Volcanic hazards and monitoring

Hazard, exposure and vulnerability

Volcanic hazard describes what may occur and how often it is expected: effusive or explosive eruptions, pyroclast fallout, lava flows, gases, earthquakes or flank landslides. In the Canaries, hazard is not uniform: it is higher in La Palma and El Hierro, where historical activity is recent, and lower in islands such as Fuerteventura or La Gomera, now inactive from a historical point of view.[1][2]

Exposure grows wherever population, infrastructure or essential services concentrate in areas of higher hazard. Vulnerability depends on construction quality, institutional response capacity and the population’s perception of risk. A distant volcano may represent no risk if no one lives within its reach, while a small eruption near a densely populated area may have high consequences.[1][2]

Seismicity

The IGN seismic network records activity in near real time and locates earthquakes associated with magma ascent, fault reactivation or adjustments of the volcanic edifice. The revised IGN seismic catalogue provides a homogeneous basis for studying the spatial and temporal distribution of earthquakes in the archipelago.[1]

A seismic swarm is not, by itself, a prediction of eruption. It indicates that the volcanic system is disturbed, but seismicity can rise and fall without leading to an eruption. Interpretation requires comparing depth, location and temporal evolution with other monitoring parameters.[1][2]

Ground deformation

Ground deformation indicates changes in the volume or pressure of a magmatic system. It is measured with GPS stations, tiltmeters and satellite radar interferometry. In episodes such as El Hierro in 2011 or La Palma in 2021, deformation preceded the eruption and helped to constrain the likely location of the focus.[1][2]

However, deformation does not always signal an imminent eruption. Volcanic edifices can inflate or deflate because of fluid movements, hydrothermal adjustments or deep processes with no direct link to a future eruption. That is why it is interpreted together with seismicity and geochemistry.[1][2]

Gases and thermal anomalies

The composition and flow of volcanic gases, especially sulphur dioxide and carbon dioxide, change when magma approaches the surface or when the hydrothermal system is altered. Systematic measurement in fumaroles, mofettes and soils makes it possible to detect trends that, combined with other data, reflect the state of the volcano.[1][2]

Thermal techniques, including infrared satellite imagery, provide information on zones of anomalous heating. They are most useful once eruptions have begun, when lava flows or hot deposits are visible, but they can also detect precursors in areas of gas discharge.[1]

Integration, uncertainty and limits of prediction

Modern monitoring integrates seismicity, deformation, gases, thermal and hydrogeology into models that try to represent the state of the volcanic system. No model is definitive: every interpretation depends on data quality, initial assumptions and the incomplete knowledge we have of deep magmatic pathways.[1][2]

Uncertainty is not a failure of science but an inherent feature of complex volcanic systems. Expressing it clearly is as important as collecting data, because it allows society to prepare for different scenarios without falling into paralysis or alarmism.[1][2]

Exact prediction of the time, place and style of a volcanic eruption is not possible with current technology. What monitoring can offer are updated probabilities and plausible scenarios that allow authorities to make gradual decisions. This limitation must be understood as part of the normal functioning of scientific knowledge, not as a hidden shortcoming.[1][2]

When monitoring detects signals compatible with an imminent eruption, the response cannot wait for absolute certainty. Risk management combines scientific knowledge with precautionary criteria, evacuation plans and transparent communication in order to reduce the impact on exposed populations.[1][2]

PEVOLCA and communication

PEVOLCA is the official framework that coordinates the response to a volcanic emergency in the Canaries. It defines alert levels, administrative responsibilities and action protocols. During the 2021 La Palma eruption, PEVOLCA served as the axis for evacuating populations, managing infrastructure and public communication.[1][2]

Scientific communication during a crisis must translate uncertainty into understandable messages. The daily IGN reports and PEVOLCA briefings during La Palma 2021 exemplify how coordination between technicians and managers can keep the population informed without generating false expectations of prediction.[1][2]