Loess in Aotearoa New Zealand (ANZ) has been studied since its first documented recognition (on Banks Peninsula) in 1878 by Julius von Haast. A decade later, John Hardcastle revealed that southern ANZ loess was both glacial in origin and contained signals of past climates. As a fine‐grained aeolian deposit dominated by quartz and feldspar (± mica), it is derived mainly from greywacke and schist rocks shattered by frost cracking at high elevations, fluvially comminuted then deflated from aggrading floodplains, and from exposed continental shelves during cold periods. Such quartzo‐feldspathic loess predominates in eastern and southern parts of both South and North islands and in Westland and Tasman. In addition, subsurface tephric loess prevails in central‐western North Island. Unlike many deposits overseas, ANZ loess generally lacks secondary calcium carbonate, is denser (with lower macro‐ and mesoporosity, higher clay content) and, although less prone to collapse, is susceptible to accelerated erosion including tunnel gullying and landsliding. Mean rates of accumulation in the Last Glacial Maximum were ~3−25 mm/century; mass accumulation rates were generally 70−150 g cm −2 yr −1 but locally could be as low as 20 g cm −2 yr −1 and as high as 360 g cm −2 yr −1 . Studies mapping and characterizing loess have been driven in part by cognizance of its importance as a widespread parent material (~60%−70% of ANZ's soils contain loess) for arable/pastoral soils underpinning ANZ's predominantly agronomy‐based economy. A key feature of ANZ loess studies has been the recognition of developmental upbuilding pedogenesis involving syn‐depositional alteration of loess as it accumulates in cold and/or cool (stadial) periods, and stronger alteration (forming more‐developed soils, which subsequently become recognizable as buried soil stratigraphic units or paleosols) during minimal accumulation in interglacial and/or warm (interstadial) periods. Multisequal loess‐paleosol successions are the result. ANZ loess‐paleosol successions have been dated and correlated via a range of dating and age‐equivalent techniques including tephrochronology and paleomagnetism. Most loess is ≤500 kyrs old, but occurrences as old as Pliocene (Otago) and c. 1.7–1.0 Ma (Waikato, Wairarapa) are recognized. Loess chronostratigraphy has enabled loess and associated buried soils/paleosols to be correlated to the Quaternary marine oxygen isotope records, which, alongside mapping efforts, have revealed landscape responses to climate and tectonic controls particularly along the eastern regions of ANZ bordering the Hikurangi Subduction Margin.
The southwest Pacific region is geologically complex and exhibits all the principal causes of tsunami generation. While contemporary events and historical catalogs indicate that trans‐Pacific tsunamis have affected this area (∼18% of tsunamis reported globally), it is unique in that a large part of the tsunami effects over the ∼200‐year historical record were triggered locally and regionally. Furthermore, tsunamis in this region are caused by a wide range of earthquakes, volcanic eruptions, submarine landslides, or, more generally, a combination of mechanisms. Due to the complex nature of tsunami generation and the generally short amount of time to tsunami onset, mitigating tsunami hazards and informing vulnerable populations are particularly challenging. This article presents a comprehensive overview of the tsunami hazards in the southwest Pacific related to its complex tectonic and geomorphic setting through examples of significant historical events that exhibit different generation mechanisms, such as the deadly 2009 Samoa‐Tonga event and the recent tsunami caused by the 2022 Hunga Tonga‐Hunga Ha‘apai eruption. We also discuss data and knowledge gaps, including seafloor mapping, palaeotsunami studies, population distribution, and hazard and risk culture, underlining the urgent need to better understand tsunami phenomena, assess the associated risk, and prepare coastal populations for this hazard.
Detrital platinum group minerals (PGM) are rare and distinctive in Pleistocene–Holocene sedimentary systems of the southern South Island, thereby enabling tracking of their long‐distance transport for ∼200 km. The first ∼100 km of transport involved Pleistocene glaciofluvial processes southwards down the Waiau River, where PGM (principally Pt–Fe and Ru–Os–Ir alloys) became hammered into flaky morphology that remained largely unchanged thereafter. When sea level was more than 40 m below the present level, PGM were discharged southwestwards toward the offshore Solander Trough. Only at times of elevated sea levels have PGM remained onshore in beach concentrates. Pleistocene sea level high‐stand beaches immediately east of the Waiau River have been uplifted tectonically and have become important secondary sources of detrital PGM. Erosion by Pleistocene coastal streams recycled flaky PGM, locally sourced equant PGM particles (principally Pt–Fe alloys and sperrylite, PtAs 2 ), and associated detrital gold. Resultant redeposited concentrates have been mined at Round Hill. At times of lowered sea level, these PGM‐bearing streams flowed southeastwards across an emergent fluvial plain on what is now Foveaux Strait. Holocene winds have formed aeolian PGM‐bearing concentrates in scattered small dune fields, which are the largest repositories for PGM along the Foveaux Strait coast. Longshore drift has been important for carrying PGM for ∼100 km through Foveaux Strait in a complex long‐term process involving interactions between sea level changes, tectonic uplift, and coastal recycling.
