Arc-arc collision plays an important role in the formation and evolution of continents (e.g., Yamamoto et al., 2009; Tamura et al., 2010). The Izu collision zone central Japan, an active collision zone between the Honshu Arc and the Izu-Bonin Arc since the middle Miocene (Matsuda, 1978; Amano, 1991; Kano, 2002; Hirata et al., 2010), provides an excellent setting for reconstructing the earliest stages of continent formation. Multi-system geo-thermochronometry was applied to different domains of the Izu collision zone, together with some previously published data, in order to reveal mountain formation processes, i.e., vertical crustal movements. For this study nine granitic samples yielded zircon U–Pb ages of 10.2–5.8 Ma (n = 2), apatite (U–Th)/He ages of 42.8–2.6 Ma (n = 7), and apatite fission-track (AFT) ages of 44.1–3.0 Ma (n = 9). Thermal history inversion modelling based on the AFT data using HeFTy ver. 1.9.3 (Ketcham, 2005), suggests rapid cooling events confined to the study region at ~5 Ma and ~1 Ma. The Kanto Mountains are thought to be uplifted domally in association with collision of the Tanzawa Block at ~5 Ma. But this uplift may have slowed down following migration of the plate boundary and late Pliocene termination of the Tanzawa collision. The Minobu Mountains and possibly adjacent mountains may have been uplifted by collision of the Izu Block at ~1 Ma. Mountain formation in the Izu collision zone was mainly controlled by collisions of the Tanzawa and Izu Blocks and motional change of the Philippine Sea plate at ~3 Ma (Takahashi, 2006). Earlier collisions of the Kushigatayama Block at ~13 Ma and Misaka Block at ~10 Ma appear to have had little effect on mountain formation. Together with ~90° clockwise rotation of the Kanto Mountains at 12-6 Ma (Takahashi & Saito, 1997), these observations suggest that horizontal deformation predominated during the earlier stage of arc-arc collision, whereas vertical movements due to buoyancy resulting from crustal shortening and thickening developed at a later stage. References: Amano, K., 1991, Modern Geol., 15, 315-329; Hirata, D. et al., 2010, J. Geogr., 119, 1125-1160; Kano, K., 2002, Bull. EQ Res. Inst. Univ. Tokyo, 77, 231-248; Ketcham, R.A., 2005, Rev. Min. Geochem., 58, 275-314; Matsuda, T., 1978, J. Phys. Earth, 56, S409-S421; Takahashi, M., 2006, J. Geogr., 115, 116-123; Takahashi, M. & Saito, K., 1997, Isl. Arc, 6, 168-182; Tamura et al., 2010, J. Petrol., 51, 823, doi:10.1093/petrology/egq002; Yamamoto, S. et al., 2009, Gond. Res., 15, 443-453.

The Heifangtai area is commonly known as the museum of loess landslides in China. Irrigation-induced loess flowslides frequently recur along the margin cliffs of the Hefaingtai terrace, causing 42 fatalities and significant economic losses, as well as major ecological and environmental problems, such as increased soil erosion rate. The initiation and mobility of these irrigation-induced loess flowslide recurrences remain undetermined. On three typical recurrences of the loess flowslides, we performed joint geophysical detection using electrical resistivity tomography (ERT) and multichannel analysis of surface waves (MASW), and also tested loess basic properties by field profile sampling. In addition, we examined the shear behaviors of saturated loess utilizing an undrained ring shear apparatus. The geophysical signatures and in-situ loess property profiles showed that hydrogeological conditions are key to the initiation of recurring loess flowslides. The results also demonstrated that liquefaction shear behaviors of saturated loess control the mobility of after-failure of the loess flowslides. Rapid criteria of liquefaction susceptibility evaluation are suggested to provide a better understanding of the dynamic mechanisms of loess flowslides. These findings shed substantial light on long-runout flowslides that occur in fine-grain soil and their implications for landslide hazard mitigation.

