River Canyon Research Articles

The Wind-Swept Nautilus, Enigmatic Clastic Pipes, and Toadstool Landforms: Geologic Features of the Paria Plateau

The Colorado Plateau occupies much of the southwestern United States including portions of Arizona, Colorado, Utah, and New Mexico. This region presents unobstructed views from mesa tops, beautifully colored soils, lone standing buttes, and canyons cut thousands of feet deep. The Colorado Plateau represents a well-preserved window into the Earth’s history. Today, the rocks of the Colorado Plateau lie roughly horizontally, as they were deposited hundreds of millions of years ago. The Plateau’s rise has motivated rivers, in their downhill progress, to carve innumerable canyons. These river canyons allow any nature-lover the opportunity to gaze at 100s of millions of years of geologic history. Within the larger Colorado Plateau, the Paria Plateau straddles the Utah and Arizona borders, and includes the Vermilion Cliff s National Monument, the Paria Canyon-Vermilion Cliffs Wilderness Area, and the southern extent of the Grand Staircase Escalante National Monument (GSENM; pre-2018 boundaries). The Paria Plateau is best known for spectacularly colored, wind-sculpted features such as Coyote Buttes and “The Wave,” where vivid colors accent cross-strata resembling a cresting ocean wave. The Plateau is also recognized for the geologically notable Vermilion Cliff s, Buckskin Gulch slot canyon, White Pocket area, and the Paria River Canyon. Although only two, dual-lane highways circumvent the plateau, several wash-boarded gravel and deeply mud-rutted roads allow access to its interior. From these dirt roads, a few sandy, four-wheel drive paths diminish as they extend and branch into the plateau’s interior. Overall, the Paria Plateau is a relatively quiet and little-visited wilderness.

Recent tectonic activity along the Bucaramanga Fault System (Chicamocha River Canyon, Eastern Cordillera of Colombia): a geomorphological approach

Recent tectonic activity along the Bucaramanga Fault System (Chicamocha River Canyon, Eastern Cordillera of Colombia): a geomorphological approach

Orogenic link ∼41°N–46°N: Collisional mountain building and basin closure in the Cordillera of western North America

AbstractPolyphase structural mapping and mineral age dating across the Salmon River suture zone in west-central Idaho (Riggins region; ∼45°30′N, ∼117°W–116°W) support a late Mesozoic history of penetrative deformation, dynamothermal metamorphism, and intermittent magmatism in response to right-oblique oceanic-continental plate convergence (Farallon–North America). High-strain linear-planar tectonite fabrics are recorded along an unbroken ∼48 km west-to-east transect extending from the Snake River (Wallowa intra-oceanic arc terrane; eastern Blue Mountains Province) over the northern Seven Devils Mountains into the lower Salmon River Canyon (ancestral North America; western Laurentia). Given the temporally overlapping nature (ca. 145–90 Ma) of east-west contraction in the Sevier fold-and-thrust belt (northern Utah–southeast Idaho–southwest Montana segment), we propose that long-term terrane accretion and margin-parallel northward translation in the Cordilleran hinterland (∼41°N–46°N latitude; modern coordinates) drove mid- to upper-crustal shortening >250 km eastward into the foreland region (∼115°W–113°W). During accretion and translation, the progressive transfer of arc assemblages from subducting (Farallon) to structurally overriding (North American) plates was accommodated by displacement along a shallow westward-dipping basal décollement system underlying the Cordilleran orogen. In this context, large-magnitude horizontal shortening of passive continental margin strata was balanced by the addition of buoyant oceanic crust—late Paleozoic to Mesozoic Blue Mountains Province—to the leading edge of western Laurentia. Consistent with orogenic float modeling (mass conservation, balance, and displacement compatibility), diffuse dextral-transpressional deformation across the accretionary boundary (Salmon River suture: Cordilleran hinterland) was kinematically linked to eastward-propagating structures on the continental interior (Sevier thrust belt; Cordilleran foreland). As an alternative to noncollisional convergent margin orogenesis, we propose a collision-related tectonic origin and contractional evolution for central portions of the Sevier belt. Our timing of terrane accretion supports correlation of the Wallowa terrane with Wrangellia (composite arc/plateau assemblage) and implies diachronous south-to-north suturing and basin closure between Idaho and Alaska.

