Rapid River Research Articles

Incision rate of the Yellow River in Northeastern Tibet constrained by 10 Be and 26 Al cosmogenic isotope dating of fluvial terraces: implications for catchment evolution and plateau building

Abstract Unlike other large rivers flowing out of Tibet, the Yellow River escapes from the plateau towards the NE crossing no less than five NW–SE striking, actively growing ranges and intervening basins. Thick Plio-Quaternary deposits and fluvial terraces testify to a phase of aggradation and sediment infill up to the average surface elevation (3200–3250 m a.s.l.) of the Gonghe, Guide and Qinghai Lake basins. A set of seven main terraces across the Gonghe Basin suggests progressive down-cutting of the Yellow River carving the 500 m deep Longyang gorge at the basin exit. 10 Be and 26 Al concentrations in quartz of surface and sub-surface samples of four terraces constrain the timing of incision by determining the burial age of the deposit and the exposure age of its surface. Modelling the depth dependence of the 10 Be concentration and the 26 Al/ 10 Be ratio allows us to constrain the onset of the ongoing phase of incision to 120–250 ka. These ages suggest long-term incision rates between 2–6 mm a −1 . Together with the present morphology of the Yellow River terraces across the Gonghe basin and the Longyang gorge, our results imply rapid river catchment evolution and interaction between river dynamics, tectonic and climate in northeastern Tibet.

The use of remote sensing products for environmental analysis in the South America (doi:10.4136/ambi-agua.160) (Portuguese)

The degradation of water resources has been detected and changes both institutional and in the legislation have been demanded. The careless use of rivers has ecological changes as direct consequence, causing serious modifications in the landscape and fluvial regime, besides altering the availability of habitats and the trophic composition of the aquatic environment. Pressed by this scenario, scientists have been developing assessment methods that are efficient both for the evaluation itself and for supporting decision taking in the environmental management processes. In this perspective, the objective of this study is to present the Rapid River Assessment Protocols (RAPs) and to emphasize how these protocols can promote the community participation in water resources monitoring. The RAPs can used to evaluate in an integrated form the characteristics of a river section according to the conservation or degradation condition of the fluvial environment and it is characterized by its economic viability and easy applicability. In regions with poor financial resources and serious problems of water quality, the RAPs can be used in environmental management programs. By using these protocols, the integration of the community in water resources monitoring generates data which represent the quality of fluvial ecosystems throughout time, without requesting high costs or specialized professionals. The RAPs in a simplified but not simplistic tool, which can be used in activities that aim at promoting a quick and reliable assessment of the “health” of a river.

Colonization to Aquifers and Adaptations to Subterranean Interstitial Life by a Water Beetle Clade (Noteridae) with Description of a NewPhreatodytesSpecies

Due to its tectonically uplifted, mountainous landscape and copious rainfall, the Japanese archipelago possesses plentiful, persistent groundwater in alluvial plains. However, Phreatodytes, an endemic water beetle genus found in groundwater, is now critically endangered due to the devastation of subterranean water ecosystems. Phreatodytes beetles were collected from driven wells near the Ooi River estuary in central Japan. The beetles were distinguished from all described species by their thoracic and genital morphologies, and described as a new species, Phreatodytes haibaraensis. The unique habitat of this species is the hyporheic zone of a gravelly riverbed in an estuary, and the habitat represents the eastern limit of the known distribution range of the genus. Molecular phylogenetic analysis based on mitochondrial and nuclear gene sequences revealed that Phreatodytes is a member of the Noteridae and forms a clade with Notomicrus. This suggests that the genus colonized the hyporheic zone from surface waters, and that it adapted to subterranean interstitial life by becoming minute and slender, by losing its eyes, pigmentation, as well as its ability to fly and swim, and by developing a permanent underwater life cycle, and erect hairlike setae on the thorax and elytra. In addition to the beetle, several stygobiontic species, including mollusks and fishes, were found in pumped groundwater. These results suggest that the gravelly riverbed of a rapid river estuary in Central Japan harbors biodiverse, locally differentiated hyporheic organisms comprising a unique subterranean interstitial ecosystem.