Deep-water megasplay faults may promote or limit earthquake rupture and tsunami genesis. To better understand how megasplay faults affect earthquake rupture and associated tsunami potential, we build on recent modeling efforts based on observations of coseismic ruptures in the Japan Trench forearc and Chile Margin. We model the upper plate as a wedge that is partitioned into a seismic (velocity-weakening) inner wedge and an outer aseismic (velocity-strengthening) wedge, combined with a splay fault rooting from the decollement. We examine the effects of dip and friction along the splay fault and the width of the outer (velocity-strengthening) wedge during earthquake rupture. Our results suggest that along-strike variations in width of the velocity-strengthening outer wedge along the Chile Margin may play a key role in splay fault activity in the rupture segment of the 2010 Maule earthquake. However, our model fit to the published slip distribution for the 2010 Maule earthquake, suggests that megasplay fault activation did not significantly impact earthquake size along the SC Chile Margin. In contrast, our model fit to the slip distribution for the 2011 Tohoku earthquake shows that megasplay fault reactivation may have moderately affected earthquake coseismic rupture. Splay faults can slip coseismically thus contributing to associated tsunamis. However, the presence of a velocity-strengthening outer wedge is the predominant constraint on rupture size and tsunami generation.

The tectonic history of Southern Africa includes Archean formation of cratons, multiple episodes of subduction and rifting and some of the world’s most significant magmatic events. These processes left behind a compositional trail that can be observed in xenoliths and measured by geophysical methods. The abundance of kimberlites in southern Africa makes it an ideal place to test and calibrate mantle geophysical interpretations that can then be applied to less well-constrained regions. Magnetotellurics (MT) is a particularly useful tool for understanding tectonic history because electrical conductivity is sensitive to temperature, bulk composition, accessory minerals and rock fabric. We produced three-dimensional MT models of the southern African mantle taken from the SAMTEX MT dataset, mapped the properties of $\sim36000$ garnet xenocrysts from Group I kimberlites, and compared the results. We found that depleted regions of the mantle are uniformly associated with high electrical resistivities. The conductivity of fertile regions is more complex and depends on the specific tectonic and metasomatic history of the region, including the compositions of metasomatic fluids or melts and the emplacement of metasomatic minerals. The mantle beneath the $\sim 2.05$ Ga Bushveld Complex is highly conductive, probably caused by magmas flowing along a lithospheric weakness zone and precipitating interconnected, conductive accessory minerals such as graphite and sulfides. Kimberlites tend to be emplaced near the edges of the cratons where the mantle below 100 km depth is not highly resistive. Kimberlites avoid strong mantle conductors, suggesting a systematic relationship between their emplacement and mantle composition.

Secondary mineral assemblages in sandstone and tuff indicate high temperature zeolite facies metamorphism; Kübler indicies of illite and Árkai indicies of chlorite in mudstone record diagenetic to high anchizone metapelitic conditions; and pyrolysis of organic matter and the color of organic matter (i.e., the Thermal Alteration Index of palynomorphs and the Conodont Alteration Index) in mudstone and hemipelagite beds suggest thermal maturation reached catagenesis to mesogenesis stages. Collectively, the mineralogic and organic thermal indicators suggest the Dezadesh Formation was subject to pressure-temperature (P-T) conditions of 2.5 kbar and 250 °C. The estimated P-T conditions, together with published thermochronometric data, shows that the Dezadeash Formation underwent rapid, short-term heating followed by gradual, long-term cooling. Moreover, a calculated tectonic subsidence curve indicates rapid, short-term subsidence, followed by gradual, long-term uplift. Secondary clay minerals associated with heating and subsidence are characterized by a restricted assemblage dominated by 2M1 illite and chlorite. The thermal history, subsidence history, and secondary clay mineral assemblage are not supportive of deposition in peripheral foreland, backarc, strike-slip, and rift basins; nor are the results corroborative with previous deformation and crustal-scale reconstructions depicting the Dezadeash Formation being underthrust >20 km beneath the Blanchard River assemblage, Kluane Schist, and Yukon composite terrane (YCT). The Dezadeash-Nutzotin basin contrasts sharply with the contemporaneous Gravina belt and Gravina sequence in southeastern Alaska that were apparently underthrust >20 km beneath the YCT. The contrasting tectono-metamorphic histories may be a manifestation of oblique collision and diachronous, south-to-north accretion of the Chitina arc and WCT to YTC.

