Formation of Volcanic Islands

Formation of Volcanic Islands

When people think of volcanoes, most would imagine a deadly explosion of liquid hot magma that ruthlessly obliterates anything in plain view. If volcanoes demolish everything in sight then how did life become what it is today? Volcanoes are not just a source of destruction and mayhem, long before civilization, while the earth was still being developed its apocalyptic surface consisted of nothing but molten rock and volcanic eruptions were a common occurrence; it was literally hell on Earth. No life, no oceans, no nothing just a sphere of fire and lava, but look at Earth today; a gorgeous blue fills all of the sky along with vast vivacious oceans containing all sorts of remarkable creatures. These “geological monsters” are actually capable of producing beautiful habitual islands such as Iceland and the entire Hawaiian chain.

Volcanic islands are made possible through their architect, plate tectonics; which is a combination of the theory of continental drift, by Wegener, and seafloor spreading, by Hess. Continental drift is the idea that at one point in time all of the continents formed a super continent called Pangea. Looking at the globe of the world, every continent looks as if it were a piece to a puzzle; which if placed back together, Pangea is made (3, Ref). Sea floor spreading on the other hand, is the theory of an underwater mountain range, the mid ocean ridge, which produces molten lava. As it cools it pushes previous plates away; creating new magma to replace what has moved. Now, the theory of plate tectonics shows there are moving plates which make up the crust of the Earth.

There are only two types of plates that compose the earth’s crust which are oceanic and continental, and among these plates there are three sorts of plate boundaries. The first is transformal, which means two plates are sliding past one another side by side such as the San Andreas Fault in California. The second type is divergent, meaning two plates are moving away from each other, mainly happening along the mid ocean ridge. The third, and most important when it comes to volcanic islands, is convergent boundary; where two plates collide into each other (4, Trujillo).

With these three kinds of boundaries and two different types of crusts, many scenarios can potentially occur. Whether it is ocean to continent transformal, continent to continent divergent, or continent to ocean convergent, but the key to unlock volcanic islands is oceanic to oceanic convergent boundary where two ocean plates collide. When this happens the older plate carrying the heavier oceanic crust will plunge under since the older plate becomes more dense as it cools and travels farther from the mid ocean ridge, while the younger and lighter plate will glide over on top of it creating a subduction zone (1, Ref). Within this subduction zone the denser plate diving into the asthenosphere is heated from the gases and pressure causing it to melt. Since molten rock is less dense, the lava rises up and creates an underwater volcano. As millions of years go by, the volcano continues to erupt underwater as long as there is a supply of magma. This generates an underwater mountain, known as a seamount (4, Trujillo). Eventually the underwater volcano piles so much erupted material, which cools on top of itself, that it breaks sea level thus creating a volcanic island, also known as an island arc. They’re named island arcs because an elegant shape of an arc is made as the volcano chain creates islands (1, Ref). An example of an Island chain is the Aleutian Islands which are located off the coast of Alaska.

All along the mid ocean ridges lies countless amounts of seamounts that couldn’t reach up to the surface to become an island. Since the mid ocean ridge is a divergent plate boundary, the plates consistently move away from the volcanic activity as new lava seeps up and cools. Existing seafloor is pushed away as new seafloor is produced; also known as seafloor spreading (4, Trujillo). This creates a small time span for the submarine mountain to develop enough molten basaltic rock into an island which is rare alongside the mid ocean ridge. Although it is rare, small islands can emerge from their seamount state along this divergent boundary. As a result of weather, wind and water crash against the small protruding island which eventually erodes it away until the island is no longer breaking the surface

(2, Rubin). “After this process occurs, the battered down island is no longer an island or a seamount because any seamount that eventually extends beyond the surface of the ocean and is eroded away, until the peak sits just under sea level, is called a guyote or tablemount.” (1, Ref)

Very few islands are found near ocean ridges due to the fact of seafloor spreading. The majority of volcanic islands are created from oceanic convergent plate boundaries, but there is yet another source of volcanic made islands. A major exception of islands found on mid ocean ridges is Iceland, the largest island in the world. This massive land mass is significant because of the size and location in the ocean. After researching all the information previously given of how few islands are created over a mid ocean ridge, there’s no way the largest island in the world could have formed from just that. Not only was Iceland nourished with new molten material through the mid-ocean ridge but also from what is called a hot spot. According to the theory of J. Tuzo Wilson in 1963, a hot spot is, “a fixed location in the earth’s mantle where thermal plumes penetrate the crust.” This means that any plate passing over the fixed hot spot will heat up and melt, causing an up rise. Iceland was generated over a mid ocean ridge, while at the same time passing over a hot spot (6, Watson). These two sources together supplied this unique island with enough molten rock to become what it is today. For roughly 55 million years this hotspot deep in the mantle contributed volcano after volcano to