Diagnostic of ribeirão Mestre d’Armas sub-basin using two methods of rapid environmental assessment, Federal District, Central Brazil

Rapid environmental assessments have been used to describe the quality and semi-quantitative attributes of the ecosystems along an environmental gradient using visual observations and few measurements. The aim of this study was to identify and measure anthropogenic impacts on ribeirão Mestre d’Armas sub-basin, Federal District, Central Brazil, and to propose its environmental zoning. This study was performed using two methods based on rapid environmental assessment: a rapid river assessment protocol, to evaluate in an integrated form the features of a lotic system section according to the conservation or degradation condition of the fluvial environment; and the Leopold matrix, to identify and evaluate the anthropogenic impacts. The environmental zoning of this sub-basin detected three areas: preserved, transition and urban areas. The environmental assessment revealed, the preserved area had lotic stretches with natural features under low magnitude of impacts, except on burned areas. In the transition area, there was a predominance of lotic stretches with altered features, due to agriculture and livestock activities of intermediate level of impacts. Finally, the urban area had altered and impacted lotic stretches of higher magnitude due to anthropogenic impacts. Thus, this study revealed large differences among the areas detected by environmental zoning, according to the methods used. These methods were considered complementary in relation to environmental diagnostic of the ribeirão Mestre d’Armas sub-basin.

Regional incision of the eastern margin of the Tibetan Plateau

New (U-Th)/He analyses from three elevation transects collected within river gorges that dissect the eastern margin of the Tibetan Plateau provide constraints on the rates and timing of accelerated river incision into the high-elevation, low-relief topography of the region. Apatite He data from the easternmost transect (Dadu River), ∼120 km from the plateau margin adjacent to the Sichuan Basin, indicate that rapid river incision of ∼0.33 ± 0.04 km/m.y. began at ca. 10 Ma and has continued to the present. Apatite He and zircon He data from the middle transect (Yalong River), collected ∼225 km SSW of the Dadu data, indicate that rapid river incision of ∼0.34 ± 0.02 km/m.y. began prior to ca. 14 Ma and continued until the early Quaternary, when it increased, likely in response to local uplift and erosion associated with active faults nearby. Apatite He and zircon He data from the westernmost transect (Yangtze River), ∼210 km W of the Yalong data, indicate that rapid river incision of ∼0.38 ± 0.04 km/m.y. began at or prior to ca. 10 Ma, though likely not prior to ca. 15 Ma, and has continued to the present. The regional consistency of these data indicates that the entire eastern margin of the Tibetan Plateau was being dissected by 10 Ma and that incision has been relatively constant and uniform in the region since that time; this pattern is consistent with an erosional response to broad regional uplift at or before 10 Ma. The larger amount, and earlier onset, of exhumation observed in the Yalong River gorge shows that certain areas on the eastern margin deviate from a simple regional pattern of epeirogenic uplift and subsequent river incision and probably reflect the superposition of local upper-crustal deformation and uplift on the broad regional pattern.

In vitro hepatic metabolism of 2,2′,4,4′,5-pentabromodiphenyl ether (BDE 99) in Chinook Salmon ( Onchorhynchus tshawytscha)

Polybrominated diphenyl ethers (PBDEs) are brominated flame retardants that persist in the environment and are present in geographically widespread fish species. PBDE concentrations can be particularly high in resident Chinook salmon ( Onchorhynchus tshawytscha) in the Puget Sound, Washington. Although PBDE residues in salmon and other fish are often dominated by lower brominated congeners, these congeners are not produced commercially in the greatest quantity, suggesting bioaccumulation of the lower molecular weight PBDEs or debromination of more fully brominated congeners. We determined the capacity of Chinook liver fractions to debrominate 2,2′,4,4′,5-pentabromodiphenyl ether (BDE 99), a model PBDE congener readily debrominated by common carp ( Cyprinus caprio). Liver subcellular fractions from two strains of Chinook were incubated with BDE 99 prior to liquid/liquid extraction followed by gas chromatography/mass spectrometry analysis (GC/MS analysis) to identify metabolites and debromination products. In contrast to common carp, debromination of BDE 99 to BDE 47 (2,2′,4,4′-tetrabromodiphenyl ether) was not observed in microsomal fractions from either strain of Chinook salmon. However, Chinook salmon liver microsomes from both Chinook strains slowly debrominated BDE 99 to BDE 49 (2,2′,4,5′-tetrabromodiphenyl ether), a unique debromination product whose formation has not been reported in other fish. Three-year-old males belonging to a Rapid River Spring Chinook salmon genetic strain showed a somewhat greater microsomal debromination capacity than older hatchery returning male Chinook, but were still inefficient in the debromination of BDE 99 relative to carp. Microsomal debromination of BDE 99 to BDE 49 was not NADPH-dependent, indicating a lack of cytochrome P450 involvement. By contrast, omission of the reductant dithiothreitol (DTT) from Chinook microsomal preparations resulted in a lack of BDE 99 debromination, suggesting the involvement of a microsomal reductase(s) or deiodinase (DI). Cytosolic fractions from Chinook salmon and Common carp debrominated BDE 99 to BDE 49 in vitro. However, carp cytosolic enzymes preferentially formed BDE 47. In summary, our data indicate significant differences among teleosts with respect to efficiency and metabolite profiles of BDE 99 debromination, and suggest that the high concentrations of BDE 47 in resident Chinook salmon from the Puget Sound are not a result of hepatic metabolism of BDE 99. The results of our study also suggest the involvement of an unidentified hepatic reductase or DI in PBDE debromination in fish.

