The steam jets on Tryggvagata in central Reykjavík are part of the city's geothermal district heating system. The city pumps naturally hot water (about 80°C or 176°F) through pipes beneath the pavements. This melts snow and ice in the winter, keeping the streets safe and clear. The visible "steam jets" are simply pressure vents or drain points where this hot water vaporizes into the colder, humid air.