The moment a towering 3,937-foot mountain of rock and ice gave way in the Dickson fjord on Greenland’s east coast, it set off a chain reaction that shook the entire planet. In September 2023, about 33 million cubic yards of debris crashed into the fjord below, creating a wave nearly 8 feet high at first. But inside the narrow channel, this wave grew into a colossal tsunami with waves as high as 650 feet, an event so powerful it sent seismic signals rippling worldwide for over a week.