Summer Movements of Sub-Adult Brook Trout, Landlocked Atlantic Salmon, and Smallmouth Bass in the Rapid River, Maine

ABSTRACT Summer movement patterns and spatial overlap of native sub-adult brook trout (Salvelinus fontinalis), non-native landlocked Atlantic salmon (Salmo salar), and non-native smallmouth bass (Micropterus dolomieu) in the Rapid River, Maine, were investigated with radio telemetry in 2005. Fishes were captured by angling, surgically implanted with radio transmitters, and tracked actively from June through September. Most brook trout (96%) and landlocked salmon (72%) displayed long distance movements (>1 km) to open water bodies (28 June to 4 July) followed by periods of time spent in presumed thermal refigia (5 July to 16 September). Summer water temperature rose above 25 °C, near the reported lethal limits for these coldwater species. In contrast, the majority of smallmouth bass (68%), a warrnwater species, did not make long distance movements from areas of initial capture, remaining in mainstem sections of the river (28 June to 16 September). Spatial overlap of smallmouth bass and brook trout in the summer is unlikely because brook trout presumably move to thermal rehgia during this time. However, interspecific competition between brook trout and landlocked salmon may occur since they select similar habitats June through September.

Quantification of the transient response to base‐level fall in a small mountain catchment: Sierra Nevada, southern Spain

We integrated optically stimulated luminescence dating and 10Be cosmogenic nuclide measurements to quantify short‐to‐medium‐term (102–104 years) catchment dynamics and response to active tectonics. In the 27 km2 Río Torrente catchment, Sierra Nevada, southern Spain, rapid base‐level fall has triggered knickpoint migration up both trunk and tributary channels, resulting in two distinct geomorphic zones: (1) a steep lower catchment with concordant rates of hillslope erosion and channel incision over both short (100 years: 5–8 mm yr−1) and medium (12 ka: 5 ± 1 mm yr−1) timescales and (2) a low‐relief soil‐mantled upland topography with uniformly low bedrock and hillslope erosion rates (0.05 ± 0.02 mm yr−1). The uniformity of erosion in this upland surface indicates that catchment topography was previously in steady state. Rapid river incision below the channel knickpoints has resulted in the development of steep landslide‐dominated hillslopes that are essentially “tracking” the incising channel. The magnitude of base‐level fall required to generate these steep hillslopes is >100 m; at least 50 m of this base‐level fall occurred during the past ∼21 ka. These steep hillslopes are eroding back into the low‐angled upland surface at a much slower rate than the channel knickpoint. Consequently, the trunk channel knickpoint has already reached the catchment headwaters while hillslopes continue to adjust to the new base level, indicating that the channel profile will regain equilibrium form long before hillslopes. Thus hillslopes are the limiting factor for the duration of landscape transience in this small mountain catchment.

