Vertical deformation at Lake Taupo, New Zealand, from lake levelling surveys, 1979-99

Lake Taupo, occupying much of the Taupo Volcanic Centre and spanning the Taupo Fault Belt, has routinely been monitored for vertical deformation since 1979 using a portable lake levelling survey technique. Regular monitoring continues to the present time. This technique is used at a number of fixed points around the lake to efficiently determine their height changes. Long-term trends and relatively short-term departures from the trends have been observed, although only one short-term event, in 1983, was confidently correlated with seismieity. That event provided clear examples of pre-, co-, and post-seismic deformation, resulting in vertical displacements exceeding 60 mm. Distinct styles of deformation have been identified, both in time and space. Four episodes of deformation have occurred during the study period, each one terminated by an abrupt transition to the next style. A clear difference in style can also be seen between the Taupo Fault Belt and the adjoining Taupo Volcanic Centre; sustained subsidence rates recorded within the Taupo Fault Belt initially exceeded 11 mm/yr following the 1983 deformation and seismic event but decreased steadily until virtually ceasing by early 1999. The subsidence zone had a half-width of 12 km and represented the southern end of an 80 km long trough extending northeastward along the axis of the fault belt. Within the Taupo Volcanic Centre, the long-term trends were far less distinct until mid 1996, when uplift of the central portion commenced abruptly, averaging c. 11 mm/yr before ceasing 3 years later.