Floods in the Southern Alps of New Zealand: the importance of atmospheric rivers

Extremely high precipitation occurs in the Southern Alps of New Zealand, associated with both orographic enhancement and synoptic‐scale weather processes. In this study, we test the hypothesis that atmospheric rivers (ARs) are a key driver of floods in the Southern Alps of New Zealand. Vertically integrated water vapour and horizontal water vapour transport, and atmospheric circulation, are investigated concurrently with major floods on the Waitaki River (a major South Island river). Analysis of the largest eight winter maximum floods between 1979 and 2012 indicates that all are associated with ARs. Geopotential height fields reveal that these ARs are located in slow eastward moving extratropical cyclones, with high pressure to the northeast of New Zealand. The confirmation of ARs as a contributor to Waitaki flooding indicates the need for their further exploration to better understand South Island hydrometeorological extremes. Copyright © 2016 John Wiley & Sons, Ltd.     

Large landslides and their effect on sediment flux in South Westland,New Zealand

Landslides and runoff are dominant erosional agents in the tectonically active alpine South Westland area of New Zealand, characterized by high uplift rates and extreme orographic precipitation. Despite a high density of shallow debris slides and flows, the geomorphic imprints of deep‐seated bedrock failures are dominant and persistent. Over 50 large (>1 km²) landslides comprising rock slide[sol ]avalanches, complex rotational and rock‐block slides, wedge failures, and deep‐seated gravitational slope deformation were detected on air photos and shaded‐relief images. Major long‐term impacts on alpine rivers include (1) forced alluviation upstream of landslide dams, (2) occlusion of gorges and triggering of secondary riparian landslides, and (3) diversion of channels around deposits to form incised meandering gorges. Remnants of large prehistoric (i.e. pre‐1840) landslide deposits possibly represent the low‐frequency (in terms of total area affected yet dominant) end of the spectrum of mass wasting in the western Southern Alps. This is at odds with high erosion rates in an active erosional landscape. Large landslides appear to have dual roles of supplying and retaining sediment. The implications of these roles are that (1) previous models of (shallow) landslide‐derived sediment flux need to be recalibrated, and (2) geomorphic effects of earthquake‐induced landsliding may persist for at least 10² years. Copyright © 2005 John Wiley & Sons, Ltd.     

Solution of marble in the karst of the Pikikiruna range,Northwest Nelson,New Zealand

The paper reports the first research on karst solution processes and rates in New Zealand. The study area is an IHD representative basin in the northwest corner of the South Island in a mountain range consisting principally of Ordovician marble. The climate is sunny and warm (17°C) in summer and wet and cool (7°C) in winter. Average precipitation is 2,158 mm of which 525 mm evapotranspires, yielding a discharge of 51–75 l/s/km² in the river basin studied. Almost half of the catchment of 45.1 km² consists of karst which occurs mainly as a doline covered plateau at 600–900 m within which most drainage is subterranean. Water tracing is with fluorescein defined drainage patterns. Marble solution was established by estimating inputs, throughputs and outputs of water and dissolved calcium and magnesium in both autogenic and allogenic karst drainage systems. Particular attention was paid to estimating errors. Water samples for chemical analysis were taken irregularly for approximately one year, and a rating curve relating chemical load to discharge was established. The best estimate of solution loss from the basin yields a mean rate of 100 ±M24 m³/km²/a. Of this 80 per cent is derived from solution of marble by autogenic waters, mostly in the top 10–30 m of the marble outcrop. The remaining 20 per cent is accomplished by allogenic stream solution. Approximately 9.9 per cent of the dissolved calcium and magnesium load leaving the basin originates from non-karst rocks and 4.6 per cent is initially introduced by rainfall. River flows that are exceeded only 5 per cent of the time transport approximately 44 per cent of the annual dissolved load, while mean to low flows that occur for 75 per cent of the time transport 35 per cent of the annual solute load. This confirms the importance of low frequency-high magnitude events, but indicates also that in corrosion systems high frequency events of moderate to low magnitude can also accomplish significant work.     

