Seasonal snow cycles and their influence on seismic velocity changes and
eruptive activity at Ruapehu volcano, New Zealand
Abstract
Understanding volcanic eruption triggers is critical towards
anticipating future activity. While internal magma dynamics typically
receive more attention, the influence of external processes remains less
understood. In this context, we explore the relationship between
seasonal snow cycles and eruptive activity at Ruapehu, New Zealand. This
is motivated by apparent seasonality in the eruptive record, where a
higher than expected proportion of eruptions (post-1960) occur in spring
(including the two previous eruptions of 2006 and 2007). Employing
recent advancements in passive seismic interferometry, we compute
sub-surface seismic velocity changes between 2005–2009 using the
cross-wavelet transform approach. Opposite trends in velocities are
identified on and off the volcano, with stations closest to the summit
recording a winter high closely correlated with the presence of snow.
Inverting for depth suggests these changes occur within the upper
200–300 m. Reduced water infiltration (as precipitation falls as snow)
is considered the likely control of seasonal velocities, while modeling
also points to a contribution from snow-loading. We hypothesise that
this latter process may play a crucial role towards explaining
seasonality in the eruptive record. Specifically, loading/unloading may
influence the volcanic system through increased degassing, thereby
increasing the likelihood of small, gas-driven, eruptions. Our findings
shed light on the complex interactions between volcanoes and external
environmental processes, highlighting the need for more focused research
in this area. Pursuing this line of inquiry has significant implications
towards improved risk and hazard assessments at not just Ruapehu, but
also other volcanoes globally that experience seasonal snow cover.