Namibia volcanic margin

Two end members of passive margin types are present on the Namibia margin: volcanic and non-volcanic. The central and southern parts of the Namibia margin feature characteristic volcanic margin elements such as thickened initial oceanic crust, seaward dipping reflectors, and high-velocity/density lower crust that extends beneath the rift zone that was formed during initial seafloor spreading in Early Cretaceous. The margin north of the Walvis FZ is non-volcanic in character and probably formed as a result of a ridge jump that occurred after cessation of the initial magmatic activity. The Walvis Ridge forms the boundary between the two margin types and resulted from the persistent magmatism associated with the Tristan plume. MCS data in conjunction with gravity modeling reveal a Paleozoic rift zone beneath the Namibia margin south of the Walvis FZ. The Paleozoic rift zone partly overlaps the Jurassic/Early Cretaceous rift zone which produced the breakup between Africa and South America. We calculate an average stretching value of =1.4 for the Paleozoic rift, based on subsidence modeling. The rift is partly bounded by low-angle faults, related to the orogenic collapse of the Pan-African fold belt, which provided a major Paleozoic sediment source. The offshore continuity of onshore ophiolitic complexes is suggested by the coast parallel high-amplitude magnetic anomaly G, and low-angle detachment faults along the southern part of the margin. The average stretching value for the Jurassic/Early Cretaceous rift is =1.7, which implies a syn-rift displacement on this margin of 70 km. The minimum igneous volume of the South Atlantic LIP was found to be in excess of 3.62×106 km³.     

Vergleichende Untersuchung der Diäten vonLymnaea auricularia undL. peregra (Gastropoda: Basommatophora) im Zürichsee

Two very similar species of freshwater snails,Lymnaea auricularia andL. peregra coexist in Lake Zürich. We examined their diets to determine possible differences. Microscopic analysis of stomach and hind gut contents revealed no marked differences between the diets of the two snail species collected from the same substrate. However, in both species we found significant differences between the composition of the substrate and that of the stomach contents, using discriminant analysis. We conclude that both species of snails feed preferentially on patches of favourable food supply and that their diets overlap almost totally. The coexistence of the two species under these conditions suggests that food does not limit their density in the area studied.     

Hazard assessment of the Tidal Inlet landslide and potential subsequent tsunami, Glacier Bay National Park, Alaska

An unstable rock slump, estimated at 5 to 10 × 10⁶ m³, lies perched above the northern shore of Tidal Inlet in Glacier Bay National Park, Alaska. This landslide mass has the potential to rapidly move into Tidal Inlet and generate large, long-period-impulse tsunami waves. Field and photographic examination revealed that the landslide moved between 1892 and 1919 after the retreat of the Little Ice Age glaciers from Tidal Inlet in 1890. Global positioning system measurements over a 2-year period show that the perched mass is presently moving at 3–4 cm annually indicating the landslide remains unstable. Numerical simulations of landslide-generated waves suggest that in the western arm of Glacier Bay, wave amplitudes would be greatest near the mouth of Tidal Inlet and slightly decrease with water depth according to Green’s law. As a function of time, wave amplitude would be greatest within approximately 40 min of the landslide entering water, with significant wave activity continuing for potentially several hours.     

Hydrometeorological thresholds for landslide initiation and forest operation shutdowns on the north coast of British Columbia

Debris flows and debris avalanches are the most widespread and hazardous types of landslides on the British Columbia north coast. Triggered by heavy rain, they pose risks to forestry workers in sparsely developed regions. The scarcity of long-term quality rain gauges and the lack of weather radar information create significant challenge in predicting the timing of landslides, which could be used to warn and, when necessary, evacuate forestry personnel. Traditional methods to relate rainfall antecedents and rainfall intensity to known landslide dates have proven to be unsatisfactory in this study due to extreme spatial variability of rainfall, enhanced by the orographic effect and the scarcity of rain gauges in a very large area. This has led to an integration of meteorological variables in a landslide advisory system that classifies three types of approaching storms by the 850-mbar wind speed and direction, the occurrence of subtropical moisture flow, and the existence of a warm layer characterized by high thickness values of the 500- to 1,000-mbar pressure levels. The storm classification was combined with a 4-week antecedent rainfall and the 24-h rainfall measured near or in the watershed where logging operations are taking place. This system, once implemented, is thought to reduce loss of life, injury, and economic losses associated with forestry works in the study area.     

