Description
Natural dunes for coast defence Praia de Espinho, Portugal
Samenvatting (Dutch description)
A case study analysis on the coastal protection efficacy of Barchan dunes.
It was on a very windy day that my husband and I took off to the beach with a fierce undulation caused by strong gusts of wind to produce this report.
This narrow strip of land bridges land and sea and harbors a notable and peculiar flora that fixes itself to the sand, locking it in space, and thereby protecting it and the shoreline from marine transgression. A dune with no vegetation is no dune, and will soon fall prey to wind fueled erosion, as well as large waves that will raze it to the ground.
Regarding fauna, it hosts many rare specimens, some of which may even be endangered! Above you can see a host of them, from organisms that attach themselves to the rocks and consume the algae that feed off of their minerals, to corals, to shelled ones that will one day become part of limestone and potentially marble.
One can see succession of sandstone rocks scattered throughout the beach, some with large marble crystals embedded in them. As marble is “metamorphosed limestone,” it is composed of recrystallized carbonate minerals, and it makes sense that you would be able to find it in a beach covered with the calcium carbonate shells of once living beings. The origin of the pressure and heat conditions that make the formation of these metamorphic rocks possible lies in the existence of a convergent plate boundary located south-southeast of the Iberian peninsula — the Iberian plate, and the African plate. Calcium carbonate is also the cementing material in sandstone. The fact that this is a continental beach (as we will discuss below) implies that these are quartz sandstones, the hardest type of sandstone.
These rocks also serve to add a layer of protection to the shoreline, by serving as a natural breakwater of sorts, decreasing the momentum of the waves much like an artificial one would. As a consequence of this, sand near the water is particularly coarse.
The sand is mostly fine, but one can easily notice a granularity gradient as they make their way down to the ocean, ranging from fine to very coarse gravel, and even cobbles. The grains are light brown, round, and even, but this homogeneity decreases the closer one gets to the sea, as mentioned earlier. Composition wise, upon closer inspection one can distinguish grains of quartz, feldspar, and mica, typical of continental sand, which is congruent with the fact Portugal is located along a passive, non-volcanic continental margin.
Beautiful as they may be, these Hottentot-figs are an exotic invasive species that are native to South Africa. They are traditionally considered a type of succulent, and they actively compete with native coastal species for nutrients, water, and light, impeding their natural development. They are being actively removed by volunteers.
Below is a compilation of the gorgeous flora that is native to this area’s dunes.
Though some areas seem barren and vegetation is spare, the dunes have come a long way.
They are divided by a small stream of fresh river water. This water is a good additional source of nutrients for the dune’s flora, and even its fauna. The force of its water is very gentle and it is unlikely to damage the surrounding dunes.
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