Estimation of Tsunami Hazard in New Zealand due to South American Earthquakes

We develop a probabilistic model for estimating the tsunami hazard along the coast of New Zealand due to plate-interface earthquakes along the South American subduction zone. To do this we develop statistical and physical models for several stages in the process of tsunami generation and propagation, and develop a method for combining these models to produce hazard estimates using a Monte-Carlo technique. This process is largely analogous to that used for seismic hazard modelling, but is distinguished from it by the use of a physical model to represent the tsunami propagation, as opposed to the use of empirical attenuation models for probabilistic seismic hazard analysis.     

基于2011年新西兰地震的CPT液化特征研究

2011年2月22日,新西兰第二大城市克赖斯特彻市附近发生Ms6.3级地震,震中位于克赖斯特彻市西南10km处,震源深度为5km.地震造成了大量的人员伤亡和经济损失,重建费用估计高达40亿新西兰元,得到共识是砂土液化为震害主因.此次地震,液化震害极为严重,喷砂冒水范围广泛分布于城市内外,引起大量次生灾害,地震也为砂土液...     

Physical and chemical effects of ingested plastic debris on short-tailed shearwaters, Puffinus tenuirostris, in the North Pacific Ocean

We investigated the plastics ingested by short-tailed shearwaters, Puffinus tenuirostris, that were accidentally caught during experimental fishing in the North Pacific Ocean in 2003 and 2005. The mean mass of plastics found in the stomach was 0.23 g per bird (n = 99). Plastic mass did not correlate with body weight. Total PCB (sum of 24 congeners) concentrations in the abdominal adipose tissue of 12 birds ranged from 45 to 529 ng/g-lipid. Although total PCBs or higher-chlorinated congeners, the mass of ingested plastic correlated positively with concentrations of lower-chlorinated congeners. The effects of toxic chemicals present in plastic debris on bird physiology should be investigated.     

Temporal variations in coda duration of local earthquakes in the Wellington region,New Zealand

Temporal variations of coda duration, relative to event magnitude, for local earthquakes near Wellington have been investigated. The region is one of plate convergence and subduction. The data consist of routinely made observations for events from 1978 through 1985 (1552 events), magnitude 1.6 to 5.2, depth 0.5 to 90.0 km. The observed average (over time) correspondence between duration (as measured from the origin time) and magnitude is reasonably well predicted by the single backscattering theory of coda formation for events of magnitude 4 or less; for larger events the observed durations are longer than predicted. This theory predicts that a temporal increase in scattering attenuation will reduce the coda duration relative to magnitude. Thus, any temporal changes in the duration-magnitude relation can be interpreted in terms of changes inQ. However, it is necessary to consider spatial biases since the observed durations are relatively long for shallow events and, for events of all depths, at stations situated in the south-eastern half of the region, usually believed part of the accretionary border. For both these situations other evidence would suggest that the scattering coefficient would be relatively high (lowQ). These observations may be due to a relatively high component of surface wave scattering and the importance of multiple scattering in the later part of the coda in regions of lowQ as suggested by finite element studies of coda formation. Despite the lack of any significant earthquakes during the 1978–1985 period there is nevertheless a significant temporal change in duration observed in the Wellington region: a change from relatively long to relatively short codas occurred in mid-1981. This change correlates well with changes in the rate of activity,b-value, radon emission, and ground tilt as derived from lake levels. It is not yet clear how all these parameters are related physically, but an episode of aseismic slip, or creep, along the plate interface below the region may have been the cause.     

Research on the multifractal characteristics of the temporal—spatial distribution of earthquakes over New Zealand area

Using the Hill estimator,general multifractal characteristics of events in the New Zealand area have been dis-cussed.Results show that the spatial distribution of shallow events has apparent clustering characteristics,inde-pendent of the threshold magnitude;but for deep events these characteristics are not clear.While the time interval distribution has obvious clustering characteristics both for deep and shallow events,although with a different scal-ing range,the Hill estimates tend to indicate that the time interval distribution has a unifractal rather than a multi-fractal nature.All above reveal that the seismicity nature for shallow and deepevents is apparently different.     

模糊-统计分析方法在新西兰地震危险性估计中的应用

把模糊聚类分析、模糊地震活动平静异常识别、模糊分维、b值谱分析等方法应用于新西兰南、北两区的地震危险性估计当中.结果表明,这5种方法在此处均可得到有效的应用.     