Thermochronologic and geomorphometric constraints on the Cenozoic landscape evolution of the Northern Andes: Northwestern Central Cordillera, Colombia

New geochronologic, thermochronologic, and geomorphometric landscape analyses were performed to discriminate the relationships between tectonics and geomorphology in the northwestern portion of the Central Cordillera, Northern Andes (Colombia). This segment of the Andean belt includes two contrasting geomorphic domains, namely the Antioqueño Plateau (AP) and the Cauca River Canyon (CRC). At present, these domains are connected fluvially by the San Andrés River Catchment (SARC) and disrupted structurally by the Espíritu Santo Fault (ESF). Zircon U/Pb ages indicate Triassic metamorphism and Late Cretaceous magmatism, suggesting the absence of major Cenozoic thermal events related to magmato-metamorphism that could affect low-temperature thermochronology datasets. New (U-Th)/He data were collected along vertical profiles and modeled numerically using HeFTy® and Age2Edot® software. The modeling results suggest a continuum rapid cooling event during the Paleocene- Eocene associated with erosional exhumation. Erosion rates derived from relationships between zircon (U-Th)/He ages and elevation, are approximately 0.2–0.6km/Ma and therefore slightly lower than estimates derived from inverse thermal modeling (ca. 0.6–0.9km/Ma), Differences between observed and estimated exhumation rates could be due to differential surface uplift and reactivation of the ESF. Such reactivation produced systematically younger (U-Th)/He ages near faulted, popped-up blocks, suggesting active deformation since the Oligocene–Early Miocene. Geomorphometric parameterization, applied to both the AP and the CRC, suggests a complex mixture of processes such as differential surface uplift, landscape rejuvenation, relief inversion, preservation of relict landscapes, and reorganization of the fluvial system. Our investigation documents: i) a phase of rapid exhumation during the Late Paleocene-Eocene that favored posterior development of low relief surfaces; ii) post-Eocene ESF reactivation, differential uplift, and relict landscape preservation on the AP; and iii) post-Oligocene landscape rejuvenation and fluvial capture of the SARC by upward progression of the erosional wave-front through the CRC.

Concepts of geoparks establishment in Bulgaria and their geothermal resources

Bulgaria is the third country in the world by number of mineral springs after Japan and Iceland. The Bulgarian-Russian collaboration in geological, environmental and landscape conservation provided a new development of the methodology for identification, evaluation and characterization of geodiversity including their geotermal resources. Individual approach to the concepts of the national geoparks stressed on their scientific and geodiversity features, environmental conditions and economic premises by defining one major geopark theme and many minor topics. Regardless of their radically different themes, the geothermal activity in geoparks is the common feature, which provides them with a great balneological potential. The concept of Geopark “Iskar Canyon” is based on the remarkable geodiversity of the Iskar River Canyon with a number of wonderful landscapes and scenic outcrops of various rock types ranging from Precambrian to Quaternary. The concept of Geopark “Belogradchik Rocks” lies on the famous Lower Triassic sandstone pinnacles. Geopark “Rila” is based on its remarkable glacial landscapes - glacier valleys, cirques, moraines, arêtes and horns. The major theme of Geopark “Burgas Lakes” is related with the ancient sea-level changes and balneo-healing properties of their humus mud. The unifying theme of these geoparks is the high spa potential of their thermal springs that have been used since the Roman Age.

