High Topographic Relief Research Articles

Topographical controls on small‐volume pyroclastic flows

AbstractEmplacement of small‐volume (<0·1 km3) pyroclastic flows is significantly influenced by topography. The Arico ignimbrite on Tenerife (Canary Islands) is a characteristic small‐volume pyroclastic flow deposit emplaced on high relief topography. The pyroclastic flow flowed down pre‐existing valleys on the southern slopes of the island. In proximal areas deep (up to 100 m) valleys acted as efficient conduits for the pyroclastic flow, which was mostly channelled; in this particular area the ignimbrite corresponds to a homogeneous, moderately welded deposit, consisting of flattened pumices in an abundant ashy matrix with a relatively low lithic fragment content. In intermediate zones significant changes occur in the steepness of the slope and, although still channelled, here the pyroclastic flow was influenced by hydraulic jumps. In this area, two different units can be clearly distinguished in the ignimbrite: the lower unit is composed of a lithic‐rich ground‐layer deposit that formed at the turbulent, highly concentrated head of the flow; the upper unit consists of a well welded pumice‐rich deposit that occasionally reveals a basal layer formed by shearing with the lower part. This division into two units is maintained as far as distal areas near the present‐day coastline, where the slope is very gentle or null and the ignimbrite is not channelled. The ground layer is not found in distal areas. The ignimbrite here only consists of the upper unit, which is occasionally repeated due to a surging process provoked by the lower flow speed, as the pyroclastic flow spread out of the channelled zone. A theoretical model on how topography controlled the deposition of the Arico ignimbrite is derived by interpreting the observed lithological and sedimentological variations in terms of changes in topography and bedrock morphology. This new model is of general applicability and will help to explain other deposits of similar characteristics.

Differential crustal deformation across the Cona-Oiga rift, southern Tibetan Plateau

The Cona-Oiga rift (COR) is the easternmost member of a series of ∼N-S trending Cenozoic rifts in the southern Tibetan Plateau. The Yarlung River flows from west to east, across the COR and exhibits diverse river morphology along strike. We analyze tributary fluvial longitudinal profiles in the Yarlung drainage and the published strain rate field on both sides of the rift in order to gain knowledge about its development and crustal deformation patterns within the plateau interior. Tributaries on the western side of the rift have relatively low normalized steepness index (ksn). Concave curves in χ-elevation plots and cross-divide contrasts in χ, mean relief, and mean gradient, indicate ongoing river reorganization in this region. In contrast, high topographic relief and steep stream channels developed on the eastern side. In addition, spatial variations in negative dilatational strain rates indicate diverse crustal shortening and regional uplift across the COR. We suggest that the Cona-Oiga rift plays an important role in accommodating deformation associated with the continuing indentation of the eastern Himalayan syntaxis. Tectonic forcing might be the dominant factor controlling landscape evolution across the COR.

Controls on the erosion of the continental margin of southeast Brazil from cosmogenic 10Be in river sediments

The Atlantic Ocean coast region of southeast Brazil contains two coast-parallel mountain ranges (the Serra do Mar and Serra da Mantiqueira) generated by tectonic activity pulses tens of millions years after the main continental rift event occurred around 120 Ma. Although the short-term erosion rates for the region are established, the relative importance of the factors controlling erosion is poorly constrained. We combine new and published catchment-averaged erosion rates (n = 48) using in situ-produced 10Be concentrations in quartz from river sediments to establish the regional erosion pattern. The river catchments are (i) escarpment topography, (ii) high-altitude low-relief and (iii) mixed topography, which record how escarpment fronts are migrating inland. Ocean-facing coastal escarpment catchments of the Serra do Mar (ε = 18–53 m/Ma) can be eroded approximately twice as fast as continent-facing escarpment catchments in the Serra do Mar and Serra da Mantiqueira (ε = 7–24 m/Ma). The correlation between the normalized channel steepness index (ksn) and slope angle indicates that river incision and hillslope erosion processes combine to maintain the high relief. The Serra do Mar catchments define a mean slope angle threshold indicating that landslides are the dominant erosional process when slope angles in excess of ~30°. Tectonic activity is low and plays no significant role in driving erosion. A first-order relationship between erosion rate and precipitation-temperature across the region implies that climate plays a key role in soil production, river incision and in triggering erosional processes. Although the high topographic relief is a pre-condition for the occurrence of significant erosion, the climatic condition is the outlining factor of the regional variation in erosion rates.

