File:Vent Geyser & Turban Geyser erupting (late afternoon, 18 May 2015) 5.jpg

English: Geysers are hot springs that episodically erupt columns of water. They occur in few places on Earth. The highest concentration of geysers anywhere is at the Yellowstone Hotspot Volcano (northwestern Wyoming, USA). Turban Geyser is a frequently erupting feature in the Grand Group of Yellowstone’s Upper Geyser Basin. It has an elongated shape (~7.5 meters long and ~3.5 meters wide) and has an irregularly scalloped margin. It is located immediately north of Grand Geyser - the tallest predictable geyser on Earth. Turban is perched above Grand such that Turban eruptions produce much overflow and runoff that drains into Grand’s vent. Turban’s raised border is composed of geyserite, a chemical sedimentary rock made of opal (= SiO2·nH2O - hydrous silica). The geyserite forms by precipitation from hot to very hot, silica-rich groundwater that emerges at springs and geysers. The silica is ultimately derived from subsurface leaching of late Cenozoic-aged rhyolite lavas, which are common at Yellowstone. The border of Turban Geyser has irregularly anastomosing ridges of geyserite and well-developed scallops at pool level (see this rare vintage photo: www.flickr.com/photos/psa104/16130976471). Turban eruptions consist of low to intermediate-sized splashing and normally occur every 20 minutes or so, with durations of about 5 minutes. Longer eruptions of Turban Geyser are associated with eruptions of adjacent Grand Geyser. Turban and nearby Vent Geyser typically erupt together during and after Grand eruptions. Post-Grand activity by Turban Geyser can continue for a couple hours.