Geochemistry and morphology of metalliferous sediments and oxyhydroxides from the Endeavour segment, Juan de Fuca Ridge

We present first data on the geochemistry, mineralogy and morphology of near-vent sediments (35 and 200 m from active vent) and ridge flank sediments (approximately 3 km from the vent field) as well as oxyhydroxide deposits from the Endeavour segment, Juan de Fuca Ridge. The purpose of the study was to understand better the origin and characteristic features of metalliferous sediments associated with base and precious metal massive sulfides in volcanic terrains. Hydrothermal components in sediments are Fe-Si ± S-rich and Mn-Fe-Si-rich phases, sulfides and barite, which were exclusively derived from plume fallout. Sulfides are only a minor constituent of near-vent sediments (2-4 wt%) and were not detected in ridge flank sediments. The study suggests that the distribution of hydrothermal phases and associated elements in near-vent and ridge flank sediments is affected mainly by processes of agglomeration, dissolution, absorption and settling that take place within a plume and to a lesser extent post-depositional processes. Rapid deposition of sulfides in the vicinity of the vents is reflected in a sharp drop of the Cu concentrations in sediments with increasing distance from the vents. Besides sulfides, important carriers of Pb, Cu, Zn and Co in near-vent sediments are Fe-Mn oxyhydroxides that occur together with silica as aggregates of gel-like material and flaky particles and as coatings on filaments. Away from the vents, trace metals are mostly in Fe-Mn oxyhydroxides and authigenic Fe-rich montmorillonite. Oxyhydroxides at the Main Endeavour field are interpreted to have originated from oxidation of mound sulfides accompanied by precipitation of primary Fe-oxyhydroxide + silica from low-temperature fluids. At the Mothra field, seafloor deposits and chimney crusts composed of Fe-oxyhydroxide ± Mn + silica are considered to be direct precipitates from hydrothermal fluids that have been less diluted with seawater. Oxyhydroxide deposits exhibit unique microtextures that resemble mineralized microorganisms and may indicate existence of diverse microbial communities.     

Late Quaternary distal tephra-fall deposits in lacustrine sediments, Kenai Peninsula, Alaska

Tephra-fall deposits from Cook Inlet volcanoes were detected in sediment cores from Tustumena and Paradox Lakes, Kenai Peninsula, Alaska, using magnetic susceptibility and petrography. The ages of tephra layers were estimated using 21 ¹⁴C ages on macrofossils. Tephras layers are typically fine, gray ash, 1-5 mm thick, and composed of varying proportions of glass shards, pumice, and glass-coated phenocrysts. Of the two lakes, Paradox Lake contained a higher frequency of tephra (0.8 tephra/100 yr; 109 over the 13,200-yr record). The unusually large number of tephra in this lake relative to others previously studied in the area is attributed to the lake's physiography, sedimentology, and limnology. The frequency of ash fall was not constant through the Holocene. In Paradox Lake, tephra layers are absent between ca. 800-2200, 3800-4800, and 9000-10,300 cal yr BP, despite continuously layered lacustrine sediment. In contrast, between 5000 and 9000 cal yr BP, an average of 1.7 tephra layers are present per 100 yr. The peak period of tephra fall (7000-9000 cal yr BP; 2.6 tephra/100 yr) in Paradox Lake is consistent with the increase in volcanism between 7000 and 9000 yr ago recorded in the Greenland ice cores.     

Gendered access to customary land in East Timor

Land tenure rights reflect the deeper structures of society, particularly gender distinctions in relation to land. Considering the structural differences between patrilineal and matrilineal customary tenure systems in East Timor are understudied, this paper explores men and women’s experiences in accessing land under such arrangements. The comparative analysis of two patrilineal with one matrilineal land tenure systems in Ainaro and Manufahi districts suggests a significant degree of flexibility within both systems with respect to the norms of gendered inheritance. Therefore, the binary constructs of ‘patrilineal’ and ‘matrilineal’ societies are limiting. Both men and women in these communities may acquire land rights under different circumstances, mainly through negotiations with their parents or hamlet chief. Daughters in the patrilineal communities could inherit family land upon their parents’ death and sons in the matrilineal community could gain land by cultivating and maintaining unclaimed customary land. Empirical evidence show that inheritance principally determines usufruct rights to land, but marriage exchange practices complicates a deeper understanding of traditional East Timorese land rights.

Factors Controlling the Fractionation and Seasonal Mobility Variations of Ga and In in Systems Impacted by Acidic Thermal Waters: Effects of Thermodynamics and Bacterial Activity

