Description: Effect of changing vegetation on denudation (part 2): Landscape response to transient climate and vegetation cover Manuel Schmid, Todd A. Ehlers, Christian Werner, Thomas Hickler, and Juan-Pablo Fuentes-Espoz Earth Surf. Dynam. Discuss., https//doi.org/10.5194/esurf-2018-13,2018 Manuscript under review for ESurf (discussion: open, 1 comment) We present a numerial modelling investigation into the interactions between transient climate and vegetation cover with hillslope and fluvial processes. We use a state-of-art landscape evolution model library (Landlab) and designed model experiments to investigate the effect of climate change and associated changes in surface vegetation cover on main basin metrics. This paper is a companion paper to Part 1 (this journal) which investigates the effect of climate change to surface vegetation cover.

Description: Tectonic controls of Holocene erosion in a glaciated orogen Byron A. Adams and Todd A. Ehlers Earth Surf. Dynam. Discuss., https//doi.org/10.5194/esurf-2018-9,2018 Manuscript under review for ESurf (discussion: open, 0 comments) Recent work has highlighted a strong, worldwide, glacial impact of orogen erosion rates over the last 2 Ma. While it may be assumed that glaciers increased erosion rates when active, the degree to which past glaciations influence Holocene erosion rates through the adjustment of topography is not known. In this study, we investigate the influence of long-term tectonic and post-glacial topographic controls on erosion in a glaciated orogen, the Olympic Mountains, USA. We present 14 new 10 Be and 26 Al analyses which constrain Holocene erosion rates across the Olympic Mountains. Basin-averaged erosion rates scale with basin-averaged values of 5-km local relief, channel steepness, and hillslope angle throughout the range, similar to observations from non-glaciated orogens. These erosion rates are not related to mean annual precipitation or the marked change in Pleistocene alpine glacier size across the range, implying that glacier modification of topography and modern precipitation parameters do not exert strong controls on these rates. Rather, we find that despite intense spatial variations in glacial modification of topography, patterns of recent erosion are similar to those from estimates of long-term tectonic rock uplift. This is consistent with a tectonic model where erosion and rock uplift patterns are controlled by the deformation of the Cascadia subduction zone.

Description: How concave are river channels? Simon M. Mudd, Fiona J. Clubb, Boris Gailleton, and Martin D. Hurst Earth Surf. Dynam. Discuss., https//doi.org/10.5194/esurf-2018-7,2018 Manuscript under review for ESurf (discussion: open, 1 comment) Rivers can reveal information about erosion rates, tectonics, and climate. In order to make meaningful inferences about these influences one must be able to compare headwaters to downstream parts of the river network. We describe new methods for normalizing river steepness for drainage area to better understand how rivers record erosion rates in eroding landscapes.

Description: Clay mineralogy, strontium and neodymium isotope ratios in the sediments of two High Arctic catchments (Svalbard) Ruth S. Hindshaw, Nicholas J. Tosca, Alexander M. Piotrowski, and Edward T. Tipper Earth Surf. Dynam., 6, 141-161, https://doi.org/10.5194/esurf-6-141-2018, 2018 For many applications in Earth sciences it is important to know where river and ocean sediments have originated. In this study we used geochemical and mineralogical tracers to characterise sediments from Svalbard. We find that the sediments are formed from two sources: old rocks in Greenland and younger rocks in Siberia. Glaciation influences how much of each end-member is present in the river sediments today, implying that the sediment composition can change through time as the climate changes.

Description: Mechanical State of Gravel Soil in Mobilization of Rainfall-Induced Landslide in Wenchuan seismic area, Sichuan province, China Liping Liao, Yunchuan Yang, Zhiquan Yang, Yingyan Zhu, Jin Hu, and D. H. Steve Zou Earth Surf. Dynam. Discuss., https//doi.org/10.5194/esurf-2018-15,2018 Manuscript under review for ESurf (discussion: open, 0 comments) Although gravel soils generated by seismic shaking in Wenchuan earthquake area have subjected to natural consolidation process for nearly ten years, geological hazards, such as slope failures with ensuing landslides, frequently are haunting the area. In this paper, artificial flume model tests and triaxial tests were used to make close observation on the mechanical state of gravel soil in Wenchuan seismic area. The results showed that: (1) The timing and patterns of landslide initiations were closely related to their initial dry densities, and the initiation processes were accompanied with a variation of dry density and void ratio; (2) Fine particle migration in soil and coarse-fine particle content rearrangement contributed to the internal micro structure reorganization, which was supposed to be the main reason for variation of dry density and void ratio; (3) Gravel soils with unchanged grain compositions, if under the same hydrostatic compression, they approached to an identical critical void ratio to fail; (4) The mechanical state of certain sort of gravel soil can be identified by its relative position between state parameter ( e, p' ) and e c -p' planar critical state line; (5) Gravel soil slope failed and then evolved into landslide under lasting rainfall leaching, while in gravel slope there co-existed soil dilatation and contraction, but the dilatation was dominant. Above research findings not only could be used to interpret landslide initiation but also would provide an insight for landslide warning forecast of gravel slope in seismic area.