Tectonic denudation and topographic development in the Spanish Sierra Nevada

The denudation history of the rapidly uplifting western part of the Spanish Sierra Nevada was assessed using apatite fission track (AFT) ages and 10Be analyses of bedrock and fluvial sediments. Major contrasts in the denudation history are recorded within the 27 km2 Río Torrente catchment. Upland areas are characterized by low‐relief, low slope angles, and locally the preservation of shallow marine sediments, which have experienced <200 m of erosion in the last 9 Myr. However, AFT age determinations from samples collected close to the marine sediments imply >2 km of denudation since circa 4 Ma. The minimum denudation rates of 0.4 mm yr−1 derived from AFT also contrast with the slow medium‐term (104 years) erosion rates (0.044 ± 0.015 mm yr−1) estimated from 10Be measurements at high elevations. The local medium‐long‐term contrasts in denudation rates within the high Sierra Nevada indicate that much of the unroofing occurs by tectonic denudation on flat‐lying detachments. In lower elevation parts of the catchment, rapid river incision coupled to rock uplift has produced ∼1.6 km of relief, implying that the rivers and adjacent hillslopes close to the edge of the orogen are sensitive to normal‐fault‐driven changes in base level. However, these changes are not transmitted into the low‐relief slowly eroding upland areas. Thus the core of the mountain range continues to increase in elevation until the limits of crustal strength are reached and denudation is initiated along planes of structural weakness. We propose that this form of tectonic denudation provides an effective limit to relief in young orogens.

TEMPORAL DYNAMICS OF ANTAGONISM AND MUTUALISM IN A GEOGRAPHICALLY VARIABLE PLANT–INSECT INTERACTION

Variation among sites and years in the local ecological outcome of interspecific interactions can generate a geographic mosaic of coevolution, as indicated by recent mathematical models. We evaluated whether local temporal dynamics of ecological outcome in the interaction between the moth Greya politella (Prodoxidae) and its host plant Lithophragma parviflorum (Saxifragaceae) are likely to mitigate or magnify geographic differences in ecological outcome found in earlier studies. The moths are highly host-specific pollinating floral parasites, and the mutualism can be swamped in some populations by the presence of effective co-pollinators. Hence, differing community contexts can shift the outcome of the interaction from mutualism to commensalism or antagonism. During each of four years, we evaluated the effect of Greya oviposition on seed development through a paired design that controlled for plant genotype and microenvironment. At Turnbull National Wildlife Refuge in Washington State, the interaction was significantly mutualistic in all four years. Mutualism in this population was indicated by a higher probability of development of capsules visited by ovipositing Greya than capsules not visited by Greya on the same plant. At Rapid River, Idaho, the interaction was commensalistic in three years and antagonistic in one year. Antagonism in this population was indicated by selective withering of capsules containing Greya eggs. Overall, the results suggest stable geographic differences in the range of ecological outcomes in this plant-insect interaction under different community contexts.

Late Cenozoic uplift of southeastern Tibet

Research Article| June 01, 2005 Late Cenozoic uplift of southeastern Tibet M.K. Clark; M.K. Clark 1Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar M.A. House; M.A. House 2Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA Search for other works by this author on: GSW Google Scholar L.H. Royden; L.H. Royden 3Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar K.X Whipple; K.X Whipple 3Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar B.C. Burchfiel; B.C. Burchfiel 3Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar X. Zhang; X. Zhang 4Chengdu Institute of Geology and Mineral Resources, Chengdu, Sichuan Province, People's Republic of China Search for other works by this author on: GSW Google Scholar W. Tang W. Tang 4Chengdu Institute of Geology and Mineral Resources, Chengdu, Sichuan Province, People's Republic of China Search for other works by this author on: GSW Google Scholar Author and Article Information M.K. Clark 1Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA M.A. House 2Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA L.H. Royden 3Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA K.X Whipple 3Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA B.C. Burchfiel 3Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA X. Zhang 4Chengdu Institute of Geology and Mineral Resources, Chengdu, Sichuan Province, People's Republic of China W. Tang 4Chengdu Institute of Geology and Mineral Resources, Chengdu, Sichuan Province, People's Republic of China Publisher: Geological Society of America Received: 08 Oct 2004 Revision Received: 28 Jan 2005 Accepted: 05 Feb 2005 First Online: 03 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 The Geological Society of America, Inc. Geology (2005) 33 (6): 525–528. https://doi.org/10.1130/G21265.1 Article history Received: 08 Oct 2004 Revision Received: 28 Jan 2005 Accepted: 05 Feb 2005 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation M.K. Clark, M.A. House, L.H. Royden, K.X Whipple, B.C. Burchfiel, X. Zhang, W. Tang; Late Cenozoic uplift of southeastern Tibet. Geology 2005;; 33 (6): 525–528. doi: https://doi.org/10.1130/G21265.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The age of surface uplift in southeastern Tibet is currently unknown, but the initiation of major river incision can be used as a proxy for the timing of initial uplift. The topographically high eastern plateau and gently dipping southeastern plateau margin are mantled by an elevated, low-relief relict landscape that formed at a time of slow erosion at low elevation and low tectonic uplift rates prior to uplift of the eastern Tibetan Plateau. Thermochronology from deep river gorges that are cut into the relict landscape shows slow cooling between ca. 100 and ca. 10–20 Ma and a change to rapid cooling after ca. 13 Ma with initiation of rapid river incision at 0.25–0.5 mm/yr between 9 and 13 Ma. A rapid increase in mean elevation of eastern Tibet beginning at this time supports tectonic-climate models that correlate the lateral (eastern) expansion of high topography in Tibet with the late Miocene intensification of the Indian and east Asian monsoons. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Tectonic control of the Tejo river fluvial incision during the late Cenozoic, in Ródão—central Portugal (Atlantic Iberian border)