Otago Schist orogenic mineral deposits with scheelite and gold in the Glenorchy area are mineralogically and geochemically similar to, but structurally different from, those at the active Macraes gold mine in East Otago. Glenorchy veins were mined for scheelite up to 1970s, and an abandoned processing battery site at Glenorchy is now being managed for its historical values. This <1 ha site has unevenly distributed remnants of tailings that consist principally of quartz and schist fragments. Minor pyrite and arsenopyrite are present, but tailings have pH 6-8. Bulk tailings tungsten (W) concentrations range from 500 mg/kg to 5 wt%. Scheelite particles in the tailings range from mm to micron scale, with abundant particles <100 & micro;m. Ore concentrates were roasted on the site to remove volatiles, resulting in essentially complete discharge of sulphur to the atmosphere, along with much of the arsenic (As). However, bulk tailings still contain As up to 4000 mg/kg. Most of this remnant As is hosted by soft particles (mm-& micro;m) of iron oxyhydroxide that also enclose fine silicates and scheelite. The Glenorchy tailings are broadly similar to those at the Macraes mine in having abundant fine scheelite that has resisted extraction by previous separation methods.
Eruptions in the Auckland Volcanic Field in Aotearoa New Zealand have not occurred since seismic monitoring began in Aotearoa New Zealand, but it is generally presumed that future eruptions from the Auckland Volcanic Field will be preceded by elevated rates of seismicity. High levels of anthropogenic seismic noise, generally low numbers of earthquakes and relatively high earthquake detection thresholds used for nationwide earthquake monitoring by the Aotearoa New Zealand national earthquake monitoring system (GeoNet) mean that the national earthquake catalogue used for volcanic monitoring contains few earthquakes in the Auckland Volcanic Field. Moreover, variations in cataloguing methods throughout the history of seismic monitoring mean that the quality and completeness of the GeoNet earthquake catalogue in Auckland are strongly heterogeneous in time precluding robust analysis of earthquake occurrence variability within the Auckland Volcanic Field and hence inhibit the identification of possible precursory changes from that background state. We apply a semi-automated workflow, incorporating modern machine-learning earthquake detection methods validated by manual review, to develop a self-consistent catalogue of seismicity in the Auckland Volcanic Field spanning 2011-2022 which we use to evaluate the background state of seismicity within the Auckland Volcanic Field in a time of quiescence. This catalogue contains 328 earthquakes within the Auckland Volcanic Field monitoring region, more than five times as many earthquakes as catalogued by GeoNet. The new catalogue is composed mostly of background seismicity with some discrete clusters. We confirm that the background rate of seismicity in Auckland is low (approximately 21 earthquakes annually above magnitude 0.6: the magnitude of completeness of this new catalogue) and provide a statistically useful indication of that background state, both in time and space, from which to characterise possible deviations prior to a future eruption within the Auckland Volcanic Field.
The Milun Fault forms the northernmost onshore segment of the Longitudinal Valley fault system, a plate-boundary suture between the Eurasian and Philippine Sea plates in eastern Taiwan, and poses a significant seismic hazard to Hualien City. Despite destructive earthquakes in 1951 and 2018, the shallow structure, long-term slip behavior, and paleoseismic history of the fault have remained poorly constrained due to limited direct exposure of its principal fault. New paleoseismic trench and borehole data provide direct constraints on the near-surface geometry of the principal fault and its associated branch faults. Trench exposures document a steeply east-dipping principal fault (similar to 80 degrees) accompanied by several branch faults, defining a zone of distributed deformation. Stratigraphic restoration, growth strata, colluvial wedges, and liquefaction features indicate five late Holocene surface-rupturing earthquakes, including the 1951 and 2018 events and three prehistoric earthquakes dated to 783-352, 2361-1302, and 3185-2303 cal yr BP. Borehole correlations indicate similar to 18.6 m of vertical separation since similar to 5.7 ka, corresponding to a long-term vertical slip rate of similar to 3.2-3.6 mm/yr. Stratigraphic relationships further indicate that the Milun Tableland emerged above sea level at approximate to 3.2 ka, implying cumulative uplift through repeated seismic events. Inter-event times range from decades to more than a millennium, and overlapping age constraints preclude definition of a characteristic recurrence interval. These results show that deformation along the Milun Fault is accommodated by a steep principal fault together with multiple branch faults, and that earthquake recurrence in this transpressional plate-boundary setting is temporally irregular.