<p><strong><em>Agave garciaruizii</em></strong><strong> (Asparagaceae) a new species from the Chorros del Varal State Reserve in western Mexico</strong></p>

A new species named Agave garciaruizii is described and illustrated here. A. garciaruizii is endemic to tropical dry forest in the Itzícuaro and Apupátaro river canyons in the Chorros del Varal State Reserve, at the southern border of the states of Jalisco and Michoacán, México. It belongs to the subgenus Littaea and to the Marginatae species group and is morphologically related to A. angustiarum and A. impressa, but differs from these species in some features of leaves, inflorescences and infructescences. Its conservation status was assessed as Endangered (EN). Additionally, morphological evidence was provided in support of A. arcedianoensis as a species distinct from A. angustiarum. A key to morphologically and geographically closely related species in the Marginatae group is presented.

Along-strike segmentation of the South China Sea margin imposed by inherited pre-rift basement structures

Multibeam bathymetric, seismic and borehole data are used to investigate a large-scale strike-slip structure, the Baiyun-Liwan Fault Zone, in the northern South China Sea. This fault zone comprises NW- to NE-striking faults and negative flower structures that were generated by oblique extensional displacement. Notably, the interpreted data reveals that the Baiyun-Liwan Fault Zone was active during the Cenozoic, recording intense magmatism, and accommodating significant intraplate deformation during progressive continental rifting and ocean spreading. It bounds two distinct crustal segments and played a significant role in segmenting the northern margin of the South China Sea. The geometry of faults and strata within the Baiyun-Liwan Fault Zone also controlled local sediment routing and depocentre evolution during the Cenozoic. As basement and syn-rift structures change markedly across the Baiyun-Liwan Fault Zone, we propose this structure to be inherited from a lithospheric-scale fault zone separating the Mesozoic arc from forearc-related terrains. We therefore stress the importance of pre-existing structures in the development of rifted margins, with the example provided by the Baiyun-Liwan Fault Zone having profound implications for palaeogeographic reconstructions in the South China Sea. At present, the Baiyun-Liwan Fault Zone is incised by the Pearl River Canyon and eroded by recurrent submarine landslides, forming a major area of sediment bypass towards the abyssal plain.

Research note: Quick assessment of recreation use and experience in the immediate aftermath of wildfire in a desert river canyon

There is limited research on recreationists’ responses to changes in resource conditions after wildfire. Existing studies often rely on presenting visitors with hypothetical wildfire scenarios or simulated changes in conditions. We completed a quick assessment of recreation visitation and visitor experience in the months immediately following an actual high-severity wildfire within a popular river canyon in Oregon, USA. We also explored the influence of wildfire on the recreation plans of campers. We found that recreation use dropped sharply in the immediate aftermath of the wildfire, but rebounded to long-term averages within months. In addition, visitors reported the burned landscape had little influence on their recreation experience. Forty-five percent of campers reported having changed a planned camping trip within the prior two years because of smoke or wildfire. Nearly half of respondents reported that potential for wildfire would be a factor in where they planned to camp in the future. Management implicationsOur findings are consistent with other studies in showing that visitation losses do happen after wildfire but are short-lived and may differ between day and overnight users.· Although visitors were often saddened to see the burned landscape, their recreation experiences and satisfaction appeared largely unchanged.· Distributing up-to-date information about conditions at recreation destinations may be useful for potential visitors concerned about smoke and wildfire.· Recreationists substitute between recreation destinations or seasons to avid wildfire or smoke. Managers may do well to prepare for receiving visitors displaced by wildfire or smoke and having more visitors outside primary recreation seasons

Geology and zircon U-Pb geochronology of the Mtkvari pyroclastic flow and evaluation of destructive processes affecting Vardzia rock-cut city, Georgia

