The underwater volcanoes of the Earth are some of the most fascinating and least understood geological formations on Earth. Most do not look like the huge mountains that are commonly associated with volcanoes. They are hidden under the surface of the ocean and form complex structures that are difficult to understand.
Understanding the formation and evolution of underwater volcanoes can help reveal how these volcanoes influence ecosystems globally. Submarine volcanic structures are not only important for geology, but also for the development of marine life unique to the area and the creation of volcanic islands.
What Is an Underwater Volcano?
Along the Earth’s plate boundaries, volcanoes are common. Magma, a superheated rock, rises through the crust along with gases and ash. Many tectonic boundaries are located beneath the ocean. About three-quarters of all volcano activity occurs underwater.
Although submarine volcanoes do not produce as dramatic an eruption as those seen on land, they are still able to shape the ocean floor. Magma that reaches the ocean floor cools quickly when it comes into contact with cold water. This is known as “pillow lava” due to its round shape. Below this layer, magma that cools more slowly continues to form the oceanic crust.
Seafloor spreading is a result of repeated eruptions along divergent boundary lines, like the Mid-Atlantic Ridge. Subduction zones are created by convergence boundaries such as those found in the Pacific Ring of Fire. These subduction zones have different volcanic activity. Continuing submarine eruptions over time can create seamounts and volcanic islands. Famous island chains like the Hawaiian Islands are created by this long-term activity.
Where do Volcanoes Form?
Volcanoes can form in a variety of geological environments, such as subduction zones, mantle hotspots, or mid-ocean mountain ridges. Subduction zones are formed when one tectonic plate dives under another, creating intense pressure and heat. Magma is created as the subducted rock melts and rises up through the crust to cause large or explosive eruptions. These zones are responsible for some of the most explosive volcanic activity on Earth. They also play a major role in the formation of new crust.
The majority of underwater volcanic activity takes place along mid-ocean Ridges where tectonic plate slowly moves apart. Magma fills in the gaps created by the plates and forms a new seafloor over time. Some submarine volcanoes also develop above mantle hotspots, isolated plumes rising from deep inside the Earth. Magma and tectonic movements are combined to determine whether underwater volcanoes will remain submerged or grow into islands. Understanding these processes is essential to studying the formation of underwater volcanic features and their impact on the seafloor.
Subduction Zones and Volcano Formation
Subduction zones have been the site of some of history’s most famous volcanic chains. Subducted rocks contain water-rich minerals that reduce the melting temperature of mantle rocks. The molten rock rises through central shafts and cracks to form volcanoes.
Shield volcanoes, which are formed by layers of lava deposited over long periods, are common in the subduction zone. Magma that is more viscous can produce violent eruptions, but less explosive eruptions create smooth lava flows. These processes reveal how volcanic eruptions develop on the seafloor.
Submarine shields are similar to their terrestrial counterparts. The lava is formed by cracks on the flanks of a volcano. It can be smooth, ropy or jagged. Underwater, the lava quickly cools to form round, pillow-shaped structures. This gives insight into seafloor geology.
Factors Determining Eruption Style
The intensity of an eruption is determined by the magma’s composition, its water content and its internal pressure. Magma with a high gas content can produce explosive eruptions, while magma of low viscosity produces steady lava flow.
Submarine volcanoes are characterised by an increase in pressure from the water above, which usually prevents explosive eruptions. Seamounts are formed by passive lava flows that spread over the seafloor. These lava flows are essential for understanding how underwater volcanoes form over geological timescales.
Things that happen when an underwater volcano erupts
The depth of an underwater eruption is a major factor in determining its effects. The weight of the water above acts as a cap to limit explosive activity at great depths. Melting rock that comes into contact with cold seawater quickly cools, forming a new crust. These deep eruptions are usually not visible from the surface of the ocean, but they constantly reshape and grow underwater volcanic structures.
Magma in shallower water heats up the water around it, transforming it into steam, resulting in explosive eruptions. Steam expands suddenly, increasing the destructive power of an eruption by ejecting rock and gas fragments. A shallow eruption can release gases and ash into the air. This will affect nearby communities, polluting the air, interfering with electricity and contaminating drinking water. These eruptions can trigger tsunamis in extreme cases. This poses additional risks for coastal ecosystems and regions.
Submarine Volcanoes & Island Formation
Submarine volcanic islands can grow depending on the magma and tectonic activities. Over millions of years, passive lava flows form underwater mountains. Explosive eruptions can occur when a volcano reaches the ocean’s surface.
Island formation is also affected by the movement of tectonic plates. The structure can remain submerged if the volcano drifts from its magma source. These processes explain why some submerged volcanoes become islands, while others remain underwater.
Volcanic Islands also form the basis for a unique ecosystem. Simple bacteria survive by consuming volcanic chemicals. As time passes, these islands are colonised by plants, birds and other organisms, resulting in diverse and sometimes endemic flora and fauna.
Underwater Lava Flows
Most submarine eruptions are caused by spreading centres where the tectonic plate slowly moves apart. When magma fills the gaps, it produces basalt, which is a dense volcanic stone. This lava cools rapidly when it meets the cold seawater and forms pillow-shaped structures. These pillow lavas vary in size, texture, and shape depending on the magma viscosity, eruption speed, and temperature. Scientists gain valuable insight into the dynamics and processes of Earth’s crust by studying these features. These lava flows play an important role in shaping the ocean floor, creating vast ridges and providing the basis for diverse marine ecologies.
Subduction zones produce magma called andesite that contains more gas. This gas-rich magma is capable of causing explosive eruptions even underwater. However, the water pressure surrounding it reduces its intensity in comparison to land-based volcanic activity. Another type of submerged volcano is the hotspot. They form on top of mantle plumes and create linear chains of seamounts or volcanic islands. These formations reveal the history and evolution of plate tectonics, but they also allow scientists to track the movements of Earth’s plates. Researchers can gain a better understanding of underwater volcanoes by examining lava flows in divergent, hotspot, and convergent settings.
The tectonic settings of submarine volcanoes
Along divergent or convergent plate boundaries, submarine volcanoes occur most frequently. Magma is formed as plates slowly separate and form new oceanic crust. The rate of eruptions at divergent boundaries is influenced by the movement of the plate and mantle. When plates collide and produce magma, they form subduction zones. The magma erupts in a similar way to volcanoes on land, but the water beneath it alters its eruption behaviour. Hotspot volcanoes are formed over rising mantle plumes and leave a linear track of seamounts. They can also create some of the biggest underwater volcanoes. Understanding these tectonic environments is crucial for predicting submarine volcano activity and studying underwater volcanic structures.
The Importance of Studying Underwater Volcanoes
Understanding the formation of underwater volcanoes can provide valuable insights into interactions between Earth and the ocean. Submarine volcanic eruptions can shape the seafloor and build crust. They also contribute to the formation of a volcanic island. These processes create habitats unique to themselves, supporting ecosystems that evolve in isolation. They also host endemic species that are found nowhere else on earth. Understanding these environments will reveal how geology influences marine life, oceanic biodiversity and the diversity of marine species.
Scientists can predict volcanic behaviour by analysing magma, eruption style and tectonic activities. The research on underwater volcanoes is beneficial to many fields, including oceanography, marine biology, and geology. These volcanoes, which are hidden under the sea, have a significant impact on Earth’s geology and ecology. They also affect the landscape of the seafloor. By studying them, we can gain a deeper understanding of the oceans as well as the dynamic processes that shape the planet’s interior.
