Original: On the afternoon of September 18, 1870, members of the Washburn-Langford-Doane Expedition traveled down the Firehole River from the Kepler Cascades and entered the Upper Geyser Basin.
Simplified: Some of the processes observed include fog formation from the interaction of cool air from above mixing with heated air from below, the recharge processes of water entering into the conduit and expanding from below, and entry of superheated steam measuring as high as 265 F (129 C) into the conduit.