Cryogenian glaciomarine megaclasts of the MacDonald Corridor, Bimbowrie Conservation Park, Olary Region, South Australia

Ten glacially related megaclasts, unique perhaps from a global perspective, have been identified in the MacDonald Corridor. Included are perhaps the largest known glacially-related basement-derived megaclasts, the Bimbowrie Megaclast measuring 1.25 km in exposed width. The MacDonald Corridor is the most outward of four half-grabens to the east of the main Adelaide Geosyncline rift complex. All four contain Neoproterozoic low-grade metasedimentary rocks situated between inliers of Paleoproterozoic–Mesoproterozoic basement at the southwestern margin of the Curnamona Province. These corridors originated as extensional structures during the last of three major episodes of rifting that led to the eventual break-up of the supercontinent Rodinia. This rift phase was synchronous with the older (Sturtian-age) of the two major Cryogenian glaciations that are recorded in the rift and sag-basin complex of the Adelaide Geosyncline in South Australia. Those megaclasts selected for description vary in size from 0.1 to 1.25 km in exposed width, and were derived from the eastern rift flank, the Kalabity Inlier They therefore comprise either Paleoproterozoic metamorphic or Mesoproterozoic rocks or a composite of both. The megaclasts fall into two groups, those contained within the sedimentary fill of the rift basin, the Bimbowrie and Adlaweena megaclasts being the largest, and those resting as erratics on the flank. Of these, the 450 m wide Old Boolcoomata Megaclast resides within the remains of a steeply dipping U-shaped glacial valley. Tectonic activity and ice action are considered to have been responsible for creating the high-relief topography of the Kalabity Inlier. Ice was also instrumental in separating the megaclasts from their source and transporting them into the tectonically active MacDonald Corridor half-graben. Additionally, the variation of floating ice-cover controlled iron deposition within the glacigene Benda Siltstone. The present morphology of the MacDonald Corridor is largely due to the Cambrian Delamerian Orogeny, which while causing some structural complexity, exhumed and tilted the infill of the corridor to view.

Enhancing UAV–SfM 3D Model Accuracy in High-Relief Landscapes by Incorporating Oblique Images

Complex landscapes with high topographic relief and intricate geometry present challenges for complete and accurate mapping of both lateral (x, y) and vertical (z) detail without deformation. Although small uninhabited/unmanned aerial vehicles (UAVs) paired with structure-from-motion (SfM) image processing has recently emerged as a popular solution for a range of mapping applications, common image acquisition and processing strategies can result in surface deformation along steep slopes within complex terrain. Incorporation of oblique (off-nadir) images into the UAV–SfM workflow has been shown to reduce systematic errors within resulting models, but there has been no consensus or documentation substantiating use of particular imaging angles. To address these limitations, we examined UAV–SfM models produced from image sets collected with various imaging angles (0–35°) within a high-relief ‘badland’ landscape and compared resulting surfaces with a reference dataset from a terrestrial laser scanner (TLS). More than 150 UAV–SfM scenarios were quantitatively evaluated to assess the effects of camera tilt angle, overlap, and imaging configuration on the precision and accuracy of the reconstructed terrain. Results indicate that imaging angle has a profound impact on accuracy and precision for data acquisition with a single camera angle in topographically complex scenes. Results also confirm previous findings that supplementing nadir image blocks with oblique images in the UAV–SfM workflow consistently improves spatial accuracy and precision and reduces data gaps and systematic errors in the final point cloud. Subtle differences among various oblique camera angles and imaging patterns suggest that higher overlap and higher oblique camera angles (20–35°) increased precision and accuracy by nearly 50% relative to nadir-only image blocks. We conclude by presenting four recommendations for incorporating oblique images and adapting flight parameters to enhance 3D mapping applications with UAV–SfM in high-relief terrain.

