Reunion island

Reunion island


New category on this blog ! I have a work about science popularization to do in English class at the university. It gaves me the idea to create a new class of articles to write some publications in English. It will be a good way to improve my English and especially my scientific vocabulary. I ask to good English speakers not to choke if I make some mistakes in my future English articles. This first article of the category will also be my final work for evaluation.

I already spoke on this blog about the subject I will deal with in this article : Reunion Island, where I went in travel for two weeks last summer. However, it is a perfect subject to do some science popularization. Moreover, I will try to develop more aspects of Life and Earth sciences thanks to this main theme and to focus on basics explanations for each one of them. Here is my article in French if you want to compare.

Let’s go for this first article in English !

Birth of Reunion island : hot spot volcanism

To speak about Reunion Island, we have to understand how the island was born. For this, we have to deal with hot spot volcanism (I love that) ! The most famous example of hot spot volcanism is the Hawaii archipelago. Mascarene archipelago (composed of Rodrigues, Mauritius and Reunion islands) was born thanks to a similar process.

A hot spot takes its source in the depths of the Earth, in a particular layer at the limit between the mantle and the core. This layer, called D’’, includes anomalies of especially hot materials. A warmer material has a less important density. At geological time scale, this hot material plume will rise through the mantle thanks to Archimedes thrust. This phenomenon of convection allows to keep the plume very hot during its rise. When it arrives near the surface (around 100 kilometers deep), the hot material merges thanks to the lower pressure to form a magma. This magma will erupt in surface. If the hot spot is under an ocean, a underwater volcano will rise.

On very active hot spots, underwater volcano will grow up until the water surface and create an island. The particularity of a hot spot is to be immobile under a mobile tectonic plate. Plate movements will allow to create an alignment of volcanic islands like Hawaii or Mascarenes archipelagos. Reunion island emerged on the Indian ocean around three millions years ago. The hot spot is currently located in South-West of the island but the magma continue to arrive to the Piton de la Fournaise. When the hot spot will be too far from the island, new volcanoes will rise and new islands will appear.

On this picture, you can see the Dolomieu crater, located on the top of the Piton de la Fournaise. The cliffs on the sides are delimiting the enclosure where the majority of lava flows erupt

Reunion island is nowadays composed of two volcanoes : the Piton des Neiges (more than 3 000 meters high), dormant since 10 000 years and the Piton de la Fournaise (more than 2 500 meters high), which erupts basaltic lava once or twice per year.

Environments and climatology

The volcanic influence on Reunion island allows many different environments and microclimates to develop. If we start on a large scale, climatic conditions in Reunion island are tropical. Indeed, the island is located around 20 degrees south latitude. One year is divided in two main season : the « winter », from May to November, which is the dry and « cool » season (despite more than 20 °C mean on the coast) and « summer », from December to April, which is the rainy and warm season, crossed by some tropical storms.

If we now cut the island in several parts, we can distinguish some regions with different climatic influences. Eastern coast is humid and cooler than the other regions of the island. Indeed, main winds of these latitudes are the trade winds, which come from the East. Trade winds which come on the Eastern coast charged themselves of humidity above the Indian ocean. The climate of central region of Reunion island is influenced by the altitude. Collapse of the Piton des Neiges volcano created three cirques (Salazie, Mafate and Cilaos) which have very important reliefs. It is possible to find rainforests and mountain coniferous forests on areas of some kilometers square (it’s very impressive) ! Finally, the Western coast is perfect for people who love to tan on the beach. Indeed, this region is protected from the humid trade winds thanks to the volcanic reliefs. It is the driest and warmest region of Reunion island.

Ecosystems and biology

Thanks to its various environments, Reunion island has a very rich biodiversity. Furthermore, because of its isolation in the Indian ocean, Reunion island has a very high rate of endemism. Many species of birds, reptiles, arthropods or trees are only living on this little piece of land lost in the vast ocean. Indeed, when an island is very isolated, species which are living on evolved completely apart from continental species. Ecosystems of Reunion island are unique but fragile : if they disappear, they can not be restored. Nowadays, human activities are threatening a lot of endemic species of the island.

Before its colonization, no mammals were living on the island except some species of bats. The terrestrial animal population was mainly composed of arthropods (insects, spiders …), some reptiles and many birds, which came from nearest islands like Madagascar. There are many endemic birds species on Reunion Island.

An endemic bird of Reunion and Mauritius islands named « Oiseau la vierge ». It is a funny little kind of sparrow which often follow you when you are hiking (sorry for the picture quality, my phone’s zoom is very bad)

Marine wildlife is very diversified too, especially on the western coast. Indeed, the protection from trade winds allows the development of a lagoon isolated from the open sea by a coral reef. This type of environment is bountiful with life : corals, fishes, shellfishes … Reunion island is also famous for the humpback whales which are living a part of the year near the coast of the island. Some species of sharks are also swimming in the neighborhood of the island, especially two species known for their aggressiveness : bull sharks and tiger sharks. Because of their presence, it is forbidden to swim in the ocean excepted in supervised areas of the lagoon, where these sharks can not come because of their size.

It is now finished for this first article in English on my blog ! I hope it gives you the desire to discover this amazing island ! I also hope you will enjoy this concept, I will now try to publish some of my articles in English. It is a good challenge for me. See you soon for the next publication !

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