Geological mapping in volcanic terrains is a challenging task as there needs to be
input from various geologists' groups and only limited, often ambiguous guidelines
exist. Volcanoes and volcanic successions are in many ways viewed and treated differently
than normal sedimentary successions. Volcanic systems are very much a part of the
normal sedimentary environment and as such need to integrated into the stratigraphic
framework of the enclosing deposits. Most volcanoes supply large volumes of material
(pyroclasts) into the sedimentary system. The type and style of eruption determines
the time frame of the process, while the type of volcano defines the interaction between
volcano and background sedimentation (e.g. monogenetic versus polygenetic volcanic
systems). A sound lithostratigraphic framework for mapping geological units in volcanic
terrains should also adopt the latest developments in volcanology and understanding
of volcanic systems. The lithostratigraphic classification needs to define the mapping
unit and apply it to the 1) proximal to distal volcanic facies, 2) eruption styles
and their temporal changes, and 3) mode of pyroclast transportation (i.e. fallout
versus pyroclastic density current). Differentiation of syn- and post-eruption re-sedimentation,
during either within- or between eruptive phases, will determine the most useful stratigraphic
nomenclature system to apply to the volcanic units. The approach to geological mapping
in ancient and modern volcanic terrains can be different but the same basic stratigraphic
principles and classification apply. The purpose of the geological mapping project,
whether it be in ancient or modern volcanic systems, will define the style and scale
of mapping. The type of output depends upon the objectives and available resources,
including the volcanological experience of the mapping team. Here we provide some
insight from a New Zealand perspective to geological mapping on active volcanic terrains
in a convergent plate margin.