Presenters-0617
Abstract
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
2Hydraulics and Geotechnics, Department of Civil Engineering, KU Leuven, Belgium
3Department of Earth and Environmental Sciences, KU Leuven, Belgium
4Department of Physical Geography, Utrecht University, Utrecht, the Netherlands
5Department of Geography, University of Exeter, Exeter, UK
Corresponding author: Danghan Xie (danghan@bu.edu)
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
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