Fumaroles, or steam vents, are the hottest of Yellowstone’s geothermal features. In Norris Geyser Basin, fumaroles have measured up to 280°F (138°C). A plentiful water supply would help cool these features, but steam vents are usually found on hillsides or higher ground above the basin’s water supply. They rapidly boil away what little water they contain, releasing steam and other gases forcefully from underground.