Constraints on the evolution of the Taranaki volcanoes,New Zealand,based on aeromagnetic data

Aeromagnetic anomalies measured over the three relict andesite volcanoes (Paritutu, Kaitake and Pouakai) in Taranaki are largely dominated by topographic effects. Three-dimensional magnetic modelling, well constrained by both contrasting levels of exposure and previous gravity models, shows that the bulk magnetization of the andesite edifice and edifice core of both Kaitake and Pouakai is 2.5–3.5 A m^-1 in a direction close to that of the present earth's field. However, the large andesite dyke/stock complexes below all three edifices and a localized area of the Kaitake edifice directly above the centre of the subedifice complex have anomalously low bulk magnetizations of 0.3–1.0 A m^-1 in the same direction. These subsurface complexes represent dyke injection from magma chambers situated in the basement, probably below 6 km depth. Here, we deduce that heat from these magma chambers drove hydrothermal convection systems causing widespread demagnetization, especially in the subedifice complexes, but also locally within the edifices themselves. A lesser degree of demagnetization at Pouakai, the youngest of the three volcanoes, may indicate a shorter and consequently more intense period of activity at this centre.     

新西兰2010年M7.1地震与2011年M6.3地震活动和灾害分析

本文对新西兰.2010年9月4日M7.1地震(国际标准时间)与2011年2月22日(国际标准时间)M6.3地震活动和灾害情况进行了分析,用同震位移方法计算了两次地震的地震烈度,结果表明尽管两次地震震级相差较大,但由于M6.3地震震源深度较浅,两次地震在地表的烈度相同.本文用主余震序列方法计算了两次地震的断层滑动参数,结...     

Tilting of active folds and drainage asymmetry on the Manawatu anticlines,New Zealand: a preliminary investigation

The apparent southward tilting of five anticlines in the Manawatu, North Island, New Zealand, is investigated using two drainage basin analysis techniques: the transverse topographic symmetry factor (T) and the asymmetry factor (AF). The techniques are used to determine whether westward‐flowing trunk streams on the gentle western limbs of five anticlines are migrating southwards across their drainage basins, concomitant with down‐tilting of the fold axes. While results show potential for the techniques to be applied in such a tectonic setting, our findings are inconclusive. This could be due to the incipient nature of the folds (c. 0·5 Ma in age), and it would seem more appropriate to apply the techniques in concert with detailed field analyses of river migration patterns. Copyright © 2008 John Wiley & Sons, Ltd.     

Blind detection of liquefaction by existing methods for New Zealand M L6.3 earthquake on Feb. 22, 2011

Real-time liquefaction monitoring and warning techniques are new ways to mitigate liquefaction hazard. A key point is to establish a reverse liquefaction detection method based on seismic records. However, the existing methods are quite limited and the reliability requires verification. On Feb. 22, 2011 an earthquake of magnitude 6.3 struck at New Zealand’s South Island. Remarkable liquefaction phenomena were reported, which provide an opportunity to verify the existing liquefaction detection methods. 27 acceleration records within 50 km to the epicenter were selected to perform a blind detection by using the existing methods, including Miyajima method, Suzuki method, Kostadinov-Yamazaki method and Yuan-Sun method. The blind detection results indicate that Yuan-Sun method gives correct results for seven confirmed sites, and Suzuki method and Yuan-Sun method yield correct detection for a reported non-liquefied site. Four methods including the Yuan-Sun method give identical detection for four sites and three methods also including the Yuan-Sun method give identical detection for ten sites. Besides, there are five sites, for which the four methods give opposite detection.     

Deformation processes in the shallow levels of an accretionary prism: The Mesozoic Torlesse Terrane, South Island, New Zealand

Abstract The deformation style of the Torlesse Terrane along the southern Kaikoura coast, South Island, New Zealand, records shallow level deformation processes within an accretionary prism during the Early Cretaceous. The beds exhibit complicated structural features resulting from multistage deformations in a lithological unit, that were intimately related with the dewatering and lithification of terrigenous sediments. The earliest phase of deformation throughout the transect studied was the development of pinch-and-swell structures and boudinage fabrics due to layer-parallel extension while the beds were poorly consolidated. This was followed locally by mesoscopic tight to close recumbent folding. The beds are cut locally by two phases of mudstone intrusions. The earlier phase was initiated by 'in situ' fluidization of mudstone layers, whereas the later phase represented intrusion of siliceous claystone probably derived from an overpressured decollement. Minor faults at high-angles to bedding by layer-normal shortening then disrupted the beds throughout the transect. The deformation was followed by formation of meso- and macroscopic scale open to gentle folds by layer-parallel shortening. Kilometer-scale differential stratal rotations were produced during the final main tectonic phase that occurred in association with post-accretion Neogene regional disturbance.     

