Harnessing Earth’s Fury: How Icelandis Learned to Slow Lava Flows at Fagradalsfjall
In March 2021, after lying dormant for 800 years, the Fagradalsfjall volcano on Iceland’s Reykjanes Peninsula erupted, spewing molten lava into the surrounding landscape. This dramatic awakening presented an opportunity and a challenge for researchers, emergency planners, and engineers alike. Traditionally, volcanic eruptions have been accepted as inevitable forces of nature—impossible to contain or direct. Yet, the 2021 eruption birthed an unprecedented large-scale field experiment attempting to control lava flows by building earthen barriers designed to slow and divert the fiery deluge threatening critical infrastructure.
Fjóla Guðrún Sigtryggsdóttir, a professor at the Norwegian University of Science and Technology (NTNU), was uniquely positioned to spearhead efforts to contain the molten threat. Already in Iceland on sabbatical and versed in embankment dam safety, Sigtryggsdóttir teamed with Icelandic authorities and engineers to rapidly design and construct defensive dams and barriers in the path of advancing lava. The goal was not to halt the volcanic force outright but crucially to buy time—delaying lava flows to reduce damage to infrastructure and provide early warning for necessary evacuations.
The volcanic terrain added complexity to this challenge. Lava flow velocity is dictated by the viscosity of the molten rock and the gradient of the landscape, variables that shift with changing eruption dynamics. Pahoehoe lava, characterized by its smooth, fluid texture, flows readily in thin, broad sheets that can accumulate behind barriers, heightening overtopping risks. Conversely, block lava presents as a sticky, bulky mass with a hardened crust capable of exerting tremendous pressure, pushing embankment dams upward in a bulldozing effect. Engineering resilient barriers that accommodate these radically different lava behaviors demanded intensive research and tough, adaptive fieldwork under hazardous conditions.
Three significant embankment dams were erected during the six-month eruption, involving a monumental effort by bulldozer and excavator operators working around the clock beneath the looming threat of flowing magma. The tallest barrier reached eight meters high, with accompanying dams extending 300 and 35 meters in length, constructed using locally sourced earth, sand, and stone. These barriers served as testbeds not only to delay lava—successfully holding back flows for up to 16 days—but also to divert molten rock lanes safely around vulnerable zones, especially critical roadways and inhabited areas.
Safety was paramount as workers operated mere meters from searing lava, often under threat of sudden fissure eruptions and maremagnum of earthquake tremors shaking the peninsula. Prior to the initial 2021 eruption, Icelandic monitoring stations had recorded more than 40,000 earthquakes, highlighting the volatile tectonic environment. Researchers and civil defense teams collaborated closely to map risk zones and develop rapid response tactics that balanced urgency with operational security. This multidisciplinary cooperation heralded a new model for active volcanic hazard mitigation.
Engineering barriers that could withstand the brutal forces of block lava required innovative design principles borrowed from embankment dam safety codes. Sigtryggsdóttir’s expertise proved invaluable—her research informed the construction guide distributed to Icelandic authorities, advocating how in situ materials could be harnessed to build robust, scalable lava containment structures. This guide not only described the physical dimensions and placement strategies of the barriers but emphasized adaptability, monitoring, and reinforcement in the face of lavas that could overpower weaker embankments.
The success of the 2021 experiment catalyzed practical applications during subsequent eruptions threatening the nearby town of Grindavík in late 2023 and early 2024. Early deployment of lava barriers, continuously informed by evolving experience and real-time data, spared many homes and key infrastructural elements from destruction. Had these defensive measures not been implemented, Sigtryggsdóttir notes, scores of residences would likely have been engulfed in molten rock. This demonstrated that while total immunity from volcanic damage is unfeasible, strategic intervention can materially improve the safety and resilience of communities in volcanic zones.
Yet challenges remain. Volcanic fissures do not always cooperate with human intentions. In spring 2025, new fissures emerged downstream of protective barriers around Grindavík, temporarily breaching defenses and reigniting fears. Fortunately, no significant damage occurred during these brief eruptions, but they underscored the unpredictable nature of volcanic processes and the limits of current control methods. Constant vigilance, continuous refinement of barriers, and dynamic adjustment to new fissure formations are necessary to adapt defensively to an ever-changing volcanic landscape.
Computer modeling plays an essential role in preempting lava flow trajectories. By inputting variables such as lava volume, viscosity, terrain slope, and evolving topography created by cooling lava layers, scientists aim to simulate how molten streams will navigate the terrain. Such simulations help optimize barrier placement and height, guiding engineers as they race against time. However, the continual reconfiguration of the landscape by advancing lava presents a moving target—each eruption rewrites geography in real time, complicating predictive efforts.
Despite technical difficulties and inherent uncertainties, the 2021 Geldingardalir volcanic field experiment demonstrated a powerful principle: volcanic lava flows can be controlled, at least to some extent. This strategic intervention represents a paradigm shift away from passive acceptance of volcanic hazards toward proactive hazard mitigation. As Sigtryggsdóttir reflects, the tangible results achieved reinforce the necessity and feasibility of applying engineering ingenuity to protect at-risk civil society and critical infrastructure in volcanic hotspots.
The lessons distilled from Iceland’s latest volcanic challenges resonate far beyond its rugged shores. Active volcanoes punctuate landscapes worldwide, threatening millions. The knowledge gained here about the construction and efficacy of lava barriers, safety protocols in hazardous fieldwork, and multi-agency emergency cooperation provides a vital template for other volcanic regions. While no method offers absolute protection, combining scientific observation, modeling, engineering, and preparedness fortifies community resilience against one of Earth’s most formidable natural forces.
Looking ahead, new eruptions will inevitably generate further insights, prompting iterative advances in lava control strategies. Iceland’s experience signifies a living laboratory where the convergence of geoscience, engineering, and civil defense illuminates paths toward safer volcanic communities. In the dance between fire and earth, human resolve and innovation prove potent allies, buying precious time and reducing harm where once only despair reigned.
Subject of Research: Not applicable
Article Title: Experience in diverting and containing lava flow by barriers constructed from in situ material during the 2021 Geldingardalir volcanic eruption
News Publication Date: 18-Mar-2025
References:
- Fjóla G. Sigtryggsdóttir, Hörn Hrafnsdóttir, Jón Haukur Steingrímsson, Ari Guðmundsson. Experience in diverting and containing lava flow by barriers constructed from in situ material during the 2021 Geldingardalir volcanic eruption. Bulletin of Volcanology (2025) 87:28. DOI: 10.1007/s00445-025-01806-3
Image Credits: Photo by Hörn Hrafnsdóttir
