In the field of geology, there are two concepts that are sometimes confused: volcanic islands and island arcs. Both are responsible for the formation of new landmasses in the ocean. However, there are some differences between volcanic islands and island arcs . To better understand these processes, you can also consult how volcanoes are classified according to their activity and shape.
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 a piece of land completely surrounded by water. They can vary in size, from small rock formations to vast landmasses. Islands can form in a variety of ways, and their origin can be related to several geological and climatic processes. Many islands are formed from volcanic activity. In areas with high seismic activity, volcanoes can erupt from the seabed, 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 volcanic islands in Spain, such as the Canary Islands.
The emergence of unique species that have evolved independently of their mainland counterparts is often a consequence of islands separating from the continent. This separation has a profound impact on the life that thrives on these islands, leading to the development of endemic species. Throughout history, human exploration of the seas has largely revolved around the search for enigmatic and hidden islands. You can also delve deeper into how islands form to better understand these processes.
What are island arches?
Island arcs, also known as volcanic island arcs or oceanic arcs, are archipelagos formed by volcanic islands. These geological formations, categorized as thermal orogens or volcanic arcs, 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, some of its material melts, forming low-density magma that rises from the lithosphere and penetrates the oceanic crust of the overriding plate until it reaches the surface. The upward movement of the magma results in the formation of a series of volcanic cones, which act as natural outlets to release the pressure accumulated beneath the overriding plate . These volcanic cones emerge above the water, forming the archipelago or volcanic island arc. To better understand these processes, you can also consult how an archipelago is formed.
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 portion of the island arc, lies the backarc zone, distinguished by a vast and deep backarc basin that may contain remnants of earlier island arcs and their corresponding basins . To better understand these processes, you can also consult how a volcanic island forms.
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 shapeIslands can be scattered anywhere in the ocean and come in a variety of shapes and sizes, from small, remote islands to large landmasses. Island arcs, on the other hand, are distributed along a curved line or arc that follows the subduction zone, forming a geologically aligned chain.
- 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.