Late Cenozoic subaerial volcanic highland crop out in Eastern Anatolia and the western part of the Lesser Caucasus, part of which, located in Georgia, is known as Samtskhe-Javakheti. The Samtskhe-Javakheti highland (∼4500 km2) is cut by the Mtkvari river canyon, where, into the thick pyroclastic flow in twelfth-century is hewn the unique city Vardzia. Despite this, characteristics of the pyroclastic flow, such as scale, source, type, genesis, isotopic age and evaluation of destructive geological processes of the Vardzia rock-cut city have not been well studied. Our research has shown that the Mtkvari pyroclastic flow is exposed at a distance of about 35 km from the Karzameti fortress to the Khertvisi fortress, it is inclined northward by 2-4°, and its thickness increases to the north from 40 m up to 80 m. These rocks represent welded, weakly welded and non-welded ignimbrites of the andesitic-dacitic composition. Isotopic parameters of these rocks (ɛNd varies between +3 and + 4, and 87Sr/88Sr between 0,70341 and 0.70450) indicate that they originated as a result of fractionation of mantle derived melts. As a result of field work, we interpret the Mtkvari ignimbrites as products of megacaldera collapse (modern Niala fields), which nowadays is filled by postcaldera domes of andesitic composition and Quaternary sediments. The result of zircon dating using the U-Pb method with LA-ICP-MS technology is 7.52 ± 0.21 Ma, which corresponds to the Late Miocene epoch. Geological research of the Vardzia rock-cut city has revealed that it is hewn into weakly welded ignimbrites and for which reason these rocks are under the intensive affecting of weathering and erosion processes. At the same time, the city is completely included in a tectonic block of 900 m length which is detached from the main body of rocks and is gradually subsiding towards the Mtkvari canyon. Nowadays Vardzia block is lowered by 30.6 m in comparison with bordering blocks. In addition, this block is split into several micro-blocks by a joint set, thus reducing its stability. The situation is worsened by the active deep fault running along the Vardzia rock-cut city, which represents a potential earthquake source.

Topographic Map Interpretation of Bighorn River-Wind River Drainage Divide Located East of Wyoming's Wind River Canyon, USA

Detailed topographic map evidence is used to test the ability of two fundamentally different regional geomorphology paradigms to explain Bighorn-Wind River drainage divide evidence in the Copper and Lysite Mountain areas between Wind River Canyon and the Bighorn Mountains. Identified divide crossings were interpreted to be places where water had once flowed across what is now a major drainage divide. More than 20 such divide crossings were identified and ranged in elevation from 1924 to 2485 meters and could all be linked to north-oriented Bighorn River tributaries and also to south-oriented streams flowing to west-oriented Badwater Creek (a Wind River tributary). Lowest elevation divide crossings were located to the north of both Copper Mountain and Lysite Mountain. An attempt was first made to explain each identified divide crossing or group of divide crossings from the accepted paradigm's perspective, which requires drainage routes to have originated on the surface of a hypothesized Oligocene and Miocene sediment cover that buried the drainage divide area with the drainage routes eroding down through the sediment cover as the drainage divide was exhumed. Next the same evidence was interpreted from a recently proposed paradigm's perspective, which requires massive south- and southeast-oriented floods to have flowed across the Missouri River drainage basin as mountain ranges and plateau areas were being uplifted. The accepted paradigm could not easily explain the large number of observed divide crossings, many divide crossing details, and why geologic maps show few or no hypothesized sediment cover remnants. The new paradigm explained the large number of observed divide crossing and most observed divide crossing details and did not require an Oligocene and Miocene sedimentary cover.

Upper Sun River Drainage Basin Origin Determined by Topographic Map Interpretation Techniques: Lewis and Clark and Teton Counties, Montana, USA

A new and fundamentally different regional geomorphology paradigm in which massive south- and southeast-oriented meltwater floods flowed across the entire Missouri River drainage basin is tested by interpreting detailed topographic maps of the Montana upper Sun River drainage basin region by trying to explain origins of previously unexplained or poorly explained erosional landforms located upstream from Sun River Canyon (which cuts across Montana’s north-to-south oriented Sawtooth Range). Mountain passes, through valleys, and other drainage divide low points along what are today high mountain ridges, including the North American east-west continental divide, are interpreted to be evidence of drainage routes that once crossed the region. These drainage divide crossings suggest that prior to erosion of present-day upper Sun River drainage basin valleys, massive floods moved in south directions across what are today the north-oriented Middle and South Fork Flathead River drainage basins into today’s upper Sun River drainage basin area and carved a complex of diverging and converging channels into what was probably a low relief surface now represented by the crests of the region’s highest mountain ridges. Further, the map evidence shows how a diverging complex of south- and southeast-oriented upstream Sun River drainage basin flood flow channels changed flow direction to cross the Sawtooth Range in a northeast direction before converging on the Montana plains at a location downstream from Sun River Canyon. The observed upper Sun River drainage basin area topographic map evidence is consistent with the new geomorphology paradigm predictions, in which massive south-oriented meltwater floods flowing across the rising rim of a continental ice sheet created deep “hole” (created by deep ice sheet erosion and ice sheet weight caused crustal warping) are diverted to flow in northeast and north directions into and across deep “hole” space being opened up by ice sheet melting.

