On November 20, 2023, the Icelandic Meteorological Office released its first hazard map detailing the unrest around Grindavík, Iceland. This crucial document highlights the affected area and designates the estimated position of a dike intrusion that emerged on November 10, marked by a dashed red line. The map further categorizes the hazards into three distinct zones—A, B, and C—alongside a comprehensive legend outlining the ongoing and anticipated threats within each zone.
Approximately 60 Hazard Assessment Maps Published from November 2023 to June 2024
The Icelandic Meteorological Office (IMO) holds a vital role in real-time natural hazard monitoring, providing timely warnings and forecasts regarding potential threats from earthquakes, volcanic activity, and glacial outburst floods. In addition, the Met Office advises local authorities on both preventative measures and emergency responses to these natural hazards. A significant part of this endeavor has been the continuous assessment and dissemination of information surrounding volcanic risks, particularly in light of recent unrest on the Reykjanes Peninsula.
At the end of October 2023, an earthquake swarm erupted north of Grindavík, leading to the detection of ground inflation in the Svartsengi area. This seismic activity peaked on November 10 with several quakes registering over magnitude 3 during a six-hour period. A notable dike intrusion—measuring 15 km—formed beneath the Sundhnúksgígar crater row, prompting the evacuation of Grindavík that same evening as the intrusion was confirmed to extend beneath the town. This sequence of events propelled the Met Office to evaluate hazards across various timescales:
- Near-real-time hazard assessment: Covers the immediate days up to a week ahead, relying on data from monitoring efforts and updated weekly.
- Short-term hazard assessment: Spans from weeks to three months, factoring in historical geological data alongside current monitoring findings.
- Long-term hazard assessment: Extends beyond three months, sometimes looking ahead to a year or more, based on established geological knowledge.
The Met Office has published near-real-time hazard assessment maps for the ongoing activity in Grindavík and the surrounding eruptions near Fagradalsfjall in 2021, 2022, and 2023. Each of these maps has varied according to the proximity of the activity to population centers and critical infrastructure.
A long-term hazard assessment for the Reykjanes Peninsula west of Kleifarvatn has been completed (available in Icelandic via the Long-term hazard assessment report), while work on a comprehensive assessment for the entire Reykjanes Peninsula is currently in progress.
As international standards for hazard mapping during volcanic crises remain sparse (volcanichazardmaps.org), this article aims to clarify the steps leading to the current hazard map published by the IMO, which has been released periodically over recent months. Here, we elaborate on the identification of various zones, the hazards considered in these assessments, and the methodologies employed to evaluate the threat level within each zone.
The Evolution of Hazard Maps from November 2023 to June 2024
From November 12 to 17, hazard assessment maps were initially distributed solely to local Civil Protection authorities. The first map focused on the area surrounding Grindavík, primarily informed by the graben formed on November 10, which dictated the extent of hazards present. Risks associated with volcanic unrest were classified as low, moderate, or high likelihood. The assessments captured potential hazards such as eruptive fissures, lava flows, gas emissions, lava bombs, and ash fall (tephra). This evaluation relied on data collected through the Met Office’s extensive monitoring network, GNSS deformation metrics, satellite imagery, and seismic activity, analyzed collaboratively during scientific meetings.
On November 17, the assessed area expanded, prompting an update to the hazard map that now included all regions affected by the magmatic intrusion. Although hazards continued to be classified into three categories, they were now labeled as A, B, and C. Further widening of the assessed area occurred on November 20, upon the map’s debut on the Met Office’s website, [www.vedur.is](http://www.vedur.is) (see Picture 1). Since that date, all hazard maps related to the area have been consistently made available on vedur.is.
The first hazard map for the unrest area around Grindavík, Iceland, published by the Icelandic Meteorological Office on November 20, 2023, illustrates the unrest area and indicates the estimated position of the dike intrusion formed on November 10. Three hazard zones—A, B, and C—are defined along with a legend detailing ongoing and anticipated hazards within each zone.
Classification of Hazardous Areas
By the end of November 2023, residents of Grindavík received unrestricted access to the town during daylight hours, a significant shift from the previously imposed restrictions. This change necessitated a reevaluation of how hazard maps were presented. Collaborating closely with Civil Protection, the decision was made to segment the region into four distinct areas:
- Zone 1: This area encompasses critical infrastructure for the entire Reykjanes Peninsula, including Svartsengi and the renowned Blue Lagoon, with the center of uplift located within it.
- Zone 4: Designated for the densest population centers, specifically Grindavík and Þórkötlustaðahverfi.
