1979 Abbotsford landslip

On 8 August 1979, a major landslip occurred in the Dunedin, New Zealand suburb of Abbotsford. It was the largest landslide in a built-up area in New Zealand's history, resulting in the destruction of 69 houses - around one sixth of the suburb - but no fatalities.

The suburb of Abbotsford sits on the slopes of a hill in the southwest of Dunedin, separated from the main urban area by open semi-rural land. The larger suburb of Green Island sits on gentler slopes immediately to the south. Between the two lies the valley of the Kaikorai Stream and its tributary, Miller Stream. At the time of the slippage, Abbotsford was within Green Island Borough.

Much of the northeastern end of Abbotsford's residential area was built on unstable ground. Schist bedrock is covered with a thick layer of mudstone, with a top coating of sand and clay-rich Cenozoic alluvial soil. This type of surface becomes slick during even moderate rainfall. Landslides of this type of material have been relatively widespread within the Greater Dunedin area throughout both recent prehistory and historical times.

The land was also sloping, and quarrying and the construction of the nearby Dunedin Southern Motorway during the 1960s and early 1970s may have further affected the land's stability. The event was non-seismic, the increased rainfall over the previous decade was the trigger and the slope gave way due to the clay seams that formed parallel to bedding. The clay seams formed due to flexural slip.

There have been numerous smaller historical slips at Abbotsford, notably during the construction of the Dunedin-Mosgiel rail line in 1914. Despite this and a 1951 University of Otago report which stated that the land was unsuitable for building, the area was chosen as viable for residential subdivision. During subdivision, extra watercourses were built to handle excess rain runoff, but these proved insufficient to handle heavy downfalls. Christie Street, which runs up Abbotsford hill in the east of the suburb had existed before World War II, but the subdivision of land around it began in earnest only from 1953.

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