QM20 Murihiku
The Murihiku 1:250,000 geological map covers 18,000 km2 of south Otago and Southland, and includes Stewart Island.Topography varies from flat-topped ranges and intervening basins in northern Southland, to prominent strike ridge topography of the Kaihiku, Hokonui, and North ranges, the jagged Takitimu Mountains, the lower bushclad Longwood and Twinlaw massifs, and the extensive Southland Plains.
Stewart Island has generally subdued bush and scrub-covered topography, with rolling hills and the swampy Freshwater Depression in the centre. Numerous other offshore islands dot the shallow waters of Foveaux Strait and the fringes of Stewart Island. The Waiau Basin lies in the far southwest, on the eastern edge of Fiordland.
The map area is mostly underlain by Paleozoic and Mesozoic sedimentary rocks of the Murihiku Supergroup, exemplified in the Southland Syncline. Permian igneous rocks, including volcanics and plutonics, form the Takitimu and Longwood ranges on the western margin of the sheet, and Paleozoic to Cretaceous granitic to gabbroic rocks dominate Stewart Island. Cenozoic marine and nonmarine sediments underlie the Te Anau and Waiau basins, and also from extensive coal measures beneath the Southland and Waimea Plains. Quaternary sediments are dominated by the wide gravel plains of the Aparima, Oreti, and Mataura catchments, and on Stewart Island, the dune fields of the Freshwater Depression.
The Murihiku area, especially the western side, includes several major active fault systems. Earthquakes and tsunami are the major geological hazards.