Volcanoes and hot springs emit some H2S , where it probably arises via the hydrolysis of sulfide minerals , i.e. MS + H2O to give MO + H2S . Volcanoes and some hot springs ( as well as cold springs ) emit some H2S , where it probably arises via the hydrolysis of sulfide minerals , i.e. MS + H2O â ' MO + H2S .