Use of Topographic Map Evidence to Test a Recently Proposed Regional Geomorphology Paradigm: Wind River-Sweetwater River Drainage Divide Area, Central Wyoming, USA

Topographic map evidence from the Wyoming Wind River-Sweetwater River drainage divide area is used to test a recently proposed regional geomorphology paradigm defined by massive south- and southeast-oriented continental ice sheet melt water floods that flowed across the entire Missouri River drainage basin. The new paradigm forces recognition of an ice sheet created and occupied deep “hole” and is fundamentally different from the commonly accepted paradigm in which a pre-glacial north- and northeast-oriented slope would have prevented continental ice sheet melt water from reaching or crossing the Wind River-Sweetwater River drainage divide. Divide crossings (or low points) are identified as places where water once flowed across the drainage divide. Map evidence is interpreted first from the accepted paradigm perspective and second from the new paradigm perspective to determine the simplest explanation. Both paradigm perspectives suggest south-oriented water crossed the drainage divide, although accepted paradigm interpretations do not satisfactorily explain the large number of observed divide crossings and are complicated by the need to bury the Owl Creek and Bridger Mountains to explain why the Wind River now flows in a north direction through Wind River Canyon. New paradigm interpretations explain the large number of divide crossings as diverging and converging channel evidence (as in flood-formed anastomosing channel complexes), Owl Creek and Bridger Mountain uplift to have occurred as south-oriented floodwaters carved Wind River Canyon, and a major flood flow reversal (caused by ice sheet related crustal warping and the opening up of deep “hole” space by ice sheet melting) as being responsible for the Wind River abrupt turn to the north. While this test only addresses topographic map evidence, Occam’s Razor suggests the new paradigm offers what in science should be the preferred Wind River-Sweetwater River drainage divide origin interpretations.

Stradanje Bošnjaka u proteklom ratu na području Sućeske u općini Srebrenica

Sućeska is a physio-geographical and anthropogeographical area in the northwestern part of the Srebrenica municipality. In the narrow sense, this area is bordered by Zeleni Jadar river canyon in the south and the valley of the Bukovica river in the north. In a broader sense, the area of Sućeska includes the area between the upper basin of the Potočari River, in the north, and plateau of Podravnje, in the south. The western border is the valley of the river Zeleni Jadar, and in the east it is the area of springs of the Kazani river and Kutlicka river. These boundaries of the Sućeska region should be taken on a conditional basis, because in the defining boundaries of an area should also be consider the anthropogeographical features of the area, such as the historical development of the area, ethno-geographical and cultural-geographical features, then the sense of mutual affiliation to some geographical area, etc. In the Middle Ages, area of Sućeska belonged to the Trebotići parish, with a much larger area, which included a large part of the upper and middle river flow of the river Zeleni Jadar.Taking into account cultural, ethnographic and historical facts, the geographic area of Sućeska includes the following inhabited places: Bostahovine, Brakovci, Bučinovići, Bučje, Kutuzero, Lipovac, Opetci, Podgaj, Podosoje, Slatina, Staroglavice, Sućeska i Žedanjsko. The area of Sućeska is approximately 64.3 square kilometers and covers the territory of thirteen populated places in the northwestern part of the municipality of Srebrenica. According to the population census of Bosnia and Herzegovina in 1991, there were 638 households in the area of Sućeska, with an average size of 5.1 members, and a total population of 3,291 members, mostly Bosniaks ethnicity. According to the latest census of the population of Bosnia and Herzegovina conducted in 2013, 1,475 people (757 women) lived in Sucesska, of which 1,461 Bosniak people (751 women). The paper presents the most important demographic consequences of war suffering of Bosniaks, in the area of Sućeska, in the municipality of Srebrenica, particulary during the genocide in so called "UN Safe Area of Srebrenica" , in July 1995. During the aggression against Bosnia and Herzegovina, 118 Bosniak were killed, including 33 of the female, of the average age of 38.1 years. The average age of killed men was 36.4 years. Number of the widows whose husbands were killed is 50, with 111 children orphans, with an average age of 10.6 years. During the genocide, 619 people were killed, including 9 women, with the average age of 60.1 years. The average age of killed men, the victims of genocide, was 35.6 years. Number of the widows whose husbands were killed is 383, with 624 children orphans, with an average age of 7.9 years. Until today, there are less than 500 Bosniaks living in the area of Sućeska, and more than 600 people whose living outside Bosnia and Herzegovina, mostly in the United States of America.

