Dunstan Mountains
The Dunstan Mountains as viewed from the Lowburn Sugarloaf
Highest point
PeakDunstan
Elevation1,667 m (5,469 ft)[1]
Coordinates44°52′S 169°35′E / 44.867°S 169.583°E / -44.867; 169.58345°02′56″S 169°22′34″E / 45.049°S 169.376°E / -45.049; 169.376
Dimensions
Length51 km (32 mi) 45°
Width19 km (12 mi) 135°
Area826 km2 (319 sq mi)
Naming
Native nameMataki-nui, Neinei-i-kura, Tiko-umu (Māori)
English translationMatakanui translates as big burn on the face
Geography
Dunstan Mountains is located in New Zealand
Dunstan Mountains
Otago, South Island, New Zealand
CountryNew Zealand
RegionOtago
Range coordinates44°52′16″S 169°35′24″E / 44.871°S 169.590°E / -44.871; 169.590
Parent rangeDunstan Mountains
Topo mapNZMS260 F41 Edition 1 1991 Limited Revision 1996
Geology
OrogenyKaikoura Orogeny
Age of rock200 Ma
Mountain typeFault-block mountain
Type of rockSchist

The Dunstan Mountains are a mountain range in Central Otago, in the South Island of New Zealand. The mountains lie on the eastern shore of the man-made Lake Dunstan and overlook the towns of Cromwell to the west, Clyde to the south and Omakau to the east. The highest named peak on the mountain range, a rocky knoll simply called Dunstan, is 1,667 m (5,469 feet).

Together with the Cairnmuir Mountains to the south, the Dunstan Mountains form the Cromwell Gorge which was dammed to form New Zealand's third-largest hydroelectric dam,[Note 1] the Clyde Dam.

The Dunstan Mountains should not be confused with the Dunstan Range, a small mountain range which lies approximately 20 km (12 mi) north of the Dunstan Mountains near the Lindis Pass.

Geography

View of the Dunstan Mountains (at right) from the Old Woman Range illustrating the asymmetric form of the mountain range: a gentle dip to the left (west) and a steep dip to the right

The Dunstan Mountains form the entrance to the Upper Clutha Valley. The northwest flank of the range is bound by a combination of Cluden Stream in the Lindis Valley, the Lindis River, the Clutha River (Māori: Mata-Au) and Lake Dunstan. Lake Dunstan follows the former Clutha River through the Cromwell Gorge demarcating the southwest limit of the mountains. The mountain range is bound to the east by the Manuherikia Valley and to the northeast by Dunstan Creek, which joins the Manuherikia River at Saint Bathans.

The Dunstan Mountains are bisected by the 4-wheel drive Thomson Gorge Road which follows Thomsons Creek, incised into the eastern flank of the range and the Rise and Shine Creek on the western flank.[2] Thomsons Saddle, between the two creeks, climbs to 980 m (3,220 ft) elevation.

The summit landscape is generally a broad, gently sloping undulatory surface which climbs steadily from the west and falls sharply to the Manuherakia Valley floor on the east. The asymmetric nature of the Dunstan Mountains is common with most of Central Otago's basin and range mountains.

Geology

Map of the Dunstan Mountains in Central Otago, South Island
Map and cross section illustrating the textural zones of the Haast Schist in the Dunstan Mountains region, Otago, New Zealand

The Dunstan Mountains, like many Central Otago mountain ranges, are asymmetric antiforms which have formed since the Neogene.[3]

The basement rock is formed from the Haast Schist Group, grey quartzofeldspathic metagreywacke interlayered with micaceous meta-argillite and greenschist formed during the Rangitata Orogeny.[4] The schist in Central Otago has a well-defined pervasive schistosity, with shallow dips defining the broad regional-scale warps in schistosity caused during Miocene deformation (the Kaikoura orogeny).[5] The warped geometries are antiformal over mountain ranges and synformal under the intervening basins.[6] Associated reverse faulting (the Otago fault system) along the south-eastern flanks of many Central Otago mountain ranges[3][7][8] (i.e. Taieri Ridge, Lammermoor Range, Rock and Pillar Range, Rough Ridge, Raggedy Range, Dunstan Mountains, Pisa Range) gives rise to the basin and range topography of parallel ridges and basins with steep south-eastern limbs and gently-dipping south-western flanks.[9]

