* {{cite Q|Q60717861|last1=Wood|first1=R.A.|last2=Pettinga|first2=J.|last3=Bannister|first3=S.|last4=Lamarche|first4=G.|last5=McMorran|first5=T.J.|year=1994}}
* {{cite Q|Q60717861|last1=Wood|first1=R.A.|last2=Pettinga|first2=J.|last3=Bannister|first3=S.|last4=Lamarche|first4=G.|last5=McMorran|first5=T.J.|year=1994}}
* {{cite book| editor-last1=Rattenbury|editor-first1=M.S.|editor-last2=Townsend|editor-first2=D.|editor-last3=Johnston|editor-first3=M.R.|year=2006|title=Geology of the Kaikoura area: scale 1:250,000 geological map 13|location= Lower Hutt|publisher= [[GNS Science]], Institute of Geological & Nuclear Sciences| isbn= 0-478-09925-8}}
* {{cite book| editor-last1=Rattenbury|editor-first1=M.S.|editor-last2=Townsend|editor-first2=D.|editor-last3=Johnston|editor-first3=M.R.|year=2006|title=Geology of the Kaikoura area: scale 1:250,000 geological map 13|location= Lower Hutt|publisher= [[GNS Science]], Institute of Geological & Nuclear Sciences| isbn= 0-478-09925-8}}
* {{cite Q|Q135932944}|last1=Morgenstern|first1=R.|last2=Litchfield|first2=N. J.|last3=Langridge|first3=R. M.|last4=Heron|first4=D. W.|year=2024}}
* {{cite book|title=Hanmer Springs Thermal Pools Reserve Management Plan 2011 |year=2011|publisher = [[Hurunui District Council]]| ref = {{harvid|HDC|2011}} |url=https://www.hurunui.govt.nz/repository/libraries/id:23wyoavbi17q9ssstcjd/hierarchy/Infrastructure_Services/Property/Parks%20and%20Reserves/Hanmer%20Springs%20Thermal%20Pools%20Reserve%20Management%20Plan%202011.pdf}}
* {{cite book|title=Hanmer Springs Thermal Pools Reserve Management Plan 2011 |year=2011|publisher = [[Hurunui District Council]]| ref = {{harvid|HDC|2011}} |url=https://www.hurunui.govt.nz/repository/libraries/id:23wyoavbi17q9ssstcjd/hierarchy/Infrastructure_Services/Property/Parks%20and%20Reserves/Hanmer%20Springs%20Thermal%20Pools%20Reserve%20Management%20Plan%202011.pdf}}
Geology
The town of Hanmer Springs is located about midway along the north side of a rhomb-shaped topographic depression approximately 15 km (9.3 mi) long and 7 km (4.3 mi) wide. This depression is part of the Hanmer basin whose maximum dimensions are approximately 20 km (12 mi) by 10 km (6.2 mi). The Hanmer plain is at an elevation of 300 m (980 ft) but is surrounded by ranges up to 1,000 m (3,300 ft) higher. The basin has formed on a bend of the active Hope Fault, with basement-derived alluvial sediments filling the depression. Within the town a hot water spring supplies a bathing complex.
The Hanmer basin formed on the dextral strike-slip Hope Fault – an active fault within the Marlborough fault system. The fault system is part of the Pacific-Australia plate boundary zone between the westward subduction of the Pacific plate east of the North Island and the oblique strike-slip of the Alpine Fault in the South Island.[5] Tectonically the basin is a pull-apart basin between the right step-over of two segments of the Hope Fault. The western part of the basin is under transtension and actively subsiding in response to north-south extension. The eastern part of the basin is undergoing transpression in response to north-south shortening caused by convergence in strike of the Hope Fault segments across the basin.[5]
Seismic and gravity studies indicate a wedge-shaped profile with sediments filling the basin to a depth of more than 1,000 m (3,300 ft) along the southern margin of the basin and thinning to less than 300 m (980 ft) along the northern margin. An oblique normal fault, the Hanmer Fault, runs along the northern basin-floor margin and passes about 300 m (980 ft) south of the thermal spring in Hanmer Springs. The fault probably reflects large-scale upper crustal collapse of the hanging-wall side of the Hope Fault.[5][9] Basin formation probably began in the mid-to-late Pleistocene based on extrapolation of average Late Pleistocene slip rates for the Hope Fault, climatic factors and the faunal content of the sediments.
