Variations Of The Inferno Crater Lake Cycles, Insights From The New Data

Abstract

Crater lakes in active volcanic vents are unique features providing an insight into the state of natural geothermal systems. Inferno Crater Lake, in the Waimangu Geothermal area near Rotorua, has regular cycles in its temperature and lake level, varying from 12 to 56 days in length. These cycles do not seem to be related to the magmatic activity of Okataina Volcanic Center, rather representing an unstable heat convection system under the lake. The cycling patterns show four different types of cycle, based on sixty-five years of data. Each kind of cycle has a specific behavior of lake temperature and water level. Type II is the most common cycle with a mean length of 33.2 days and one overflow. When successive overflows happen, we have a cycle of type I, with an average length of 56.1 days. The lack of overflow defines the other two types; type III for short cycles lasting about 12.0 days, or a type IV whose mean length is 30.0 days. Even if types I to III show some tendency to repeat, no features of the cycle can be used to predict which type will occur next. All the types of cycle start with the same rapid rise of lake temperature and level. Heavy rainfall and seismic and hydrothermal events do not generate any particular type of cycle. Finally, the regular oscillations which occur during a cycle with an average period of 2.2 days could be generated by accumulating steam pressure in a volume under the lake, similar to a geyser mechanism.