Long-term patterns of hillslope erosion by earthquake-induced landslides shape mountain landscapes

Widespread triggering of landslides by large storms or earthquakes is a dominant mechanism of erosion in mountain landscapes. If landslides occur repeatedly in particular locations within a mountain range, then they will dominate the landscape evolution of that section and could leave a fingerprint in the topography. Here, we track erosion provenance using a novel combination of the isotopic and molecular composition of organic matter deposited in Lake Paringa, New Zealand. We find that the erosion provenance has shifted markedly after four large earthquakes over 1000 years. Postseismic periods eroded organic matter from a median elevation of 722 +329/−293 m and supplied 43% of the sediment in the core, while interseismic periods sourced from lower elevations (459 +256/−226 m). These results are the first demonstration that repeated large earthquakes can consistently focus erosion at high elevations, while interseismic periods appear less effective at modifying the highest parts of the topography

Insights into the ecological impact of trout introduction in an oligotrophic lake using sedimentary environmental DNA

Introduced trout can induce trophic cascades, however, a lack of pre-introduction data limits knowledge on their impact in many lakes. Traditional paleolimnological approaches have been used to study historic species changes, but until recently these have been restricted to taxa with preservable body-parts. To explore the ecosystem effects of Salmo trutta (brown trout) introduction on an oligotrophic lake in Aotearoa-New Zealand, we used a multi-marker sedimentary environmental DNA (sedDNA) approach coupled with pigments to detect changes across multiple trophic levels. DNA was extracted from core depths capturing approximately 100 years before and after the expected arrival of S. trutta, and metabarcoding was undertaken with four primer sets targeting the 12S rRNA (fish), 18S rRNA (eukaryotes) and cytochrome c oxidase (COI; eukaryotes) genes. The earliest detection of S. trutta eDNA was 1906 (1892–1919 CE with 95% high probability density function) suggesting their introduction was shortly before this. Native fish diversity (12S and 18S rRNA) decreased after the detection of S. trutta, albeit the data was patchy. A shift in overall eukaryotic and algal communities (18S rRNA and COI) was observed around 1856 (1841–1871 CE) to 1891 (1877–1904 CE), which aligns with the expected S. trutta introduction. However, taxonomy could not be assigned to many of the 18S rRNA and COI sequences. Pigment concentrations did not change markedly after S. trutta introduction. SedDNA provides a new tool for understanding the impact of disturbances such as the introduction of non-native species; however, there are still several methodological challenges to overcome

Earthquakes drive large-scale submarine canyondevelopment and sediment supply to deep-ocean basins

Although the global flux of sediment and carbon from land to the coastal ocean is well known, the volume of material that reaches the deep ocean—the ultimate sink—and the mechanisms by which it is transferred are poorly documented. Using a globally unique data set of repeat seafloor measurements and samples, we show that the moment magnitude (Mw) 7.8 November 2016 Kaikōura earthquake (New Zealand) triggered widespread landslides in a submarine canyon, causing a powerful “canyon flushing” event and turbidity current that traveled >680 km along one of the world’s longest deep-sea channels. These observations provide the first quantification of seafloor landscape change and large-scale sediment transport associated with an earthquake-triggered full canyon flushing event. The calculated interevent time of ~140 years indicates a canyon incision rate of 40 mm year−1, substantially higher than that of most terrestrial rivers, while synchronously transferring large volumes of sediment [850 metric megatons (Mt)] and organic carbon (7 Mt) to the deep ocean. These observations demonstrate that earthquake-triggered canyon flushing is a primary driver of submarine canyon development and material transfer from active continental margins to the deep ocean.peer-reviewe

Populism, inequality and representation: Negotiating ‘the 99%’ with Occupy London

When Occupy London emerged with a global wave of protest movements in October 2011, it embodied and advanced discursive forms that have characterised the unsettling of political consensus following the financial crisis. The central claim that ‘We are the 99%’ staged a fundamental tension, between a populist appeal to the figure of ‘the people’, and a contrary orientation seeking to critique inequality while rejecting forms of representation and identity. This article – which draws on three years of ethnographic fieldwork with Occupy London (October 2011–October 2014) and a critical theorisation of the figure of ‘the people’ in radical movements – follows movement participants’ negotiation of the tension at the heart of the discourse of ‘the 99%’. It offers an account of the conflicting meanings and practices that emerged, arguing that the result was a creative contradiction that sustained the movement for a time, while setting the terms of its ultimate breakdown. Identifying the concept of ‘representation’ as the site of particular controversy, this is unpicked through a number of key figures (Pitkin, Marx, Spivak, Puchner, Deleuze and Guattari) as the basis for an empirical account of Occupy’s practice of assembly, which offered partial, imperfect ‘solutions’ to these tensions. The article concludes with some implications for the limits and possibilities of both a grassroots populism and a politics against representation, in the context of political developments since

Petrophysical, Geochemical, and Hydrological Evidence for Extensive Fracture-Mediated Fluid and Heat Transport in the Alpine Fault's Hanging-Wall Damage Zone

