| Abstract |
Changes in thermal activity, including steam eruptions, the appearance of new fumaroles and the ceasing of older ones, have continued to occur at Craters of the Moon thermal area. These changes began in the early 1950's, when the pre-exploitation heat output was relatively stable at about 40 MW. Qualitative assessment of the changes since the last comprehensive survey in 1978 suggest that the total heat output has not significantly changed from value of 220 ±40 MW. An historically significant change occurred in February 1987 when the famous Karapiti Blowhole suddenly ceased activity. The simultaneous appearance of a weakly steaming hole -30 m away suggests that roof collapse into an underlying cavern probably shut off steam flow to the Karapiti Blowhole. Subsurface collapse of abraded feed zones to fumaroles may be a relatively common cause of fumarole changes and new steam eruptions. |