In the 1950s and 1960s Alan Pullar (left) and Colin Vucetich worked for the Soil Bureau, Department of Scientific and Industrial Research, mapping soils in different parts of the North Island. Vucetich worked around Rotorua and Pullar in Gisborne and Whakatāne. They recognised that the soils were formed on volcanic ash layers, which were often well exposed in road cuttings. The men started tracing out distinctive ash layers across the region. Work on ash layers (later called tephrostratigraphy) was outside official Soil Bureau policy, and was banned until the late 1960s.

Much of the work was therefore done in weekends and holidays on what they called ‘secret correlation missions’. Radiocarbon dating provided a check on the accuracy of their work. Between 1964 and 1973 they published a series of papers on the sequence and characteristics of the main volcanic eruptions in the Rotorua region. This work has been the foundation for later volcanological studies.