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'''Derek Nueharth''' - "Evolution of divergent and strike-slip boundaries in response to surface processes"
Plate tectonics describes the movement of rigid plates at the surface of the Earth as well as their complex deformation at three types of plate boundaries: 1) divergent boundaries such as rift zones and mid-ocean ridges, 2) strike-slip boundaries where plates grind past each other, such as the San Andreas Fault, and 3) convergent boundaries that form large mountain ranges like the Andes. The generally narrow deformation zones that bound the plates exhibit complex strain patterns that evolve through time. During this evolution, plate boundary deformation is driven by tectonic forces arising from Earth’s deep interior and from within the lithosphere, but also by surface processes, which erode topographic highs and deposit the resulting sediment into regions of low elevation. Through the combination of these factors, the surface of the Earth evolves in a highly dynamic way with several feedback mechanisms. At divergent boundaries, for example, tensional stresses thin the lithosphere, forcing uplift and subsequent erosion of rift flanks, which creates a sediment source. Meanwhile, the rift center subsides and becomes a topographic low where sediments accumulate. This mass transfer from foot-to hanging wall plays an important role during rifting, as it prolongs the activity of individual normal faults. When rifting continues, continents are eventually split apart, exhuming Earth’s mantle and creating new oceanic crust. Because of the complex interplay between deep tectonic forces that shape plate boundaries and mass redistribution at the Earth’s surface, it is vital to understand feedbacks between the two domains and how they shape our planet.
Here, we use numerical models to provide insight on how surface processes influence tectonics at divergent and strike-slip boundaries through two studies. The first study takes a detailed look at the evolution of rift systems using two-dimensional models. Specifically, we extract faults from a range of rift models and correlate them through time to examine how fault networks evolve in space and time. By implementing a two-way coupling between the geodynamic code ASPECT and landscape evolution code FastScape, we investigate how the fault network and rift evolution are influenced by the system’s erosional efficiency, which represents many factors like lithology or climate. The second study uses the two-way numerical coupling between tectonics and landscape evolution to investigate how a strike-slip boundary responds to large sediment loads, and whether this is sufficient to form an entirely new type of flexural strike-slip basin.
'''Danghan Xie''' - "Responses of mangrove forests to sea-level rise and human interventions: a bio-morphodynamic modelling study"
Co-Authors - Christian Schwarz2,3, Maarten G. Kleinhans4 and Barend van Maanen5<br>
2Hydraulics and Geotechnics, Department of Civil Engineering, KU Leuven, Belgium <br>
3Department of Earth and Environmental Sciences, KU Leuven, Belgium <br>
4Department of Physical Geography, Utrecht University, Utrecht, the Netherlands<br>
5Department of Geography, University of Exeter, Exeter, UK <br>
Corresponding author: Danghan Xie (danghan@bu.edu) <br>
Mangroves preserve valuable coastal resources and services along tropical and subtropical shorelines. However, ongoing and future sea-level rise (SLR) is threatening mangrove habitats by increasing coastal flooding. Changing sediment availability, the development of coastal structures (such as barriers), and coastal restoration strategies (such as mangrove removal) not only constrain the living space of mangrove forests but also affect coastal landscape evolution. Due to limitations in studying various temporal and spatial scales in the field under SLR and human interventions, insights thus far remain inconclusive. Results of bio-morphodynamic model predictions can fill this gap by accounting for interactions between vegetation, hydrodynamic forces, and sediment transport.
Here, we present a numerical modeling approach to studying bio-morphodynamic feedbacks within mangrove forests through a coupled model technique using Delft3d and Matlab. This approach takes into account (1) multiple colonization restrictions that control not only the initial mangrove colonization but also the subsequent response to SLR, (2) the possibility of coastal progradation and seaward mangrove expansion despite SLR under high sediment supply, (3) modulation of tidal currents based on vegetation presence and coastal profile evolution which, in turn, affect mangrove growth and even species distributions, and (4) profile reconfiguration under SLR which may contribute to the infilling of new accommodation space.
Our model results display both spatial and temporal variations in sediment delivery across mangrove forests, leading to species replacements arising from landward sediment starvation and prolonged inundation. The strength of bio-morphodynamic feedbacks depends on variations in mangrove root density, which further steers the inundation-accretion decoupling and, as a result, mangrove distribution. Moreover, an extended analysis studying mangrove behaviors is conducted under varying coastal conditions, including varying tidal range, wave action, and sediment supply. The results indicate that mangroves in micro-tidal systems are most vulnerable, even if sediment availability is ample. Ultimately, coastal restoration strategies like mangrove removal aiming to reduce local mud might not be achieved due to sediment redistribution post mangrove removal, which could enhance coastal muddification.