PM1 carbonaceous aerosols during winter in a typical valley city of western China: Vertical profiles and the key influencing factors

To fill the blank on vertical profiles of carbonaceous aerosols during winter, the first in situ vertical measurements of organic and elemental carbon (OC, EC) from ground level to 620 m were conducted by means of high topographic relief in a typical valley city of Lanzhou, northwest China. The key factors (meteorology and sources) affecting the vertical distributions also were revealed by clustering technique and principal component analysis. Mean OC and EC concentrations were (16.2 ± 8.9) μg m−3 and (5.1 ± 2.1) μg m−3 during the study periods near the ground. More uniformly vertical distributions of carbonaceous aerosols during daytime than those during nighttime with OC (EC) decreasing rates of ∼1.45 (∼0.32) μg m−3 100 m−1 during nighttime and ∼0.84 (∼0.09) μg m−3 100 m−1 during daytime. Three distinct types of OC (EC) vertical profiles were determined by clustering technique. The cluster with high concentrations of OC (33.7 ± 5.7 μg m−3) and EC (10.5 ± 7.7 μg m−3) near the ground surface was induced largely by temperature inversion around the ground. The OC (EC) differences between the surface and the hilltop increased by 14.21 (2.45) μg m−3 when inversion layer depth increased by 100 m. Winter carbonaceous aerosols were more significantly affected by atmospheric stratification near the ground, while those were impacted together by vertical and horizontal dispersions at the hilltop. The primary emissions from coal combustion or biomass burning for heating at the hilltop and motor vehicles near the ground also had an important effect on OC (EC) vertical profiles. The emissions from coal burning and gasoline vehicles accounted for 60%–70% of carbonaceous aerosols in urban areas of Lanzhou. Furthermore, the contributions of gasoline vehicles during daytime near the surface (∼20%) and biomass burning at the hilltop (∼15%) were larger due to the impact of human activities.

A long-term, temporally consistent, gridded daily meteorological dataset for northwestern North America

We describe a spatially contiguous, temporally consistent high-resolution gridded daily meteorological dataset for northwestern North America. This >4 million km2 region has high topographic relief, seasonal snowpack, permafrost and glaciers, crosses multiple jurisdictional boundaries and contains the entire Yukon, Mackenzie, Saskatchewan, Fraser and Columbia drainages. We interpolate daily station data to 1/16° spatial resolution using a high-resolution monthly 1971–2000 climatology as a predictor in a thin-plate spline interpolating algorithm. Only temporally consistent climate stations with at least 40 years of record are included. Our approach is designed to produce a dataset well suited for driving hydrological models and training statistical downscaling schemes. We compare our results to two commonly used datasets and show improved performance for climate means, extremes and variability. When used to drive a hydrologic model, our dataset also outperforms these datasets for runoff ratios and streamflow trends in several, high elevation, sub-basins of the Fraser River.

Assessing landslide characteristics in a changing climate in northern Taiwan

This study analyzed landslide characteristics under extreme precipitation with regard to present and future scenarios, in order to analyze the effects of climate change on landslide activities. For our study area, we selected two adjacent catchments in northern Taiwan: the Shihmen Reservoir catchment, an area with high-relief topography that is susceptible to landslides at present, and the Xindian River catchment, an area with gentle topography that is not prone to landslides at present. This study established empirical relationships between landslide-area characteristics and rainfall conditions according to rainfall-induced landslides during past typhoon events. The relationships were applied to estimate landslide-area characteristics caused by typhoon events for the base period (1979–2003) and the end of the 21st century (2075–2099) according to the climate change scenario of representative concentration pathways 8.5 (RCP8.5) and dynamical downscaling of rainfall data in Taiwan. We also analyzed rainfall amounts at different recurrence intervals from different rainfall durations for the two catchments. We found that the area with high-relief topography (the Shihmen Reservoir catchment) is relatively prone to landslides currently and that the cumulative rainfall is a key factor controlling landslide-area characteristics. On the other hand, the area with gentle topography (the Xindian River catchment) is less prone to landslides at present, and the rainfall intensity is a key factor controlling landslide-area characteristics. Under the effects of climate change in the near future, both landslide severity and landslide frequency will increase more in areas with gentle topography than in areas with high-relief topography, in response to the more frequent occurrence of a strong typhoon with higher rainfall intensity.

