Imagine standing on solid ground that didn’t exist just hours before. Within only 11 hours, it led to the development of a new island that’s now visible from space when an underwater volcano in the South Pacific began its spectacular eruption. This isn’t science fiction, but rather one of Earth’s most fascinating geological processes happening right before our eyes. From Hawaiʻi to Indonesia to Iceland, hundreds of islands across the globe have been formed by submarine volcanoes.
The formation of new islands through underwater volcanic activity represents one of nature’s most dramatic and rapid transformations. Earth’s ocean floor contains millions of these volcanoes, but few grow tall enough to form islands. Yet when they do break through the surface, they create entirely new ecosystems and landmasses that scientists can study in real time. Let’s explore this incredible process that’s literally reshaping our planet today.
The Deep Ocean Foundation
Submarine volcanoes are exactly what they sound like – volcanoes located beneath the ocean’s surface. Because they erupt into water instead of air, submarine volcanoes behave quite differently than terrestrial volcanoes. Most people picture explosive eruptions when they think of volcanoes, but underwater eruptions follow different rules entirely. It’s uncommon for submarine volcanoes to have explosive eruptions. The sheer weight of the water above them creates very high pressure, usually resulting in what are known as passive lava flows along the seafloor.
Most divergent plate boundaries are at the bottom of the oceans, and so most volcanic activity on Earth is submarine, forming new seafloor. Black smokers (also known as deep sea vents) are evidence of this kind of volcanic activity. These underwater furnaces work constantly beneath miles of ocean, building the foundation for what might one day become your next vacation destination.
The Chemistry of Creation
“The first thing you need is a supply of magma,” he says. “Typically, in the origin of most oceanic island volcanoes or submarine volcanoes, you need to melt the Earth’s mantle.” This melting process happens deep within Earth, where temperatures reach thousands of degrees. In much the same way that plumes rise in a lava lamp, plumes of mantle magma (molten rock) are thought to rise from a source within Earth’s deep mantle. When such a plume rises into the shallow mantle, it partially melts.
The interaction between water and molten rock creates unique conditions. Pillow lava is a common eruptive product of submarine volcanoes and is characterized by thick sequences of discontinuous pillow-shaped masses which form underwater. Even large submarine eruptions may not disturb the ocean surface, due to the rapid cooling effect and increased buoyancy in water. This rapid cooling process forms the building blocks that will eventually reach toward the surface.
Building Mountains Beneath the Waves
Volcanic islands typically progress through five stages of growth and eventual decline: Submarine volcano formation: the process begins underwater. Magma rises through cracks in the ocean floor, erupting as a submarine volcano. These eruptions release gases, ash, and lava. Think of it like building a skyscraper from the basement up, except the basement is the ocean floor and you’re using molten rock.
These passive flows harden into rock and build up the height of the underwater mountain over millions of years. The process requires incredible patience from a geological perspective. Eventually, some volcanoes reach heights above the seafloor where lower pressure allows for explosive eruptions. Submarine volcanoes that do not reach sea level are called seamounts.
The Dramatic Moment of Emergence
Over millions of years, continued eruptions build the underwater volcano upward. Eventually, it grows tall enough to break the water’s surface, forming a new volcanic island. This breakthrough moment represents one of Earth’s most spectacular transformations. When underwater volcanoes, also known as seamounts, erupt, the build of lava occasionally breaks the surface of the water. This causes an island to form.
The emergence process can happen with stunning speed once conditions align properly. The water was shallow(130 m), so the island didn’t have to make a huge thickness of land to get above the surface. Before breaking the surface, there was a lot of bubbles, floating pumice, ash clouds, but the interval from the start of the eruption to breaking surface was days. When Surtsey Island emerged off Iceland’s coast, it provided scientists with their first opportunity to witness this process in detail.
