Scott, B.J.; Cody, A.D. 1982 The 20 June 1981 hydrothermal explosion at Tauhara Geothermal Field, Taupo. Lower Hutt: New Zealand Geological Survey. Report NZGS 103 33 p.
Abstract: On the morning of 20 June 1981 at about 0725 h (+/- 5 min) a hydrothermal explosion occurred within the Tauhara Geothermal Field, at a site near the Taupo Pony Club grounds on the north-east margin of Taupo township. The eruption cloud of steam, gases, rock and mud particles rose more than one hundred metres in the air and distributed fine debris over 800 m to the north-east. A crater 1640 m2 was formed by explosion, and collapse resulting from the eruption, in a basin of previously hot ground. Volume of ejected material is estimated at 6800 m3. A few days after the explosion, the area was only slightly active. The 1981 explosion was centred some 100 m north-east of a similar hydrothermal explosion crater formed on about 28 March 1974. Solid ejecta from the 1981 explosion includes clasts of Taupo Pumice, partially silicified pumice breccia, and dense siliceous sinter. Low grade hydrothermal alteration is evident in many clasts. Available stratigraphic data suggests that the explosion extended to about 15-20 m depth. In this report we endeavour to provide a comparatively detailed description and analysis of the hydrothermal explosion. Studies of previous activity, eyewitness accounts, explosion effects, lithology and ballistics of the ejecta, ground temperatures, climatological data, and the post-eruption earth deformation are presented. Field studies were conducted on 22, 23, 24, 26 June and 16 July. A model is also presented in an attempt to explain the cause of the explosion.