Measurements of submicron particles vertical profiles by means of topographic relief in a typical valley city, China

To reveal PM1 vertical profiles and key affecting factors in a typical urban valley, daytime and nighttime PM1 (the particles with diameters less than 1 μm) samples were collected with medium volume air samplers during 26 December 2017 to 11 January 2018 at five different altitudes by means of high topographic relief at urban areas of Lanzhou. The synchronous boundary layer temperature and humidity profiles were observed by a microwave radiometer. Daytime PM1 concentrations reduced by about 3.86 μg m−3 when the height above the surface increased by 100 m, which was much lower than that for nighttime (5.68 μg m−3 100 m−1) as particles were easily accumulated near the surface when the air was stable during the nighttime. The three typical PM1 vertical profiles were identified by K-means clustering technique. The most frequent cluster with elevated PM1 concentrations near the surface was closely related to temperature inversion around the ground, while the cluster with relatively uniform PM1 within the boundary layer was mainly induced by unstable atmospheric stratification and thus relatively good vertical dispersion. About 50%–60% of PM1 variations could be attributed to atmospheric stratification near the surface in the valley city, which was much higher than that at the hilltop. The PM1 difference increased by 47.14 (36.91) μg m−3 when inversion layer thickness (intensity) increased by 100 m (1 °C 100 m−1). The newly calculated inversion index considering both inversion layer thickness and intensity explained about 87% of PM1 differences between near the surface and at the hilltop. The vertical dispersion had a more significant effect on PM1 than horizontal dispersion near the surface, while PM1 was more largely affected by horizontal dispersion at the hilltop, which was closely related to the valley terrain.

A proximal record of caldera-forming eruptions: the stratigraphy, eruptive history and collapse of the Palaeogene Arran caldera, western Scotland

Caldera-forming volcanic eruptions are among the most dangerous, and can generate extensive pyroclastic deposits and deliver ash into global atmospheric circulation systems. As calderas collapse, the eruptions can deposit thick proximal ignimbrite sequences and thinner ignimbrites more distally. However, the proximal record of caldera collapse is often obscured by later intrusions, volcanism, faults, alteration, water and sediments, which significantly limits our understanding of these eruptions. A Palaeogene caldera system in central Arran, western Scotland, preserves a rare proximal caldera-fill succession, the Arran Volcanic Formation. This caldera largely comprises highly heterogeneous ignimbrites and minor intra-caldera sedimentary rocks. The current level of erosion, and the general absence of faults, intrusions and sediments, allows a complex stratigraphy and collapse history to be determined, which can be linked to changing eruptive styles at a constantly evolving volcano. The first recorded phase was eruption of a homogeneous rhyolitic lava-like tuff, deposited from high temperature, high mass-flux pyroclastic density currents generated from low fountaining columns that retained heat. A succeeding phase of highly explosive Plinian eruptions, marked by a thick blanket of massive lapilli tuffs, was then followed by piston-like caldera collapse and erosion of steep caldera walls. Volcanism then became generally less explosive, with predominantly lava-like and eutaxitic tuffs and cognate spatter-rich agglomerates interbedded with non-homogenous lapilli tuffs. High topographic relief between distinct units indicate long periods of volcanic quiescence, during which erosive processes dominated. These periods are, in several places, marked by sedimentary rocks and evidence for surface water, which includes a localised basaltic-andesitic phreatomagmatic tuff. The caldera-forming eruptions recorded by the Arran Volcanic Formation provide an important insight into caldera collapse processes and proximal ignimbrite successions. The lack of thick autobreccias and lithic-rich lapilli- and block-layers indicates that subsidence was relatively gradual and incremental in this caldera, and not accompanied by catastrophic wall collapse during eruption. The relatively horizontal nature of the caldera-fill units and paucity of intra-caldera faulting indicate that piston subsidence was the dominant method of collapse, with a relatively coherent caldera floor bounded by a steeply dipping ring fault. Possible resurgence may have caused later doming of the floor and radial distribution of subsequent ignimbrites and sedimentary rocks. Our work emphasises the continued need for field studies of caldera volcanoes.