For quantitative understanding of thermal features of fossil fluid activity derived from the Philippine Sea slab, we applied fluid-inclusion and thermochronometric analyses to hydrothermal veins and their host rocks outcropping in the Hongu area in southwestern Japan. Although hydrothermal events at ~150{degree sign}C and ~200{degree sign}C were identified by fluid-inclusion analyses of quartz veins, no thermal anomaly was found associated with the veins’ host rocks. Cooling ages showed no variation as a function of distance from the veins. Using zircon, we determined U-Pb ages of 77.3-66.9 Ma in the youngest population, fission-track pooled ages of 34.1-24.0 Ma, and (U-Th)/He single-grain ages of 23.6-8.7 Ma. Apatite yielded pooled fission-track ages of 12.0-9.0 Ma. All these ages can be explained by fluid flow that occurred either (1) before ~10 Ma at a depth where ambient temperature is higher than closure temperature of the apatite fission-track system (90{degree sign}C-120{degree sign}C, equivalent to ~3-km depth) or (2) after ~10 Ma but of such duration that is too short to have annealed fission tracks in apatite, which process requires ~10 yr at ~150{degree sign}C or as short as a few months at ~200{degree sign}C. Apatite fission-track ages of ~10 Ma might reflect regional mountain uplift and exhumation related to rapid subduction of the Philippine Sea slab and associated with clockwise rotation of the Southwest Japan Arc.

Based on well-developed hydraulic geometry relations for width and depth, classic studies initially interpreted the Mid-Atlantic White Clay Creek (WCC) as a quasi-equilibrium, alluvial channel. Subsequent studies document the legacy of colonial-age watershed disturbances and urban development, confounding earlier classifications. To investigate this matter, we contribute new data from reach-scale geomorphic mapping, and observations and modeling of bed material transport. WCC’s longitudinal profile reflects a history of bedrock incision, while hydraulic geometry equations for width and depth indicate quasi-equilibrium cross-sectional adjustment. Alluvial landforms such as pools and riffles, bars, and actively forming floodplains occur at all 12 study sites, but exposures of bedrock and colluvium are also common. The ratio of bankfull to threshold Shields stress averages 1.41 (range 0.41-2.63), suggesting that WCC is an alluvial, threshold, gravel-bed river. However, a numerical model of WCC bed material transport and grain size, calibrated to bedload tracer data, demonstrates that 22% (range 8-73%) of bed material is composed of immobile, locally sourced cobbles and boulders, while the remaining bed material represents mobile, sand to cobble-sized alluvium; this leads us to classify WCC as a semi-alluvial river. Additional computations suggest that channel morphology is insensitive to bed material supply. Field observations imply that bankfull Shields stresses do not represent channel adjustments to achieve stable banks; rather, width adjustment likely reflects cohesive bank processes. Despite the numerous and contradictory labels applied to WCC (i.e., quasi-equilibrium, Anthropocene, bedrock, semi-alluvial, gravel-bed), each term contributes insight that any single conceptual model would be unable to provide alone.