Underlying the basin sediments and forming the surrounding ranges is Late Jurassic to Early Cretaceous greywacke of the Pahau Terrane.[12] The greywacke consists of indurated thin-to-medium bedded and commonly graded sandstone and mudstone, and also thick, poorly bedded sandstone. The greywacke has undergone low-grade metamorphism varying from zeolite facies to prehnite–pumpellyite facies. The overlying basement-derived sediments are alluvial/fluvial fan and terrace deposits consisting of poorly sorted sandy gravel, silt, peat and clay. Glacial deposits from Late Pleistocene are also recognised. The oldest sediments are probably mid-to-late Pleistocene coinciding with the beginning of the formation of the depression.
Hot spring
The hot spring at Hanmer Springs is one of about 25 hot springs located along the central and northern parts of the Southern Alps, parallel to the Alpine Fault and Marlborough fault system. Groundwater percolates down through the basin sediments and into fractured basement to a depth of at least 2 km (6,600 ft) where it becomes heated to 180-200°C . The high temperatures are attributed to rapid uplift of up to 10 mm (0.39 in) per year along the Alpine Fault which brings hot, deep rock that was originally buried at a depth of 10 km (6.2 mi) or more to shallow depths. The heated water loses heat by conduction as it rises towards the surface and at Hanmer Springs its temperature is 52°C when it comes out of the borehole at the thermal pools complex.[17][18] The first known European discovery of the hot spring was in 1859. Since then the natural upward flow of heated water has diminished and is currently drawn from the borehole at about 70 m (230 ft) depth – depending on seasonal fluctuations.[17]
Heat exchangers cool the water down to a range of 32-42°C for use in the bathing pools.[17] The Hanmer Springs Thermal Pools Reserve Management Plan 2011 states that the draw-off of thermal water will be limited to 17.5 litres per second until the year 2039.
The thermal water from the springs contains methane gas. When the water is brought to the surface the gas is released.[20] In the early period of the development of the springs, the gas was captured and stored for use in heating, lighting and cooking in the sanitorium. A gasometer installed in 1898 is listed as one of the historic items within the Queen Mary Hospital (Former) and Hanmer Springs Thermal Reserve Historic Area.[21] In 2018, the pool complex commissioned a microturbine to generate electricity from the gas, reducing the electricity consumption of the complex, and avoiding the release of 100,000 cubic metres of methane into the atmosphere each year.[20]
References
Sources cited
- Graham, I.J., ed. (2015). “Astride a Plate Boundary/Mineral Waters”. A continent on the move: New Zealand geoscience revealed. GSNZ miscellaneous publications (2nd ed.). Wellington: Geoscience Society of New Zealand. p. 105. ISBN 978-1-877480-47-8.
- Wood, R.A.; Pettinga, J.; Bannister, S.; Lamarche, G.; McMorran, T.J. (1994). “Structure of the Hanmer strike-slip basin, Hope fault, New Zealand”. Geological Society of America Bulletin. 106 (11) (published November 1994): 1459–1473. Bibcode:1994GSAB..106.1459W. doi:10.1130/0016-7606(1994)106<1459:SOTHSS>2.3.CO;2. ISSN 0016-7606. Wikidata Q60717861.
- Rattenbury, M.S.; Townsend, D.; Johnston, M.R., eds. (2006). Geology of the Kaikoura area: scale 1:250,000 geological map 13. Lower Hutt: GNS Science, Institute of Geological & Nuclear Sciences. ISBN 0-478-09925-8.
- Hanmer Springs Thermal Pools Reserve Management Plan 2011 (PDF). Hurunui District Council. 2011.