Allogenic forcing of the late Quaternary Rhine–Meuse fluvial record: the interplay of sea-level change, climate change and crustal movements

The Rhine–Meuse system in the west‐central Netherlands is a continental‐scale fluvial system bordered by an extremely wide continental shelf. Consequently, late Quaternary eustatic sea‐level changes have resulted in dramatic shoreline displacements, by as much as 800 km. In addition, changes in climate have been severe, given the latitudinal and palaeogeographic setting of the Rhine–Meuse system. We investigated the relative importance of these allogenic controls on fluvial aggradation and incision during the last two glacial–interglacial cycles. We used optical dating of quartz from ～30 samples in a cross‐section perpendicular to the palaeoflow direction, allowing us to correlate periods of aggradation and incision with independent records of sea‐level change, climate change and glacio‐isostatic crustal movements. We found the long‐term aggradation rate to be ～8 cm kyr^?1, a value similar to previous estimates of tectonic subsidence rates in the study area. Several excursions from this long‐term aggradation trend could be identified for the last glacial–interglacial cycle. Dry climatic conditions with relatively high sediment supply induced aggradation during oxygen‐isotope stages (OIS) 4 and 3. Build‐up of a glacio‐isostatic forebulge during OIS 2 is a likely cause of incision around the Last Glacial Maximum, followed by an aggradation phase during forebulge collapse. Sea‐level highstands during OIS 5 have likely resulted in the aggradation of coastal prisms, but only minor, basal estuarine deposits have been preserved because these coastal prisms were prone to erosion during ensuing sea‐level falls. Overall, the sedimentary record is dominated by strata formed during time intervals when the study area was completely unaffected by sea‐level control, and our evidence shows that the falling‐stage systems tract has the highest preservation potential. Our study highlights the importance of considering the complex interplay of both upstream and downstream controls to obtain a comprehensive understanding of the evolution of basin‐margin successions.     

Mapping and clustering the adoption of carbon pricing policies: what polities price carbon and why?

Carbon pricing, including carbon taxes and emissions trading, has been adopted by different kinds of polities worldwide. Yet, beyond the increasing adoption over time, little is known about what polities – countries as well as sub- and supranational entities – adopt carbon pricing and why. This paper explores patterns of adoption (both implemented policies and those scheduled to be) through cluster analysis, with the purpose of investigating factors that could explain polities’ decisions to adopt carbon pricing. The study contributes empirically by studying carbon taxes and emissions trading together and by ordering the polities adopting carbon pricing into clusters. It also contributes theoretically, by exploring constellations of variables that drive the adoption of carbon pricing within individual clusters. We investigated 66 adopted policies of carbon pricing, which were divided into five clusters: early adopters, North-American subnational entities, Chinese pilot provinces, second-wave developed polities, and second-wave developing polities. The analysis indicates that the reasons for adopting carbon pricing have shifted over time. While international factors (climate commitments or influences from polities within the same region) are increasingly salient, domestic factors (including crises and income levels) were more important for the early adopters.

Key policy insights

• Carbon pricing has become a global mainstream policy instrument.

• Economic and fiscal crises provide windows of opportunity for promoting carbon pricing.

• The international climate regime can support the adoption of carbon pricing through mitigation commitments and international financial and technical assistance.

• Learning between polities from the same region is a useful tool for promoting carbon pricing.

• Carbon intensive economies tend to prefer emissions trading over carbon taxes.

