Echinus (e-KI-nus) Geyser was a perennial crowd-pleaser which typically erupted every 35 to 75 minutes. Late in 1998, this geyser altered its interval and for the next few years became less frequent and predictable. For the last several years, Echinus eruptions have been extremely rare. When active, its pool fills gradually with water;then suddenly, bursts of steam and water explode 40 to 60 feet (12 to 18 m) skyward. Eruptions can last from about 4 minutes to as long as 118 minutes. The major eruptions were believed to be caused by a secondary water source which has mysteriously vanished. Like other geysers and hot springs, Echinus Geyser can change without warning, and is subject to many unseen changes and forces underground.
Echinus is the largest acid-water geyser known. Its waters are almost as acidic as vinegar with a pH ranging from 3.3 to 3.6. Acid geysers are extremely rare with the majority of the planet's total being found here at Norris Geyser Basin.