In the geological field there are two concepts that are sometimes confused. We are talking about volcanic islands and island arcs. Both are responsible for the formation of new land in the ocean. However, there are some differences between volcanic islands and island arcs.
Therefore, in this article we are going to tell you what the differences are between volcanic islands and two island arcs.
What is an island?
An island is an area of land completely surrounded by water. They can range in size from small rock formations to vast land masses. Islands can form in various ways, and their origin may be related to various geological and climatic processes. Many islands are formed from volcanic activity. In places where seismic activity is high, volcanoes can rise from the seafloor, depositing lava and other volcanic materials that eventually accumulate to form an island. When several islands are grouped together within a specific ocean region, they are called an archipelago. There are some islands of volcanic origin in Spain as are the Canary Islands.
The emergence of unique species that have evolved independently of their continental counterparts is often a consequence of the separation of islands from the mainland. This separation has a profound impact on the life that thrives on these islands, leading to the development of endemic species. Along the history, Man's exploration of the seas revolved mainly around the search for enigmatic and hidden islands.
What are island arches?
Island arcs, known as volcanic island arcs or ocean arcs, are archipelagos formed by volcanic islands. These geological formations, categorized as thermal orogens or volcanic arcs, They are formed through a process called thermal orogeny. This occurs when two fragments of oceanic crust from different tectonic plates undergo orogenesis.
The Volcanic Arc is a type of orogenesis that occurs when the oceanic crust of one tectonic plate subducts beneath the crust of another plate, exerting pressure and causing the melting of its basal material. In the context of island arcs, the subducting plate experiences increasing temperatures and pressures as it deepens, causing volatilization of some components.
Consequently, a part of its materials melts, giving rise to low-density magmas that rise from the lithosphere and cross the oceanic crust of the oppressed plate until reaching the surface. The upward movement of magma results in the formation of a series of volcanic cones, which act as natural outlets to release pressure built up beneath the oppressed plate. These volcanic cones emerge above the water forming the archipelago or arc of volcanic islands.
A distinctive volcanic island formation can be identified by the presence of an oceanic trench along its convex side, known as the forearc zone, which serves as a boundary between interacting tectonic plates. On the opposite side, the concave part of the island arch, is the posterior arch area, which is distinguished by a vast and deep back-arc basin that may contain remains of earlier island arcs and their corresponding basins.
Like other volcanic arcs, backarc basins are influenced by subduction processes that initiate mechanisms that lead to the formation of oceanic lithosphere, causing extension and expansion (such expansion can be observed in the Sea of Japan, for example) .
What are the differences between volcanic islands and island arcs?
Although both are geological formations that take place in the ocean, they have some differences:
- Geological origin: Islands can have different origins, such as underwater volcanoes, coral atolls, or fragments of continents separated by rising sea levels. On the other hand, island arcs form specifically in subduction zones, where an oceanic plate sinks beneath a continental plate, generating volcanic activity that gives rise to a chain of islands along the subduction line.
- Distribution and shape: Islands can be scattered anywhere in the ocean and can come in various shapes and sizes, from small remote islands to large land masses. Island arcs, on the other hand, are distributed along a curved line or arc that follows the subduction zone.
- Geological processes: While islands can form by a variety of geologic processes, such as volcanic activity, sedimentation, or sea level rise, island arcs are the direct result of the subduction of an oceanic plate beneath a continental plate.
- Biodiversity: Both islands and island arcs can support a wide diversity of life, both in their marine and terrestrial ecosystems. However, island arcs tend to be more biologically diverse due to the variety of habitats they offer, including volcanic slopes, coral reefs, and deep waters.
Examples of islands
- Easter Island: Located in the Pacific Ocean, this island is famous for its enigmatic stone statues called moai.
- Bora Bora Island: Located in French Polynesia on the Pacific Ocean, Bora Bora is famous for its crystal-clear waters, white sand beaches, and luxurious resorts.
- Santorini Island: In the Aegean Sea, this volcanic island is known for its dramatic cliffs, whitewashed villages, and spectacular sunsets.
- Galapagos Island: They are famous for their unique biodiversity and endemic species, including giant tortoises and Darwin's finches.
Examples of island arcs
- Arc of the Antilles: This island arc stretches along the edge of the Caribbean Sea, from the Bahamas Islands in the north to the Windward and Leeward Islands in the south.
- Aleutian Arch: Located in the northeast Pacific Ocean, this island arc stretches from Alaska to the Kamchatka Peninsula in Russia.
- Indonesian Arc: This extensive island arc lies between the Asian continent and Australia, encompassing thousands of volcanic islands and coral islands.
- Japan Arc: Located on the edge of the Pacific plate, this island arc stretches along the east coast of Japan and comprises thousands of volcanic islands.
I hope that with this information you can learn more about the differences between volcanic islands and island arcs.