Lonquimay

Lonquimay is a striking, snow-capped stratovolcano located in the Araucanía Region of southern Chile. Rising to 2,865 meters (9,400 ft), its truncated, varying cone creates a dramatic silhouette against the Andean sky. It sits within the protected Malalcahuello-Nalcas National Reserve, an area renowned for its ancient forests and volcanic landscapes. While its beauty attracts thousands of tourists annually, Lonquimay is a potent geological force, responsible for one of the most chemically toxic eruptions recent history.

The Christmas Eruption of 1988

Lonquimay gained international notoriety on December 25, 1988, when a fissure opened on its northeastern flank.

• Birth of Navidad: The eruption did not occur at the main summit but rather created a brand new parasitic cone. Since it began on Christmas Day, the new volcano was named Crater Navidad (Christmas Crater).
• The Flow: For 13 months, this vent spewed a continuous river of blocky andesitic lava that traveled over 10 kilometers down the Lolco river valley. The volume was immense, burying forests and ranch land under a wall of black rock up to 60 meters thick.
• The Fluorine Disaster: The most insidious aspect of this eruption was not the lava, but the gas. The magma was unusually rich in fluorine. As the fine ash settled on the grass in the surrounding valleys, it coated the vegetation in toxic hydrofluoric acid. Thousands of cattle, sheep, and horses died from osteofluorosis—a horrifying condition where the bones become brittle and teeth disintegrate. It was an environmental and economic catastrophe for the local Pehuenche and settler communities, leading to major health studies on the effects of volcanic fluorine on human populations.

Ecological Wonder: The Araucaria Forests

The slopes of Lonquimay are home to one of the world’s most unique ecosystems: the Araucaria forest.

• Living Fossils: The Araucaria araucana, or Monkey Puzzle Tree, is a living fossil dating back to the Mesozoic era. These trees, with their thick, fire-resistant bark and umbrella-like canopies, have evolved to survive in volcanic terrain.
• Volcanic Bonsai: Near the tree line and close to the lava flows, one can see widespread “dwarfing” of the vegetation. The stark contrast between the black volcanic sand (scoria) and the dark green, reptilian branches of the Araucaria trees creates a prehistoric landscape that feels like walking into a dinosaur habitat.
• Resilience: Following the 1988 eruption, the recovery of the forest has been slow but steady. The Araucaria trees that were not buried have shown remarkable resilience to the heavy ash loads, though the long-term effects of the fluorine soil contamination are still being studied by ecologists.

The Spirit of the Pehuenche

The area around Lonquimay is the ancestral homeland of the Pehuenche people, a branch of the Mapuche nation.

• People of the Pine: The name “Pehuenche” literally translates to “People of the Pehuén” (the Mapuche name for the Araucaria tree). Their culture is inextricably linked to the forest and the volcanoes. The piñón (the nut of the Araucaria) is a staple food source, harvested every autumn in a sacred gathering practice known as the piñoneo.
• Volcanic Deities: For the Pehuenche, the volcano is not just a geological feature but a powerful spirit entity (Pillán). Eruptions are often interpreted as manifestations of spiritual discontent or imbalance. During the 1988 eruption, local Machis (shamans) performed distinct ceremonies (Nguillatun) to appease the spirit of the mountain, asking for the lava to spare their winter grazing lands.
• Cultural Resilience: The survival of the Pehuenche culture despite centuries of colonization and the environmental pressures of living in a volcanic zone is a testament to their deep ecological knowledge. They have learned to read the signs of the mountain—changes in bird behavior, the smell of the water, the shifting winds—long before modern science established observatories.

Volcanic Architecture and Geomorphology

Lonquimay offers a masterclass in stratovolcano construction.

• The Truncated Cone: Unlike the perfect cone of Osorno or Fuji, Lonquimay appears slightly truncated. This is due to a history of summit collapses and the migration of the active vent. The main crater is large and oval-shaped, measuring about 700 meters across, and is filled with a glacier that feeds the headwaters of the Biobío River.
• The Cordón Fisural: Lonquimay is part of a larger fissural volcano complex. The “Cordón Fisural Oriental” is a line of volcanic vents stretching 10 kilometers to the northeast. This structural weakness in the crust is what allowed the Navidad cone to form so easily. It suggests that future eruptions are just as likely to occur on the flanks as at the summit.
• Lava Types: The lava produced by Lonquimay shifts between andesite and dacite. The 1988 flows were blocky “aa” lavas, extremely viscous and slow-moving, forming walls of rock up to 20 meters high that advanced like a tank tread. These flows have now cooled into a chaotic, jagged landscape that is almost impossible to traverse on foot, creating a natural fortress of stone.