     

Integrating geochronologic and instrumental approaches across the Bengal Basin

Constraining time is of critical importance to evaluating the rates and relative contributions of processes driving landscape change in sedimentary basins. The geomorphic character of the field setting guides the application of geochronologic or instrumental tools to this problem, because the viability of methods can be highly influenced by geomorphic attributes. For example, sediment yield and the linked potential for organic preservation may govern the usefulness of radiocarbon dating. Similarly, the rate of sediment transport from source to sink may determine the maturity and/or light exposure of mineral grains arriving in the delta and thus the feasibility of luminescence dating. Here, we explore the viability and quirks of dating and instrumental methods that have been applied in the Bengal Basin, and review the records that they have yielded. This immense, dynamic, and spatially variable system hosts the world's most inhabited delta. Outlining a framework for successful chronologic applications is thus of value to managing water and sediment resources for humans, here and in other populated deltas worldwide. Our review covers radiocarbon dating, luminescence dating, archaeological records and historical maps, short-lived radioisotopes, horizon markers and rod surface elevation tables, geodetic observations, and surface instrumentation. Combined, these tools can be used to reconstruct the history of the Bengal Basin from Late Pleistocene to present day. The growing variety and scope of Bengal Basin geochronology and instrumentation opens doors for research integrating basin processes across spatial and temporal scales. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.     

Ice cap erosion patterns from bedrock 10Be and 26Al,southeastern Tibetan Plateau

Quantifying glacial erosion contributes to our understanding of landscape evolution and topographic relief production in high altitude and high latitude areas. Combining in situ ¹⁰Be and ²⁶Al analysis of bedrock, boulder, and river sand samples, geomorphological mapping, and field investigations, we examine glacial erosion patterns of former ice caps in the Shaluli Shan of the southeastern Tibetan Plateau. The general landform pattern shows a zonal pattern of landscape modification produced by ice caps of up to 4000 km² during pre-LGM (Last Glacial Maximum) glaciations, while the dating results and landforms on the plateau surface imply that the LGM ice cap further modified the scoured terrain into different zones. Modeled glacial erosion depth of 0–0.38 m per 100 ka bedrock sample located close to the western margin of the LGM ice cap, indicates limited erosion prior to LGM and Late Glacial moraine deposition. A strong erosion zone exists proximal to the LGM ice cap marginal zone, indicated by modeled glacial erosion depth >2.23 m per 100 ka from bedrock samples. Modeled glacial erosion depths of 0–1.77 m per 100 ka from samples collected along the edge of a central upland, confirm the presence of a zone of intermediate erosion in-between the central upland and the strong erosion zone. Significant nuclide inheritance in river sand samples from basins on the scoured plateau surface also indicate restricted glacial erosion during the last glaciation. Our study, for the first time, shows clear evidence for preservation of glacial landforms formed during previous glaciations under non-erosive ice on the Tibetan Plateau. As patterns of glacial erosion intensity are largely driven by the basal thermal regime, our results confirm earlier inferences from geomorphology for a concentric basal thermal pattern for the Haizishan ice cap during the LGM. © 2018 John Wiley & Sons, Ltd.     

Oblique aggradation: a novel explanation for sinuosity of low‐energy streams in peat‐filled valley systems

Low‐energy streams in peatlands often have a high sinuosity. However, it is unknown how this sinuous planform formed, since lateral migration of the channel is hindered by relatively erosion‐resistant banks. We present a conceptual model of Holocene morphodynamic evolution of a stream in a peat‐filled valley, based on a palaeohydrological reconstruction. Coring, ground‐penetrating radar (GPR) data, and ¹⁴C and OSL dating were used for the reconstruction. We found that the stream planform is partly inherited from the Late‐Glacial topography, reflecting stream morphology prior to peat growth in the valley. Most importantly, we show that aggrading streams in a peat‐filled valley combine vertical aggradation with lateral displacement caused by attraction to the sandy valley sides, which are more erodible than the co‐evally aggrading valley‐fill. Owing to this oblique aggradation in combination with floodplain widening, the stream becomes stretched out as channel reaches may alternately aggrade along opposed valley sides, resulting in increased sinuosity over time. Hence, highly sinuous planforms can form in peat‐filled valleys without the traditional morphodynamics of alluvial bed lateral migration. Improved understanding of the evolution of streams provides inspiration for stream restoration. Copyright © 2016 John Wiley & Sons, Ltd.