Hunga Tonga-Hunga Ha’apai (hung-uh tahng-uh-hung-uh ha-ah-PIE) is an underwater volcano in Tonga, a nation of 170 islands in the Pacific Ocean. In December 2021, it started erupting on and off. Then, on January 15, 2022, it exploded, blasting a huge plume of ash, rocks, and water vapor into the air. This eruption had major effects around the globe.