National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2016

Subaerial and sublacustrine hydrothermal activity at Lake Rotomahana

Stucker, V.K., C.E.J. de Ronde, B.J. Scott, N.J. Wilson, S.L. Walker, and J.E. Lupton

J. Volcanol. Geoth. Res., 314, 156–168, doi: 10.1016/j.jvolgeores.2015.06.017, Special issue: The Lake Rotomahana Geothermal System and Effects of the 1886 Mt. Tarawera Eruption (2016)

Lake Rotomahana is a crater lake in the Okataina Volcanic Centre (New Zealand) that was significantly modified by the 1886 Tarawera Rift eruption. The lake is host to numerous sublacustrine hydrothermal vents. Water column studies were conducted in 2011 and 2014 along with sampling of lake shore hot springs and crater lakes in Waimangu Valley to complement magnetic, seismic, bathymetric and heat flux surveys. Helium concentrations below 50 m depth are higher in 2014 compared to 2011 and represent some of the highest concentrations measured, at 6 × 10−7 ccSTP/g, with an end-member 3He/4He value of 7.1 RA. The high concentrations of helium, when coupled with pH anomalies due to high dissolved CO2 content, suggest the dominant chemical input to the lake is derived from magmatic degassing of an underlying magma. The lake shore hot spring waters show differences in source temperatures using a Na–K geothermometer, with inferred reservoir temperatures ranging between 197 and 232 °C. Water δ18O and δD values show isotopic enrichment due to evaporation of a steam heated pool with samples from nearby Waimangu Valley having the greatest enrichment. Results from this study confirm both pre-1886 eruption hydrothermal sites and newly created post-eruption sites are both still active.

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