The “Mera” lahar deposit in the upper Amazon basin: Transformation of a late Pleistocene collapse at Huisla volcano, central Ecuador

The Sub-Andean zone east of the Cordillera Real, Ecuador and out to the Amazon basin's western margin has been the depository of voluminous lahars related to volcanic activity in the Andean highlands. These lahars arrived to the Sub-Andean zone via gravitational transport through narrow river canyons and emplaced volumes surpassing several cubic kilometers over robust inundation zones. This paper discusses the origin, flow route, depositional zone, terrace formation and geomorphic significance of the most important lahar deposit yet mapped in this region, that of the Mera lahar, which likely formed from a late Pleistocene collapse of Huisla volcano, followed by impounding by temporary dams behind drainage-blocking debris avalanche deposits (DAD), then subsequent rupture of the blockage. The actual deposit of the Mera lahar has a thickness between 30 and 70 m, is mainly comprised of DAD breccia, is matrix-supported (c 70%), of reddish gray color and is well-consolidated. Based on geochemical and petrographic similarities, Huisla volcano's DAD is the best candidate for the lahar's source. Huisla volcano is located some 90 km up valley of the bulk of Mera lahar's mapped deposit. Clasts of Mera lahar rocks and Huisla's DAD breccias have 57–61 wt% SiO2, corresponding to andesites of the calc-alkaline series with mean values of 1–1.5 wt% for K2O. The mapped Mera lahar deposit has an actual volume estimated in 1.2 km3 compared to its original estimated volume of 5.4 km3. Cross-sectional widths of 1.5 to 4.5 km span and extend laterally beyond the actual Pastaza river channel where the lahar's deposition produced high-standing isolated surfaces that are notable local geomorphic features of the upper Sub-Andean zone. The flow modeling program LaharFlow, employing the modern landscape as the topographic base, adequately simulates the flow route and inundation zones of the Mera lahar.

Rare earth elements as tracers for microbial activity and early diagenesis: A new perspective from carbonate cements of ancient methane-seep deposits

Ancient methane-seep carbonates are geological archives of environmental conditions and record past microbial activity. To better understand the information stored in this archive, a comparison was made of phase-specific major, trace, and rare earth element (REE) patterns, mineralogies, and textures of two early diagenetic carbonate phases in five ancient methane-seep deposits including Oligocene limestones from the Satsop and Canyon rivers (Washington State), the Cretaceous Tepee Buttes (Colorado), and the Carboniferous Ganigobis limestones (Namibia). (1) Cryptocrystalline, yellow aragonite and (2) banded and botryoidal aggregates of clear, fibrous aragonite typify many Phanerozoic seep limestones, and are common features of authigenic seep carbonates forming close to the sediment-water interface today. Light REE enrichment in yellow aragonite is observed together with high organic matter contents, indicated by intense autofluorescence of yellow aragonite, and occurs in combination with low Mg/Sr ratios. Conversely, heavy REE enrichment is observed in neomorphic yellow calcite spar typified by high Mg/Sr ratios, indicating progressive diagenetic alteration during early diagenesis in marine pore waters affected by a succession of biogeochemical reactions. These observations suggest that REE contents and patterns of early diagenetic carbonate phases are a function of the quality of preservation. Transformation of primary aragonite to calcite resulting from changing pore water compositions during later-stage early diagenesis is apparently capable to significantly modify elemental composition. The new results reveal that rare earth elements do not necessarily behave conservatively if early diagenesis is controlled to a large extent by evolving pore water compositions in environments strongly affected by biogeochemical processes. For such settings a careful assessment of diagenetic alteration is consequently required before calcite resulting from aragonite transformation can be used for reliable paleoenvironment reconstruction.

