Rihanna's home island is an accretionary prism | Barbados – Lesser Antilles Volcanic Arc

Hey there 🌞 I'm SO happy you're here!

Barbados is a dream destination for many. But few know why this tiny island in the Atlantic exists at all. Let me tell you the story of the formation of Barbados. And if you ever travel there, remember this magnificent story.

 

Yesterday I went for a walk with my boyfriend in the nearby park. I told him about a cool thing that I've read about Barbados, the island Rihanna is from.

Which I hadn't known before, he told me, and I thought it's a cool headline.

In case you're lost, here's a Google Earth image of the Lesser Antilles. They're located between the Caribbean Sea (west) and the Atlantic (east). They're clearly arranged in a curve, an arc!

A little off, to the east, is Barbados. Well that's strange, has the island done something wrong and got thrown out of the friend group? 

How can it be that a small, flat island that merely consists of coral sand exists so close to volcanic islands made out of volcanic rocks?

You think: well, it's just there. Does there HAVE to be a reason for this?

But, I'm telling you, that is no conincidence!

Google Earth image of the Lesser Antilles

You might have heard that the La Soufrière Volcano on St. Vincent and the Grenadines is erupting (second island counting from the south).

This stuff always fascinates me (that's why I study geo sciences haha), so I wanted to know why there is volcanism at all. I hadn't learned a lot about the tectonic situation in the Caribbean, so I did a little research.

I quickly found out that my initial assumption was correct and that indeed this volcanism is subduction volcanism. So what does that mean?

In short: the island of St. Vincent and the Grenadines, where the volcano La Soufrière is located, is part of the Lesser Antilles Volcanic Arc. This volcanic arc lies directly above the subduction zone.

A subduction zone is a region on Earth where two tectonic plates collide. The one plate with the greater density, usually the oceanic plate, will be subducted. This only means that it'll dive down below the other plate which is less dense.

In this case, in the Lesser Antilles Islands region, there are two oceanic plates colliding. This kind of tectonic setting is creating the volcanic island arc.

Here's a schematic cross-section of a subduction zone. You can see the one plate (here called lithosphere) that is being subducted.

 

Cross-section of a subduction zone with volcanic arc on the Science of Travel Blog

While the plate is being dragged down, the crust (subducting lithosphere) starts to melt at a certain depth (why it melts is content for another blog or podcast, it's not only the incresing heat and pressure). The magma rises and forms the magmatic arc.

And now Barbados is joining the stage. You can also see a yellow triangle called accretionary prism. Remember this for later.

At the Lesser Antilles, the Atlantic plate is being subducted below the Caribbean plate (there are discussions about which plate, the Atlantic or American or both, is being subducted, as the boundaries are not super clear, but that's not important for now).

As the now molten magma rises, it penetrates the crust and forms volcanoes on the surface, such as the currently, violently, erupting La Soufrière Volcano.

BTW: This is a different kind of volcanism than in Iceland. In Iceland, two things happen:

  1. The North American and Eurasian Plate don't collide, but are moving away from each other. 
  2. Hot magma is rising as plumes from the deep, very deep mantle to the upper mantle and penetrates the crust.

At subduction zones, as in the Lesser Antilles Islands region, plates collide! This creates different types of volcanoes and different kinds of rocks than in Iceland (or Hawai'i - but that is yet another type of volcanism).

Another thing that happens at subduction zones is that the subducted plate, that is the plate that is being pulled down, is covered with sediments that were deposited on the ocean floor. 

The Atlantic plate is being forced against the Caribbean Plate and the sediments won't be subducted, but they will be shoved together into a huge pile! Imagine shoveling snow against a wall. At the thickest point, this accretionary prism is 20km (12 miles) thick!

These sediment hills are called accretionary prism in geology. 

And they can even breach the ocean surface and, thus, create flat islands.

This is exatly how Barbados was formed. 

My boyfriend wasn't too exicted about this knowledge.

I THINK IT'S AWESOME. 

What do you think? Did you know this already?

Let me know in the comments.

Be kind and love nature, 

Daniela 

 

 


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Source

R. Macdonald, C.J. Hawkesworth, E. Heath (200): The Lesser Antilles volcanic chain: a study in arc magmatism, Earth-Science Reviews, Volume 49, Issues 1–4, Pages 1-76, ISSN 0012-8252, https://doi.org/10.1016/S0012-8252(99)00069-0 (https://www.sciencedirect.com/science/article/pii/S0012825299000690)

Title image 

Photo by Anthony Ingham on Unsplash  

Subduction Zone Cross-Section

A schematic cross-section of an island arc from trench to back-arc basin by Zyzzy2, CC BY-SA 3.0

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