Deep seated gravitational slope deformation, sackung, predisposing factors, geomorphometry, inventorymapping, Wellington area, New Zealand

Sackung is a type of deep seated gravitational slope deformation which affects mountain ridges. It ischaracterized by typical linear morphostructures like scarps, antiscarps, trenches and double ridges(Agliardi et al., 2001). Formation of sackung is very often attributed to deglaciation of valleys and resulting debuttressing of slopes. However this direct relationship is still arguable since numerous examples ofsackung were described with substantial lag time between deglaciation and sackung formation or arelocated in the totally non-glaciated environments. Thus other factors like geomorphometry, anisotropy ofrock mass, tectonic shattering, earthquakes or climate may play crucial role in the evolution of sackung(Agliardi et al., 2009, 2001; Pánek et al., 2015).Purpose of this this contribution is to present preliminary results of mapping, geomorphometric and spatial analysis of sackung in the Taraura (1570 m asl) and Remutaka (940 m asl) ranges. Quaternary glaciation was only limited to small six cirque and valley glaciers in the Tararua range (Adkin, 1911; Brook and Brock, 2005), thus this study area provides great opportunity to investigate other factors which predispose sackung formation. Both ranges are part of the New Zealand?s North Island axial ranges. The bedrock is composed of greywacke, the strong sandstones which are sporadically interbedded with mudstones. The area is crossed by numerous faults and is seismically active (Begg and Johnston, 2000). Mean annual precipitations exceed 4000 mm in the Tararua range whereas in the Remutaka range are around 2500 mm. We mapped sackung lineaments in both ranges with usage of high resolution LiDAR derived DEM and aerial photographs. In the area of ~3,000 km2 we mapped scarps and antiscarps with overall length 307 km. Further spatial and statistical analysis were conducted in the GIS and R to reveal the predisposing factors.