This work assessed both the fractionation and the seasonal mobility variations of Ga and In in systems impacted by acidic thermal waters. This was accomplished by performing thermodynamic calculations using the PHREEQC algorithm and by assessing the activity of acidophilic iron-oxidizing bacteria. The pH of the Kusatsu thermal waters in Gunma Prefecture, central Japan, is rapidly increased following the addition of a lime suspension. After an abrupt pH increase, under which conditions free ions of Ga and In and their complexes with Cl^? and SO₄^2? exist only in negligible quantities, the majority of dissolved Ga and In is removed by sorption onto suspended hydrous ferric oxides (HFOs). These HFOs are then transported to an artificial lake without significant sedimentation along the river. Subsequently, the suspended HFOs settle out and are added to sediments without significant fractionation between Ga and In. The Tamagawa thermal waters in Akita Prefecture, northeast Japan, are also treated with lime. However, complete neutralization requires mixing with some tributary streams, leading to a gradual downstream increase in pH. Dissolved Ga is, in general, sorbed by HFOs in upstream areas, leading to wide dispersal of Ga across the entire watershed. In comparison, In is transported to the lake inlet predominantly as a Cl^? complex species without significant removal along the river, with the majority being precipitated in an artificial lake, where Cl^? concentrations are too low to form stable complex species with In, and thus, dissolved In is sorbed by HFOs. As a result, In is effectively concentrated within downstream lakebed sediments, whereas Ga is dispersed along the river. Seasonal variations in Ga mobility within the Tamagawa field between snowmelt and low-flow seasons are primarily controlled by pH, because hydrolysis reactions of these metals, which are related to sorption reactions, tend to occur in the upstream regions in the snowmelt season. However, under warmer conditions, HFO formation preferably occurs due to the activity of acidophilic iron-oxidizing bacteria. Thus, under similar pH variations, dissolved Ga is more effectively removed by HFOs during warmer seasons. On the contrary, because HFOs are abundantly formed in low-flow season, even under colder conditions, before In hydrolysis reaction starts to occur, In mobility is less affected by water temperature and then bacterial activity.     

Karrat Fjord (Greenland) tsunamigenic landslide of 17 June 2017: initial 3D observations

On 17 June 2017, a landslide-generated tsunami reached the village of Nuugaatsiaq, Greenland, leaving four persons missing and presumed dead. Here, we present a preliminary high-resolution analysis of the tsunamigenic landslide scar based on three-dimensional (3D) reconstructions of oblique aerial photographs taken during a post-failure reconnaissance helicopter overflight. Through a 3D quantitative comparison with pre-failure topography, we estimate that approximately 58 million m³ of rock and colluvium (talus) was mobilized during the landslide, 45 million m³ of which reached the fjord, resulting in a destructive tsunami. We classify this event as a “tsunamigenic extremely rapid rock avalanche,” which likely released along a pre-existing metamorphic fabric, bounded laterally by slope-scale faults. Further analysis is required to properly characterize this landslide and adjacent unstable slopes, and to better understand the tsunami generation.     

Late Triassic sauropodomorph and Middle Jurassic theropod tracks from the Xichang Basin,Sichuan Province,southwestern China:First report of the ichnogenus Carmelopodus

Upper Triassic and Middle Jurassic strata of the Xichang Basin in Sichuan Province, southwestern China, yielded important dinosaur ichnofossils. From the Xujiahe Formation of the Yiguojiao tracksite, we report a Late Triassic footprint assemblage in China and the first discovery of diagnostic Triassic sauropodomorph tracks in this region. The tracks share a number of features in common with the ichnogenera Eosauropus(Late Triassic) and Liujianpus(Early Jurassic). The neighboring Bingtu tracksite is stratigraphically younger(Shaximiao Formation, Middle Jurassic) and preserves small tridactyl theropod tracks that represent the first occurrence of the ichnotaxon Carmelopodus in China and Asia. While these tracks are morphologically comparable to those from the Middle Jurassic type locality in North America, the specimens from China show the proximal margin of the digit IV impression in a more cranial position, which may indicate a trackmaker with a relatively short metatarsal IV. In addition to the skeletal record, the Carmelopodus footprints document the presence of small theropods in the dinosaur fauna of the Middle Jurassic Shaximiao Formation.     

Individual risk evaluation for landslides: key details

Risk-taking is an essential part of life. As individuals, we evaluate risks intuitively and often subconsciously by comparing the perceived risks with expected benefits. We do this so commonly that it passes unnoticed, like when we decide to speed home from work or go for a swim. The comparison changes, however, when one entity (such as a government) imposes a risk evaluation on another person. For example, in a quantitative risk management framework, the estimated risk is compared with a tolerable risk threshold to decide if the person is ‘safe enough’. Landslide risk management methods are well established and there is consensus on tolerable life-loss risk thresholds. However, beneath this consensus lie several key details that are explored by this article, along with suggestions for refinement. Specifically, we suggest using the risk unit, micromort (one micromort equals a life loss risk of 1 in 1 million), in describing risk estimates and thresholds, to improve risk communication. For risk estimation, we provide guidance for defining and combining landslide scenarios and for recognizing where unquantified risk from low-probability/high-consequence scenarios ought to inform risk management decisions. For risk tolerance thresholds, we highlight the pitfalls of selecting unachievably low thresholds and suggest that there is no single universal threshold. Additionally, we argue that gross disproportion between costs and benefits of further risk reduction, which is integral to the As Low As Reasonably Practicable (ALARP) principle, is a commonly unachievable and counter-productive condition for risk tolerance, and other conditions centered on proportionality often apply. Finally, we provide several figures that can be used as risk communication tools, to provide context for risk estimates and risk tolerance thresholds when these values are reported to decision makers and the public.