The Torlesse Composite Terrane (TCT) forms many of the mountain ranges in Aotearoa New Zealand and has provided enormous quantities of coarse-grained sediment to Te Riu-a-Maui/Zealandia's basins since the mid-Cretaceous. Tracing the provenance of these sediments to certain regions of the TCT can indirectly reconstruct exhumation patterns associated with the development of the Australian-Pacific plate boundary. Supplemented by new analyses, we are now able to include one of the new constituent terranes of the TCT (the Kaweka Terrane), which had not been recognised when the previous geochemical classification was developed. We train four different machine learning algorithms using samples from Te Waipounamu/the South Island to classify TCT-derived sandstone conglomerate clasts into four different petrofacies/terranes of the TCT using log-transformed trace element ratios. Balanced accuracies for the four algorithms used are 77% (linear support vector machine), 69% (k-nearest neighbours), 75% (random forest), and 77% (neural network). This rises to 80% when an equal voting system is used. These accuracies are similar to existing classifications for the TCT but include the Kaweka Terrane as a classification option. We then show an example of how this updated classification can be applied to late Cenozoic TCT-derived conglomerate clasts.
Activity on low deformation rate faults are challenging to quantify and comparatively understudied. One such fault, the Mangatangi Fault, strikes NE-SW along the southeastern flanks of the Hunua Ranges c. 52 km south of New Zealand's most populous city, Auckland. It is part of a series of regional normal faults that reactivated since the Miocene; yet, its slip rate and earthquake recurrence interval is poorly constrained. In this study, we present geomorphic, geochronological, and geophysical data supporting vertical fault displacement rates of 0.017-0.27 mm yr-1. Holocene rates (0.14-0.27 mm yr-1) compared to long-term rates (0.017-0.049 mm yr-1) highlight temporal variability in fault behaviour and earthquake clustering. The maximum earthquake magnitude is estimated as MW 6.8-6.9, with a recurrence interval ranging anywhere between 8100-127,100 years. Although ruptures along the Mangatangi Fault are interpreted to be infrequent over geologic timescales, dating of truncated sediments in the piedmont scarp constrain at least two Late Quaternary events, including one in the early Holocene. These results indicate that the Mangatangi Fault may pose greater seismic hazard to the Auckland area than previously considered, which, given high exposure and vulnerability, could translate into significant risk.
Mordenite is a naturally occurring zeolite mineral that is the seventh most common zeolite mineral globally, forming at low temperatures (>= 100 degrees C) in hydrothermal systems. In New Zealand, extensive deposits of mordenite are commonly associated with areas of hydrothermal alteration, particularly in the Coromandel and Taupo Volcanic Zones. Mordenite can form fibrous minerals, and several industries have the potential to disturb these naturally occurring mineral fibres, causing them to become aerosolised and potentially respirable. Nevertheless, mordenite is not currently known to be carcinogenic, in contrast to the fibrous zeolite, erionite. Indeed, erionite is a Group 1 carcinogen that has been linked to malignant mesothelioma due to its fibrous-asbestiform shape and biodurability. In this study, mordenite from New Zealand is characterised and compared to erionite, using X-ray powder diffraction (XRPD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and an automated scanning electron microscope (SEM), in order to understand the extent, occurrence and morphology of mordenite in New Zealand. It also enables the evaluation of potential health implications, including whether these naturally occurring mineral fibres are respirable.
The evolution of pore fluid pressure ( ) in the most seaward portion of a subduction accretionary prism plays an essential role in the cycle of tsunamigenic earthquakes. Based on recent geophysical observations, here we propose a testable conceptual model for this evolution for northern Cascadia offshore of Washington. During a large subduction earthquake, stress increase on the near-trench part of the megathrust causes compressive stress loading and increase in the outer wedge. Following the earthquake, drainage through pore space and permeable fault zones allows to return to the background preseismic state. Using simple dynamic Coulomb wedge and fluid pressure diffusion models, we demonstrate the feasibility of this conceptual model. With reasonable parameters, the models predict a low-to-moderate above hydrostatic in most of the interseismic period, and a coseismic elevation of by similar to 15-20 MPa near the base of the outer wedge. The postseismic drainage timescale is estimated to be several to tens of years, consistent with the present-day overall absence of active seafloor venting above the northern Cascadia outer wedge. The efficient postseismic drainage over many earthquake cycles may contribute to the over-consolidation of the outer wedge.