The Dunstan Mountains are a doubly-plunging domal culmination[3] with limbs dipping to the north-west, north-east, south-east and south-west. The core of the mountains in the south are Textural Zone (TZ) IV strongly foliated and segregated garnet-biotite-albite zone schists of the Rakaia terrane. These schists are separated to the north by the gently northeast-dipping normal-slip Thomsons Gorge Fault which places chlorite zone TZ III schist against TZ IV.[3][10] This low-angle fault zone has resulted in shear zone-hosted gold mineralisation in the form of the Rise and Shine Shear Zone near the Bendigo Goldfields. The Thomson Gorge Fault is a major metamorphic discontinuity, placing lower-grade TZ III schist against higher-grade TZ IV schists; similar low-angle faults are observed in the Cairnmuir Mountains on the south-western side of the Cromwell Gorge where the same relationships are observed.[3][7] The TZ IV core of the Dunstan Mountains, including the Cairnmuir Mountains, are therefore considered a single range-scale footwall block[3] with the TZ III schists of southern Cairnmuir Mountains and northern Dunstan Mountains as the southern and northern hanging wall blocks, respectively.[3]

Landslides

Large-scale landslides are a common feature in the Cromwell Gorge and represent a significant geological hazard following the impoundment of the Clutha River behind the Clyde Dam. Seventeen large schist landslides have been mapped along the 18 km (11 mi) length of the gorge.[11][12] These landslides underwent extensive geo-engineering in the early 1990s to mitigate their movement,[12][13] and all now have extremely low movement rates as a result.[12][14] Engineering works included extensive drainage to draw down the groundwater level, toe buttresses and in the case of the Cairnmuir Landslide, a drainage blanket. Thirteen large-diameter tunnels extend into the toes of several landslides in order to drain groundwater which otherwise lubricates the basal shear zone. Combined with smaller drainage tunnels (49 in total),[15] the total extent of the tunnels is 18.5 km (11.5 mi).[16]

On 13 July 2020 a new slip near Cromwell occurred above Deadman's Point Bridge on the true left of Lake Dunstan. The difficulty in accessing the slip resulted in a rather novel remediation technique; helicopters with monsoon buckets were used to sluice loose material and dislodge unstable rock by dropping large quantities of water directly onto the slip.[14][17][18][19] With the establishment of a safe bench to work from, excavators and an abseiling team cleared the remaining loose material over the following days.[20][19]

Cairnmuir Mountains from Lake Dunstan, Central Otago. The earthworks and terraces of the Cairnmuir Landslip is visible in the upper centre-left of the photo, while the Cairnmuir tunnel used to drain groundwater from the basal shear zone is visible in the centre of the photo, several metres above lake level.

History

Etymology

The Dunstan Mountains was named in 1857 by the Chief Surveyor of the Otago Province, John Turnbull Thomson and his assistant Alexander Garvie. The origin of the name Dunstan, as used in Central Otago, is uncertain, but thought to originate either from Dunstanburgh Castle[21] in Northumberland, England, or as a reference to Dunstan, the patron saint of goldsmiths.[22]

Much of the Māori naming of the Dunstan Mountains has been lost to time with the best account being compiled in 1930 by Herries Beattie in the Otago Daily Times.[23] Early Māori settlers referred to the Dunstan Mountains by geographic subdivision into lower (southern), central and upper (northern) portions of the range:

  • Tiko-umu – southern end of the range including Leaning Rock. No translation is given for Tiko-umu although tiko has several definitions[24] such as protrude or be conspicuous, while umu means an earth oven[24]
  • Mataki-nui – central portion of the range with Castle rock as its pivot. Sherwood-Roberts (1913) gives the translation for Matakanui (note difference in spelling) as big burn on the face[25]
  • Neinei-i-kura – northern portion of the range
  • Kura-matakitaki – the extension from Dunstan Peak to the Old Man Peak on the Dunstan Range. Kura-matakitaki was apparently a celebrated woman of olden times[26]

The very characteristic rocky tor on the southern end of the Dunstan Mountains, 'Leaning Rock', is called Haehaeata in Māori which means torn in the morning.[23] Leaning Rock was known as 'The Old Woman' by early goldminers in the region,[22] with the Dunstan Mountains being erroneously referred to as the Old Woman Range.[Note 2]

Other traditional Māori named peaks on the Dunstan Mountains are Ritua (Cloudy Peak),[26] O-puaha (Dunstan Peak),[26] Mt Makariri (meaning cold),[24] Mt Kamaka (meaning rock),[24] Mt Apiti and Mt Kīnaki.

