Geology of the Fiordland Area - GNS Science

earthquakes along the Puysegur subduction zone. Thelocal effects of wave reflection and refraction on tsunamitravelling up fiords and across lakes are complex and notwell understood. Although the tsunami hazard is high, therisk is only high in those few places where population andinfrastructure are concentrated, such as ilford, West Armand Deep Co e.Flooding sedimentation and avalancheFiordland receives extremely high rainfall, and floods arecommon. Sedimentation, by sheet flooding on river flatsand deltas, and from debris flows on steeper surfaces suchas screes and alluvial fans, is a more significant hazard.Debris flows, especially in the run-out zones of landslides,can be particularly damaging when they contain ery largeboulders. While infrastructure is generally designed towithstand floods, it is seldom capable of surviving majordebris flows. As roads and tracks are usually committed tospecific routes along valleys and across fans, there is littlethat can be done to mitigate this hazard. Fiordland is alsosubject to avalanche hazard from winter snowfall. Theilford Road is well known to be at risk, but most alleyshave equal exposure to this hazard.olcanic eruptionsThe Solander islands in western Fo eaux Strait are theeroded remnants of a young subduction-related olcano.Seismic data show that se eral other subduction-relatedolcanic centres ha e been acti e off southern Fiordlandsince the Pliocene (Turnbull ruski 1993; Sutherland etal. 2006b). No ash deposits associated with these volcanoeshave been identified on land, and the Solander volcano isquiescent, but with on-going subduction there remains apossibility of renewed olcanic acti ity in this icinity. Anyacti ity should be signalled by swarms of low-magnitudeearthquakes that would precede an eruption by weeks ormonths.Figure 77 In the Gold Arm of Charles Sound, the August 2003 earthquake triggered a rockslide (right) which in turnproduced a tsunami (seiche). Vegetation was completely stripped from the adjacent and opposite shorelines, and a helipadwas damaged. The surrounding rocks are diorite of the Misty Pluton.From Hancox et al.(2003).84