Biodiversity: Life in the Ash

The Malalcahuello-Nalcas National Reserve is a biodiversity hotspot.

• The Green Transition: The reserve sits in a transition zone between the temperate rainforests of the south and the drier sclerophyllous forests of the north. This creates a unique mix of species.
• Fauna: The forests are home to the elusive Darwin’s Fox (Lycalopex fulvipes), one of the most endangered canids in the world. Pumas patrol the tree line, hunting European hares and small deer like the Pudu.
• Avian Life: The skies are ruled by the Andean Condor, while the dense understory is the territory of the Magellanic Woodpecker (Campephilus magellanicus), whose rhythmic drumming echoes through the Araucaria trunks.
• Adaptation: The plants here have adapted to frequent ash fall. Many species have tough, waxy leaves that shed volcanic dust easily. The soil, constantly replenished by volcanic ejecta, is immensely fertile, allowing for rapid regeneration of the forest floor after fires or smaller eruptions.

Geological Context: The Andes in Motion

Lonquimay sits in a complex tectonic neighborhood.

• The Liquiñe-Ofqui Fault: The volcano lies directly on the Liquiñe-Ofqui Fault Zone, a massive 1,000-kilometer-long strike-slip fault that runs parallel to the Andean chain. This fault acts as a highway for magma, allowing it to ascend easily to the surface. It is the reason for the linear alignment of volcanoes in this region, including Lonquimay’s neighbors, Tolhuaca and Llaima.
• Eruptive Style: Lonquimay is capable of both effusive (lava-producing) and explosive eruptions. Its main summit crater is filled with a glacier, but historical activity has focused on flank vents. This unpredictability—not knowing where the next hole will open—complicates hazard zoning for the nearby towns of Malalcahuello and Lonquimay.

Tourism: Skiing on a Volcano

Despite its dangers, Lonquimay is a recreational hub.

• Corralco Ski Resort: Located on the southeastern slopes, Corralco is one of South America’s premier ski destinations. Skiers literal carve turns on the flanks of an active volcano. The lack of trees above 1,600 meters creates vast, open powder fields.
• Hiking Crater Navidad: In the summer, a popular trail leads hikers to the rim of the extinct Navidad cone. The ground is still warm in places, and steam vents (fumaroles) serve as a reminder that the magma chamber beneath is still cooling. Looking into the crater, one can see the colorful deposits of sulfur and iron oxidized by the volcanic gases.
• The Volcanic Cycle Route: The roads surrounding Lonquimay are part of a scenic cycle route that passes through lava fields, bamboo forests, and thermal hot springs heated by the volcano’s geothermal energy.

Monitoring and Future Risks

The Southern Andes Volcano Observatory (OVDAS) keeps a close watch on Lonquimay.

• Seismic Swarms: The primary precursor to activity here is seismic swarms. Before the 1988 eruption, residents felt localized earthquakes for weeks. Today, sensitive instruments can detect these tremors long before they are felt by humans.
• Visual Supervision: Webcams pointed at the Navidad cone and the main summit allow vulcanologists to monitor fumarole activity in real-time. Any change in the color or vigor of the steam plumes is investigated immediately.
• Awareness: The local population, having lived through the “Christmas Eruption,” is acutely aware of the risks. Evacuation plans are integrated with the tourist infrastructure to ensure that if Lonquimay wakes again—perhaps on another holiday—the human cost will be minimal.

Conclusion

Lonquimay is a volcano of contrasts. It is a place of breathtaking alpine beauty, where ancient trees guard snow-covered slopes. Yet, it is also a chemical factory that once poisoned a valley. Its 1988 eruption remains a pivotal case study in medical geology, teaching us that the dangers of a volcano are not always as visible as flowing lava, but can be as invisible as the gas on the wind. To visit Lonquimay is to respect this duality, enjoying the playground of the slopes while acknowledging the fire that built them.