Description: Morphology of bar-built estuaries: relation between planform shape and depth distribution Jasper R. F. W. Leuven, Sanja Selaković, and Maarten G. Kleinhans Earth Surf. Dynam. Discuss., https//doi.org/10.5194/esurf-2018-18,2018 Manuscript under review for ESurf (discussion: open, 0 comments) Fluvial-tidal transitions in estuaries are used as major shipping fairways and are characterised by complex bar and channel patterns with a large biodiversity. Habitat suitability assessment and study of interactions between morphology and ecology therefore require bathymetric data. While imagery offers data of planform estuary dimensions, only for a few natural estuaries bathymetries are available. Here we study the relation between along-channel planform geometry, obtained as the outline from imagery, and hypsometry, which characterises the distribution of along-channel and cross-channel bed-levels. We fitted the original function of Strahler (1952) to bathymetric data along four natural estuaries. Comparison to planform estuary shape shows that hypsometry is concave at narrow sections with large channels, while complex bar morphology results in more convex hypsometry. We found a relation between hypsometric function shape and the degree to which the estuary width deviates from an ideal convergent estuary, which is calculated from river width and mouth width. This implies that the occurring bed level distributions depend on inherited Holocene topography and lithology. Our new empirical function predicts hypsometry and along-channel variation in intertidal and subtidal width. Combination with the tidal amplitude allows an estimate of inundation duration. A validation of the results on available bathymetry shows that predictions of intertidal and subtidal area are accurate within a factor 2 for estuaries of different size and character. Locations with major human influence deviate from the general trends, because dredging, dumping, land reclamation and other engineering measures cause local deviations from the expected bed-level distributions. The bathymetry predictor can be used to characterise and predict estuarine subtidal and intertidal morphology in data-poor environments.

Description: Effect of changing vegetation on denudation (part 1): Predicted vegetation composition and cover over the last 21 thousand years along the Coastal Cordillera of Chile Christian Werner, Manuel Schmid, Todd A. Ehlers, Juan Pablo Fuentes-Espoz, Jörg Steinkamp, Matthew Forrest, Johan Liakka, Antonio Maldonado, and Thomas Hickler Earth Surf. Dynam. Discuss., https//doi.org/10.5194/esurf-2018-14,2018 Manuscript under review for ESurf (discussion: open, 0 comments) Vegetation is crucial for modulating rates of denudation and landscape evolution, and is directly influenced by climate conditions and atmospheric CO 2 concentrations. Using transient climate data and a state-of-the-art dynamic vegetation model we simulate the vegetation composition and cover from the Last Glacial Maximum to present along the Coastal Cordillera of Chile. In part 2 we assess the landscape response to transient climate and vegetation cover using a landscape evolution model.

Description: Numerical modelling of landscape and sediment flux response to precipitation rate change John J. Armitage, Alexander C. Whittaker, Mustapha Zakari, and Benjamin Campforts Earth Surf. Dynam., 6, 77-99, https://doi.org/10.5194/esurf-6-77-2018, 2018 We explore how two landscape evolution models respond to a change in climate. The two models are developed from a divergent assumption on the efficiency of sediment transport. Despite the different resulting mathematics, both numerical models display a similar functional response to a change in precipitation. However, if we model sediment transport rather than assume it is instantaneously removed, the model responds more rapidly, with a response time similar to that observed in nature.

Description: Scales of collective entrainment and intermittent transport in collision-driven bed load Dylan B. Lee and Doug Jerolmack Earth Surf. Dynam. Discuss., https//doi.org/10.5194/esurf-2018-8,2018 Manuscript under review for ESurf (discussion: open, 3 comments) The transport of pebbles in a river is smooth and continuous under high flow conditions, but under typical flows becomes erratic and unpredictable. We perform experiments to learn more about the origins of this unpredictable, intermittent behavior. Our results show that this unpredictability is similar to how infrequent avalanches occur in a sandpile. Transport events are similar in size but become more infrequent and erratic as the river transports less and less sediment.

Description: Statistical modeling of the long-range dependent structure of barrier island framework geology and surface geomorphology Bradley A. Weymer, Phillipe Wernette, Mark E. Everett, and Chris Houser Earth Surf. Dynam. Discuss., https//doi.org/10.5194/esurf-2018-5,2018 Manuscript under review for ESurf (discussion: open, 0 comments) This research presents a new method for quantifying the geologic controls on modern barrier island evolution. We used statistical time series analysis to evaluate the scale-dependent vs. scale-independent behavior of a barrier island in south Texas, USA. By integrating subsurface geophysical with surface geomorphological measurements we show that the island exhibits both free, and forced evolutionary behavior that has important implications for how the island may respond to rising sea levels.