What makes Yellowstone’s geysers and hot springs so fascinating to many visitors is their dynamic nature. While some geysers, such as Old Faithful and Great Fountain, have been steadily active throughout most of the park’s recorded history, others are quite rare and irregular. For example, Steamboat Geyser, the world’s tallest geyser when active, has had intervals ranging from 5 days to 50 years; the most recent eruption was on October 2, 1991.
Today, intense “geyser gazing” interest is focused on the Upper Geyser Basin where Giant Geyser is showing signs of rejuvenation after about 40 years of near dormancy. Since July 1996 there have been 10 major eruptions; the most recent was on February 24, 1997. Each eruption lives up to the geyser’s name: scalding water rocketing up to heights of 195 feet (60 meters) or more (twice the usual height of Old Faithful), with eruption durations of more than an hour, and a massive flood of hundreds of thousands of gallons of water cascading off its sinter platform into the Firehole River.
Geysers are–in a geologic perspective–very unstable and short-lived. Violent change can occur at any time and with little or no warning. The magnitude 7.5 Hebgen Lake earthquake of August 17, 1959, caused many hot springs to erupt as geysers, destroyed or damaged others such as Sapphire Pool, and created new thermal features.
Even without earthquakes, Yellowstone’s hydrothermal features change. For example, in the 1880s Excelsior Geyser was hurling desk-sized rocks in eruptions that were 290 feet (90 meters) high and at least 145 feet (50 meters) across. Excelsior then slumbered for 95 years until September 14, 1985, when it roared back to life for 47 hours and turned the Firehole River muddy white from bank to bank. Excelsior has not erupted since. Likewise, Black Opal Pool in Biscuit Basin, a short distance north of Old Faithful, exploded during the spring of 1925 and ejected thermally cemented sandstone 975 feet (300 meters) away in a lateral blast. Since then, Black Opal Pool has remained a hot pool.
Norris Geyser Basin is especially dynamic. Nearly every year in mid- to late-summer, the area is subject to a basin-wide thermal disturbance producing wild fluctuations in temperatures, discharges, eruptive activity, and water clarity. At the start of one such disturbance, Porkchop Geyser suddenly doubled its eruption height and, within seconds, “blew-up,” scattering rock fragments at the feet of eight surprised park visitors.
The spectacular changes in Yellowstone’s hydrothermal features continue to occur quite frequently. Whether it is the creation of a violent new mud volcano in the back country or the re-awakening of a long dormant large geyser, Yellowstone’s visitors will be just as amazed and entertained during the next 125 years as they have been in the first.
** This press release was written by Rick Hutchinson, Yellowstone’s research geologist, shortly before his untimely death in his beloved Yellowstone backcountry.