Nishinoshima is a volcanic island in the Ogasawara Arc that has exhibited intermittent activity since 2013, including four major eruptive episodes: 2013-2015 (Episode 1), 2017 (Episode 2), 2018 (Episode 3), and 2019-2020 (Episode 4). Previous studies reported a change in eruption style-from a Strombolian eruption with lava flows (Episode 1 to the early phase of Episode 4) to violent Strombolian eruptions (mid to late phase of Episode 4)-accompanied by a shift in the bulk chemical composition of volcanic ash from andesite to basaltic andesite. However, the number of tephra samples from Episode 4 remains limited, and additional data are required to clarify the details about changes in chemical composition during this episode. In this study, we present the major and trace element compositions of offshore tephra collected from Episode 4. We analyzed <1 mm ash samples from the topmost sediments around Nishinoshima Island, collected from the seafloor during Cruise KR20-E06 by R/V Kairei in December 2020. The bulk chemical compositions indicate that these samples were classified into andesite and basaltic andesite and were deposited during the mid- to late phase of Episode 4. Furthermore, their chemical compositions fall between those of the Nishinoshima andesites and the Episode 4 basalts reported previously. This suggests that the magma composition associated with the eruption shifted from andesite to basaltic andesite within a period of only 1.5 months. In addition, the samples show both vertical and spatial compositional variations. The former may reflect gravitational settling of ash particles through the water column and their floating behavior at the sea surface, whereas the latter may be influenced by eruption timing, local wind directions, or ocean currents.
Subglacial Lake Qilin (SLQ), in the center of Princess Elizabeth Land (PEL), East Antarctica, is a potential drilling target for detecting extreme-life and studying ice sheet evolution, due to its tectonic origin, stability, thick sediments and isolation by 3600 m thick ice. Prior to drilling, an ideal site is needed to meet scientific goals, requiring characterization of water circulation and subglacial hydrology-related basal melting/refreezing. This study quantifies SLQ's basal melt rate using an optimized 1D steady-state thermodynamic model and multi-source remote sensing/geophysical data. The model improves accuracy via dynamic thermal boundaries and a temperature gradient correction. Results show the lake center has a high annual mean basal melt rate of 2.195 mm a-1, increasing northward. Sensitivity analysis indicates geothermal heat flux has the most significant effect on melt rate, compared to ice thickness and temperature gradient.
A recently discovered fossil locality in glauconitic Ruatangata Sandstone near Kaeo, Northland, New Zealand, contains the most species-rich Eocene (middle Eocene, Bortonian Stage) molluscan fauna in the North Island. Most shells have dissolved away leaving a rich collection of molds and casts of 60 molluscan taxa (31 bivalves, 29 gastropods). Twenty-nine are confidently and 11 tentatively identified to species level, 17 to genus and 3 to family level. A new species of mussel, Botula kaeoensis Eagle n. sp., is described. It is the only New Zealand record of this subtropical genus. Also present is the earliest New Zealand fossil record of the limpet genus Cellana. The record of Costacallista hectori extends its time range up into the late middle Eocene (Bortonian). The autecology of each species is summarised and shows that a wide range of sessile and mobile trophic types are represented. Analysis of the depth ranges of their extant relatives shows that the fauna is a mixture of sublittoral, inner shelf, mid shelf-upper bathyal taxa that lived on a variety of hard and soft shore substrates. All bivalves are disarticulated single valves, and we infer the Kaeo fauna was brought together at mid-outer shelf depths by storm waves and bottom currents.
The southern coast of Java, Indonesia, is a high-risk region characterized by intense seismic activity where the 17 July 2006 Mw 7.7 Java tsunami earthquake occurred and generated devastating tsunami. This study investigates the prolonged crustal deformation following this event by analyzing over a decade (2010-2022) of Global Navigation Satellite System (GNSS) data from stations along the southern coast of West Java. We quantify the contributions of two primary postseismic mechanisms-viscoelastic relaxation and afterslip-alongside ongoing interseismic coupling on the megathrust. Our results indicate that surface deformation was dominated by postseismic processes in the immediate years after the earthquake, with velocities of 2-3 mm/yr directed southward. Over time, the influence of postseismic deformation decayed significantly; viscoelastic relaxation diminished by 79% by 2019-2022. Afterslip distribution and moment release increased then decreased over the studied periods, releasing seismic moments equivalent to Mw 6.4-6.6. Concurrently, the deformation pattern gradually transitioned, revealing the increasing dominance of interseismic coupling as postseismic deformation progressively diminishes. The study highlights a transitional phase between postseismic and interseismic deformation along the Java subduction zone. These findings underscore the critical importance of long-term geodetic monitoring for refining seismic hazard assessments in subduction zones.