International audienceFault rock assemblages reflect interaction between deformation, stress, temperature, fluid, and chemical regimes on distinct spatial and temporal scales at various positions in the crust. Here we interpret measurements made in the hanging‐wall of the Alpine Fault during the second stage of the Deep Fault Drilling Project (DFDP‐2). We present observational evidence for extensive fracturing and high hanging‐wall hydraulic conductivity (∼10−9 to 10−7 m/s, corresponding to permeability of ∼10−16 to 10−14 m2) extending several hundred meters from the fault's principal slip zone. Mud losses, gas chemistry anomalies, and petrophysical data indicate that a subset of fractures intersected by the borehole are capable of transmitting fluid volumes of several cubic meters on time scales of hours. DFDP‐2 observations and other data suggest that this hydrogeologically active portion of the fault zone in the hanging‐wall is several kilometers wide in the uppermost crust. This finding is consistent with numerical models of earthquake rupture and off‐fault damage. We conclude that the mechanically and hydrogeologically active part of the Alpine Fault is a more dynamic and extensive feature than commonly described in models based on exhumed faults. We propose that the hydrogeologically active damage zone of the Alpine Fault and other large active faults in areas of high topographic relief can be subdivided into an inner zone in which damage is controlled principally by earthquake rupture processes and an outer zone in which damage reflects coseismic shaking, strain accumulation and release on interseismic timescales, and inherited fracturing related to exhumation

Bedrock geology of DFDP-2B, central Alpine Fault, New Zealand

<p>During the second phase of the Alpine Fault, Deep Fault Drilling Project (DFDP) in the Whataroa River, South Westland, New Zealand, bedrock was encountered in the DFDP-2B borehole from 238.5–893.2 m Measured Depth (MD). Continuous sampling and meso- to microscale characterisation of whole rock cuttings established that, in sequence, the borehole sampled amphibolite facies, Torlesse Composite Terrane-derived schists, protomylonites and mylonites, terminating 200–400 m above an Alpine Fault Principal Slip Zone (PSZ) with a maximum dip of 62°. The most diagnostic structural features of increasing PSZ proximity were the occurrence of shear bands and reduction in mean quartz grain sizes. A change in composition to greater mica:quartz + feldspar, most markedly below c. 700 m MD, is inferred to result from either heterogeneous sampling or a change in lithology related to alteration. Major oxide variations suggest the fault-proximal Alpine Fault alteration zone, as previously defined in DFDP-1 core, was not sampled.</p

Deposition and preservation of tephra in marine sediments at the active Hikurangi subduction margin

Highlights • Sedimentary characteristics and geochemistry of tephra deposits are reported across 21 cores. • Four types of tephra lithofacies are distinguished. • Geomorphic sub-environments play a key role in tephra preservation. • Isolated semi-confined basin settings generally preserve the highest number of tephra deposits. • For eruptions VEI≥6 volcaniclastic sediments may swamp the marine system for centuries. Tephra (volcanic ash) deposits are important isochronous markers for correlating marine sediments or events recorded in marine sediment cores. However, the active tectonics that are commonly associated with volcanic activity at plate tectonicboundaries also drive large-scale deformation, leading to steep and variable local and regional bathymetry (e.g., ridges, basins and canyons systems). This complex bathymetry influences gravity-flow behaviour and paths, which can rework and redeposit tephras, resulting in stratigraphic complexities. Such as, the mis-identification of primary versus reworked tephra deposits, and in turn lead to the development of inaccurate chronostratigraphies. Here we present 36 tephra deposits from 21 shallow marine sediment cores that traverse the length of the southern and central margin of eastern North Island, New Zealand. Using major and trace element geochemical compositions for glass shards from the tephras, we correlate these deposits to three major rhyolitic eruptions from the Taupō Volcanic Zone (TVZ) approximately 200 km west, including; Taupō (1718 cal yrs. BP), Kaharoa (636 cal yrs. BP), and Kawakawa/Oruanui (KOT; 25.4 ka). Based on their morphology, depositional character and inferred emplacement mechanisms, the tephra deposits are grouped into four lithofacies types; (1) primary deposits, (2) volcaniclastic-rich turbidites, (3) blebs/pods of volcaniclastic-rich material, and (4) complex deposits. Primary deposits form syn-eruptively through airfall onto the ocean surface, settling over hours to days through the water column under diffuse vertical gravity currents. Volcaniclastic-rich turbidites are formed through secondary redeposition and entrainment by post-eruptive turbidity currents, while blebs/pods of material are interpreted to have formed by erosion and/or bioturbation. Complex deposits form through the interaction of all these mechanisms producing an overthickened array of primary and redeposited units within a single facies. Herein, we argue that redeposited units of volcaniclastic-rich turbidites or small blebs/pods can be used as tentative chronological markers if the geochemical composition of the glass shards have a homogeneous signature, i.e. a single eruptive source. Where the glass shards in redeposited units have mixed geochemical compositions, and are not stratigraphically associated with a primary deposit source, they cannot be used as chronological marker horizons. This emphasises the need for accurate and rigorous data reduction without overlooking the importance of data points that are statistical outliers. We also show that the highest preservation of tephra deposits is found in semi-confined isolated basin settings, including a wide range of deposit types. Due to erosive sediment flows that bypass through submarine distributary systems, these major sediment dispersal pathways preserve few volcaniclastic deposits. Our findings have important implications not only for identifying primary or redeposited characteristics in marine tephras for building accurate chronostratigraphies, but also as a guide geomorphic sub-environments with the best preservation of tephras in marine sedimentary systems

Supplementary material 2 from: Schallenberg LA, Thomson-Laing G, Kelly D, Pearman JK, Howarth JD, Vandergoes MJ, Puddick J, Fitzsimons S, Rees A, Wood SA (2023) Insights into the ecological impact of trout introduction in an oligotrophic lake using sedimentary environmental DNA. Metabarcoding and Metagenomics 7: e111467. https://doi.org/10.3897/mbmg.7.111467

Supplementary data