Description: ABSTRACT This commentary uses Google Books N-grams to briefly explore the changing use of the word geomorphology in books published in British English and American English. Both show a decline in the use of the term geomorphology in recent years. A singular feature of the British data is a very sharp rise and fall in the use of term geomorphology in books published since 1980. The steep falling limb (post 1993) of this curve is of particular concern and several possible explanations are put forward including, since 1986, the influence exerted by Research Assessment Exercises on publication practice in UK universities. The N-gram trends pose important questions for all geomorphologists and we should monitor them to gain a better understanding of where we need to be most visible to ensure the long-term health of our discipline. Copyright © 2014 John Wiley & Sons, Ltd.

Description: ABSTRACT Grain size properties and the variation of organic matter in coastal beach and dune environments are assumed to be controlled by the intensity of aeolian processes, time and the sediment source. However, assumptions are based on relatively limited empirical studies. In this study, we examined which environmental variables are the main predictors of multiple topsoil properties. To achieve this, we analysed an extensive dataset systematically collected across all beach zones and a large geographical area at the Finnish Baltic Sea coast characterized by postglacial land uplift. We included a comprehensive set of predictors in the analysis and applied boosted regression trees, a modern modelling technique particularly suited for analysis without prior assumptions of the data model. The results suggest that mean grain size and sorting are mainly determined by northing and fetch. Northing, disturbance and fetch predicted the variation of soil organic matter while litter cover was strongly related to disturbance. Based on the analyses, we were able to identify the main drivers of multiple topsoil properties on land uplift beaches. Parent material is suggested to determine sediment textural properties, which largely masks the effects of transient processes. Mean grain size and sorting are highly interdependent: grains become finer and sorting improves with increasing shore exposure. The intensity of momentary geomorphic processes controls the accumulation of litter whereas the slower accumulation of organic matter in the soil is influenced also by the static exposure setting. Skewness and kurtosis of the grain size distribution are mainly influenced by unmeasured processes, potentially relating to the geomorphological origin of the sediment. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Increased bank stability by riparian vegetation can have profound impacts on channel morphology and dynamics in low-energy systems, but the effects are less clear in high-energy environments. Here, we investigate the role of vegetation in active, aggrading braided systems at Mount Pinatubo, Philippines, and compare results with numerical modelling results. Gradual reductions in post-eruption sediment loads have reduced bed reworking rates, allowing vegetation to finally persist year-round on the Pasig-Potrero and Sacobia Rivers. From 2009-2011, we collected data detailing vegetation extent, type, density, and root strength. Incorporating these data into RipRoot and BSTEM models shows cohesion due to roots increases from zero in unvegetated conditions to 〉10.2 kPa in densely-growing grasses. Field-based parameters were incorporated into a cellular model comparing vegetation strength and sediment mobility effects on braided channel dynamics. The model shows both low sediment mobility and high vegetation strength lead to less active systems, reflecting trends observed in the field. The competing influence of vegetation strength vs. channel dynamics is a concept encapsulated in a dimensionless ratio between timescales for vegetation growth and channel reworking known as T* . An estimated T* between 1.5 – 2.3 for the Pasig-Potrero River suggests channels are still very mobile and likely to remain braided until aggradation rates decline further. Vegetation does have an important effect on channel dynamics, however, by focusing flow and thus aggradation into the unvegetated fraction of braidplain, leading to an aggradational imbalance and transition to a more avulsive state. The future trajectory of channel-vegetation interactions as sedimentation rates decline is complicated by strong seasonal variability in precipitation and sediment loads, driving incision and armoring in the dry season. By 2011, incision during the dry season was substantial enough to lower the water-table, weaken existing vegetation, and allow for vegetation removal in future avulsions. This article is protected by copyright. All rights reserved.

