Artificial island

Lore & Background

Artificial islands have a long history, with Neolithic examples like crannógs and Nan Madol predating later constructions by thousands of years. Ancient examples include the stilt crannogs of prehistoric Wales, Scotland, and Ireland, the ceremonial centers of Nan Madol in Micronesia, and the floating islands of Lake Titicaca. The Aztec city of Tenochtitlan stood on a small natural island surrounded by countless artificial chinampas islands. In the Solomon Islands, the people of Langa Langa Lagoon and Lau Lagoon built about 60 artificial islands on the reef, including Funaafou, Sulufou, and Adaege, formed one rock at a time for protection from attack and to avoid mosquitoes.

Reader's Guide

Artificial islands have been constructed for millennia for residential, industrial, commercial, structural, and strategic purposes. In modern times, they are usually formed by land reclamation, though some result from valley flooding. The legal definition of artificial islands remains unclear. These islands provide valuable real estate, isolation for specific uses (e.g., Dejima for European merchants, Ellis Island for immigration processing), and protection from rising sea levels. Their construction involves significant engineering challenges, including wave size and structural integrity considerations.

Did You Know?

• The earliest known artificial islands date back to Neolithic crannógs and Nan Madol, thousands of years before Al-Sayah Island in Bahrain.
• The Flevopolder in the Netherlands is a large polder connected to the mainland, not an artificial island.
• The people of Lau Lagoon in the Solomon Islands built artificial islands one rock at a time for protection and health reasons.
• China's artificial island on Fiery Cross Reef houses military barracks and a runway for military aircraft.

Seventy Million Years of Fire

The volcanic story of the Canary Islands stretches back roughly 70 million years, making it one of the longest-running episodes of island-building in the Atlantic. During the first tens of millions of that span, every eruption took place beneath the waves, slowly stacking lava on the ocean floor. It was not until about 20.2 million years ago that accumulated basalt finally breached the surface at several sites, giving birth to the first landmasses. The eastern islands—Lanzarote and Fuerteventura—were the first to rise above the waves, and each island further west followed in sequence, with the westernmost reaching the surface as recently as 1.1 million years ago. Even before the main islands appeared, a cluster of seamounts had been erupting across a broad swathe of the seafloor, including one as far as 380 kilometres north of Lanzarote. The northernmost of these, the Lars seamount, dates to about 68 million years ago, and the seamounts grow progressively younger as you track them southwestward. This long, layered record of submarine and subaerial volcanism makes the archipelago a natural laboratory for understanding how oceanic islands mature over deep geological time.

A Volcanic Province Far from Plate Edges

Unlike most volcanic regions on Earth, the Canary Islands do not sit at a divergent or convergent plate boundary. They rest on the African tectonic plate, well within its interior, far from any active margin. This makes them a textbook case of intraplate volcanism—magma punching through the crust from below without the aid of plate separation or subduction. The oceanic crust beneath the islands is among the oldest in the Atlantic, formed between 175 and 150 million years ago during the breakup of Pangaea, when North America and Northwest Africa began to drift apart. That ancient seafloor, built from igneous and sedimentary layers, provides the foundation on which the volcanic province later developed. The Canary Islands occupy one end of a geological spectrum of deep-ocean volcanic islands, with the Hawaiian archipelago at the opposite extreme. While Hawaiian islands are eventually carried away from their volcanic source and sink, the Canaries have not experienced significant subsidence, meaning their evolutionary sequence—submarine, shield-building, erosional, and post-erosional—plays out without the dramatic drowning phase seen in the Pacific.

From Seamount to Skyline

The seven main islands—Lanzarote, Fuerteventura, Gran Canaria, Tenerife, La Gomera, La Palma, and El Hierro—each began life as an isolated submarine volcano on a seafloor ranging from 1,000 to 4,000 metres deep. Over millions of years, successive lava flows piled upward until the peaks finally broke the surface. The total volume of volcanic rock in the archipelago is staggering: approximately 124,600 cubic kilometres. Yet only about 4 percent of that mass—roughly 4,940 cubic kilometres—sits above the waves; the remaining 96 percent is hidden beneath the ocean. The western islands retain a larger share of their volume above sea level (about 7 percent) compared with the eastern ones (around 2 percent). The archipelago stretches 450 kilometres from east to west, with minor islets and rock formations dotting the waters around each main island. Lanzarote and Fuerteventura are joined by the Canary Ridge and were once a single landmass, sometimes called Mahan, during the Last Glacial Maximum around 20,000 years ago, when global sea levels were lower. Today an 11-kilometre-wide, 40-metre-deep strait separates them.

A Living Volcanic Landscape

The Canary Islands are not a geological relic; they remain an active volcanic province. During the Holocene—the last 11,700 years—eruptions have occurred on every main island except La Gomera, underscoring how recently the volcanic engine has been firing. The most recent eruption on land took place in 2021, while the latest underwater event was recorded in 2011–2012, reminding residents and scientists alike that the threat is not confined to visible peaks. The broader Canary Volcanic Province, which extends up to 400 kilometres north of the archipelago, has produced activity continuously since roughly 70 million years ago. The Selvagen Islands, located about 200 kilometres to the north, were the first landmasses to emerge in this region, appearing between 30 and 25 million years ago, long before the main Canary Islands. This unbroken chain of volcanic events—from the oldest seamounts to the freshest lava flows—means the region is a living record of Earth's internal heat still shaping the surface, and it guarantees that the geological story of the Canaries is far from finished.

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