Steamboat Geyser, the world's tallest active geyser, erupted for the first time in almost nine years early on the morning of May 2nd. Eruptions of the geyser, located in the Norris Geyser Basin, are entirely unpredictable, with the last eruption on October 2, 1991.
A park employee traveling to work around 7 a.m. spotted a very tall vapor column as he neared the geyser basin and - suspecting a possible eruption - stopped to investigate. Two park visitors, sleeping in their pickup camper truck at the Norris parking area, told him that they were abruptly awakened about 5 a.m. by what they thought was an earthquake. Frightened, they drove south toward Madison, but upon looking back noted the huge vapor plume and returned to the geyser basin.
By the time the park employee arrived, a very heavy, wet mist enveloped most of the area around the geyser, and Steamboat - emitting a tremendous roar - was in the full steam phase, with a huge vapor plume approximately 500 feet tall.
Steamboat Geyser rarely erupts in major phase. More commonly, Steamboat ejects water in frequent bursts of 10 to 40 feet. During a major eruption, Steamboat can reach heights of over 300 feet, showering viewers with mineral-rich waters.
For hours following its rare three to 40 minute-long major eruptions (water phase), Steamboat thunders with powerful jets of steam; this steam phase can continue as long as 12 hours after the cessation of the water phase.
Steamboat's unpredictability makes this observance even rarer. Intervals vary from three days to fifty years (Steamboat was dormant from 1911-1961). In recent years, Steamboat has erupted in 1989 (three times), 1990 (one time), and 1991 (one time).