1979 Abbotsford landslip
Encyclopedia
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.
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. An earthquake that struck the area in 1974 also may have stressed the hillside.
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.
Several houses needed to be demolished because of slippage caused during the construction of the Dunedin Southern Motorway in 1966 and 1968.
From 1968, cracks started appearing in houses in Christie Street, with evidence of subsidence and earth movement becoming more common in the following years. 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 half a metre. This was followed by further breaks in both water and sewerage pipes during June. Between 1 July and 16 July, four houses were evacuated; six more were to become empty before the end of the month. During July, Cabinet
ministers Bill Young
and Derek Quigley
visited the area, but Prime Minister Robert Muldoon
refused to call a state of civil emergency
or allow the Earthquake and War Damage Commission
to pay full compensation on damaged or destroyed houses.
By mid-July, the land was moving at close to 25 millimetres (one inch) per day. 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). Heavy rain during late July led to an increase in the rate of slippage, and non-residents were barred from visiting the area. By early August the rate of slippage had increased to over one metre per day. More houses were evacuated during this time. At the instigation of Green Island
mayor Vic Crimp, a state of civil emergency was finally declared starting at 8 am on 6 August and the area was partially evacuated. Plans were drawn up on 7 August for the complete evacuation of the area, though this had not been completed by the time the slip occurred.
, Charles Street. A large area of open land belonging to the Orchard Sun Club was also part of the slip. Sixty-nine houses were destroyed, either directly in the slip or later for safety reasons. At the foot of the hill, much of Miller Park sports ground and neighbouring Armstrong Lane were inundated.
The slip involved some 5 million cubic metres of sand and colluvium
up to 40 metres in thickness. A 150 metres (492.1 ft) wide rift up to 16 metres (52.5 ft) in depth was left at the head of the slip.
Hundreds of people were left homeless, though - largely through good luck - no lives were lost and the worst injuries were very minor. Some residents only had seconds to leave their homes, and a group of seventeen residents had to be rescued from a small moving island of solid land.
10-13 million,. Some houses survived the slide relatively intact and were moved to new locations. A Commission of Inquiry into the reasons for the slip sat for 58 days and produced its report in November 1980. The Commission concluded that the area had a geological predisposition to slippage, with potentially unstable weak clay layers, rich in montmorillonite
clay. The situation was aggravated by the removal of sand from the toe of the hill at a quarry (Harrison's Pit) and during construction of both the residential area and motorway. Though not directly referred to in the Commission's findings, it is possible that a minor earthquake in the area in 1974 also contributed to the slide.
The landslip led to changes in building and subdivision practices in New Zealand, with geological assessment of the land now common prior to the approval of any land development. Land cover and landslip insurance regulations were also substantially rewritten in 1984 as a direct result of the Abbotsford landslip.
Much of the land which suffered slippage has since been landscaped into parkland, with stands of trees added to help stabilise the earth.
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
occurred in the Dunedin
Dunedin
Dunedin is the second-largest city in the South Island of New Zealand, and the principal city of the Otago Region. It is considered to be one of the four main urban centres of New Zealand for historic, cultural, and geographic reasons. Dunedin was the largest city by territorial land area until...
, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
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.
Geography
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 IslandGreen Island, New Zealand
Green Island is an island off the coast of Dunedin, New Zealand, also the name of one of the city's suburbs. The suburb is not on the sea — formerly a borough, it took its name from the Green Island bush, uncleared native forest extending from the valley where the town is centred over the hills...
sits on gentler slopes immediately to the south. Between the two lies the valley of the Kaikorai Stream
Kaikorai Stream
The Kaikorai Stream is a short river which runs through Otago, in New Zealand's South Island. The entirety of its length is within the city of Dunedin....
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
Schist
The schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is...
bedrock is covered with a thick layer of mudstone
Mudstone
Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...
, with a top coating of sand and clay-rich Cenozoic
Cenozoic
The Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...
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
Dunedin Southern Motorway
The Dunedin Southern Motorway is the main arterial route south from the South Island city of Dunedin, part of New Zealand's State Highway 1. It is one of the world's southernmost motorways.-Route:...
during the 1960s and early 1970s may have further affected the land's stability. An earthquake that struck the area in 1974 also may have stressed the hillside.
Background
There have been numerous smaller historical slips at Abbotsford, notably during the construction of the Dunedin-MosgielMosgiel
Mosgiel is an urban satellite of Dunedin in Otago, New Zealand, fifteen kilometres west of the city's centre. Since the re-organisation of New Zealand local government in 1989 it has been inside the Dunedin City Council area, but was physically separate from the contiguous suburbs until...
rail line in 1914. Despite this and a 1951 University of Otago
University of Otago
The University of Otago in Dunedin is New Zealand's oldest university with over 22,000 students enrolled during 2010.The university has New Zealand's highest average research quality and in New Zealand is second only to the University of Auckland in the number of A rated academic researchers it...
report which stated that the land was unsuitable for building , the area was chosen as viable for residential subdivision
Subdivision (land)
Subdivision is the act of dividing land into pieces that are easier to sell or otherwise develop, usually via a plat. The former single piece as a whole is then known in the United States as a 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.
Several houses needed to be demolished because of slippage caused during the construction of the Dunedin Southern Motorway in 1966 and 1968.
