Yellowstone National Park's Steamboat Geyser — the world's tallest — has erupted for the first time in more than eight years. Wednesday night's nine-minute blast sent steaming hot water an estimated 200 to 300 feet in the air. For hours following its rare 3 to 40 minute major eruptions, Steamboat thunders with powerful jets of steam. As befitting such an awesome event, full eruptions are entirely unpredictable. In recent years, Steamboat has had several major eruptions.  In the past, it's gone as long as 50 years without a major event. In 1964, it erupted a record 29 times.