U–Pb detrital zircon ages of sediments from the Firgoun and Niamey areas (eastern border of West African Craton, West Niger)

This study uses field observations and new U–Pb ages of detrital zircon grains from three samples to question the stratigraphic position of the Firgoun and Niamey siliciclastic sediments, presumed to be Neoproterozoic in age. Sharing several lithological similarities with the Late Cryogenian “Triad” of the Taoudenni, Gourma, and Volta basins, the uppermost siliciclastic sediments of the Firgoun and Niamey areas were likely also deposited during this period. This is corroborated by matrix-supported diamictites with faceted or striated pebbles as well as by structures resembling cryoturbation processes. However, the detrital zircon U–Pb age record that we present here for the lowermost deposits of Firgoun and Niamey provides mainly Paleoproterozoic ages, and very few Archean ages, altogether in a range from 1822±9 to 3392±9 Ma. Therefore, the new data only show that the Firgoun and Niamey sediments were deposited before about 1800 Ma. Nevertheless, the U–Th–Pb zircon age data allows examining the possible provenance of the sediments. We show that the latter was likely in the westerly close vicinity of the studied areas. The Archean zircons are likely inherited, and possibly originating from a more westerly source. The nearby source of the Niamey and Firgoun sediments suggests that a high topographic relief was still existing in the south-central part of the West African Craton in the Mid Neoproterozoic.

The Alpine Fault Hangingwall Viewed From Within: Structural Analysis of Ultrasonic Image Logs in the DFDP‐2B Borehole, New Zealand

AbstractUltrasonic image logs acquired in the DFDP‐2B borehole yield the first continuous, subsurface description of the transition from schist to mylonite in the hangingwall of the Alpine Fault, New Zealand, to a depth of 818 m below surface. Three feature sets are delineated. One set, comprising foliation and foliation‐parallel veins and fractures, has a constant orientation. The average dip direction of 145° is subparallel to the dip direction of the Alpine Fault, and the average dip magnitude of 60° is similar to nearby outcrop observations of foliation in the Alpine mylonites that occur immediately above the Alpine Fault. We suggest that this foliation orientation is similar to the Alpine Fault plane at ∼1 km depth in the Whataroa valley. The other two auxiliary feature sets are interpreted as joints based on their morphology and orientation. Subvertical joints with NW‐SE (137°) strike occurring dominantly above ∼500 m are interpreted as being formed during the exhumation and unloading of the Alpine Fault's hangingwall. Gently dipping joints, predominantly observed below ∼500 m, are interpreted as inherited hydrofractures exhumed from their depth of formation. These three fracture sets, combined with subsidiary brecciated fault zones, define the fluid pathways and anisotropic permeability directions. In addition, high topographic relief, which perturbs the stress tensor, likely enhances the slip potential and thus permeability of subvertical fractures below the ridges, and of gently dipping fractures below the valleys. Thus, DFDP‐2B borehole observations support the inference of a large zone of enhanced permeability in the hangingwall of the Alpine Fault.

High-relief topography of the Nima basin in central Tibetan Plateau during the mid-Cenozoic time

There remains inconsistence of uplift history of the Tibetan Plateau. Here, we estimated paleoelevation of mid-Cenozoic Nima basin located in central Tibet using multi proxies. They included meteoric water and vegetation isotope proxies based on hydrogen and carbon isotopic compositions (δD and δ13C), respectively, of terrestrial plant wax lipid of n‑alkanes and temperature proxy derived from microbial membrane lipid of branched glycerol dialkyl glycerol tetraethers (brGDGTs). Lipid analysis on sedimentary rocks in the Nima basin yielded −222 ± 12‰ and −30.0 ± 0.7‰ for δD and δ13C of n-C29 alkane, respectively, and brGDGT-derived mean annual air temperature (MAAT) of 21.5 ± 3.1 °C for the paleo basin. Using the sea-level meteoric water δ18O and Miocene Siwalik paleovegetation δ13C as low elevation references, values of δD and δ13C of n-C29 alkane in this study suggested paleoelevations of 4546 m and 2800 m, respectively. Whereas by using a subtropical sea surface temperature as a reference, brGDGT-derived MAATs suggested a paleoelevation of 893 m. We believed that the three estimates reflect a high-relief topography in the study basin during the mid-Cenozoic, representing elevations of orographic barrier of southerly oceanic moisture, basin catchment and basin lake level, respectively. This scenario implies a low elevation of the basin relative to the Lhasa Terrane located to the south during the mid-Cenozoic, hence challenging the classical crustal thickening models assuming a simple crustal thickening-uplift relationship.