The Shields parameter based on median grain size D50 and bankfull depth is often used to interpret river morphology, but it may not always be a useful index of sediment transport processes. At 12 sites of the White Clay Creek (WCC), PA, the ratio of bankfull Shields stress to threshold Shields stress averages 1.41 (range 0.41-2.63), suggesting that these channels are alluvial near-threshold gravel-bed rivers. However, field mapping indicates confinement by bedrock and colluvium, and a channel slope dominated by bedrock incision and knickpoint migration. A numerical model of WCC bed material transport and grain size, calibrated to bedload tracer data, demonstrates that 22% (range 8-73%) of the bed material is composed of a population of immobile cobble and boulder-sized sediment supplied through local colluvial processes and bedrock erosion, and a separate population of mobile sand, pebble- and cobble-sized alluvium. Computations also suggest that channel morphology is only weakly coupled to upstream sediment supply. Additional analyses further imply that width adjustment may reflect a balance between cohesive bank erosion and floodplain deposition, though channels nonetheless may be closely scaled by cohesive bank erosion thresholds. WCC represents an example of a continuum of underappreciated, but relatively common, threshold alluvial-colluvial-bedrock rivers with partially immobile beds and widths scaled by cohesive bank erosion thresholds. Fluvial geomorphologists will need to look beyond simple sediment transport metrics to fully understand and classify these stream channels.

Natural methane gas release from the seafloor is a widespread phenomenon that occurs at cold seeps along most continental margins. Since their discovery in the early 1980s, seeps have been the focus of intensive research, partly aimed to refine the global carbon budget. However, deep-sea research is challenging and expensive and, to date, few works have successfully monitored the variability of methane gas release over long time periods (> 1 yr). Long-term monitoring is necessary to study the mechanisms that control seabed gas release. The M³ project, funded by the German Ministry of Education and Research, aims to study the temporal and spatial variability of gas emissions at the Southern Hydrate Ridge (SHR) by acoustically monitoring and quantifying gas effluxes over several years. Located 850 m deep on the Cascadia accretionary prism offshore Oregon, the SHR is one of the most studied seep sites and persistent but variable gas release has been observed for more than 20 years. Since 2015, the Ocean Observatories Initiative’s (OOI) Cabled Array observatory, provides power supply and two-way communication to the SHR, making it an ideal site for continuous long-term monitoring work. In this work, we present how we will take advantage of the OOI infrastructure and deploy several instruments on the seabed for at least 1.5 year. A multi-beam “overview” sonar mounted on a rotor will identify every gas bubble stream located within 200 m from the sonar location. A scanning “quantification” sonar will be used to estimate the amount of gas that is released from discrete gas streams. A camera system and a CTD probe will help process and analyze the hydro-acoustic data. All instruments will be powered and controlled from land through the OOI infrastructure. We present the instrument design, the operation protocol, as well as the data processing steps and expected results.

The 2019 Museum Fire burned in a mountainous region near the city of Flagstaff, AZ, USA. Due to the high risk of post-wildfire debris flows and flooding entering the city, we deployed a network of seismometers within the burn area and downstream drainages to examine the efficacy of seismic monitoring for post-fire flows. Seismic instruments were deployed during the 2019, 2020, and 2021 monsoon seasons following the fire and recorded several debris flow and flood events, as well as signals associated with rainfall, lighting and wind. Signal power, frequency content, and wave polarization were measured for multiple events and compared to rain gauge records and images recorded by cameras installed in the study area. We use these data to demonstrate the efficacy of seismic recordings to (1) detect and differentiate between different energy sources, (2) estimate the timing of lightning strikes, (3) calculate rainfall intensities, and (4) determine debris flow timing, size, velocity, and location. This work confirms the validity of theoretical models for interpreting seismic signals associated with debris flows and rainfall in post-wildfire settings and demonstrates the efficacy of seismic data for identifying and characterizing debris flows.

