The city of Auckland lies on an active volcanic field. Emergency planning to manage
risk associated with future volcanic activity is complicated by the uncertainty associated
with the likely location of the next event. Linear alignments of vents indicate that
locations of these features are controlled by areas of weakness in the subjacent crust.
A dominant north-easterly strike for these areas is identified from an analysis of
nearest-neighbour directions of identified vents. The Hough Transform method is used
to locate prominent vent alignments, which trend northeast and northwest sub-parallel
to regional faults and indicate both northwest-southeast and northeast-southwest extension
during Quaternary volcanism. Their relative timing is however unknown at this stage.
It is proposed that the probability of future activity is higher along an inferred
north-westward extension of the only active fault in the field, the Wairoa North fault.
This line also contains the most recently active vents (c. 700 a BP) in the field
at Rangitoto and Motukorea.