The dehydration, rehydration and tectonic setting of greenstone belts in a portion of the northern Kaapvaal Craton, South Africa

High-grade gneiss terranes and low-grade granite-greenstone terranes are well known in several Archaean domains. The geological relationship between these different crustal regions, however, is still controversial. One school of thought favors fundamental genetic differences between high-grade and low-grade terranes while others argue for a depth-controlled crustal evolution. The detailed examination of well-exposed Archaean terranes at different metamorphic grades, therefore, is not only an important source of information about the crustal levels exposed, but also is critical to the understanding of the possible tectonic and metamorphic evolution of greenstone belts with time. Three South African greenstone belts are compared

Landslides, threshold slopes and the survival of relict terrain in the wake of the Mendocino Triple Junction

Establishing landscape response to uplift is critical for interpreting sediment fluxes, hazard potential, and topographic evolution. We assess how landslides shape terrain in response to a wave of uplift traversing the northern California Coast Ranges (United States) in the wake of the Mendocino Triple Junction. We extracted knickpoints, landslide erosion rates, and topographic metrics across the region modified by Mendocino Triple Junction migration. Landslide erosion rates mapped from aerial imagery are consistent with modeled uplift and exhumation, while hillslope gradient is invariant across the region, suggesting that landslides accommodate uplift, as predicted by the threshold slope model. Landslides are concentrated along steepened channel reaches downstream of knickpoints generated by base-level fall at channel outlets, and limit slope angles and relief. We find evidence that landslide-derived coarse sediment delivery may suppress catchment-wide channel incision and landscape denudation over the time required for the uplift wave to traverse the region. We conclude that a landslide cover effect may provide a mechanism for the survival of relict terrain and orogenic relief in the northern Californian Coast Ranges and elsewhere over millennial time scales

Triamidoamine-supported zirconium: Hydrogen activation, Lewis acidity, and: Rac -lactide polymerization

Investigation of a triamidoamine-supported zirconium hydride intermediate, important to a range of catalytic reactions, revealed the potential Lewis acidity of [κ5-N,N,N,N,C-(Me3SiNCH2CH2)2NCH2CH2NSiMe2CH2]Zr (1). A preliminary study of 1 as a precursor for the polymerization of rac-lactide showed modest activity but indicated that five-coordinate zirconium complexes with tetra-N donor ligands may be an avenue for further development in group 4 metal lactide polymerization catalysis

Short communication: Cosmogenic noble gas depletion in soils by wildfire heating

Measurements of cosmic-ray-produced beryllium-10, neon-21, and helium-3 in quartz in a soil profile from a forested landscape in the Oregon Coast Range show that the cosmogenic noble gases 21Ne and 3He are depleted relative to 10Be in the shallow subsurface. The noble gases are mobile in mineral grains via thermally activated diffusion and 10Be is not, implying that noble gas depletion is the result of surface heating by wildfires and subsequent mixing of partially degassed quartz downward into the soil. Cosmogenic noble gas depletion by wildfire heating of soils is a potential means of estimating wildfire intensity and/or frequency over pre-observational timescales.</p

Beyond the angle of repose: A review and synthesis of landslide processes in response to rapid uplift, Eel River, Northern California