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

AbstractFault 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.

COMPARISON AND ANALYSIS OF THE EFFECTIVE OBSERVATION AREA OF THE TENSOR CSAMT BY NUMERICAL MODELING

AbstractAccording to the response formulas of the scalar CSAMT (controlled source audio‐frequency magnetotelluric) method, its programs can be designed in several manners with different sources such as a vertical double dipole source and a three‐dipole source of varied geometries. Through numerical simulation, this study obtains the value distributions of X‐ and Y‐direction components of the resultant electromagnetic (EM) field, which permit to further analyze the effective observational area. The results show that the distribution of crosslike source exhibits scattered weak responses, representing a smaller effective observational zone. Meanwhile, its requirement to the terrain condition of the working site is very harsh, thus cannot work well in mountainous areas with high topographic relief. Based on the principle of the rotating three‐dipole device, we propose a new device composed of multiple dipole sources for the CSAMT which can facilitate integrated measurement of tensors of the EM field. Compared with the cross‐like source, this approach can realize measurement throughout the whole area without weak‐value zones. Moreover, this new device is easy to deploy in various terrains. The results of this study provide a technical basis for further engineering production of tensor measurement.

Discriminative Features Based on Two Layers Sparse Learning for Glacier Area Classification Using SAR Intensity Imagery

Accurate and instant information about changes of snow and glaciers covered areas plays a vital role in hydrological and climatological research and implications. Among all the observation methods, spaceborne remote sensing has a great advantage in monitoring the glaciers located in cold high-altitude regions and inaccessible areas on a large scale. Unlike optical sensors, the synthetic aperture radar (SAR) sensor can obtain images with low limitations in terms of weather phenomena and illumination as some glaciers frequently located in cloudy regions. In this paper, we propose a multiclasses classification method for large area glacier using spaceborne single-polarimetric SAR intensity image. The proposed method takes advantage of the discrimination ability of sparse representations of features, based on which a linear classifier called supervised neighborhood embedding is constructed. Finally, we develop a gradient descent method to alternatively update the dictionary and projection matrix. Two study areas are chosen to represent the discriminative characteristics of glaciers. In the Taku glacier in Alaska, compared to the state-of-the-art methods, our proposed method achieved a suitable performance with the overall classification accuracy of ${\text{90.34}}\%$ , and especially for bare ice of ${\text{91.38}}\%$ . In the Baltoro glacier in Karakoram characterized by high-relief topography and thick debris cover, the overall accuracy of ${\text{72.63}}\%$ and debris accuracy of $\text{90.14}\%$ are obtained.

An assessment of differences in gridded precipitation datasets in complex terrain

Hydrologic modeling and other geophysical applications are sensitive to precipitation forcing data quality, and there are known challenges in spatially distributing gauge-based precipitation over complex terrain. We conduct a comparison of six high-resolution, daily and monthly gridded precipitation datasets over the Western United States. We compare the long-term average spatial patterns, and interannual variability of water-year total precipitation, as well as multi-year trends in precipitation across the datasets. We find that the greatest absolute differences among datasets occur in high-elevation areas and in the maritime mountain ranges of the Western United States, while the greatest percent differences among datasets relative to annual total precipitation occur in arid and rain-shadowed areas. Differences between datasets in some high-elevation areas exceed 200mmyr−1 on average, and relative differences range from 5 to 60% across the Western United States. In areas of high topographic relief, true uncertainties and biases are likely higher than the differences among the datasets; we present evidence of this based on streamflow observations. Precipitation trends in the datasets differ in magnitude and sign at smaller scales, and are sensitive to how temporal inhomogeneities in the underlying precipitation gauge data are handled.