- Zones 2 and 3: These zones capture most areas impacted by the dike intrusion and seismic activity, including regions assessed as the most vulnerable to fissure openings. The boundary between Zones 2 and 3 is established at Stóra-Skógfell, with Zone 3 extending from the northern edge of Zone 4 to Stóra-Skógfell itself.
As the volcanic unrest escalated, most of the activity remained concentrated in Zone 3. Moreover, the previous three categories (A, B, C) evolved into five classifications: low, moderate, considerable, high, and very high, a system that remains in place today.
The zone classifications have primarily remained intact since December 8, despite the introduction of additional zones following the eruption at Sundhnjúkur crater row that commenced on December 18. Two new zones—Zone 5, located northeast of Zone 1, and Zone 6, situated to the east of Zones 2 and 3—were established. This expansion enabled evaluations of hazards related to lava flows and gas pollution into neighboring areas.
On February 20, after the evacuation of Grindavík was lifted by the National Police Commissioner, an additional area—Zone 7—was incorporated into the published map. Furthermore, in light of lava from the February 8 eruption covering Grindavíkurvegur, the main road into Grindavík, traffic was redirected to Nesvegur, a road that partially falls within Zone 7. By March 7, Zones 2 and 3 were merged.
Classification of Hazards and Assessment Procedure
The near-real-time hazard assessments, defined to span the days immediately following an event up to a week out, are derived from comprehensive evaluations made during collaborative scientific meetings convened by the Met Office. A team of scientists scrutinizes all pertinent data—including real-time seismicity, deformation, and gas measurements—integrating their specialized knowledge of the area to gauge the likelihood of any hazards developing or impacting the designated zones. Despite the extensive expertise available and a wealth of monitoring data, the unpredictable nature of volcanic unrest introduces inherent uncertainties into these assessments.
To maintain transparency and consistency, the Met Office adheres to a structured procedure for assessing hazards across various zones. Seven primary hazards are evaluated for each zone:
- Earthquakes: Monitoring seismic events as potential precursors to dike migration and volcanic eruptions.
- Sinkholes: Identifying the risk of sudden openings due to subsurface instability.
- Fault movements: Tracking the activation or expansion of existing faults, particularly within graben regions.
- Eruptive fissures: Assessing the potential emergence of fissures through which magma might reach the surface.
- Lava flow: Evaluating the potential for lava to cause significant damage to infrastructure, influenced by its temperature, composition, and the surrounding terrain.
- Tephra fallout: Understanding the emissions released into the atmosphere, which can impact visibility and air quality.
- Gas pollution: Measuring the atmospheric release of gases during eruptions, which can jeopardize air quality depending on local weather conditions.
Table 1 summarizes the seven hazards integral to the real-time hazard assessment process, providing essential insights into their definitions and assessment criteria.
The likelihood of each hazard materializing is rated on a five-point scale derived from a matrix that, among other things, reflects scientific consensus on the exposure to various risks (see Picture 2). For instance, zones with a cumulative hazard assessment score below 0.9 are classified as low risk (marked green), whereas scores exceeding 24 indicate very high risk (depicted in purple). Each hazard rated high or very high is prominently displayed on the hazard map.
Figure 2 illustrates a sample hazard matrix employed to gauge risk levels across different zones, spotlighting those categorized as considerable, high, or very high.
Distinguishing Hazard Assessment from Risk Assessment
The integration of hazards into the map and zonal divisions primarily reflects the needs of responders and those overseeing critical infrastructure in the area (Pallister et al., 2019). The modifications made after December 8, 2023, notably catered to stakeholder needs more effectively than previous iterations, facilitating more robust risk assessments moving forward.
Understanding the distinction between hazard and risk can often prove challenging. The World Meteorological Organization outlines the terms as follows:
- Hazard: a threatening event (general term) and the likelihood of a natural disaster occurring within a defined time frame and area.
- Risk: the potential damage that a specific hazard may inflict within a given area over a defined period.
In essence, a hazard assessment identifies possible events, their causes, and their likelihood of occurrence. In contrast, a risk assessment examines the potential impacts of those hazards, proposing mitigation strategies to reduce both their frequency and consequences.
It’s vital to recognize that the hazard assessment conducted by the Icelandic Meteorological Office for the unrest region not only identifies existing hazards but also indicates the likelihood that these issues may arise suddenly. Risk assessments evaluate the interplay between hazards, vulnerabilities (like infrastructure and populations), and protective measures (such as evacuations and barriers) in specific areas. Thus, a significant hazard does not automatically correspond to high risk if effective mitigation strategies are in place to safeguard lives and property.