La Palma Eruption’s Effects on Local Ecology

The 2021 eruption of the Cumbre Vieja volcano on La Palma drastically altered the island’s environment. Beyond immediate destruction, it triggered long-term ecological changes that continue to shape local habitats and species interactions.

Volcanic Gases And Atmospheric Composition

The eruption released a complex mixture of gases, significantly affecting air quality. Sulfur dioxide (SO₂) was among the most abundant emissions, with satellite data from the European Space Agency (ESA) indicating a peak daily output of 50,000 metric tons. This gas reacts with atmospheric moisture to form sulfuric acid aerosols, contributing to acid rain and degrading air quality over vast distances. Elevated SO₂ levels were detected as far as mainland Europe.

Carbon dioxide (CO₂) also surged, accumulating in low-lying areas and posing asphyxiation risks to humans and wildlife. Measurements by the Instituto Geográfico Nacional (IGN) showed localized CO₂ concentrations exceeding 50,000 ppm near lava flows, well above the Occupational Safety and Health Administration (OSHA) permissible exposure limit of 5,000 ppm. Such high levels can displace oxygen, creating hazardous conditions in poorly ventilated spaces.

Hydrogen sulfide (H₂S) and hydrofluoric acid (HF) were present in lower concentrations. H₂S, with its characteristic rotten egg odor, can cause respiratory distress above 10 ppm, while HF poses severe risks due to its ability to penetrate tissues and disrupt calcium metabolism. These gases prompted temporary evacuations in certain areas as authorities monitored air quality.

Volcanic gases also influenced local weather patterns. The formation of vog (volcanic smog) resulted from SO₂ reacting with sunlight, oxygen, and water vapor, producing fine sulfate particles that reduced visibility and aggravated respiratory conditions. Studies from past eruptions, such as Kīlauea in Hawaii, show prolonged vog exposure increases hospital admissions for asthma and other pulmonary diseases. Similar health concerns were reported on La Palma.

Soil Changes And Local Biota

The eruption profoundly altered La Palma’s soil composition, creating a patchwork of volcanic deposits and disrupted ecosystems. Tephra—fragments of volcanic rock and ash—blanketed large areas, modifying soil structure and nutrient availability. Thick ash layers reduced oxygen penetration and water retention, making conditions inhospitable for many plant roots and soil-dwelling organisms. Studies of past eruptions, such as Mount St. Helens in 1980, show such deposits can take years to weather into biologically viable soil, depending on rainfall, microbial activity, and the presence of pioneer species.

Fresh volcanic ash, rich in minerals like silica, iron, and magnesium, initially lacks the organic matter necessary for plant life. Weathering and microbial colonization gradually improve soil fertility. However, soluble fluorides in the ash can be toxic to plants and animals. Research from the Eyjafjallajökull and Holuhraun eruptions in Iceland showed fluoride-rich ash leaching into soil and water systems, leading to bioaccumulation in vegetation and risks to herbivorous species. On La Palma, initial soil tests by the Instituto Geológico y Minero de España (IGME) detected elevated fluoride levels in some areas, raising concerns for grazing livestock and endemic plants.

Microbial communities also faced significant disruption. Volcanic activity can sterilize upper soil layers due to extreme heat, drastically reducing bacterial and fungal populations essential for organic decomposition and nutrient cycling. A study in Soil Biology & Biochemistry on microbial recovery after the 2010 Merapi eruption in Indonesia found bacterial diversity remained suppressed for years before gradually rebounding. On La Palma, preliminary assessments suggest nitrogen-fixing bacteria, crucial for soil fertility, have been slow to return in heavily affected zones, impacting native vegetation.

Invertebrates, particularly soil-dwelling species, suffered immediate losses. Earthworms, which aerate soil and facilitate organic matter decomposition, are highly sensitive to changes in pH and texture. Thick ash deposits likely caused widespread mortality, as seen in the 1991 Mount Pinatubo eruption. Arthropods, including beetles and ants, also struggled to recolonize due to lost plant cover and altered microhabitats. However, opportunistic scavengers and detritivores, such as certain mites and springtails, tend to thrive in disturbed environments with abundant decaying organic matter.

Aquatic Habitat Shifts

The eruption reshaped La Palma’s aquatic ecosystems as volcanic material altered coastal waters and inland freshwater systems. Lava flows reaching the ocean triggered thermal and chemical reactions, producing steam plumes laden with hydrochloric acid and fine particulate matter. These changes created localized zones of extreme acidity, temporarily reducing marine biodiversity. Fish kills were reported, likely due to rapid pH shifts and oxygen depletion, mirroring patterns observed in the 2018 Kīlauea eruption in Hawaii.

Volcanic ash deposition affected sediment dynamics and nutrient cycling. Fine ash particles suspended in the water column reduced sunlight penetration, disrupting photosynthesis in seagrasses and phytoplankton. This decline in primary production affected food webs, as herbivorous species experienced reduced foraging opportunities. Over time, however, volcanic ash can contribute to nutrient enrichment, as seen after the 2011 Puyehue-Cordón Caulle eruption in Chile, where silica, iron, and phosphorus in the ash boosted phytoplankton blooms.

Changes in sediment composition also had physical consequences. In coastal zones, volcanic debris altered seafloor topography, burying benthic organisms and reshaping coral reefs. Coral communities, highly sensitive to sedimentation, suffered smothering effects that reduced photosynthesis and disrupted symbiotic relationships with algae. Inland, ash deposits altered river and stream ecosystems by changing flow patterns and increasing turbidity. Elevated sediment loads clogged fish gills, reduced spawning success in species requiring clear water, and shifted macroinvertebrate populations that serve as food for larger aquatic organisms.

Plant And Animal Responses

The eruption forced rapid adaptations among La Palma’s plant and animal populations. Vegetation in the path of lava flows was obliterated, while surrounding areas suffered from falling ash, heat exposure, and chemical deposition. Many native plants, particularly those with thin leaves or shallow roots, struggled due to disrupted photosynthesis and water uptake. However, species with fire-resistant traits, such as the Canary Island pine (Pinus canariensis), demonstrated resilience. Its thick bark and ability to resprout from scorched trunks allowed for quicker recovery.

Animal populations faced challenges from habitat loss, food shortages, and altered microclimates. Birds dependent on forests relocated as nesting sites were buried or rendered uninhabitable. Some species, such as Berthelot’s pipit (Anthus berthelotii), adapted by shifting to open habitats with less ash accumulation. Ground-dwelling reptiles, including the La Palma wall lizard (Gallotia galloti palmae), suffered increased mortality due to heat-retaining volcanic deposits raising surface temperatures beyond their tolerance. Conversely, scavengers and opportunistic feeders—such as certain insects—flourished, taking advantage of the abundance of decaying organic matter left in the eruption’s wake.