An ambitious vision of a city built from lava

CNN

04-07-2025

Erupting from fiery volcanoes, lava has historically been an uncontrollable force that destroys buildings and neighborhoods in its wake. But what if that force could instead be redirected and harnessed to create whole cities? An ambitious project from Icelandic firm s.ap arkitektar, presented at this year's Venice Architecture Biennale (running until November 23), proposes just that.
Whereas lava naturally cools on the landscape to become volcanic rock such as basalt, 'Lavaforming' — which envisions molten rock as a new form of building material — lays out strategies for cooling it in controlled ways so that it can set into walls, columns and other architectural elements capable of producing new settlements. Along with collaborators, s.ap arkitektar has made a film imagining the year 2150, when such building technology could become a reality, reshaping the world in the process.
Founded by Arnhildur Pálmadóttir and operated with her son Arnar Skarphéðinsson, s.ap arkitektar has been undertaking research and conducting tests to explore how something that is seen primarily as a threat can be transformed into a renewable resource capable of producing sustainable buildings. But just how realistic is the future of lava cities?
Iceland is one of the most active volcanic regions in the world, situated on a rift between two tectonic plates. Home to around 30 volcano systems, the country on average experiences an eruption every five years. It was during one such occurrence — the 2014 Holuhraun eruption — that Pálmadóttir realized there was a 'huge amount of material coming up from the ground,' she explained over video call from the capital Reykjavík. She thought: 'wow, we could build a whole city in one week with that.'
The 'Lavaforming' project started in earnest a few years later as a 'thought experiment,' added Skarphéðinsson. It also aimed to be a critique of the building industry's reliance on concrete and the carbon emissions resulting from its production. (It is estimated that due to heating lime and clay at high temperatures to create cement, a key ingredient of concrete, the material's production accounts for approximately 8% of global CO2 emissions, which contribute to global warming and climate degradation.)
'We think that lava can compete with concrete, but be more sustainable,' said Pálmadóttir, adding that lava 'has all the materialities that concrete has, depending on how it cools down.' If lava cools quickly, explained Pálmadóttir, it turns into a hard, glass-like material — obsidian. If it cools slowly, it is more likely to crystallize, which can work well for creating columns and structural elements. If the lava cools quickly and also gets air in it, meanwhile, a pumice-like, highly insulative material is created.
The carbon emitted by hot lava spewing from a volcano would be released into the atmosphere anyway, she said, no matter how it is cooled and used — so better to make the most of it and avoid additional emissions from concrete production.
s.ap arkitektar has put forward three speculative methods for turning lava into architecture.
In the first, carefully designed networks of trenches are dug at the foot of active volcanoes for molten lava from eruptions to be directed into, where it can cool to create structural walls or foundations for a city; such trenches could also channel lava into a factory that molds the lava into bricks that can be moved and used elsewhere. The hope is that by redirecting the lava into trenches, surrounding communities would also be protected from the damaging force of the lava during an eruption.
The second method harnesses the technology of 3D printing, imagining future 3D-printing robots which could traverse a landscape of molten lava after an eruption and use the lava to 'print' elements of buildings. The technology for such robots does not yet exist, however.
The third technique involves tapping into magma under the ground, directing lava into new, specially constructed chambers where it could cool into prefabricated, replicable architectural elements. The team believes accessing such subterranean magma would take a similar approach to that of geothermal energy production — which harnesses heat from the Earth's core and is a significant source of energy in Iceland. Though, s.ap arkitektar do not yet know if such a process would be geologically safe.
The architects concede that the practicalities of 'Lavaforming' are not yet fully worked out and relies on further research and technological development, not to mention wider buy-in. But they feel their proposal is becoming more realistic as the project evolves. Since the project's launch in 2022, s.ap arkitektar have increasingly engaged with scientists, who have worked on lava flow prediction models and visualized them in 3D software, making lava flow simulations for eruptions in Iceland and undertaking 'lava tests' in which volcanic rock is heated to become molten lava again, and cooled in controlled ways to make prototype building elements.
Relying on eruptions anchors the proposal to time and place, but s.ap believes its idea could have value in volcanically active Iceland, as well as other locations where there is 'slow-flowing lava,' said Pálmadóttir, adding that Hawaii is 'really similar' to Iceland geologically, as are the Canary Islands in the Atlantic Ocean.
Volcanic rock is not a new building material — it has been used throughout time, like stone, for structural elements such as walls. It can be found all over the world, and once quarried, is used as stackable rocks, bricks, panels, or crushed into gravel to be used as aggregate in concrete.
Basalt, the most common volcanic rock, has been used to build structures including the 13th-century Qasr al-Azraq ('Blue Fortress') in Jordan, the 15th-century Château d'Anjony in France, the Gateway of India (1924) in Mumbai, and the Herzog & de Meuron-designed Dominus Winery (1997) in Napa Valley, California. More recently, basalt was used in the Nashan Geological Museum (2021) in Yangzhou, China, the Radisson Resort & Spa (2023) in Lonavala, India, and an impressive private home called Casa Basaltica (2023) in Querétaro, Mexico. Architects appreciate the material for its strength, durability, insulating properties, rugged texture and often dark tones.
The way s.ap wants to use volcanic rock, however, is very different — and relies on working with it in its molten state. The practice wants to harness lava as a 'mono material,' cooling it in controlled and varied ways — which has 'never been done before,' said Skarphéðinsson — to achieve different material qualities within one single form, from solid blocks to pumice-like insulative stone and glass-like sheets for windows.
Much of s.ap's inspiration stems from nature, which, as Pálmadóttir said, 'has been creating forms and structures out of lava from the beginning of time.' She references the caves formed by bubbles in lava after an 18th-century eruption on the island of Lanzarote (part of the Canary Islands), which 20th-century architect César Manrique used as subterranean rooms for his own home in 1968.
Whether we end up living in cities made of lava relies on complicated practical factors, from technology and safety to funding and political appetite. But for now, s.ap's vision is simply to make people think a little differently. 'How can we change systems to respond to the global (climate) emergency?' asked Pálmadóttir. 'How does architecture and the built environment need to address this differently? We hope other places will look at this project as an inspiration.'