Staircases of strath terraces and strongly incised valleys are the most typical landscape features of Portuguese rivers. This paper examines the incision achieved during the late Cenozoic in an area crossed by the Tejo river between the border with Spain and the small town of Gavião. In the more upstream reach of this area, the Tejo crosses the Ródão tectonic depression, where four levels of terraces are distinguished. During the late Cenozoic fluvial incision stage, the Ródão depression underwent less uplift than the adjacent areas along the river. This is reflected by the greater thicknesses and spatial extent of the terraces; terrace genesis was promoted by impoundment of alluvium behind a quartzitic ridge and the local presence of a soft substratum. Outside this tectonic depression, the Tejo has a narrow valley incised in the Hercynian basement, with some straight reaches that probably correspond to NE–SW and NNW–SSE faults, the terraces being nearly absent. Geomorphological evidence of tectonic displacements affecting the Ródão dissected terrace remnants is described. Geochronological dating of the two younger and lower terrace levels of this depression suggests a time-averaged incision rate for the Tejo in the Ródão area, of ca. 1.0 m/ka over the last 60 thousand years. A clear discrepancy exists between this rate and the 0.1 m/ka estimated for the longer period since the end of the Pliocene. Although episodes of valley incision may be conditioned by climate and base-level changes, they may also have been controlled by local factors such as movement of small fault-bounded blocks, lithology and structure. Regional crustal uplift is considered to be the main control of the episodes of valley incision identified for this large, long-lived river. A model is proposed in which successive regional uplift events—tectonic phases—essentially determined the long periods of rapid river downcutting that were punctuated by short periods of lateral erosion and later by some aggradation, producing strath terraces.

Gymnostoma tasmanianum sp. nov., a Fossil Casuarinaceae from the Early Oligocene of Little Rapid River, Tasmania, Australia

Macrofossils of Casuarinaceae from Early Oligocene sediments at Little Rapid River, Tasmania, are assigned to a new species, Gymnostoma tasmanianum. This is only the second species of fossil Gymnostoma to be formally described and the first species of Gymnostoma to be described from Tasmania. The species is known from both vegetative and reproductive organs. The new taxon is distinguished from other known species by its small stomata, short article length and tooth width, small length:width ratio of articles, glabrous articles, stomata in two to five rows, and teeth elongate with acute apices and sinuses. The fossil record shows that Gymnostoma once had a much wider distribution in Australia than its current occurrence in far north Queensland.

Nothofagus kiandrensis (Nothofagaceae subgenus Brassospora), a new macrofossil leaf species from Miocene sediments at Kiandra, New South Wales

Nothofagus subgenus Brassospora is now confined to New Guinea and New Caledonia. Despite an impressive and highly diverse south-eastern Australian fossil pollen record for the subgenus (from Eocene, Oligocene and Miocene sediments), macrofossil finds have been rare and restricted to Tasmanian sites. Until now, only two subgenus Brassospora leaf species, N. serrata and N. mucronata (Early Oligocene, Little Rapid River, Tasmania) have been described. Nothofagus kiandrensis, from Early Miocene sediments at Kiandra NSW, is the first reported leaf species of subgenus Brassospora from mainland Australia.