Controls of contour currents on intra-canyon mixed sedimentary processes: Insights from the Pearl River Canyon, northern South China Sea

Abstracts Contour currents are ubiquitous in global oceans, the role of which in shaping submarine morphology and controlling deep-water sedimentary processes has long been underestimated. This study uses 3D seismic and piston-core data to investigate the seismic geomorphology and lithofacies within the upper segment of the Pearl River Canyon (PRC), northern South China Sea, to better understand the mixed sedimentary processes within the submarine canyons. Within the upper segment of the PRC, various morphosedimentary features are recognized according to their seismic expressions in map and section views, including gravity flow-dominated (slope failures, turbidity channels and gullies) and contour current-dominated features (contourite drifts, contourite channels, contourite terrace, and sediment waves). The piston cores contain abundant shelf-derived coarse sediments within several contourite intervals, implying that the contourites were very likely sourced from pre-existing gravity-flow deposits. AMS 14C dating results further indicate that the contourites were mostly deposited during and after the last glacial maximum (LGM), suggesting active gravity flows during the same period. Silt-free sandy contourites are preferentially observed at the canyon thalweg, which may be related to intense contour currents. All the above evidence implies that the study area was influenced by mixed sedimentary processes, including gravity flows and vigorous contour currents. Further analyses suggest that the South China Sea Branch of Kuroshio (SCSBK) and Intermediate Water Current (IWC) greatly influenced the late Quaternary sedimentary processes within the PRC. Specifically, the SCSBK was responsible for the formation of the upper-slope contourites and associated contourite channels near the shelf edge. The SCSBK also promoted the occurrence of upper slope failures and gravity flows when the sea level was much higher than the shelf edge, and contributed to the LGM and post-LGM gravity-flow deposits. In contrast, the IWC was responsible for the formation of contourite drifts along the southwestern flank of the PRC. The IWC intensified when flowing along the canyon thalweg and fault scar, contributing to the formation of contourite channel. Under the influence of winnowing processes from the intense IWC, silt-free medium sands are exposed at the canyon thalweg. The mixed sedimentary processes that are highlighted in this study may have been a potentially underestimated mechanism in explaining the formation of high-quality deep-water sands within submarine canyons.

Miconia rheophytica (Melastomataceae: Miconieae), a new and endangered species from the Magdalena Medio region of Colombia

Miconia rheophytica is described, illustrated, and compared with presumed relatives in the Octopleura clade. It is distinguished by its narrowly elliptic to ovate-lanceolate leaf blades with entire to subentire margins that have evenly spaced spreading smooth eglandular trichomes 0.8−1.4 mm long, an indumentum of dendritic trichomes with short axes and terete radiating arms on distal internodes, adaxial petiole surfaces, and primary and secondary veins on abaxial leaf surfaces, unribbed hypanthia that are constricted and tapered distally below the torus and covered with a mixture of basally roughened trichomes and dendritic trichomes with short axes, anthers with two ± truncate apical pores, eglandular anther appendages, 3-locular ovary, and berries that are bright blue at maturity. It is known only from flash-flooded riverbanks in three river canyons in the Magdalena Medio region of Antioquia, Colombia. A conservation assessment of “Endangered” is recommended for this species based on IUCN Red List Categories and Criteria.

