Geology of the Fiordland Area - GNS Science

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The most frequent landslide hazard in Fiordland is posedby hea y rain e ents. Nearly e ery rainstorm triggersshallow slope failures in steep, peaty soils that are poorlybonded to underlying rock, and usually laden with trees.Such landslides frequently block the ilford Road (e.g.Wandres et al. 1998), and both the Borland Saddle andWilmot Pass roads are often cut by minor rain-triggeredlandslides. Walking tracks and huts are also ulnerable(Thomson 1994; Fig. 76), but huts are normally re-sitedonce a landslide or a alanche risk has been recognised.Future large earthquakes (M7.5–8 or greater) on the AlpineFault and the subduction zone beneath Fiordland will almostcertainly trigger rock falls, rock slides and rock a alanchesthroughout Fiordland. ecause of their potentially greatersize, earthquake-triggered landslides (such as Green Lake;Hancox & Perrin 2009) present a greater hazard than raininducedlandslides to the ilford and other roads, mountainhuts and tracks, and tourist centres like ilford Sound.TsunamiFlooding and damage due to tsunami are possible alongall sea and lake shorelines within the Fiordland map area.Tsunami are generated by sudden large mo ements of thesea floor or lake beds, caused by local or distant earthquakes,submarine olcanic eruptions, submarine or sub-lacustrinelandslides, or delta collapse initiated by strong earthquakeshaking. Tsunami are known to ha e affected coastalFiordland in about 1820 and 1826 (Downes et al. 2005).During the 2003 Fiordland earthquake, a rockfall into oldArm, Charles Sound, created a locally damaging tsunami4–5 m high (Fig. 77; Hancox et al. 2003). Tsunami damagefrom the 2009 earthquake, in contrast, was minimal (Wilsonet al. 2009).Tsunami generated by distant e ents take many hours toreach New Zealand, sufficient time for Civil Defence totake appropriate action. The risk from distant e ents isrelati ely low as there are few potential sources in thesouthern Tasman Sea. Locally generated tsunami are ofmore concern, as wa e heights may be large enough tobe damaging and life-threatening, possibly catastrophic,and tra el times too short for warnings to be issued. Localtsunami may persist for up to twel e hours, and distantsource tsunami for as long as three days. Tsunami may alsobe caused by landsliding into or beneath lakes followingearthquakes (Forsyth et al. 2006). A major rock fall intoany Fiordland lake could ha e potentially disastrousresults for lakeshore constructions and their occupants.The marine tsunami hazard in Fiordland was studied andmodelled by Downes et al. (2005). Their work suggestsoffshore segments of the Alpine Fault may rupture in an7.8 earthquake and create tsunami up to 4 m high alongthe western Fiordland coast. The southern coast may beaffected by tsunami of up to 4 m, emanating from majorFigure 75 Ridge rents at the head of an incipient major landslide, caused by gravitational collapse of glacially oversteepenedslopes north of Poteriteri Peak. Lake Poteriteri (right) is covered in fog.82
Figure 76 The epler Track crosses the runout zone of the 198 Iris Burn landslide (open ground, centre), which beganin bluffs of jointed Hunter Intrusives diorite and was probably triggered by heavy rain (Thomson 199 ). This view upstreamalso shows the debris of a much older landslide, which forms the forested mound in the middle right distance. Beyond themound lie the Iris Burn Hut and the upper river flats.Photo CN47924b: D.L. Homer.83
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1 : 2 5 0 0 0 0 G e o l o g i c a l
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Geology of theFiordland AreaScale 1
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CONTENTSABSTRACT ..................
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FrontispieceA pekapeka (neck pendan
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Fiordland’s proximity to the acti
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INTRODUCTIONTHE QMAP SERIESThis geo
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ThesesPublished papersPublished map
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GEOMORPHOLOGYThe uplifted Fiordland
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TributaryglaciersTrunkglaciersQuate
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to 14 000 years BP, when the major
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Figure 10 A fossil marine arch, ero
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Figure 14 The northern Fiordland co
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STRATIGRAPHYPaleozoic metasedimenta
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ABCFigure 17 dgecumbe Group formati
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thin marble (Fig. 18C), with interb
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quartzofeldspathic biotite gneiss,
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ACBFigure 23 Ordovician Fanny Bay G
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Paleozoic metamorphic rocks of unce
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28PERMIAN TO URASSIC SEDIMENTARY AN
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Figure 28 Latest Cambrian to earlie
Page 42 and 43: etasedimentary xenoliths are common
Page 44 and 45: Late Triassic to Cretaceous plutoni
Page 46 and 47: heterogeneous, metre- to kilometre-
Page 48 and 49: The Malaspina Pluton ( wm; 117-114
Page 50 and 51: granite, leucogranite and tonalite
Page 52 and 53: and comprises weakly foliated, loca
Page 54 and 55: sedimentary rocks extend offshore t
Page 56 and 57: AFigure 47 ocene sedimentary rocks
Page 58 and 59: Figure 49 Oligocene sedimentary roc
Page 60 and 61: graded sandstone and mudstone (Cart
Page 62 and 63: sequence of Oligocene graded sandst
Page 64 and 65: oup, and is restricted to the area
Page 66 and 67: QUATERNARYExtensi e Quaternary depo
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Page 70 and 71: y the present-day coast. The ice le
Page 72 and 73: eorge Sound, and remnants of well-r
Page 74 and 75: TECTONIC HISTORYFiordland has a lon
Page 76 and 77: A B CDFigure 65 Fiordland plutonic
Page 78 and 79: Major active faultsOffshore volcani
Page 80 and 81: a zone of amphibolite facies gneiss
Page 82 and 83: GEOLOGICAL RESOURCESAlmost the whol
Page 84 and 85: HydrocarbonsSequences within the Cr
Page 86 and 87: ENGINEERING GEOLOGYThis section pro
Page 88 and 89: GEOLOGICAL HA ARDSThe numerous geol
Page 90 and 91: NDCenozoic to Holocene faultsABCact
Page 94 and 95: earthquakes along the Puysegur subd
Page 96 and 97: ACNOWLEDGMENTSapping of Fiordland w
Page 98 and 99: ishop, D. . 1991: High-le el marine
Page 100 and 101: Ewing, T.A.; Weaver, S.D.; Bradshaw
Page 102 and 103: Lee, W. .; Ward, C. .; Wilson, . .
Page 104 and 105: Schacht, B. 1984: Interpretation re
Page 106 and 107: Ward, C. . 1986: Speculations on th
Page 108: The geology of Fiordland is describ
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Geology of the Fiordland Area - GNS Science

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