Cyclic activity in the crater lakes of Waimangu hydrothermal system, New Zealand

Abstract

Frying Pan and Inferno Crater lakes occupy craters formed on 10 June 1886 during the Tarawera Rift eruption. These lakes are the largest and most spectacular hot springs in New Zealand, and together they display interrelated cyclic variations about a 38 day cycle. The lake occupying Inferno Crater fluctuates from overflow to about 8 m below overflow, although exceptionally the water level has receded below 12 m, which is at least an order of magnitude larger than other known geyser like hot springs. The temperature fluctuates sympathetically with the water level in the range 35.0 to 84.5°C. Four distinct stages are recognised with the following average parameters; the first lasts 7.7 days, water level and temperature rise respectively 4.7m and 17.3°C, while the lake volume increases by 23 800 m 3. The second lasts 14.7 days, water level rises 3.99 m, the temperature remains steady about 60.7°C, lake volume increases 22 000 m 3. The third is an overflow of 79.1 litre sec −1 for 51.3 hours peaking at 70.6°C. In the fourth stage, lake level recedes 7.9m decreasing lake volume 45 800 m 3 over 15.1 days, and the lake temperature falls 26.4°C. The discharge of nearby Frying Pan Lake varies inversely with the water level of Inferno Crater Lake by 20.2 ± 2.7 litre sec −1 and also responds to a previously unrecognised cycle of about 20 days duration. The temperature of the discharge also responds to the 20 and 38 day cycles, but shows no correlation with discharge volume. Ambient air temperature strongly influences the discharge temperature, which ranges annually between 44.3°C and 56.6°C with a mean of 50.1°C. A slight decrease of about 1.4°C is apparent between 1972 and 1990. The mean annual discharge from Frying Pan Lake has decreased from 122.2 to 104.1 litre sec −1 between 1972 and 1990.