The mineral dolomite (CaMg(CO3)2) forms in only small quantities in modern oceans, cannot be precipitated abiotically from unmodified seawater in laboratory experiments, yet comprises much of the carbonate rock record. The challenge of explaining the apparent temporal discrepancy in dolomite, the “dolomite problem,” has fascinated carbonate sedimentologists for centuries. Yet, this pursuit has lacked a quantitative tabulation of dolomite in the rock record. Here, we use the North American rock record, as archived in Macrostrat, to assemble a record of dolomite abundance through geologic time. The completeness and age resolution of our dataset allow us to compare dolomite abundance with environmental variables, including stromatolite abundance, evaporite occurrences, sea level, glaciation, and temperature. We use these comparisons to test the assumption that the bulk of the geologic dolomite record was formed via secondary diagenetic processes. We find no monotonic decrease in abundance with age-the expected result if late diagenesis affects the bulk of the record. Dolomite was just as abundant during the first half of the Paleozoic as it was during most of the Neoproterozoic, a challenge to canonical thinking. We show that a number of dolomite precipitation mechanisms known from modern environments and experimentally grown dolomite can explain many of the patterns we observe in the North American dolomite record. Perhaps dolomite is not such a problem after all.

Volcanism is the dominant natural source of mercury (Hg) to the atmosphere, biosphere, ocean and sediments. In recent years, sedimentary Hg contents have emerged as a tool to reconstruct volcanic activity, and particularly activity of (subaerially emplaced) large igneous provinces (LIP) in geological deep time. More specifically, Hg has shown potential as a useful proxy to illuminate the previously elusive impact of such large-scale volcanism on marine and terrestrial paleo-environments. While Hg is now widely applied as volcanism tracer, non-volcanic factors controlling sedimentary Hg content are generally not well constrained. Part of this uncertainty stems from our inability to directly observe a natural unperturbed “steady-state” environment as a baseline, as the modern Hg cycle is heavily influenced by anthropogenic activity. Here we focus on the effects of ambient redox conditions in the water column and shallow sediments (early diagenesis), quantify their influence on the geological Hg record and thereby constrain their potential impact on the use of Hg as a proxy for deep-time volcanic activity. Constraining these factors is of critical importance for the application of Hg as a proxy. Many periods in the geological past for which records have been generated, such as the Mesozoic Oceanic Anoxic Events, are marked by a variety of high-amplitude environmental perturbations, including widespread deoxygenation and deposition of organic-rich sediments. We estimate the impact of redox changes and early diagenesis on the geological Hg record using a suite of (sub)recent–Pleistocene and Upper Cretaceous sediments representing oxic to euxinic marine conditions. Our sample set includes a transect through an oxygen minimum zone and cores that record transient shifts in oxygenation state, as well as post-depositional effects – all unrelated to volcanism, to the best of our knowledge. We find substantial alterations to the Hg record and the records of organic carbon and total sulfur, which are typically assumed to be the most common carrier phases of Hg in marine sediments. Moreover, these biases can lead to signal-alterations on a par with those interpreted to result from volcanic activity. Geochemical modifications are ubiquitous and their potential magnitude implies that the factors leading to biases in the geological record warrant careful consideration before interpretation. Factors of particular concern to proxy application are (1) the disproportionate loss of organic carbon and sulfur compounds relative to Hg during oxidation that strongly modulates normalized Hg records, (2) the evasion of Hg in anoxic and mildly euxinic sediments and (3) sharp focusing of Hg during post-depositional oxidation of organic matter.

We investigate the magnetic fabrics of Impact melt breccia at the Dhala impact structure to understand its emplacement mechanism. Our results show that the pseudo-single domains of Ti-poor magnetite and Ti-hematite are the prime magnetic carriers in the impact melt breccia. The magnetic fabrics from most sites reveal a general westward flow of impact melt breccia (IMB), with magnetic lineations of individual specimens trending between NW and SW. This indicates the emplacement of IMB in a semi-molten state with temperatures below c. 1500°C, which is the melting point of Ti-magnetite. Occurrence of poorly sorted clasts implies that IMB was emplaced as surficial flow rather than aerial. The variation in the dips of magnetic fabrics among individual specimens from a site resembles a pyroclastic flow rather than a ground-hugging volatile- and melt-rich flow. We, therefore, suggest that the IMB at Dhala was ballistically ejected and then moved in a semi-molten state as surficial pyroclastic-like flow with temperatures below c. 1500°C. Most flow vectors aligned between NW-SW, may represent a dominant westward excavation flow of the IMB (rather than radially outward flow), which may be activated by an east-to-west directed impactor striking at an impact angle below 50°.

