Underwater volcanoes, also known as undersea volcanoes, are natural disasters of very high intensity that are capable of destroying life whenever they occur. However, sometimes due to volcanic eruptions, beautiful islands are created and this could be the possibility of the beginning of life. Underwater volcanoes are rifts that arise in the Earth’s crust but are submarines. The occurrence of these volcanoes is not limited to deep bodies of water such as seas and oceans. Underwater volcanoes can also exist in shallow bodies of water. Up to 5000 or more active underwater volcanoes have been detected and recorded. Of the total volume of magma erupted annually during volcanic activity, nearly 75% is estimated to explode as a result of underwater volcanic eruptions. The largest underwater volcano active today is Kolumbo in the Aegean Sea on the island of Santorini in Greece. Its last eruption occurred in 1650. The explosion was so massive that it affected areas within 150 km of its vent.
Formation of underwater volcanoes
The shifting and mutual collision of tectonic plates cause the eruption of underwater volcanoes. Underwater volcanoes are only found at plate boundaries, where two tectonic plates meet.
The earth’s crust is fractionated into tectonic plates, which can be underwater or continental. Plates interreact at tectonic plate boundaries, where earthquakes and volcanic eruptions are commonplace. Some volcanoes form in subduction zones, where a dense oceanic plate sinks beneath a less dense continental plate. Other volcanoes form in productive regions, where two tectonic plates are moving distant from one another. Magma rises to fill the void amidst the plates, resulting in the development of volcanoes.
There are three forms of tectonic plate boundaries:
- Convergent boundaries
- Divergent boundaries
- Transform boundaries.
Underwater volcanoes develop exclusively at convergent and divergent boundaries.
Convergent plate boundaries
Underwater volcanoes that lie on the ocean floor, are very common. Many forms at great depths, rendering them unable to reveal their explosive presence due to the extreme weight and cooling effect of the ocean water above them. Others that form in shallower waters may reveal their presence by blowing steam and rocky debris above the sea surface. Sometimes submarine volcanoes can form steep columns above their vents. Some grow so large that they reach the surface of the ocean and form new islands. The San Juan Islands in Washington State may have formed due to these eruptions.
- Oceanic-Oceanic plate convergence- When two oceanic plates collide, the heavier plate sinks beneath the lighter one into the mantle. This step is known as subduction and the region is called a subduction zone. Subduction causes a few of the rocks beyond the subduction zone to heat and causes magma to raise, which in turn leads to submarine volcanoes.
- Oceanic-Continental plate convergence- This phenomenon is characterized by the collision of oceanic and continental plates. When the two plates collide with great force, the oceanic crustal plate sinks under subduction, and high arcs or underwater volcanoes form on the crustal plate.
- Continental-continental plate convergence- When two continental plates collide, the plates are pushed together or, in a few cases, one plate cuts into the other (called subduction). Thus, extensive mountain ranges are formed.
Divergent plate boundaries
Divergent plate boundaries are areas where new oceanic crust is formed due to two plates or crusts moving away from each other due to convection currents in the water. When these plates pull apart, a crack forms between them, and the magma that lies beneath the crust rises slowly and gradually through the crack. Over time, layers of lava accumulate to form underwater volcanoes. These volcanoes only erupt very gently. The Mid-Atlantic Ridge is the most common and well-known example of a ridge that formed at a divergent boundary. The distance of this ridge extends from the Arctic Ocean to almost the southernmost tip of Africa. Plate divergence occurs only when both plates belong to the same class, either oceanic-oceanic or continental-continental.
- Oceanic-oceanic plate divergence-This phenomenon involves two oceanic plates moving apart due to bottom convection currents and the presence of water exerting enormous pressure on these plates. When two plates move apart, cracks or fissures are created that are filled with molten magma that rises and finds its way into the rift. Due to the presence of water, this molten magma solidifies very quickly, creating underwater volcanoes or volcanic islands.
- Continental-continental plate divergence- Divergence also occurs in continental environments, leading to the formation of oceans. The continents are stretched and the crust is thinned, giving rise to a rift valley. The continents are stretched and the crust is thinned, giving rise to a rift valley. Continental sediments surround the subsiding margins and form continental shelves that are uplifted. The ocean expands and gives rise to the mid-ocean ridge.
What are Hotspots?
Hotspots are specific points within tectonic plates characterized primarily by Areas where mantle plumes have formed and Areas that have experienced massive volcanic activity in the past. Hotspots are capable of continuously creating volcanoes or classes of volcanoes (shield volcanoes) on the oceanic crust. Volcanic hotspots are formed when extremely hot lava generated by the outer core of the Earth’s crust moves upward in a current, forming a layer on the ocean floor. The constant eruption of lava and its constant settling on the ocean floor leads to the formation of layers that can sometimes rise above the surface of the water. These are capable of rising high enough above the surface of the water to form volcanic islands.
Facts related to underwater volcanoes
- Volcanic eruptions in shallow water can throw submarine material into the air. The Hawaiian Islands were formed because of such volcanic eruptions.
- One of the most recent examples of underwater volcanic eruptions is the island of Surtsey in the south of Iceland. The earth’s surface under the sea was uplifted during the explosion, leading to Surtsey Island’s formation!
- Water exerts a higher (about 250 times more significant pressure) pressure on the earth’s surface than air. This greater pressure can lead to an underwater blast.
- Magma exists in the mantle, the floor beneath the Earth’s surface. When the crack releases the pressure, the magma rises with the gases. This is known as an underwater volcano eruption.
- Underwater volcanoes that are very close to each other and that are found in the form of a chain or ring are referred to as a “ring of fire”.
- More research is needed to understand the role of these volcanic eruptions in global warming. These eruptions have been found to lead to warmer water and higher CO2 levels.
- Because most underwater volcanoes erupt at a depth of about 2,200 meters below sea level, where the pressure exceeds 218 atmospheres, water cannot boil. The absence of a boiling sound makes it difficult to detect an underwater eruption, even with hydrophones.
- Nowadays, remotely operated vehicles are used to study the effects and patterns of underwater volcanic eruptions. Scientists are studying the adaptations of marine life in the deep and hot environment surrounding volcanoes.
- Seamounts are nothing more than structures formed by extinct volcanoes under the sea. They emerge from the sea floor but remain deep below sea level (hundreds to thousands of meters below it). So they are not described as “islands”. Such seamounts can suddenly rise to at least 1,000 meters above the sea floor during underwater eruptions.
Formation of oceanic islands
Oceanic islands are islands that rise to the surface of the ocean from its bottom. Countless islands around the world vary in size, climate, and biodiversity. Oceanic islands are formed by the explosion of underwater volcanoes. Layers of lava gradually build up and eventually break through the water’s surface to form an island. Volcanoes can be established at plate boundaries or hotspots. Oceanic islands have unique characteristics due to their isolation. These islands are typically far from continents—especially oceanic islands that have been formed by hotspots. Isolation is a key factor affecting the island’s biology. Species abundance is negatively allied with island desolation– the more distant an island is, the more limited species lives on it. For almost 25 years, scientists have been trying hard to capture an underwater volcanic eruption on camera, and they finally succeeded. They believe that further analysis of underwater volcanoes will give them a clear insight into (i) the ways of life and adaptation styles in such extreme conditions; (ii) how heat spreads from the Earth’s interior to its surface; and (iii) excessive understanding of the cycles of various components (oxygen, sulfur, etc.) in the oceans.
Humera Ansari (Content writer Intern)