The geothermal area of Norris Geyser Basin is the hottest and most dynamic part of the volcanic caldera of Yellowstone. It is located near the northwestern edge of the caldera, where major faults in the Earth’s crust intersect with the ring-fracture zone that resulted from the cataclysmic eruption 630,000 years ago.
The magma chamber lies closest to the surface beneath Norris Geyser Basin and causes the highest soil temperatures. Silica-rich water of high acidity reaches the surface through vents of hot springs. The water contains sulfuric acid, which forms when dissolved hydrogen sulfide reacts with atmospheric oxygen. Bacteria that feed on sulfur accelerate the transformation of hydrogen sulfide into sulfur and sulfuric acid. Only a few thermoacidophilic archaea can thrive under these harsh conditions.
The water temperature drops significantly at the surface, causing the silica to precipitate. Terraces of sinter develop across the gently sloping terrain. The water temperature, and therefore the rate of sinter precipitation, is highest around the vent. The terraces develop in the direction of water flow and diminish in size as the water becomes colder. The small silver-gray nodules of geyserite also form from silica-rich water. The movement of the water transports the individual nodules, gradually rounding them.
The blue sky and scattered clouds are reflected in the shallow, warm waters, creating the impression of flowing quicksilver shortly before dusk.