Early deformation fabrics of melange in the Mesozoic Waipapa Terrane, North Island, New Zealand

Abstract The Waipapa Terrane in northern North Island, New Zealand, is a Mesozoic accretion-ary complex formed along the Gondwana margin. It contains abundant melange rocks with distinctive characteristics. Precise analyses of their mesoscopic fabrics in Waiheke Island near Auckland have revealed the following sequence of deformation. The earliest phase of deformation of the sandstone/mudstone association, which is the main constituent of this terrane, originated by chaotic mixing of sand and mud due to liquidization of water-saturated, poorly consolidated sediments. The second phase was characterized by hydrofracturing and subsequent forceful injection of ductile mud into rather brittle sand. Local intrusions of sand forming dykes and sills followed these events, as well as intrusions of pelagic/hemipelagic green argillite originally underlying the sandstone/mudstone association. An abundant occurrence of these mixing and multi-stage injection/intrusion fabrics strongly suggest that the Waipapa Terrane around the study area was a site of high pore-fluid pressure. Scaly-foliated melange fabrics with monoclinic symmetry, originating from layer-parallel shearing, were then locally superimposed on the pre-existing melange fabrics. Similar scaly-foliated fabrics also developed in the chert beds originally intercalated between the green argillite and the uppermost part of the oceanic crust. These scaly fabrics might have been related to the regional stacking and juxtaposition of the accreted sediments. The sequence and variation in style of deformation forming the melange fabrics presumably reflected changes in porosity and state of compaction of accreted sediments in a shallow tectonic level.     

The Role of Fluvial and Glacial Erosion in Landscape Evolution: The Ben Ohau Range,New Zealand

A morphometric comparison of valleys has been made for the Ben Ohau Range in the central Southern Alps of New Zealand. The range is undergoing rapid tectonic transport and uplift. The humid north of the range is a glacial trough-and-arête landscape, with a temperate glacial climate. The dry south has rounded divides and plateau remnants dissected by fluvial valleys. Assuming that space–time substitution allows today's spatial valley-form transition to represent evolutionary stages in valley development, the tectonic history allows time constraints to be placed on the rate of transition to an alpine glacial landscape. Morphometric change has been quantified using hypsometric curves, and distance–elevation plots of cirque and valley-floor altitudes. Ancestral fluvial valleys have less concave long profiles but are stepped at altitude owing to the presence of high-level cirques and remnant plateau surfaces, and possess a low proportion of land area at low elevation. Increasing glacial influence is manifest as smoother, more deeply concave long profiles and U-shaped cross-profiles associated with a higher proportion of the land area at lower elevation. The full morphological transition has involved up to 2.4 km of vertical denudation over the 4 Ma lifetime of the mountain range, of which 80 per cent would have occurred by preglacial fluvial erosion. Combining the trajectory of tectonic transport with reconstructed glaciation limits and climatic history, it is indicated that about 200 ka of temperate glacial erosion produces recognizable trough-and areête topography. Mean and modal relief increase where glacial activity is confined to cirques, but decrease when trough incision by ice becomes established as a dominant process in the landscape. © 1997 by John Wiley & Sons, Ltd.     

Geology and thermochronometry of the east edge of the Median Batholith (Median Tectonic Zone): a new perspective on Permian to Cretaceous crustal growth of New Zealand

