The Norris Geyser Basin is the hottest geyser basin in the park and is located near the northwest edge of Yellowstone Caldera
near Norris Junction and on the intersection of three major faults. The Norris-Mammoth Corridor is a fault that runs from Norris north through Mammoth to the Gardiner, Montana, area. The Hebgen Lake fault runs from northwest of West Yellowstone, Montana, to Norris. This fault experienced an earthquake in 1959 that measured 7.4 on the Richter scale (sources vary on exact magnitude between 7.1 and 7.8; see 1959 Yellowstone earthquake).
Norris Geyser Basin is so hot and dynamic because these two faults intersect with the ring fracture zone that resulted from the creation of the Yellowstone Caldera of 640,000 years ago. The Basin consists of three main areas: Porcelain Basin
, Back Basin
, and One Hundred Springs Plain. Unlike most of other geyser basins in the park the waters from Norris are acidic rather than alkaline (for example, Echinus Geyser
has a pH of ~3.5). The difference in pH allows for a different class of bacterial thermophiles to live at Norris, creating different color patterns in and around the Norris Basin waters.
The Ragged Hills that lie between Back Basin and One Hundred Springs Plain are thermally altered glacial kames. As glaciers receded the underlying thermal features began to express themselves once again, melting remnants of the ice and causing masses of debris to be dumped. These debris piles were then altered by steam and hot water flowing through them. Madison lies within the eroded stream channels cut through lava flows formed after the caldera eruption. The Gibbon Falls
lies on the caldera boundary as does Virginia Cascades
Norris Geyser Basin periodically undergoes a large-scale, basin-wide thermal disturbance lasting a few weeks. Water levels fluctuate, and temperatures, pH, colors, and eruptive patterns change throughout the basin. During a disturbance in 1985, Porkchop Geyser
continually jetted steam and water; in 1989, the same geyser apparently clogged with silica and blew up, throwing rocks more than 200 feet (61 m). In 2003 a park ranger observed it bubbling heavily, the first such activity seen since 1991. Activity increased dramatically in mid-2003. Because of high ground temperatures and new features beside the trail much of Back Basin was closed until October. In 2004 the boardwalk was routed around the dangerous area and now leads behind Porkchop Geyser.
North of Norris, Roaring Mountain
is a large, acidic hydrothermal area (solfatara) with many fumaroles. In the late 19th and early 20th centuries, the number, size, and power of the fumaroles were much greater than today. The fumaroles are most easily seen in the cooler, low-light conditions of morning and evening. Artists' Paintpots is a small hydrothermal area south of Norris Junction that includes colorful hot springs and two large mudpots.