A formation made possible by volcanism

The insular region of the Caribbean is characterized by a geological history linked to volcanoes and tectonic plates. First of all, 56 millions of years ago, various volcanoes in the area emerged from the depths of the oceans by accumulation of products erupting, creating volcanic islands.

Over the years (several millions of years), the sea level has varied, that has created the coral.
When the water level rises as the volcano emerges or a part of its relief creates a shallow bedrock (not more than 30 meters deep), coral forms and hosts marine biodiversity.

This is how the limestone arc (external arc) was formed that has not known anymore any volcanic activity for several millions of years. It was covered by limestone sediments thus
creating islands predominantly calcareous.

The volcanic arc (common internal arc), for its part, is younger, has recent volcanic activity with about twenty active volcanoes (terrestrial and undersea).

Also, these two arcs, located near the Caribbean plate, form the insular part of the Caribbean zone. In addition, there are the Bahamas and the Greater Antilles (Hispaniola, Cuba, Jamaica,
Puerto Rico) located further North on the North American plate.

And, even if they are separated (Greater and Lesser Antilles) by the Anegada passage, they
together form the Caribbean biodiversity hotspot. These are territories with rich, varied and
threatened landscapes and species. Overall, there are wet and green territories but also semi-
arid and dry islands. It’s in the end this disparate set, which allows such biodiversity, that binds
them.

Distribution into plates

In the Caribbean region, there are two types of plates:

Continental plate: Caribbean Plate

Oceanic plates: North American Plate, South American Plate, Nazca Plate, Coco Plate

Oceanic plates, heavier than the Caribbean (continental) plate, slide beneath it by about 2 cm every year. This phenomenon, widely observed on other plates around the globe, creates a subduction zone.

In our case, the Caribbean plate is moving eastward and overriding the oceanic (North American) plate. This sliding, which causes explosive volcanoes, also causes the earthquakes we know today.

The planet has 4 tectonic plates and 46 much smaller plates.

1. Islands with recent and dominant volcanism

These are the islands located in the volcanic arc. From Saba in the North to Grenada in the
South via Dominica, Saint-Vincent and Basse-Terre in Guadeloupe with the highest peak in
the Lesser Antilles, Soufriere, culminating at 1467 m in altitude. These are islands with young
and active volcanism. They are lush and rich in biodiversity.

Given their relief, they are witness to the foehn effect. This phenomenon occurs when the cloud
masses located at sea level, pushed by the wind, undergo an orographic ascent (by colliding
with the relief, they rise in altitude). During this ascent, the cloud masses cool and condense,
generating orographic rains on the opposite sides. These are the sides so-called “windward” of
these islands which then have a high rainfall. Thus, the islands of the volcanic arc are much
wetter and greener than the islands of the limestone arc.

2. Mixed islands with double dominance: volcanic and limestone

Guadeloupe (volcanic Basse-Terre and limestone Grande-Terre) and the Greater Antilles are
mixed territories. There is a very heterogeneous and interesting biodiversity due to this
particular geological fact.

Guadeloupe, interesting archetype of the double dominance shows us the difference in
landscape that these two geological formations. Basse-Terre has a lush vegetation especially
at altitude and mostly evergreen (remaining green all year) while Grande-Terre has a mostly
stunted vegetation developing through sea winds and the ocean.

The island of Cuba, known for its endemic wealth, is made up of plains and low plateaus of
limestone rocks, slightly raised, limestone table crossed by volcanic rises, mountain
complexes, pit (- 7239 m), coral islets…this diversity of soil and thus of habitats and landscapes
explains its specific wealth.

3. Limestone islands

The islands from Saint-Martin to La Grande Terre (in Guadeloupe) come from the
predominantly limestone arc with ancient and passed volcanism. These are territories with coral
basis whose reefs have the same name, they are one of the wealth of the marine world.

To conclude, we can say that the geology of the Caribbean is important to be known in order
to understand the functioning of this biodiversity hot point. It is definitely observed that with
their formation the islands are bounded, particularly through the arcs that characterize them.
These islands are interdependent although separated by water.

The area has about 11,000 species of plants whose 72% of them are endemic. In the marine
environment, there are 25 kinds of coral, 117 sponges, 663 mollusks, 1,400 fish,76 sharks. And
this area has about 10,000 square kilometers of reefs, 22,000 square kilometers of mangroves
and up to 33,000 square kilometers of sea grasses.