Abstract We report new field, petrological and isotopic data and interpretations from one of New Zealand’s major basement geological boundaries, the contact between the east side of the Median Batholith (formerly Median Tectonic Zone) and the allochthonous Mesozoic terranes of the Eastern Province. In the Nelson and Hollyford–Eglinton areas this contact is a Cenozoic fault, the Median Tectonic Line of earlier workers. However, in the Longwood Range, unfaulted pre-Cenozoic geological relations are preserved intact. Our new Ar–Ar, U–Pb and isotopic data show that the Median Batholith in the Longwood Range consists of two suites. (i) Eastern, isotopically primitive (⁸⁷Sr/⁸⁶Sr_i = 0.702 to 0.703; ?_NdT = + 7 to + 8) trondhjemite and gabbroic rocks of Permian age that we believe are part of the intraoceanic Brook Street arc of the Eastern Province. (ii) Western, isotopically more evolved (⁸⁷Sr/⁸⁶Sr_i = 0.703 to 0.704; ?_NdT = + 3 to + 5) quartz diorites, quartz monzodiorites and rare granites of Middle Triassic to Early Jurassic age that we correlate with a pulse of magmatism elsewhere in the Median Batholith. Field observations in the Longwood Range indicate intrusive, not faulted, contacts between these units and constrain accretion of the Brook Street Terrane to Gondwana to have occurred 230–245 Ma. Intra-batholith shear zones (T ~ 600°C and P ~ 0.2–0.3 GPa) were active at approximately 220 Ma. Modelling of K-feldspar Ar incremental heating ages indicate that most of the Longwood Range had cooled below 175°C by the Middle Jurassic and experienced no subsequent reheating. Significant additional post-accretionary Early Cretaceous and Cenozoic thermotectonic activity in Median Batholith in the Hollyford-Eglinton area is indicated by a new 140 ± 2 Ma U-Pb zircon date on a Largs ignimbrite, as well as by Cenozoic K-feldspar Ar–Ar ages in the Middle Triassic Mistake Diorite.     

Stratigraphic spatial variation on the inner shelf of a high-yield river,Waiapu River,New Zealand: Implications for fine-sediment dispersal and preservation

The inner shelves of active, energetic continental margins are frequently defined as regions of sediment segregation and fine-sediment bypassing. The Waiapu River, North Island, New Zealand presents an opportunity to study fine-sediment segregation and strata formation in a spatially constrained, highly energetic, aggradational setting, with one of the highest sediment yields on earth. We present evidence that the inner shelf of the Waiapu River plays a significant role in both the fate of fine-grained (<63 μm) riverine sediments and the formation of continental margin stratigraphy. Results obtained from high-resolution interferometric bathymetry and high-frequency seismic mapping ground-truthed by cores show significant stratigraphic spatial variation preserved on the Waiapu inner shelf. This spatial variation is likely controlled by spatially-distinct sediment deposition and resuspension processes as well as antecedent geology. Two distinct depositional regions are interpreted as: (1) surface plume-dominated with partial resuspension, characterized by acoustically transparent seismic reflection profiles and muddy sands; and (2) event-layer dominated, characterized by thickly laminated sediments. A modern-day bathymetric low overlying an observed paleochannel may influence the fate of hyperpycnal flows transiting the shelf via bathymetric steering. Fining-upward sequences found over the entire shelf are interpreted to represent deforestation-induced sedimentation that has overwhelmed the ability of the energetic system to resuspend and segregate fine sediments. We conclude that the primary control on strata formation on the inner shelf of the Waiapu River is local sediment supply.     

Seismicity in the Rotorua and Kawerau geothermal systems,Taupo Volcanic Zone,New Zealand,based on improved velocity models and cross-correlation measurements

We analyze earthquakes occurring in and around the Rotorua and Kawerau geothermal systems, Taupo Volcanic Zone, New Zealand. The two data sets contain 504 and 1875 shallow (≤ 20 km deep) earthquakes, respectively, and span the 21 year period between 1984 and 2004. The arrival time data for these earthquakes are first used to calculate 1-D P- and S-wave seismic velocity models and accompanying station correction terms for both areas. In order to address the non-uniqueness of the joint hypocenter-velocity model estimation problem, we analyze suites of 1000 velocity models computed from random initial models. The final velocity models are well constrained, particularly at depths between 4 and 15 km, and consistent with the results obtained in previous seismic refraction studies of the central Taupo Volcanic Zone. Using a combination of cross-correlation-derived and catalog-based arrival times, we relocate subsets of the Rotorua and Kawerau data sets. In Rotorua, the relocated earthquakes cluster near the geothermally active parts of Rotorua City and beneath the Mount Ngongotaha rhyolite dome. Earthquake clusters and alignments reveal seismogenic structures in the mid-crust whose positions and geometries are consistent with previously published fault mechanisms and known near-surface faults. In Kawerau, the earthquakes within the geothermal field align along northeast-trending lineations, consistent with the predominant alignment of surface-mapped faults in the area.