Conductivity anomalies provide evidence of large scale hydrothermal venting in Lake Taup

Lake Taupo (Taupo moana) in the central North Island is the largest freshwater lake in Aotearoa/New Zealand. Taupo is also a frequently active and potentially hazardous caldera volcano. Water quality monitoring in Lake Taupo shows possible chemical linkages between the lake and hydrothermal systems under the lake around the Horomatangi Reef. We found that hydrothermal venting, discovered in Lake Taupo in 1998, is not a steady emission of bubbles and geothermal fluid but occasional larger fluid discharges also occur as pulses. These larger discharges contain sulphate and manifest in vertical water column profiles as conductivity anomalies. These appear to be linked to magmatic activity, which can cause earthquakes and other volcanic unrest under the lake. Rising plumes of warm water from these larger hydrothermal events can entrain sediment and other nutrients such as dissolved organic nitrogen up to the lake surface and they can continue for several months. Periods of volcanic unrest are well documented at Taupo volcano and have recently occurred in 2008-9, 2019 and 2022-23. Lake water quality data suggest that the conductivity anomalies may reflect a magmatic 'pulse' of this active volcano and provide evidence of large scale hydrothermal venting in Lake Taupo.