1979 Abbotsford landslip

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.

[1] 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.

Schist bedrock is covered with a thick layer of mudstone, with a top coating of sand and clay-rich Cenozoic alluvial soil.

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.

Despite this and a 1951 University of Otago report which stated that the land was unsuitable for building [citation needed], the area was chosen as viable for residential subdivision.

[2] 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.

In November 1978, water mains ruptured in Christie Street, and in May 1979 the Green Island Borough Council had to replace drains which had separated by as much as 50 centimetres (20 in).

The chance of a major slip was discussed, but it was felt that there would be considerable warning before this happened, and as such residents were not officially evacuated (although several left their homes of their own volition).

At the instigation of Green Island mayor Vic Crimp, a state of civil emergency was finally declared starting at 8 am on 6 August[4] and the area was partially evacuated.

The situation was aggravated by the removal of sand from the toe of the hill at a quarry (Harrison's Pit)[5] and during construction of both the residential area and motorway.