The planet’s geological forces are overwhelmingly destructive, often seen in the sudden, intense energy release of a natural disaster. Events like powerful earthquakes, massive landslides, or devastating tsunamis reshape coastlines and flatten landscapes in moments. It is a profound paradox that within this category of intense geological phenomena, a single type of event acts not only as a destroyer but also as a creator of new land. This rare process constructs brand-new, isolated landmasses.
Volcanic Eruptions: The Primary Force
Volcanic eruptions are the one natural disaster capable of creating entirely new islands from the ocean floor. These events meet the criteria of a natural disaster due to their sudden onset, high-energy output, and potential for widespread devastation, including massive ash clouds, pyroclastic flows, and tsunamis. The formation of new land occurs in two primary tectonic settings globally, both involving the movement of molten rock to the surface.
One setting is at subduction zones, where one tectonic plate slides beneath another, leading to the formation of volcanic arcs, such as those found along the Pacific Ring of Fire. The other main mechanism is a fixed mantle plume, or hot spot, where magma rises through the middle of a plate, as seen in the Hawaiian island chain and Iceland. The creation of Surtsey off the coast of Iceland (1963–1967) is a well-documented example of this process.
More recently, the 2014–2015 eruption that formed the Hunga Tonga-Hunga Ha‘apai island in the South Pacific demonstrated the powerful creative force of the Ring of Fire. These eruptions build up material over time until a new peak breaks the ocean surface. The energy released during such an island-forming event is immense, often involving explosive interaction between magma and seawater.
How Submarine Volcanoes Build Land
The creation of a new island begins deep beneath the waves with a submarine eruption, where magma rises through fissures in the seafloor. At great depths, the immense pressure of the water suppresses the volatile gases within the magma, resulting in quiet, effusive eruptions that form distinctive, rounded structures known as pillow lava. Over thousands of years, these repeated flows gradually construct a massive underwater mountain, or seamount, that inches closer to the surface.
As the seamount’s vent rises to a depth of approximately 150 meters, the water pressure is no longer sufficient to contain the magmatic gases. When the hot magma meets the cooler seawater, the water rapidly flashes to steam, causing violent, explosive eruptions known as phreatomagmatic or Surtseyan activity. These explosions shatter the lava into fine-grained ash and rock fragments called tephra, which pile up around the vent to form a cone that eventually breaks the ocean surface.
The final stage of island growth is subaerial, or above-water. The ash-producing phase gives way to effusive flows of basaltic lava, which is less viscous and spreads out over the loose tephra cone. This hard, dense rock forms a protective cap that shields the fragile underlying ash from ocean erosion, stabilizing the landmass and marking the birth of a more permanent island. Islands formed by hot spots, like the shield volcanoes of Hawaii, tend to be built from this less explosive, flowing basalt, which contributes to their long-term stability.
Island Longevity: When New Land Disappears
The immediate fate of a newly formed volcanic island is often one of rapid destruction, as the ocean works to dismantle the fresh, unconsolidated material. Wave erosion is the most powerful and immediate force, quickly washing away the loose, fragmented ash and tephra that characterize the early stages of island formation. Many such formations are transient, surviving only a few months or years before succumbing entirely to the sea.
The long-term survival of an island depends heavily on the production of dense, erosion-resistant material, such as hardened lava flows, that can cap and protect the softer ash interior. On islands like Surtsey, a process called palagonitization occurred, where the hot, water-saturated ash chemically reacted to form a type of hardened rock, similar to concrete, which dramatically increased its durability. Without this rapid stabilization, the island remains vulnerable, as demonstrated by the initial Hunga Tonga-Hunga Ha‘apai island, which was destroyed by a subsequent, more explosive eruption in 2022.
Over millions of years, even successfully stabilized islands face destruction from two slower-acting geological processes. Gravitational collapse and general weathering erode the exposed land, while the immense weight of the volcanic mountain causes the underlying oceanic crust to depress. This subsidence, combined with the slow movement of the tectonic plate away from the source of magma, means that the island slowly sinks back into the ocean, eventually becoming a flat-topped seamount below the waves. The fundamental longevity is determined by the island’s initial geological composition and its tectonic setting.