Orakei Korako, mud pools. At Orakei Korako the local rocks, including the 186 AD Taupo Ignimbrite, get altered by acid over time to clay. It is this liquid clay that forms the thick, muddy pools. Steam and carbon dioxide (CO2) are discharged by numerous small vents in the pool floor. The bubbling in the pools is caused by carbon dioxide gas being released with the ascending steam. The temperature in mud pools is usually less than 100°C Mud pools are always acidic and occur above the water table No silica sinter forms here because silica cannot be carried in the steam phase