In late December of 2021, the seafloor near the tiny South Pacific Island nation of Tonga began to rumble. The restive Hunga Tonga–Hunga Haʻapai volcano was waking up. In the wee hours of January 15, after days of tremors, the bottom of the ocean finally cracked, disgorging the largest explosion on record. Four blasts of molten rock that packed 1 billion tons of force each sent a plume 36 miles into the sky. The blast was so powerful it could be heard in Alaska, 6,000 miles away. For days afterw...