Māori

The first settlers in the region of the Dunstan Mountains were the Māori as they travelled through Central Otago en route to the West Coast on pounamu expeditions, as well as in search of seasonal food resources.[27][28] The low Thomson Gorge Saddle over the Dunstan Mountains was not the usual route for early Māori however, who used the Lindis Pass in preference to access their summer camps at Lake Hāwea and Lake Wānaka.[2][29] The Cromwell Gorge was more-frequented, with early Māori archaeological sites concentrated through the gorge on the true left of the former Clutha River. These sites include small Moa hunter camps with associated Moa bones.[30] Four sites have been identified at Rockfall I and II, Italian Creek, Muttontown Gully and Clyde West.[30]

One of the most significant Māori archaeological finds was that of a paddle in Bendigo.[31][32] Bendigo itself was not important in terms of Māori camp sites, but an established Māori path over Thomsons Saddle, likely used when the Clutha River was in flood,[28][32] meant that the area had limited Māori artefacts. Early miners in Bendigo Gully reported in 1872 that they had found pounamu weapons and implements in the gravels they were sluicing. The Māori paddle was found by John Evan, who gave it to Vincent Pyke who then donated it to the Otago Museum, which recorded its acquisition in 1877.[32][33]

Pastoral farming

Much of the Dunstan Mountains is used for pastoral farming with stations extending from the range spine to both the Clutha and Manuherikia Valleys. The larger pastoral leases on the north-west flank of the Dunstan Mountains are Northburn, Bendigo and Cluden Stations.[34] On the south-east flank the leases are smaller and more numerous but the larger stations are Moutere, Matakanui, and Lauder.[34]

Gold mining

Quartz Reef Point, Northburn Station, Central Otago, New Zealand

Alluvial gold was first discovered in the Cromwell Gorge by prospectors Horatio Hartley and Christopher Reilly in 1862. Hartley and Reilly found 87 lb (32 kg) of gold on a bend of the Clutha River near Brewery Creek,[35] spurring the first gold rush into the Central Otago region.

Historic gold diggings are primarily located along the foot of the south-eastern flank of the Dunstan Mountains (Manuherikia Valley) and include Tinkers,[36][37] Drybread,[38] Cambrians[39] and Devonshire diggings.[40] The most famous gold mining area on the Dunstan Mountains is that of Bendigo Goldfields, located on the north-western flank of the range. Gold was discovered in Bendigo Creek as a result of the rush to the Dunstan area in September 1862 following Hartley and Reilly's discovery. Close to Bendigo are the Quartz Reef Point Diggings[41] on Northburn Station with their characteristic herringbone tailings.

Notes

  1. ↑ List of power stations in New Zealand
  2. ↑ The Old Woman Range is located some 20 km to the southwest of the Dunstan Mountains

