Abstract
The Southern Alps Ka Tiritiri-o-te-Moana of New Zealand offers an effective case study to
understanding the role of landslide derived sediment influxes to fluvial systems. Rapid rates
of uplift and tectonism, in combination with high precipitation readily produce both mass
movement events and the cascading evacuation of sediment from alpine systems. In-channel
morphological responses were assessed across seven catchment and landslide case studies in
the Mount Aspiring/Tititea region of the Southern Alps. Specifically, surveys spanned across
micro-, meso- and macro- spatial and temporal data sets, sampling in-situ grain size,
catchment flow dynamics, planform morphological change and case study specific elevation
surveys. In understanding morphological responses in relatively immediate timeframes,
alpine sediment cascades can be better managed, whilst also offering insight into the
trajectories of change responsible for landscape memory and sensitivity. Where the
magnitude and frequency of perturbations within catchments determines the propensity of
systems to undergo phase shifts and return to previous states (landscape memory). The
separation of case studies into discrete classifications of landslide interfaces with channel
networks provided predictable morphological reworking where scales of sediment inputs
exceeded that of existing network competence and capacity (blockage/obliteration and
nil/buffered). Classifications remained over-simplistic at classifying median impact
landslides, where the interaction of sediment inputs and catchment processes require further
dissection (point/riparian). UAV surveying of the Rees Puahiri case study identified fine
grain sediment delivery from and reworking below landslide inputs across point/riparian
systems – a pattern not captured in the lower resolution surveying of other catchments.
Failure to capture sediment activity in remaining point/riparian case studies, however, does
not disprove reworking processes, rather highlights the need for fine scale survey methods
and the simplification of classifications.