Description: ABSTRACT To further develop prediction of the range of morphological adjustments associated with sediment pulses in bar-pool channels, we analyze channel bed topographic data collected prior to and following the removal of two dams in Oregon: Marmot Dam on the Sandy River and Brownsville Dam on the Calapooia River. We hypothesize that, in gravel-bed, bar-pool channels, the response of bed relief to sand and gravel sediment pulses is a function of initial relief and pulse magnitude. Modest increases in sediment supply to initially low-relief, sediment-poor cross-sections will increase bed relief and variance of bed relief via bar deposition. Modest increases in sediment supply to initially high-relief cross-sections, characteristic of alternate bar morphology, will result in decreased bed relief and variance of relief via deposition in bar-adjacent pools. These hypothesized adjustments are measured in terms of bed relief, which we define as the difference in elevation between the pool-bottom and bar-top. We evaluate how relief varies with sediment thickness, where both relief and mean sediment thickness at a cross-section are normalized by the 90 th percentile of observed relief values within a reach prior to a sediment pulse. Field measurements generally supported the stated hypotheses, demonstrating how introduction of a sediment pulse to low-relief reaches can increase mean and variance of relief, while introduction to high-relief reaches can decrease the mean and variance of bed relief, at least temporarily. In general, at both sites, the degree of impact increased with the thickness of sediment delivered to the cross-section. Results thus suggest that the analysis is a useful step for understanding the morphological effects of sediment pulses introduced to gravel-bed, bar-pool channels. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Proglacial groundwater-fed features, such as seeps, substantially impact proglacial geomorphology, hydrology, and ecology. However, there is a paucity of research on the impacts of climate change and glacier retreat on the extent of these important features. This paper aims to investigate the impact of glacier retreat on proglacial groundwater levels and on the extent of groundwater-fed seeps. Research has taken place in western Skeiðarársandur, the large proglacial outwash plain of Skeiðarárjökull, a retreating temperate glacier in SE Iceland. Changes in the extent of proglacial groundwater seeps were mapped using historical aerial photographs from 1986, 1997, and 2012. Proglacial groundwater levels were monitored in shallow boreholes between 2000 and 2012. The western margin of Skeiðarárjökull has retreated approximately 1 km beyond its position in 1986. However, this retreat was punctuated by short periods of readvance. The geomorphology and groundwater systems at the site were substantially impacted by the November 1996 jökulhlaup, whose deposits altered approximately 18% of the area of groundwater seeps. The surface areas of groundwater seeps and lakes in the study area have declined by ~97% between 1986 and 2012. Most of the decline took place after 1997, when the mean annual rate of retreat increased threefold. Groundwater levels also declined substantially between 2000 and 2012, although this trend varies spatially. The paper provides a conceptual model of the controls on proglacial shallow hydrological groundwater systems. Direct impacts of glacier retreat are suggested as the main cause for the declines in proglacial groundwater levels and in the extent of groundwater seeps. These declines are expected to adversely impact sandur ecology. This article is protected by copyright. All rights reserved.

Description: ABSTRACT A reliable characterization of bedload transport is required to gauge the engineering and theoretical issues related to the dynamics of sediments transport in rivers. However, while significant advances have been made in the development of monitoring techniques, robust quantitative predictive relationships have proven difficult to derive. In this article, we develop a dedicated signal processing technique aimed at improving the usage of impact plate measurements for material transport characterization. Our set-up consists of a piezoelectric hydrophone mounted on the bottom side of a stainless steel plate, thus acting as a “sediment vibration sensor”. While the classical analysis with such systems is usually limited to rather simple procedures, such as impact counting, a large amount of useful information is contained in the actual waveform of the impact signal, which conveys the force and the contact time that the bedload imposes on the plate. An advanced signal processing technique called “first arrival atomic decomposition” is used to improve the characterization of bedload transport by analysing the amplitude and frequency attributes of each single impact. This new processing approach proves to be well suited for bedload transport monitoring using plate systems and allows us to establish a relationship between the median grain size ( D 50 ) and the impact signal properties. This link is first observed and validated with controlled flume experiments and then applied to continuous impact records in a small gravel-bed river during a flood event. The estimated D 50 offers a novel possibility to observe the time-varying grain size distribution of bedload transport. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The multipart Riffeltal rock glacier, located in a tributary valley of the Kaunertal, Tyrol, Austria is investigated to enlarge the knowledge about spatial and temporal development of rock glaciers in and at the margins of proglacial areas and to get a better understanding about glacier-rock glacier interactions. The subject of interest consists of a complex system of two adjacent rock glacier tongues and various superposed lobes with differing ages, origin and root zones, and therefore diverse development. To determine the reasons for their diverging development, the internal structure and permafrost occurrence on and in the surrounding area of the rock glacier were studied by application of geomorphological mapping, geophysical methods and measurement of the basal temperature of the winter snow cover (BTS). Permafrost modelling was performed on the basis of BTS data and land surface parameters derived from a high resolution airborne laserscanning (ALS) DEM. Additionally, the ALS data were used to measure vertical and horizontal changes of the rock glacier surface between 2006 and 2012. Glacier-rock glacier interactions during and since the Little Ice Age (LIA) are evident for the development of the studied rock glacier. A geomorphic map gives important information about the connection between glacial advance or retreat and permafrost or ground ice occurrence. The combination of all information helps in the analysis of diverse kinematic action of neighbouring rock glacier tongues. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Reef islands on the Great Barrier Reef are influenced by a range of environmental factors. for a meta-analysis of 103 islands expresses variation in island size (area and volume) as a function of latitudinal and cross shelf gradients in regional oceanographic factors (exposure to incident waves, tidal range and tropical cyclone frequency) and local physical factors (position on the shelf, area, length and depth of supporting reef platform, vegetative cover). Models performed well for unvegetated sandcays (R 2  = 0.89), vegetated sandcays (R 2  = 0.72) and low wooded islands (R 2  = 0.78), with a moderate level of variation explained when all islands were simultaneously regressed (R 2  = 0.58). Future island dynamics were simulated for anticipated changes in cyclone regime, wave activity and sea level. For 38 islands mapped on the 1973 Royal Society and Universities of Queensland Expedition to the Northern Great Barrier Reef , change over the same 22 year period (1973 to 1995) was determined andthe relative magnitude of observed and modelled changes was compared and found to be consistent through rank correlation analysis (Γ = 0.84 for unvegetated sandcays, Γ = 0.81 for vegetated sandcays). Simulations of island area or volume change from 2000 to 2100 indicated that under a 30% decrease in tropical cyclone activity, unvegetated sandcays continue to accrete at a lower rate, whereas all island types erode under a 38% increase in tropical cyclone activity. Vegetated sandcays initially accrete at higher levels of cyclone activity, entering an erosive state with a 60% increase in activity. Low wooded islands are unresponsive to environmental change. A sensitivity analysis of vegetated and unvegetated sandcays indicated that the presence of vegetation increases the tropical cyclone activity threshold at which islands begin to erode. Greatest sedimentary losses occur within the central band of high cyclone activity between Cooktown and Mackay. This article is protected by copyright. All rights reserved.