From 1968, cracks started appearing in houses in Christie Street, with evidence of subsidence and earth movement becoming more common in the following years. 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 half a metre. This was followed by further breaks in both water and sewerage pipes during June. Between 1 July and 16 July, four houses were evacuated; six more were to become empty before the end of the month. During July, Cabinet
New Zealand Cabinet
The Cabinet of New Zealand functions as the policy and decision-making body of the executive branch within the New Zealand government system...
ministers Bill Young
Bill Young (New Zealand)
William "Bill" Lambert Young, CMG, was a New Zealand politician, born in Kawakawa. He attended Ngawha Native School where his parents were teachers, and then Wellington College....
and Derek Quigley
Derek Quigley
Derek Francis Quigley, QSO is a former New Zealand politician. He was a prominent member of the National Party during the late 1970s and early 1980s, and was known for his support of free market economics and trade liberalization...
visited the area, but Prime Minister Robert Muldoon
Robert Muldoon
Sir Robert David "Rob" Muldoon, GCMG, CH served as the 31st Prime Minister of New Zealand from 1975 to 1984, as leader of the governing National Party. Muldoon had been a prominent member of the National party and MP for the Tamaki electorate for some years prior to becoming leader of the party...
refused to call a state of civil emergency
Civil Emergency
Civil Emergency is the third full-length studio album release by the Indonesian Death metal/Grindcore band Tengkorak.-Track listing:...
or allow the Earthquake and War Damage Commission
Earthquake Commission
The Earthquake Commission provides primary natural disaster insurance to the owners of residential properties in New Zealand. The Government-owned Crown entity manages assets of $5.93 billion NZD...
to pay full compensation on damaged or destroyed houses.
By mid-July, the land was moving at close to 25 millimetres (one inch) per day. 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). Heavy rain during late July led to an increase in the rate of slippage, and non-residents were barred from visiting the area. By early August the rate of slippage had increased to over one metre per day. More houses were evacuated during this time. At the instigation of Green Island
Green Island, New Zealand
Green Island is an island off the coast of Dunedin, New Zealand, also the name of one of the city's suburbs. The suburb is not on the sea — formerly a borough, it took its name from the Green Island bush, uncleared native forest extending from the valley where the town is centred over the hills...
mayor Vic Crimp, a state of civil emergency was finally declared starting at 8 am on 6 August and the area was partially evacuated. Plans were drawn up on 7 August for the complete evacuation of the area, though this had not been completed by the time the slip occurred.
The hill gives way
At around 9.07 pm on 8 August, Abbotsford hill gave way. In all, some 18 hectares (44.5 acre) of land — nearly half of it residential — moved a distance of 48 metres (157.5 ft) down the hill in a mere 15 minutes. This land included most of the eastern side of Christie Street, most parts of Mitchell and Edward Streets east of Christie Street, the short Gordon Street, and the cul-de-sacCul-de-sac
A cul-de-sac is a word of French origin referring to a dead end, close, no through road or court meaning dead-end street with only one inlet/outlet...
, Charles Street. A large area of open land belonging to the Orchard Sun Club was also part of the slip. Sixty-nine houses were destroyed, either directly in the slip or later for safety reasons. At the foot of the hill, much of Miller Park sports ground and neighbouring Armstrong Lane were inundated.
The slip involved some 5 million cubic metres of sand and colluvium
Colluvium
Colluvium is the name for loose bodies of sediment that have been deposited or built up at the bottom of a low-grade slope or against a barrier on that slope, transported by gravity. The deposits that collect at the foot of a steep slope or cliff are also known by the same name. Colluvium often...
up to 40 metres in thickness. A 150 metres (492.1 ft) wide rift up to 16 metres (52.5 ft) in depth was left at the head of the slip.
Hundreds of people were left homeless, though - largely through good luck - no lives were lost and the worst injuries were very minor. Some residents only had seconds to leave their homes, and a group of seventeen residents had to be rescued from a small moving island of solid land.
Aftermath
The state of civil emergency continued until 18 August. Total damage was estimated at $NZNew Zealand dollar
The New Zealand dollar is the currency of New Zealand. It also circulates in the Cook Islands , Niue, Tokelau, and the Pitcairn Islands. It is divided into 100 cents....
10-13 million,. Some houses survived the slide relatively intact and were moved to new locations. A Commission of Inquiry into the reasons for the slip sat for 58 days and produced its report in November 1980. The Commission concluded that the area had a geological predisposition to slippage, with potentially unstable weak clay layers, rich in montmorillonite
Montmorillonite
Montmorillonite is a very soft phyllosilicate group of minerals that typically form in microscopic crystals, forming a clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite family, is a 2:1 clay, meaning that it has 2 tetrahedral sheets sandwiching a central...
clay. The situation was aggravated by the removal of sand from the toe of the hill at a quarry (Harrison's Pit) and during construction of both the residential area and motorway. Though not directly referred to in the Commission's findings, it is possible that a minor earthquake in the area in 1974 also contributed to the slide.
The landslip led to changes in building and subdivision practices in New Zealand, with geological assessment of the land now common prior to the approval of any land development. Land cover and landslip insurance regulations were also substantially rewritten in 1984 as a direct result of the Abbotsford landslip.
Much of the land which suffered slippage has since been landscaped into parkland, with stands of trees added to help stabilise the earth.