Denudational history along a transect across the Drakensberg Escarpment of southern Africa derived from apatite fission track thermochronology

The denudational history of a ∼500 km long transect across the Drakensberg Escarpment on the high‐elevation passive margin of SE Africa is quantified on the basis of thermal history modeling of apatite fission track data for 15 deep borehole samples, supplemented by an additional 10 outcrop samples. A minimum of 4.5 km of denudation since formation of the margin ∼130 Myr ago is estimated for the coastal zone, with a marked Early Cretaceous episode of accelerated denudation broadly coincident with continental breakup. Samples from the Swartberg borehole (SW 1/67) located ∼30 km seaward of the present position of the Drakensberg Escarpment indicate a total depth of denudation of 3.1 ± 1.2 km since ∼91 Myr, with a phase of accelerated denudation of 2.1 ± 0.9 km at a mean rate of 95 ± 43 m/Myr between ∼91 and 69 Myr. Samples from the Ladybrand borehole (LA 1/68) west of the Lesotho Highlands indicate 1.7 ± 0.5 km of denudation since ∼78 Myr, with a phase of accelerated denudation at 82 ± 43 m/Myr from ∼78 to 64 Myr. Average denudation rates declined to about 10 m/Myr during much of the Tertiary. Although the apatite fission track data do not provide any direct constraints on the denudational history of the Lesotho Highlands, interpolation between the two boreholes, constrained by geological evidence and extrapolated in situ‐produced cosmogenic 36Cl‐derived denudation rate estimates, suggests a pattern of denudation compatible with numerical modeling studies of escarpment evolution involving rapid river incision seaward of a preexisting inland drainage divide. These patterns of denudation are incompatible with constant retreat of the Drakensberg Escarpment from an initial position near the present coast. We suggest that the Drakensberg Escarpment formed by rapid post‐breakup river incision seaward of a preexisting drainage divide located just east of the present escarpment location and became pinned at this divide with subsequent retreat rates of only 100–200 m/Myr.

Geomorphic change in high mountains: a western Himalayan perspective

Globally significant interactions between climate, surface processes, and tectonics have recently been proposed to explain climate change and mountain building. Assessing climate-driven erosion processes and geomorphic change in high-mountain environments, however, is notoriously difficult. In the western Himalaya, the coupling of climate, surface processes, and tectonics results in complex topography that frequently records the polygenetic nature of topographic evolution over the last ∼100 ka. Depending upon the erosional history of a particular landscape, temporal overprinting of geomorphic events can produce unique topographic properties which define the spatial complexity of the topography. Field work coupled with analysis of the topography using digital elevation models (DEMs) enable low- and high-frequency spatial patterns and scale-dependent properties of the topography to be detected and associated with geomorphic events caused by climate and tectonic forcing. We conducted spatial analysis of the topography at Nanga Parbat in northern Pakistan to demonstrate the utility of geomorphometry and to characterize dramatic geomorphic change over the past 100 ka. Results indicate rapid river incision, extensive glaciation, and variable denudation rates by mass movement, glaciation, and catastrophic flood flushing. Furthermore, topographic and chronologic evidence indicate that glaciation is strongly controlled by the southwestern monsoon, and that modern fluvial systems are still responding to tectonic forcing and deglaciation. Scale-dependent analysis of the topography revealed that different erosion processes uniquely alter the spatial complexity of the topography, such that the greatest mesoscale relief appears to be caused by glaciation. Collectively, our results indicate that topographic development in the western Himalaya is inherently polygenetic in nature, with glaciation, fluvial and slope processes all playing important roles at different times, and that they can do so sequentially on the same portion of the landscape. Given the rapidity of major changes in climate and glaciation over the last ∼100 ka, the landscape cannot be in steady-state.

The impact of episodic fault‐related folding on late Holocene degradation terraces along Waipara River, New Zealand

The Waipara River flows eastwards through growing folds in the tectonically active foothills of New Zealand's Southern Alps. In the middle Waipara region, flights of degradation terraces are widespread and rise to 55 m above river channels. Ages of terrace surfaces and paleoearthquakes on four faults are constrained by radiocarbon samples and weathering‐rind dates from surface cobbles of Torl esse Group sandstone. Terrace ages indicate rapid incision (c. 30–100 mm/yr) of Waipara River and three tributaries during the late Holocene. Cumulative‐incision curves suggest a 15–25 m lowering of regional base level over the last thousand years and an additional 20–25 m of local incision 200–600 yr BP along Waipara River where it crosses Doctors Anticline. Rapid river incision was strongly influenced by rock uplift on the anticline associated with fault rupture during an earthquake 300–400 yr BP. From incision data we infer that the earthquake was preceded and followed by aseismic fold growth. Tectonic uplift during folding was probably, at most, one‐third of local river incision; this discrepancy may relate to the short sample period and to locally elevated stream erosive power due in part to a reduction in floodplain width.

