Submarine volcanoes can create new islands because volcanic activity under the ocean leads to the formation of underwater mountains that can eventually emerge from the water and form dry land.
Beneath the oceans, the earth's crust is in constant motion due to the movement of tectonic plates. When two plates move apart, it creates fissures through which magma rises from the Earth's mantle. This often occurs at mid-ocean ridges, vast underwater volcanic chains extending thousands of kilometers. When one plate slides beneath another, however, magma can also form, rise to the surface, and give birth to a volcano. Gradually, eruption after eruption, this accumulated lava eventually creates a true underwater mountain: a future submarine volcano.
Underwater, when the pressure becomes too great, a volcanic eruption eventually occurs. The molten lava then quickly erupts from the underwater volcano. Upon contact with the cold water, it cools down and solidifies almost immediately, forming pieces of volcanic rock called pillow lava. Gradually, these rocks stack and accumulate on the ocean floor, creating a sort of ever-taller underwater mountain. As the volcanic eruptions continue, this mountain grows and grows, until it eventually exceeds sea level: a new volcanic island has just been born.
Underwater, during a volcanic eruption, lava flows and hardens quickly upon contact with cold water. This phenomenon leads to a progressive accumulation of volcanic rocks around the crater. Gradually, these successive layers of lava stack up, the structure grows, and eventually reaches the water's surface. Once above the water, the volcanic island often continues to grow with each new eruption. The process may seem quick, but it can sometimes take many years, even centuries, for an island to truly emerge. In short, it all relies on this game of accumulating cooled lava that builds an island from the seabed to the surface.
When a new volcanic island emerges, it disrupts the entire surrounding marine area. The burning lava in contact with water causes abrupt changes in the temperature and chemical composition of the waters. This often leads to the immediate death of part of the local marine fauna, but it also creates new opportunities. Little by little, these pieces of volcanic rock will serve as a habitat for new biological life. Mosses, lichens, and seabirds come to settle on the pristine island. Over time, larger plants take root, allowing various animal species to arrive in turn. Ultimately, these islands become true natural laboratories for studying how ecosystems are created and evolve from nothing.
The island of Surtsey, off the coast of Iceland, suddenly emerged from the waves in 1963 after a series of spectacular underwater eruptions. Now protected and reserved exclusively for scientific research, it demonstrates how life gradually colonizes a new territory. More recently, the island of Hunga Tonga-Hunga Ha'apai, near the Tonga Islands, made its appearance in 2015 thanks to an impressive eruption that quickly created a visible land mass. These islands are born from violent volcanic explosions beneath the ocean, which accumulate large amounts of rocks and ash until they emerge above the surface, capturing the attention of researchers wanting to follow their evolution.
The Hawaiian Islands are actually the emerged summits of an immense underwater mountain range formed by a fixed volcanic hotspot located beneath the constantly moving tectonic plate.
The Icelandic island of Surtsey, which emerged suddenly in 1963 as a result of an underwater eruption, now serves as a valuable natural laboratory where scientists study how life gradually colonizes a new island.
When lava comes into contact with cold water, it solidifies, often forming what are called 'pillow lavas', rounded and characteristic structures frequently found on the ocean floor.
Some recently formed volcanic islands sometimes disappear quickly due to marine erosion, making their lifespan very limited — sometimes only a few years.
No, not all new volcanic islands are permanent. Some disappear quickly due to wave erosion, while others, benefiting from enough solidified lava, last for decades or even become permanent.
The main risks are related to volcanic activity (explosions, lava flows, emission of toxic gases). Additionally, marine disturbances such as local tsunamis, sudden changes in the seabed, and the disruption of shipping routes can also pose safety concerns.
The formation of an island immediately disrupts its marine environment by altering underwater currents, temperature, and the chemical composition of the water. In the short term, this can be destructive for existing ecosystems. In the long term, the island can become a suitable habitat for a great diversity of marine and terrestrial life.
Even though scientists can detect the precursors of a possible underwater eruption (earthquakes, increased volcanic gas emissions, thermal anomalies, and heightened seismic activity), accurately predicting the exact time or location where an island will emerge remains very challenging.
It largely depends on volcanic activity. Some islands can emerge within a few days or weeks during a particularly intense eruption, while others require several months or even years of repeated lava accumulation to surface.
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