Vertical Land Motion as a Driver of Coastline Changes on a Deltaic System in the Colombian Caribbean

Juan Felipe Gómez,Eva Kwoll,Manoochehr Shirzaei,Ian J Walker

doi:10.3390/geosciences11070300

Juan Felipe Gómez, Eva Kwoll + Show 2 more

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https://doi.org/10.3390/geosciences11070300

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Abstract

To face and properly mitigate coastal changes at a local level, it is necessary to recognize and characterize the specific processes affecting a coastline. Some of these processes are local (e.g., sediment starvation), while others are regional (e.g., relative sea-level change) or global (e.g., eustatic sea-level rise). Long tide gauge records help establish sea-level trends for a region that accounts for global (eustatic, steric) and regional (isostatic) sea-level changes. Local sea-level changes are also the product of vertical land motion (VLM), varying depending on tectonic, sedimentological, and anthropogenic factors. We investigate the role of coastal land subsidence in the present-day dynamics of an abandoned delta in the Colombian Caribbean. Satellite images and synthetic aperture radar acquisitions are used to assess decadal-scale coastline changes and subsidence rates for the period 2007–2021. We found that subsidence rates are highly variable alongshore. Local subsidence rates of up to −1.0 cm/yr correspond with an area of erosion rates of up to −15 m/yr, but coastal erosion also occurs in sectors where subsidence was not detected. The results highlight that local coastline changes are influenced by multiple, interacting drivers, including sand supply, coastline orientation and engineering structures, and that subsidence alone does not explain the high rates of coastal erosion along the study area. By the end of the century, ongoing coastal erosion rates of up to −25 m/yr, annual rates of subsidence of about −1 cm/yr, and current trends of global sea-level rise are expected to increase flooding levels and jeopardize the existence of the deltaic barrier island.

Highlights

The Intergovernmental Panel on Climate Change forecasts rates of sea-level rise (SLR)between 8 and 16 mm/yr by the end of the century, resulting in a global sea-level rise between 0.52 to 0.98 m for a high greenhouse gas emission scenario [1]
In the case of the Magdalena River, we argue that downward trends in vertical land motion (VLM) reflect ongoing subsidence associated with modern fluvio-lacustrine sediments [26,61] that overlie relict sediments from a former delta that migrated westward after the mid-Holocene [21]
This study combined satellite images and interferometric synthetic aperture radar (InSAR) data to examine the interplay of vertical land motion (VLM) (2007–2021) and coastline changes (2010–2020) along a deltaic barrier in the Colombian Caribbean

Summary

Introduction

Between 8 and 16 mm/yr by the end of the century, resulting in a global sea-level rise between 0.52 to 0.98 m for a high greenhouse gas emission scenario [1]. Adding to the predicted increases of global mean sea level (GMSL), the upward or downward movement of the land surface— known as vertical land motion (VLM)—may exacerbate relative sea-level (RSL) changes at local scales. Changes in RSL result from the combined effect of the mean sea-level height (i.e., GMSL) and VLM [2], and it is measured relative to a local tide gauge benchmark [3]. Within the various causes of VLM, this work focuses on subsidence, defined as the downward movement of the land surface with respect to a datum or point of reference [5], and how it relates to coastal morphodynamics. Subsidence is driven by factors such as natural sediment compaction [6], fault displacements [5], or human actions (e.g., groundwater extraction [7], withdrawal of petroleum and natural gas [8], soil desiccation [9])

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