The Rangit & imacr;kei Valley in the lower North Island of New Zealand contains flights of river terraces that are influenced by changes in sediment supply, stream power and base level associated with Quaternary climate events over the last similar to 350 thousand years. Despite providing a valuable record of past environmental change, most work on the Rangit & imacr;kei terraces remains unpublished, and a majority of the stratigraphic units lack formal definition. Our study presents a review of the Rangit & imacr;kei River terraces and new reference and type sections for the lithostratigraphic units formed during the Otira Glaciation, building on the seminal work of Derek Milne. Site selection is based on outcrop quality, ease of access and health and safety considerations whilst aiming to preserve historic precedence and geographic proximity to associated place names. A conceptual model of Rangit & imacr;kei terrace formation is presented, highlighting the transition out of full glacial conditions where reduced sediment supply and increased stream power result in incision, upstream knickpoint migration, reworking of alluvium and terrace formation. This model provides an update on earlier work by incorporating concepts around knickpoint retreat and the complex response of the fluvial system to produce multiple terrace levels within a single terrace set.
We compared temporal variability in dust and loess accretion in New Zealand's South Island with glacial activity in the central Southern Alps, considered the main mechanism of silt production, in (i) a proximal loess deposit at Barrhill, Rakaia River and (ii) a distal dust record from a peat mire in Central Otago. We applied novel luminescence dating approaches at Barrhill, targeting both polymineral silt and K-feldspar sand. Results demonstrated loess accretion began from similar to 8.5 +/- 1.7 ka, with accumulation rates increasing by 7 times after similar to 2 ka, before decreasing toward the present. In the peat record, trace-element geochemistry was used to distinguish New Zealand-sourced dust from Australian dust. Like Barrhill, deposition of New Zealand-sourced dust increased by similar to 4 times from similar to 3 ka, while also recording high deposition during the Little Ice Age. Changing dustiness in both records is attributed to climate-modulated sediment production. At Barrhill, this was linked directly to glacial advances in the Rakaia catchment, while in the more distal peat mire it likely resulted from enhanced periglacial activity. Together, both records demonstrate that dustiness closely tracks glacial variability in the South Island, highlighting potential for further detailed studies of dust production and glacial dynamics from New Zealand's loess.
Sources of radioactivity in heavy mineral concentrate (HMC) from the Holocene beach sand placer at Barrytown, Central Westland were investigated using analytical scanning electron microscopy and radiometric counting. The primary radioactive species are thorium, uranium and daughter radon in monazite and uranothorite. Both minerals exhibit evidence of in-situ alteration, facilitating release of radon and other radionuclides into the environment. The measured radioactivity of the bulk HMC is 0.22 Bequerels/gram for the solids and 505 Bequerels/per cubic meter for radon off-gas. Magnetic separation into 0.25, 0.45, 0.75, 1.2, and >1.2 (nonmagnetic) Franz isodynamic separator fractions segregates and (magnetically) concentrates radioactivity. The uranothorite-rich 1.2 Amp fraction is the most radioactive at 78 Bequerels/gram (solids) and 9665 Bequerels/per cubic meter (radon). Median radon levels measured at residences in and around the Barrytown community exceed those measured elsewhere in New Zealand.
Cenozoic magmatism is widespread in northern Victoria Land and is associated with the development of West Antarctic Rift System. However, the petrogenesis of dykes and volcanic rocks and the significant time lag (several tens of million years) between extension and magmatism remain poorly understood. In this study, we evaluate the spatial and temporal variations in near-primary basalt compositions, reconstruct the mantle source lithologies, and estimate the melting conditions based on the published data. Most of rocks are characterized by low CaO and Zr/Hf, high (Dy/Yb)N, (La/Yb)N, Fe/Mn and FCKANTMS, and high 143Nd/144Nd coupled with low 87Sr/86Sr, consistent with generation by about 5% partial melting of garnet pyroxenite in the asthenosphere, with a minor contribution from underlying garnet peridotite. Estimated temperatures (1252 degrees C-1435 degrees C) and pressures (1.1-2.9 GPa) increase systematically with decreasing age since around 12 Ma. The compositional variability indicates that the mantle source metasomatism predated Cretaceous rifting, whereas rift-related extension was insufficient to induce the decompression and heating required for producing widespread volcanism. We propose that Miocene lithospheric delamination triggered efficient asthenospheric upwelling, leading to sequential melting of shallow pyroxenite followed by deeper peridotite and producing the large magma volumes responsible for the widespread volcanism in the region.