Iceland’s Spectacular Reykjanes Peninsula
No volcanic eruption had occurred for approximately 800 years on the Reykjanes Peninsula until 19 March 2021 when a fissure vent appeared in Geldingadalir to the south of Fagradalsfjall mountain. This awakening caught global attention as it marked the beginning of what experts call a new volcanic period. The volcano lies on the North Atlantic Ridge, which is the boundary between the Eurasian and North American oceanic plates. The plates are moving apart at an average rate of about 20 mm a year. As the stress builds, it allows the intrusion of magma into fractures.
After the eruption of the Fagradalsfjall volcano on 19 March 2021, National Geographic’s experts predicted that this “may mark the start of decades of volcanic activity”. The eruption was small leading to a prediction that this volcano was unlikely to threaten “any population centers”. The Reykjanes Peninsula showcases how underwater volcanic processes extend onto land, creating a natural laboratory for understanding island formation. The eruption was the tenth to have occurred on the Reykjanes Peninsula since March 2021 and the seventh in 2024.
Tonga’s Explosive Island Creation
Hunga Tonga-Hunga Ha’apai first formed between Dec. 2014 and Jan. 2015, when the previously underwater volcano erupted. When all the dust, rock, and ash settled, a newly-formed island remained between two older islands, with a summit reaching 400 feet high. It was the first of its kind to form in 53 years, so scientists have been able to study its birth and evolution in vivid detail from space. This Pacific island became a living laboratory for scientists until its dramatic destruction.
The Hunga Tonga-Hunga Ha’apai island emerged from the Pacific Ocean due to volcanic activity in 2014 and 2015. Its short, seven-year existence gave scientists a rare window to study how life develops on new land masses, until the devastating Tonga eruption in 2022 blasted it away. The island’s rapid formation and equally rapid destruction demonstrate both the creative and destructive power of underwater volcanic forces.
Home Reef’s Recurring Island Show
This isn’t the first time that Home Reef has birthed islands. Eruptions recorded in 1852, 1857, 1984 and 2006 all produced new land masses, according to NPR’s Joe Hernandez. But these islands all eventually disappeared. Home Reef, located in Tonga’s waters, offers a perfect example of how temporary some volcanic islands can be. Waves and currents eroded the volcanic rock, per IFL Science, breaking down the young land masses. The 2006 island, for example, sank within two years.
The eruption showed four distinct phases: During September–October 2022, lava flows formed a ~ 54,900 m² circular island. In the following three eruption phases, the island grew towards the south (September–November 2023) and east (January 2024 and June–September 2024), expanding the island’s area to over 122,000 m². This cyclical process of creation and destruction showcases the dynamic nature of volcanic island formation.
The Race Against Erosion
While the island quickly grew over the past 16 days of lava flow, it is not expected to last. While islands created by underwater volcanoes can persist for years, they are typically short lived. For example, Home Reef has had four periods of eruptions. The survival of a newly formed volcanic island depends on a delicate balance between volcanic output and erosional forces.
Volcanic activity at the site has since subsided, and the newly formed island has somewhat shrunk because its “crumbly” formation is easily washed away by waves, Usui said. The new island could survive longer if it is made of lava or something more durable than volcanic rocks such as pumice. The composition of volcanic material determines whether an island becomes a permanent feature or merely a temporary geological spectacle. Building the island is quick. Keeping the island is hard – barring further eruptions, Surtsey has a remaining life expectancy of a century or so before it erodes completely.
The formation of new islands through underwater volcanic activity represents one of Earth’s most dynamic processes. From Iceland’s ongoing eruptions to Tonga’s spectacular displays, we’re witnessing planetary forces that have shaped our world for billions of years. These volcanic birthplaces remind us that our planet remains very much alive and continues to create new land even as we watch. What fascinates you most about these underwater architects reshaping our world? The speed of their creation or their battles against the relentless sea?
Hi, I’m Andrew, and I come from India. Experienced content specialist with a passion for writing. My forte includes health and wellness, Travel, Animals, and Nature. A nature nomad, I am obsessed with mountains and love high-altitude trekking. I have been on several Himalayan treks in India including the Everest Base Camp in Nepal, a profound experience.
