High-resolution SAR analysis of the 2012 Te Maari eruption, New Zealand

SAR amplitude change detection provides a weather-independent means of tracking volcanic deposits and associated hazards in near real-time. We use high resolution X-band COSMO SkyMed (CSK) images to generate amplitude change difference maps to identify backscatter responses to the 6th of August 2012 eruption at Upper Te Maari crater, New Zealand. This explosive eruption was hydrothermally driven and triggered by landslide induced unroofing, producing a > 2 km long debris flow, ballistics and wet pyroclastic surges. Surge deposits produced both increase and decrease in amplitude, depending on pre-eruption surface cover properties. Alpine, unvegetated areas east of the crater showed a decrease in amplitude produced by surge blanketing, while rougher, vegetated areas showed an increase in amplitude when draped by wet surge material. The debris flow propagation and deposits caused significant landscape changes, marked by an increase in backscatter due to the emplacement of coarse material enhancing surface roughness. These deposits caused the damming of the Mangatipua Stream and the creation of an ephemeral lake which breached on the 15th October following heavy rainfall, remobilising sediments as a hyperconcentrated flow. We have shown that the evolution in size of the ephemeral lake can be traced using high resolution radar making it a valuable tool for hazard monitoring. Our results highlight that, in high resolution SAR data, surface roughness exerts a stronger influence on radar backscattering than soil moisture for volcanic deposits.