In mountainous settings, increases in rock uplift are often followed by a commensurate uptick in denudation as rivers incise and steepen hillslopes, making them increasingly prone to landsliding as slope angles approach a limiting value. For decades, the threshold slope model has been invoked to account for landslide-driven increases in sediment flux that limit topographic relief, but the manner by which slope failures organize themselves spatially and temporally in order for erosion to keep pace with rock uplift has not been well documented. Here, we review past work and present new findings from remote sensing, cosmogenic radionuclides, suspended sediment records, and airborne lidar data, to decipher patterns of landslide activity and geomorphic processes related to rapid uplift along the northward-migrating Mendocino Triple Junction in Northern California. From historical air photos and airborne lidar, we estimated the velocity and sediment flux associated with active, slow-moving landslides (or earthflows) in the mélange- and argillite-dominated Eel River watershed using the downslope displacement of surface markers such as trees and shrubs. Although active landslides that directly convey sediment into the channel network account for only 7% of the landscape surface, their sediment flux amounts to more than 50% of the suspended load recorded at downstream sediment gaging stations. These active slides tend to exhibit seasonal variations in velocity as satellite-based interferometry has demonstrated that rapid acceleration commences within 1 to 2 months of the onset of autumn rainfall events before slower deceleration ensues in the spring and summer months. Curiously, this seasonal velocity pattern does not appear to vary with landslide size, suggesting that complex hydrologic–mechanical feedbacks (rather than 1-D pore pressure diffusion) may govern slide dynamics. A new analysis of 14 yrs of discharge and sediment concentration data for the Eel River indicates that the characteristic mid-winter timing of earthflow acceleration corresponds with increased suspended concentration values, suggesting that the seasonal onset of landslide motion each year may be reflected in the export of sediments to the continental margin. The vast majority of active slides exhibit gullied surfaces and the gully networks, which are also seasonally active, may facilitate sediment export although the proportion of material produced by this pathway is poorly known. Along Kekawaka Creek, a prominent tributary to the Eel River, new analyses of catchment-averaged erosion rates derived from cosmogenic radionuclides reveal rapid erosion (0.76 mm/yr) below a prominent knickpoint and slower erosion (0.29 mm/yr) upstream. Such knickpoints are frequently observed in Eel tributaries and are usually comprised of massive (> 10 m) interlocking resistant boulders that likely persist in the landscape for long periods of time (> 105 yr). Upstream of these knickpoints, active landslides tend to be less frequent and average slope angles are slightly gentler than in downstream areas, which indicates that landslide density and average slope angle appear to increase with erosion rate. Lastly, we synthesize evidence for the role of large, catastrophic landslides in regulating sediment flux and landscape form. The emergence of resistant blocks within the mélange bedrock has promoted large catastrophic slides that have dammed the Eel River and perhaps generated outburst events in the past. The frequency and impact of these landslide dams likely depend on the spatial and size distributions of resistant blocks relative to the width and drainage area of adjacent valley networks. Overall, our findings demonstrate that landslides within the Eel River catchment do not occur randomly, but instead exhibit spatial and temporal patterns related to baselevel lowering, climate forcing, and lithologic variations. Combined with recent landscape evolution models that incorporate landslides, these results provide predictive capability for estimating erosion rates and managing hazards in mountainous regions

Historic drought puts the breaks on earthflows in Northern California

California's ongoing, unprecedented drought is having profound impacts on the state's resources. Here we assess its impact on 98 deep-seated, slow-moving landslides in Northern California. We used aerial photograph analysis, satellite interferometry, and satellite pixel tracking to measure earthflow velocities spanning 1944–2015 and compared these trends with the Palmer Drought Severity Index, a proxy for soil moisture and pore pressure that governs landslide motion. We find that earthflow velocities reached a historical low in the 2012–2015 drought, but that their deceleration began at the turn of the century in response to a longer-term moisture deficit. Our analysis implies depth-dependent sensitivity of earthflows to climate forcing, with thicker earthflows reflecting longer-term climate trends and thinner earthflows exhibiting less systematic velocity variations. These findings have implications for mechanical-hydrologic interactions that link landslide movement with climate change as well as sediment delivery in the region

Oregon 2100: projected climatic and ecological changes

Greenhouse climatic warming is underway and exacerbated by human activities. Future outcomes of these processes can be projected using computer models checked against climatic changes during comparable past atmospheric compositions. This study gives concise quantitative predictions for future climate, landscapes, soils, vegetation, and marine and terrestrial animals of Oregon. Fossil fuel burning and other human activities by the year 2100 are projected to yield atmospheric CO2 levels of about 600-850 ppm (SRES A1B and B1), well above current levels of 400 ppm and preindustrial levels of 280 ppm. Such a greenhouse climate was last recorded in Oregon during the middle Miocene, some 16 million years ago. Oregon’s future may be guided by fossil records of the middle Miocene, as well as ongoing studies on the environmental tolerances of Oregon plants and animals, and experiments on the biological effects of global warming. As carbon dioxide levels increase, Oregon’s climate will move toward warm temperate, humid in the west and semiarid to subhumid to the east, with increased summer and winter drought in the west. Western Oregon lowlands will become less suitable for temperate fruits and nuts and Pinot Noir grapes, but its hills will remain a productive softwood forest resource. Improved pasture and winter wheat crops will become more widespread in eastern Oregon. Tsunamis and stronger storms will exacerbate marine erosion along the Oregon Coast, with significant damage to coastal properties and cultural resources

Frost for the trees: Did climate increase erosion in unglaciated landscapes during the late Pleistocene?