The Late Miocene Biogenic Bloom (LMBB) is a late Miocene to early Pliocene oceanographic event characterized by high accumulation rates of opal from diatoms and calcite from calcareous nannofossils and planktic foraminifera. This multi-million year event has been recognized in sediment cores from the Pacific, Atlantic and Indian Oceans. The numerous studies discussing the LMBB lead us to believe that this event is omnipresent in all oceans, although this hypothesis need to be tested. Moreover, the origin of this event is still widely discussed. In this study we aim to provide a comprehensive overview of the geographical and temporal aspects of the LMBB by compiling published ocean drilling (DSDP, ODP and IODP) records of sedimentation rates, CaCO\textsubscript{3} and opal and terrigenous accumulation rates that cover the late Miocene and early Pliocene interval. Our data compilation shows that traces of the LMBB are present in many different locations but in a very heterogeneous way, highlighting that the LMBB is not a pervasive event. The compilation in addition shows that the sites where the LMBB is recorded are mainly located in areas with a high productivity regime (i.e. upwelling systems). We suggest that the most likely hypothesis to explain the LMBB is a global increase in upwelling intensity due to an increase in wind strength or an increase in deep water formation, ramping up global thermohaline circulation.

The dissolution and mobilization of non-aqueous phase liquids (NAPL) blobs in Surfactant-Enhanced Aquifer Remediation (SEAR) processes are upscaled using dynamic pore network modelling of three-dimensional and unstructured networks. We considered corner flow and micro-flow mechanisms including snap-off and piston-like movement for two-phase flow. Moreover, NAPL entrapment and remobilization were evaluated using force analysis to develop capillary desaturation curve (CDC) and predict the onset of remobilization and complete removal of entrapped NAPL blobs. The corner diffusion mechanism was also applied in the modeling of interphase mass transfer to represent NAPL dissolution as the dominant mass transfer process. Our model showed that although surfactants enhance NAPL recovery during two-phase flow, surfactant-enhanced remediation of residual NAPL through dissolution is highly dependent on surfactant type. When sodium dodecyl sulfate (SDS), as a surfactant with high critical micelle concentration (CMC) and low micelle partition coefficient ( ) was injected into a NAPL contaminated site, reduction in mass transfer rate coefficient (due to considerable changes in interface chemical potentials) significantly reduced NAPL recovery after the end of two-phase flow. However, Triton X-100 (with low CMC and high ) improved NAPL recovery. This is because by enhancing solubility at surfactant concentrations greater than CMC, Triton X-100 overcompensates the interphase mass transfer reduction.

The analysis of large samples of hydrologic catchments is regularly used to gain understanding of hydrologic variability and controlling processes. Several studies have pointed towards the problem that available catchment descriptors (such as mean topographic slope or average subsurface properties) are insufficient to capture hydrologically relevant properties. Here, we test the assumption that catchment location, i.e. the relative properties of catchments in relation to their surrounding neighbours, can provide additional information to reduce this problem. We test this idea in the context of Great Britain for a widely discussed problem, that of catchment water balance errors due to subsurface losses. We test three hypotheses while considering different locational aspects (1) location to coast, (2) location next a relevant neighbour and (3) location within the drainage basin, utilizing only basic and widely available geological and topographical information. We find that subsurface losses from catchments with a highly permeable geology connection to the coast are in order of 20% water balance error. We define a simple topographic-geologic index that is able to partially explain water balance issues between neighbours of highly permeable catchments. The results imply that location, geology and topography combine to define the differences of water balances of UK catchments compared to what we would expect from their climatic setting alone. The simple index defined here can easily be derived globally and tested regarding its wider applicability.