The structure and volcanism of the Quaternary volcanic belt in the North Island of New Zealand are discussed in the light ot geophysical evidence. The two major structural features outlined by the gravity survey are the Kaingaroa Plateau, in which the Mesozoic basement rocks are above sea-level, and the Taupo-White Island Depression, in which the basement reaches depths of at least 12,000 ft. Between the two are basement blocks at various stages of subsidence. These features can be closely correlated with surface topography, which indicates recent structural evolution; there is also evidence for a genetic relation between the hydrothermal fields and basement faults.