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Author Topic: How are islands produced in the ocean?  (Read 11592 times)

Bryan Howser

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How are islands produced in the ocean?
« on: 10/07/2008 21:56:53 »
Bryan Howser asked the Naked Scientists:

My name is Bryan and I am a nursing student in New Mexico US. I look forward to listening to your podcast weekly on my way to school.

I have a question involving plate drift. On the map some of the islands and continents seem to fit perfectly together, making continental drift obvious. Other places however, don't seem to fit the model.

So how do islands like the Indonesian islands fit into the picture? Are islands just the results of volcanoes? Do they connect to continental plates? If so, were they at one point above water?

Thank you,
B

What do you think?


 

Offline frethack

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How are islands produced in the ocean?
« Reply #1 on: 11/07/2008 06:39:54 »
The Indonesian islands are a volcanic arc caused by the subduction of one oceanic plate beneath another, and volcanic activity along with warping of the plate from the collision generally contribute.  Oceanic plates are generally composed of mafic material (relatively low in silica/aluminum and high in iron/magnesium), and are usually only a few miles in thickness, though they are very dense.  Oceanic plates dont have to connect with continental plates, but areas such as the western US are an accretion of these island arcs as they collide with the larger continental landmass. 


 

Offline Bass

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How are islands produced in the ocean?
« Reply #2 on: 11/07/2008 06:48:54 »
Bryan
I'm going to assume the islands that you refer to are volcanic island arcs (not all islands in the ocean are volcanic).  Island arcs form when an oceanic plate is subducted beneath another oceanic plate- Indonesia is a great example.  The resulting heat from the subduction causes volcanoes to erupt more or less parallel to the subduction zone trench, creating arc-shaped islands.  Japan is another island arc.  Almost all island arcs end up eventually smashing into and being accreted by continents.
 

Offline daveshorts

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How are islands produced in the ocean?
« Reply #3 on: 04/08/2008 16:03:04 »
Another way of making islands is by stretching a piece of crust, such as in Greece. Here the crust is being stretched and breaking up into a series of blocks, as they rotate the corners rise up, forming islands.

The top corners of the blocks form a lot of the islands.
 

lyner

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How are islands produced in the ocean?
« Reply #4 on: 08/08/2008 12:41:55 »
Quote
On the map some of the islands and continents seem to fit perfectly together, making continental drift obvious.
Oh the power of hindsight!
When I was a lad, it wasn't 'obvious' to anyone. Yes, I admit it's obvious  or, rather, 'very reasonable' now but it took a long time and some real inspiration to spot such an unthinkably obvious thing.
 

Offline tangoblue

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How are islands produced in the ocean?
« Reply #5 on: 11/03/2009 19:47:51 »
erosion
 

Offline JimBob

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How are islands produced in the ocean?
« Reply #6 on: 11/03/2009 22:56:04 »
I can think of three other way to make islands - first sea level rise has resulted in the isolation of land masses from continents. Example: Gotland in the Baltic Sea. Second, coral growth and in the past before corals as well as today, calcareous and silica sponges and crynoids (also spelled crinoids) also formed islands. Example: islands of the Great Barrier Reef off the coast of Oz. Third - rifting. Madagascar and THE ISLANDS OF GREAT BRITAIN AND IRELAND are an example of this type of island. All three were separated by rift from the main continental mass. The rifted blocks do not necessarily need to rotate to form islands.


 

Offline Mazurka

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How are islands produced in the ocean?
« Reply #7 on: 12/03/2009 16:08:56 »
I don't think anyone has mentioned hotspots yet.

The Hawaiian Islands and the chain of sub sea mountains to the west are considered a classic example of a "mantle plume".  This is where for (hotly debated reasons), a hot spot has formed due to convection currents within the earths mantle.  This melts the oceanic crust that lies above it, forming a volcano, which if it continues for long enough will reach the surface and become an island.

Without getting into an argument about it and with the greatest of respect, the UK's geological histroy is a bit more complicated than simply rifting... 
 

Offline JimBob

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How are islands produced in the ocean?
« Reply #8 on: 12/03/2009 21:44:22 »
Good Spot there, lad.
 

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How are islands produced in the ocean?
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