References

  1. ↑ "NZ Topo Map". Retrieved 5 August 2023.
  2. 1 2 "Thomson Gorge Road Brochure" (PDF). Otago Goldfields Heritage Trust. Otago Goldfields Heritage Trust. February 2007. Retrieved 29 June 2023.
  3. 1 2 3 4 5 6 7 Mortimer, N.; Lee, J.; Stockli, D. F. (2023). "Terrane and core complex architecture of the Otago Schist in the Dunstan and Cairnmuir Mountains, New Zealand, from U-Pb and (U-Th)/He zircon dating". New Zealand Journal of Geology and Geophysics. doi:10.1080/00288306.2023.2176892 – via Taylor & Francis Online.
  4. ↑ Beanland, S.; Berryman, K. R. (1989). "Style and episodicity of late Quaternary activity on the Pisa-Grandview Fault Zone, Central Otago, New Zealand". New Zealand Journal of Geology and Geophysics. 32: 451–461 – via Informa.
  5. ↑ Craw, D. (1995). "Reinterpretation of the erosion profile across the southern portion of the Southern Alps, Mt Aspiring area, Otago, New Zealand". New Zealand Journal of Geology and Geophysics. 38 (4): 501–507 – via Informa.
  6. ↑ Turnbull, I. M. (1981). "Contortions in the schists of the Cromwell district, Central Otago, New Zealand". New Zealand Journal of Geology and Geophysics. 24 (1): 65–86 – via Taylor & Francis Online.
  7. 1 2 Turnbull, I. M. (2000). "Geology of the Wakatipu area : scale 1:250,000". Institute of Geological and Nuclear Sciences Ltd. Retrieved 13 August 2023.
  8. ↑ Forsyth, P. J. (2001). "Geology of the Waitaki area : scale 1:250,000". Institute of Geological and Nuclear Sciences Ltd. Retrieved 13 August 2023.
  9. ↑ Ballance, P. (2009). New Zealand Geology: An Illustrated Guide (PDF) (2 ed.). Auckland, NZ: GSNZ Miscellaneous Publication 148. ISBN 978-0-473-41925-7.
  10. ↑ Martin, A.P.; MacKenzie, D. (2016). "Rise and Shine Orogenic Gold Prospect, Otago – Exploration Summary" (PDF). Mineral deposits of New Zealand–exploration and research. AusIMM Monograph. 31: 149–156 – via ResearchGate.
  11. ↑ Turnbull, I. M. (1987). Sheet 133 Cromwell: Geological map of New Zealand. 1:63,360 Sheet S133. Wellington, New Zealand: Department of Scientific and Industrial Research.
  12. 1 2 3 O'Brien, G. A.; Cox, S. C.; Townend, J. (2016). "Spatially and temporally systematic hydrologic changes within large geo-engineered landslides, Cromwell Gorge, New Zealand, induced by multiple regional earthquakes". J. Geophys. Res. Solid Earth. 121: 8750–8773 – via AGU.
  13. ↑ Nathan, S. (2021). "Geology and the Clyde Dam". Geoscience Society of New Zealand Journal of the Historical Studies Group. 68: 42–52 – via ResearchGate.
  14. 1 2 Petley, D. (15 July 2020). "Cromwell: helicopter sluicing to manage a landslide". AGU Blogosphere. Retrieved 20 August 2023.
  15. ↑ O'Brien, G. (2014). Earthquake-induced hydrologic changes in the geoengineered schist landslides of Cromwell Gorge, Central Otago. Wellington, New Zealand: Masters Thesis, Victoria University.
  16. ↑ Edwards, J. (30 March 2016). "Hundreds venture underground to slip zone". Otago Daily Times. Retrieved 22 August 2023.
  17. ↑ "Cromwell slip site – road to continue as single lane, sluicing ongoing today and next few days". Waka Kotahi NZ Transport Agency. 15 July 2020. Retrieved 20 August 2023.
  18. ↑ McKenzie-McLean, J. (15 July 2020). "Choppers sluicing unstable Otago highway rockface after massive slip". Stuff. Retrieved 20 August 2023.
  19. 1 2 "Choppers sent in as massive landslip closes road in Cromwell Gorge". New Zealand Herald. 13 July 2020. Retrieved 20 August 2023.
  20. ↑ "Large Cromwell slip cleared". Otago Daily Times. 14 August 2020. Retrieved 20 August 2023.
  21. ↑ Joyce, L. (2012). Gold Rush: Central Otago 1862 (PDF). Clyde, NZ: Promote Dunstan Inc. ISBN 978-0-473-20171-5.
  22. 1 2 "Dunstan Mountains". New Zealand Gazetteer. Retrieved 5 August 2023.
  23. 1 2 Beattie, H. (8 November 1930). "The Southern Maori". Otago Daily Times. No. 21178. p. 2.
  24. 1 2 3 4 "kamaka". Te Aka Māori Dictionary. Retrieved 13 August 2023.
  25. ↑ Sherwood-Roberts, W. H. (13 September 1913). "Place names of Otago and Southland". Southland Times. No. 17448. p. 9. Retrieved 13 August 2023.
  26. 1 2 3 "Mata Au - Clutha River". Hokonui Rūnanga. Retrieved 5 August 2023.
  27. ↑ Hamel, G. E. (1993). The Rich Fields of Bendigo (PDF). Dunedin, NZ: Unpublished report to the Department of Conservation. Retrieved 22 August 2023.
  28. 1 2 "History of Bendigo". Department of Conservation. Retrieved 20 August 2023.
  29. ↑ Chinn, B. (2015). A Pretty Good Place to Live: Lake Hawea & Hawea Flat (PDF).
  30. 1 2 Hamel, Jill (2001). The Archaeology of Otago (PDF). Wellington, New Zealand: Department of Conservation. ISBN 0-478-22016-2. Retrieved 21 August 2023.
  31. ↑ "Paddle, D20.226". Otago Museum. Retrieved 20 August 2023.
  32. 1 2 3 "Tarras Maori". Tarras. Retrieved 20 August 2023.
  33. ↑ Skinner, H. D. (1948). "Paddle forms in Murihiku". Journal of the Polynesian Society. 57 (3): 256–267.
  34. 1 2 "Map of the pastoral runs of South Island, New Zealand". National Library of New Zealand. 1966. Retrieved 20 August 2023.
  35. ↑ "Hartley and Reilly". Central Otago District Council. Retrieved 25 August 2023.
  36. ↑ "Tinkers Diggings". mindat.org. Retrieved 24 August 2023.
  37. ↑ Craw, D.; Bartle, A.; Fenton, J.; Henderson, S. (2013). "Lithostratigraphy of gold-bearing Quaternary gravels, middle Manuherikia Valley, Central Otago, New Zealand". New Zealand Journal of Geology and Geophysics. 56 (3): 154–170 – via Taylor & Francis Online.
  38. ↑ "Drybread Diggings". mindat.org. Retrieved 26 August 2023.
  39. ↑ "Cambrians (Welshmans Gully, Four Mile)". mindat.org. Retrieved 26 August 2023.
  40. ↑ "Devonshire Diggings". mindat.org. Retrieved 26 August 2023.
  41. ↑ "Northburn (Quartz Reef Point tailings)". mindat.org. Retrieved 26 August 2023.
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