Further reading:
* Xie, D., Schwarz, C., Brückner, M. Z., Kleinhans, M. G., Urrego, D. H., Zhou, Z., & Van Maanen, B. (2020). Mangrove diversity loss under sea-level rise triggered by bio-morphodynamic feedbacks and anthropogenic pressures. Environmental Research Letters, 15(11), 114033. https://doi.org/10.1088/1748-9326/abc122
* Xie, D., Schwarz, C., Kleinhans, M. G., Zhou, Z., & van Maanen, B. (2022). Implications of Coastal Conditions and Sea‐Level Rise on Mangrove Vulnerability: A Bio‐Morphodynamic Modeling
(Thanks to Adam LeWinter and Tim Stanton)</i></span><br><br>Rates of coastal cliff erosion are a function of the geometry and substrate of the coast; storm frequency, duration, magnitude, and wave field; and regional sediment sources. In the Arctic, the duration of sea ice-free conditions limits the time over which coastal erosion can occur, and sea water temperature modulates erosion rates where ice content of coastal bluffs is high. Predicting how coastal erosion rates in this environment will respond to future climate change requires that we first understand modern coastal erosion rates.<br><br>Arctic coastlines are responding rapidly to climate change. Remotely sensed observations of coastline position indicate that the mean annual erosion rate along a 60-km reach of Alaska’s Beaufort Sea coast, characterized by high ice content and small grain size, doubled from 7 m yr-1 for the period 1955-1979 to 14 m yr-1 for 2002-2007. Over the last 30 years the duration of the open water season expanded from ∼45 days to ∼95 days, increasing exposure of permafrost bluffs to seawater by a factor of 2.5. Time-lapse photography indicates that coastal erosion in this environment is a halting process: most significant erosion occurs during storm events in which local water level is elevated by surge, during which instantaneous submarine erosion rates can reach 1-2 m/day. In contrast, at times of low water, or when sea ice is present, erosion rates are negligible.<br><br>We employ a 1D coastal cross-section numerical model of the erosion of ice-rich permafrost bluffs to explore the sensitivity of the system to environmental drivers. Our model captures the geometry and style of coastal erosion observed near Drew Point, Alaska, including insertion of a melt-notch, topple of ice-wedge-bounded blocks, and subsequent degradation of these blocks. Using consistent rules, we test our model against the temporal pattern of coastal erosion over two periods: the recent past (~30 years), and a short (~2 week) period in summer 2010. Environmental conditions used to drive model runs for the summer of 2010 include ground-based measurements of meteorological conditions (air temperature, wind speed, wind direction) and coastal waters (water level, wave field, water temperature), supplemented by high temporal frequency (4 frames/hour) time-lapse photography of the coast. Reconstruction of the 30-year coastal erosion history is accomplished by assembling published observations and records of meteorology and sea ice conditions, including both ground and satellite-based records, to construct histories of coastline position and environmental conditions. We model wind-driven water level set-up, the local wave field, and water temperature, and find a good match against the short-term erosion record. We then evaluate which environmental drivers are most significant in controlling the rates of coastal erosion, and which melt-erosion rule best captures the coastal history, with a series of sensitivity analyses. The understanding gained from these analyses provides a foundation for evaluating how continuing climate change may influence future coastal erosion rates in the Arctic.
* Project Team 1: '''Exploring the effects of rainstorm sequences on a river hydrograph''', Brooke Hunter presenting (Brooke Hunter, University of Oregon, Celia Trunz, University of Arkansas, Lisa Luna, University of Potsdam, Tianyue Qu, University of Pittsburgh and Yuval Shmilovitz, The Hebrew University of Jerusalem ).
* Project Team 2: '''Coupling grids with different geometries and scales: an example from fluvial geomorphology''', Rachel Bosch presenting (Rachel Bosch, University of Cincinnati, Shelby Ahrendt, University of Washington, Francois Clapuyt, Université Catholique de Louvain, Eric Barefoot, Rice University, Mohit Tunwal, Penn State University, Vinicius Perin, North Carolina State University, Edwin Saavedra Cifuentes, Northwestern University, Hima Hassenruck-Gudipati, University of Texas Austin and Josie Arcuri, Indiana University).
* Project Team 3: '''Lagrangian particle transport through a tidal estuary''', Rachel Allen presenting (Rachel Allen, UC Berkeley, Ningjie Hu, Duke University, Jayaram Hariharan, University of Texas, Aleja Geiger-Ortiz, Colby College and Collin Roland, University of Wisconsin).
* Project Team 4: '''Using Landlab to Model Tectonic Activities in a Landscape Evolution Model''', Gustav Pallisgaard-Olesen presenting (Gustav Pallisgaard-Olesen, Aarhus University, Xiaoni Hu, Penn State University, Eyal Mardar, Colorado State University, Liang Xue, Bowling Green State University, and Chris Sheehan, University of Cincinnati).
* Project Team 5: '''Land geomorphology evolution over a continuous permafrost region by applying Ku-model and hillslope diffusion model''', Zhenming Wu presenting( Zhenming Wu, University of Reeding and Fien De Doncker, University of Lausanne).
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