanic eruption sites in the northern hemisphere: the 2008 Kasatochi eruption in the Aleutian islands of Alaska, the 2009 Sarychev eruption in Russia, and the 2015 Calbuco eruption in southern Chile. At all three eruption sites, the team found key differences in ice crystal formation before and after volcanic eruptions.
“During these past 10-20 years, we’ve only had a few major volcanic eruptions with the right kind of data,” Liu said. “We can observe the size and concentration of ice crystals and vertical profiles of different types of aerosols like ash or sulfate in the atmosphere so we can compare before and after eruptions to measure the changes. We found out that after an eruption, the ice crystal concentration is reduced, the size of the ice crystal becomes larger and cirrus clouds occur at lower altitudes.”
Liu said volcanic ash acts as a catalyst for ice formation and encourages liquid water to freeze at warmer temperatures, reducing the overall amount of cirrus clouds and their thickness.
“The volcanic ash is a good nucleus to form ice crystals and lowers the barrier to form ice crystals compared with homogeneous freezing, which requires more humidity and colder temperatures,” he said.
By understanding the extent that volcanic ash changes the climate, Liu said researchers can improve climate models and gain insight into future climate solutions.
“We know, during volcanic eruptions, that volcanoes can inject volcanic ash directly into the stratosphere or troposphere,” he said. “There’s still some unknown on how high these cloud altitudes are when they are formed. It could influence our understanding of the radiation that hits the Earth’s surface.”
Liu said the team is exploring a method that would inject volcanic ash into the upper troposphere or lower stratosphere to reduce cirrus cloud absorption of heat, leading to a cooling effect on the planet.
“Clouds play a major role in the temperature and radiation that reaches the surface, and overall, our understanding is pretty limited. But, there are conversations on using volcanic ash to create different temperature outcomes,” he said.
