Substrate controls on the meter-scale surface roughness of rocky coasts, Oregon, USA.
Abstract
The erosion of rocky coasts is a balance between the resisting strength of the substrate and the erosive action of biotic and abiotic processes. The less resisting strength a rock has, the less force from waves and other abiotic processes are needed to erode the rock. While the relationship between rock hardness and average platform slope is well documented, substrate controls on the meter-scale organization of rocky shores is still unclear. Here, we examine the effect of substrate on the topographic roughness of the shore platform, with the expectation that harder rocks will produce more complex, or rougher, platform topography. Because softer rocks, like sandstone, are highly erodible, we predict that locations with soft rocks will have more planar shore platforms. To test the link between rock hardness and meter-scale shore platform morphology, we examined six locations on the Oregon Coast, USA with varying rock types. At each site, we collected rock hardness data along a transect using a Schmidt hammer. To quantify topography, we processed hand-held photographs of each site using structure-from-motion photogrammetry in Agisoft PhotoScan, calculating surface roughness and related statistics in CloudCompare. Our preliminary results confirm that sites with softer rocks tend to have smoother shore platforms. However, our observations indicate that the spatial organization of the tide pools could protect rocks from the erosive effect of waves. For example, one location we visited had an outcropping of tall, hard rocks that worked as a barrier against the force of the waves, protecting the rocks from incoming waves and sediment. By characterizing the topographic roughness and texture of rocky coast environments in detail, our work documents the effects of substrate strength at a spatial scale relevant to intertidal biodiversity.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP23C2302W
- Keywords:
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- 0442 Estuarine and nearshore processes;
- BIOGEOSCIENCESDE: 1625 Geomorphology and weathering;
- GLOBAL CHANGEDE: 1641 Sea level change;
- GLOBAL CHANGEDE: 3020 Littoral processes;
- MARINE GEOLOGY AND GEOPHYSICS