Understanding climatic influences on the rates and mechanisms of landscape erosion is an unresolved problem in Earth science that is important for quantifying soil formation rates, sediment and solute fluxes to oceans, and atmospheric CO2 regulation by silicate weathering. Glaciated landscapes record the erosional legacy of glacial intervals through moraine deposits and U-shaped valleys, whereas more widespread unglaciated hillslopes and rivers lack obvious climate signatures, hampering mechanistic theory for how climate sets fluxes and form. Today, periglacial processes in high-elevation settings promote vigorous bedrock-to-regolith conversion and regolith transport, but the extent to which frost processes shaped vast swaths of low- to moderate-elevation terrain during past climate regimes is not well established. By combining a mechanistic frost weathering model with a regional Last Glacial Maximum (LGM) climate reconstruction derived from a paleo-Earth System Model, paleovegetation data, and a paleoerosion archive, we propose that frost-driven sediment production was pervasive during the LGM in our unglaciated Pacific Northwest study site, coincident with a 2.5 times increase in erosion relative to modern rates. Our findings provide a novel framework to quantify how climate modulates sediment production over glacial-interglacial cycles in mid-latitude unglaciated terrain

Toward improved prediction of the bedrock depth underneath hillslopes: Bayesian inference of the bottom‐up control hypothesis using high‐resolution topographic data

The depth to bedrock controls a myriad of processes by influencing subsurface flow paths, erosion rates, soil moisture, and water uptake by plant roots. As hillslope interiors are very difficult and costly to illuminate and access, the topography of the bedrock surface is largely unknown. This essay is concerned with the prediction of spatial patterns in the depth to bedrock (DTB) using high‐resolution topographic data, numerical modeling, and Bayesian analysis. Our DTB model builds on the bottom‐up control on fresh‐bedrock topography hypothesis of Rempe and Dietrich (2014) and includes a mass movement and bedrock‐valley morphology term to extent the usefulness and general applicability of the model. We reconcile the DTB model with field observations using Bayesian analysis with the DREAM algorithm. We investigate explicitly the benefits of using spatially distributed parameter values to account implicitly, and in a relatively simple way, for rock mass heterogeneities that are very difficult, if not impossible, to characterize adequately in the field. We illustrate our method using an artificial data set of bedrock depth observations and then evaluate our DTB model with real‐world data collected at the Papagaio river basin in Rio de Janeiro, Brazil. Our results demonstrate that the DTB model predicts accurately the observed bedrock depth data. The posterior mean DTB simulation is shown to be in good agreement with the measured data. The posterior prediction uncertainty of the DTB model can be propagated forward through hydromechanical models to derive probabilistic estimates of factors of safety.Key Points:We introduce an analytic formulation for the spatial distribution of the bedrock depthBayesian analysis reconciles our model with field data and quantifies prediction and parameter uncertaintyThe use of a distributed parameterization recognizes geologic heterogeneitiesPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137555/1/wrcr22005.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137555/2/wrcr22005_am.pd

Biologically inspired simulation of livor mortis

We present a biologically motivated livor mortis simulation that is capable of modelling the colouration changes in skin caused by blood pooling after death. Our approach consists of a simulation of post mortem blood dynamics and a layered skin shader that is controlled by the haemoglobin and oxygen levels in blood. The object is represented by a layered data structure made of a triangle mesh for the skin and a tetrahedral mesh on which the blood dynamics are simulated. This allows us to simulate the skin discolouration caused by livor mortis, including early patchy appearance, fixation of hypostasis and pressure induced blanching. We demonstrate our approach on two different models and scenarios and compare the results to real world livor mortis photographic examples