Climatic variability in Mfabeni peatlands (South Africa) since the late Pleistocene

It has been postulated that a bipolar seesaw interhemispheric mechanism dominated the relationship between the Northern and Southern hemisphere climates since the late Pleistocene. A key test for this proposition would be to undertake palaeoenvironmental studies on terrestrial archives in climatically sensitive regions. Southern Africa's contemporary C3 and C4 terrestrial plant distributions display a definitive geographical pattern dictated by different growing season rainfall and temperature zones; however, the region is generally archive poor due to its overall semi-arid climate and high relief topography. The Mfabeni peatland, with a basal age of c. 47 k yrs calibrated before present (kcal yr BP), is one of the oldest continuous coastal peat deposits in Southern Africa. Molecular leaf wax isotopes (δ13Cwax) were generated for a 810 cm long core, and combined with previously published bulk geochemical (δ13Cbulk, %TOC), palynological, and stratigraphic data, to reconstruct the late Pleistocene and Holocene palaeoenvironments. We interpreted environmental shifts associated with the Heinrich 4, Last Glacial Maximum, deglacial and Holocene periods, which are consistent with adjacent Indian Ocean sea surface temperature records. However, the other shorter climate perturbations during the Heinrich 5, 3, 2, 1, Antarctic cold reversal and Younger Dryas, were muted, most likely due to local hydrological overprinting on the Mfabeni record. A general anti-phase sequence was observed between the Mfabeni record and better established Northern Hemisphere events, underpinning the bipolar seesaw interhemispheric mechanism proposed for global climate forcing since the Late Pleistocene.

Late Jurassic - Early Cretaceous paleoenvironmental evolution of the Transbaikal basins (SE Siberia): implications for the Mongol-Okhotsk orogeny

The Late Jurassic - Early Cretaceous tectonic evolution of SE Siberia was marked by the closure of the Mongol-Okhotsk ocean. While this geodynamic event led to compressive deformation and denudation in a wide area encompassing the North-Altay, Sayan and Baikal Patom ranges, it was contemporaneous to widespread extension from the Transbaikal region situated immediately north of the suture zone to the Pacific plate, affecting eastern Mongolia and northeastern China. In this study we review the paleontological and sedimentological data available in the Russian literature and provide new macro-floral and palynological data from the Mesozoic sediments of three Transbaikal basins. These data are used to describe the paleoenvironmental and paleoclimatic evolution of the Transbaikal area in order to assess the topographic evolution of the region in relation with the closure of the Mongol-Okhotsk ocean. We establish that the Transbaikal basins evolved in a continuously extensional tectonic setting from at least the Early-Middle Jurassic to the Early Cretaceous. The associated sedimentary environments are characterized by retrogradation from alluvial fan–braided river dominated systems prevailing during the Early to Middle Jurassic initial opening of the basins to meandering river– lacustrine systems that developed during the Late Jurassic - Early Cretaceous interval. No evidence of high relief topography was found and we conclude that, while compression and denudation occurred in the North Altai, Sayan and Patom ranges, in the Transbaikal region, the docking of the Mongolia-North China continent to Siberia was a “soft collision” event, possibly involving a major strike-slip displacement that did not lead to an orogenic event implying strong compressive deformation, crustal thickening and topography building.

Analyzing rainfall-induced mass movements in Taiwan using the soil water index

This study applied the soil water index (SWI), which can represent the conceptual soil water contents as influenced by present and antecedent rainfall, for analyzing rainfall-induced mass movements in Taiwan. The SWI has been used in Japan for nationwide mass movement warnings. This study examined whether the SWI can be also applied to Taiwan, which has a climatic condition and high-relief topography similar to Japan. We used data for mass movements for 2006–2012 (n = 263) for the main analyses and those for 2013 (n = 19) for verification. The SWI values before the rainfall events that triggered mass movements were used as the indicator of the antecedent rainfall condition. We found that when SWI values before rainfall events increased from 35, the upper threshold of rainfall conditions needed for triggering mass movements significantly decreased. The mass movements in 2013 support this finding. We classified rainfall conditions for triggering mass movements into two types, short duration–high intensity (SH) and long duration–low intensity (LL), based on a principal component analysis (PCA). The SH type is associated with a rapid increase in SWI, and the LL type is associated with a gradual rise and subsequent constancy of SWI except in some extremely long rainfall events. Based on this result, we modeled the general trend of the time series changes in SWI for the two types, which was verified using the mass movements in 2013.