Description: ABSTRACT We present a new numerical surface process model allowing us to take into account submarine erosion processes due either to submarine landslides or to hyperpycnal currents. A first set of models show that the frequency of hyperpycnal flows influences the development of submarine canyons at the mouth of continental rivers. Further experiments show that an increase in submarine slope leads to faster regressive canyon erosion and a more dentritic canyon network, whereas increasing the height of the unstable sediment pile located on the shelf break leads to wider and less dendritic canyons. The models are then applied to the western segment of the north Ligurian margin (northwestern Mediterranean), which displays numerous submarine canyons with various sizes and morphologies. From west to east, canyon longitudinal profiles as well as margin-perpendicular profiles progressively change from moderately steep, concave-up shapes to steeper linear to convex-up shapes suggesting increasing eastward margin uplift. Moreover, the foot of the margin is affected by a marked slope increase with evidences of mass transport due to landslides. Numerical models which reproduce well the North Ligurian margin morphologic features indicate that the western part of the margin is submitted to rather low (i.e. 0.4 mm yr −1 ) uplift and intense submarine erosion due to frequent hyperpycnal currents, whereas the eastern part bears more rapid (i.e. 0.7 mm yr −1 ) uplift and has little or no hyperpycnal currents. Copyright © 2014 John Wiley & Sons, Ltd.

Description: ABSTRACT Landscapes exposed by glacial retreat provide an ideal natural laboratory to study the processes involved in transforming a highly disturbed, glacially influenced landscape to a stable, diverse ecosystem which supports numerous species and communities. Large-scale vegetation development and changes in sediment availability, used as a proxy for paraglacial adjustment following rapid deglaciation, were assessed using information from remote sensing. Delineation of broad successional vegetation cover types was undertaken using Landsat satellite imagery (covering a 22 year period) to document the rate and trajectory of terrestrial vegetation development. Use of a space-for-time substitution in Glacier Bay National Park, Alaska, allowed ‘back-calculation’ of the age and stage of development of six catchments over 206 years. The high accuracy (89.2%) of the remotely sensed information used in monitoring successional change allowed detection of a high rate of change in vegetation classes in early successional stages (bare sediment and alder). In contrast, later successional stages (spruce and spruce-hemlock dominated forest) had high vegetation class retention, and low turnover. Modelled rates of vegetation change generally confirmed the estimated rates of successional turnover previously reported. These data, when combined with the known influence of terrestrial succession on soil development and sediment availability, suggest how physical and biological processes interact over time to influence paraglacial adjustment following deglaciation. This study highlights the application of remote sensing of successional chronosequence landscapes to assess the temporal dynamics of paraglacial adjustment following rapid deglaciation and shows the importance of incorporating bio-physical interactions within landscape evolution models. This article is protected by copyright. All rights reserved.