Laboratory experiments with an FM-CW reflectometry system proposed for detecting and monitoring bridge scour in real time

Thousands of bridges throughout the United States have been identified as being scour critical (i.e., susceptible to failure from pier and (or) abutment scour). Scour occurs during times of rapid river flow when sediments, including rocks, gravel, and silt, are transported by the currents, undermining bridge pier foundations and similar structures. It can be increased by the presence of an ice cover. The scour process is dynamic; erosion and deposition can occur during the same high-energy river event, so the worst-case and the net effect cannot be easily predicted or dynamically monitored using previously available equipment. Herein, a technique and system (U.S. Patent #5,790,471) employing frequency modulated - continuous wave (FM-CW) reflectometry are discussed. This system is proposed for continuous monitoring of the extent of scour around riverine structures. A bench scale version of the system with a 490-MHz linearly swept bandwidth was implemented and tested in the laboratory, where sediments were incrementally added to a water-filled plastic barrel containing an 86-cm-long scour probe. Reflectometer data were taken after each increment of sediment was added. The data indicating the sediment boundary were plotted in a waterfall format that clearly shows the progressive sedimentation. This system has the potential for continuous round-the-clock operation and accuracy to within 5 cm of sediment depth. Key words: reflectometry, real-time monitoring, frequency modulated continuous wave, scour, sediment transport.

Eucryphia (Cunoniaceae) reproductive and leaf macrofossils from Australian cainozoic sediments

The first fossil capsule of Eucryphia,E. reticulata R.W.Barnes & G.J.Jord. sp. nov.,is described from Lea River (Early Oligocene), and, like capsules of the twoextant South American species of E. glutinosa (Poepp. etEndl.) Baill. and E. cordifolia Cav., is large and has arelatively large number of valves. The capsule occurs with aEucryphia leaf macrofossil that was probably a leaflet from a compound leaf as it is highly falcate. The leaflet may be derived fromthe same parent plant as E. reticulata but in theabsence of an organic connection it is described as a new species,E. leaensis R.W.Barnes & G.J.Jord. sp. nov.Additional leaf macrofossil specimens of E. aberensisR.S.Hill from the type locality (Loch Aber; Middle–Late Eocene) and anew locality record for the species, Little Rapid River (Early Oligocene),indicate that the species had compound leaves formed by serrate and entiremargin leaflets. Another incomplete Eucryphia capsuleoccurs at Little Rapid River (Early Oligocene) but it is too poorly preservedto assign it to an extant or extinct species. It may be derived from the sameparent plant asE. aberensis, with which it occurs, but cannot be confirmed as there is no organic connection. A new leaf macrofossil with serrate margins, E. mucronata R.W.Barnes & G.J.Jord. sp. nov., is also described from ?Latest Eocene–EarlyOligocene sediments at Wilson’s Creek, central Tasmania. Leafmacrofossils previously assigned to E. aff.milliganii from Early Pleistocene sediments at RegattaPoint in western Tasmania are shown to be conspecific with the two extant Tasmanian species, E. lucida (Labill.) Baill. andE. milliganii Hook.f. ssp.milliganii on the basis of foliar hair distribution patterns and density. The oldest fossil Eucryphiaspecies, E. falcata R.S. Hill (Lake Bungarby; LatePaleocene), had compound leaves formed by leaflets with serrate margins, whichis possibly the plesiomorphic condition for all Cunoniaceae genera. WithinEucryphia, there has been an evolutionary trend towardssimple leaves with entire margins and well-developed peltiform cuticular extensions.

Laboratory Investigation of Time-Domain Reflectometry System for Monitoring Bridge Scour

Bridge scour is a severe problem that costs millions of dollars of damage to infrastructure annually and causes occasional loss of life. Scour occurs during times of rapid river flow and can be increased by icing conditions when sediments, including rocks, gravel, and silt, are transported by the currents, undermining bridge pier and abutment foundations and other structures. Scour is dynamic; during a single high-flow event, scour may occur during rising stages and near the peak. Deposition of sediments into the scoured area may occur during falling stages and during low flow. The worst case and the net effect cannot be easily predicted. Monitoring scour is difficult, and existing instruments have limitations that prevent their use in some situations. A technique and system employing time-domain reflectometry can be used to constantly monitor the extent of scour around riverine structures. This system is capable of continuous round-the-clock operation and can indicate changes in sediment depth of less then 5 cm.