Analyses of the magnitude and frequency of a 400-year flood record in the Fish River Basin, Namibia

Ephemeral rivers in dryland regions exhibit a high interannual variability of streamflow regime, mainly dominated by floods. In these environments, floods are a water resource and a potential hazard with important socioeconomic implications. The Fish River (86,600 km2) is the largest ephemeral stream in Namibia and, recently, also the focus of new development plans, including construction of the largest dam in Namibia. The hydrological analysis to support decisions implies large uncertainties owing to spatial-limited and short hydrological records (since 1962). Here we investigate the current and past patterns of extreme floods combining instrumental, historical, and palaeoflood records. Palaeoflood studies were performed at two reaches with preserved sedimentary evidence: at the upper sector (Vogelkranz) upstream of Hardap Dam (~13% catchment area) and in the lower part of the river, in the Fish River Canyon National Park (70% catchment area). In the Hardap reach, the palaeoflood record identified at least eight large floods during the last 350 years, with the largest flood reaching a minimum discharge of 4800 m3 s−1 (150-year return period). In the Fish River Canyon reach, the sedimentary record shows at least 12 large floods over the last 400 years, the largest with an estimated minimum discharge of 8700 m3 s−1. The elevation of alluvial surfaces without flood evidence provided an upper bound for flood stages, associated with discharges of 6400 m3 s−1 and 16,140 m3 s−1 for the upper and mid-lower Fish River respectively. In the upper reach, the flood frequency analysis (FFA) combining systematic and palaeoflood data provided lower discharges (~25%) of the flood quantiles than the ones using only systematic data sets. In the Fish River Canyon reach, incorporation of the palaeoflood data into the FFA results in slightly higher values in the magnitude of the higher flood quantiles (~4–7%). The FFA analysis using an upper limited lognormal distribution function (LN4) fitted with palaeoflood data shows a good performance with a slow behaviour approaching the upper limit. Our flood frequency results suggest that the Hardap Dam should increase the spillway capacity and safety check flood of the original design in order to satisfy the dam safety criteria. However, the projected reevaluation figures calculated from conventional hydrological methods results in an overestimation of the safety floods according to our estimations.

Observations and Predictability of Gap Winds in the Salmon River Canyon of Central Idaho, USA

This work investigates gap winds in a steep, deep river canyon prone to wildland fire. The driving mechanisms and the potential for forecasting the gap winds are investigated. The onset and strength of the gap winds are found to be correlated to the formation of an along-gap pressure gradient linked to periodic development of a thermal trough in the Pacific Northwest, USA. Numerical simulations are performed using a reanalysis dataset to investigate the ability of numerical weather prediction (NWP) to simulate the observed gap wind events, including the timing and flow characteristics within the canyon. The effects of model horizontal grid spacing and terrain representation are considered. The reanalysis simulations suggest that horizontal grid spacings used in operational NWP could be sufficient for simulating the gap flow events given the regional-scale depression in which the Salmon River Canyon is situated. The strength of the events, however, is under-predicted due, at least in part, to terrain smoothing in the model. Routine NWP, however, is found to have mixed results in terms of forecasting the gap wind events, primarily due to problems in simulating the regional sea level pressure system correctly.

Style, identity, and resource competition on the border: The incised stones of the Sacramento River Canyon

In this paper, we look at the emergence of territorial behavior through the lens of ritual and stylistic expression. Our task is made approachable by an extraordinary Archaic-age collection of over 1500 incised stones recovered from the Sacramento River Canyon in northern California. This location marks a major ecological boundary where quintessential Californian food staples, such as oak, grey pine, and salmon, abruptly become much more discontinuous and less productive. We position the incised stones in terms of their signaling potential, particularly their role in ritual behaviors that promoted in-group cooperation and solidarity that, in turn, were crucial for the defense and territorial control of these productive resource tracts. The appearance of such ritual expression at approximately 6000 to 5000 years ago may mark a fundamental transition in demography, land-use, and social complexity observed throughout much of California at this time.