Felflöden

Felflöden, or "rock avalanches," are rapid and massive movements of rock debris down steep slopes or cliffs. These geological phenomena occur when large volumes of rock become destabilized and slide or fall under the influence of gravity. Unlike traditional landslides, which often involve soil and smaller rock fragments, rock avalanches typically consist of coherent blocks of bedrock that disintegrate as they descend, creating a turbulent, fluid-like flow.

The primary causes of rock avalanches include geological weaknesses such as faults, fractures, or weathering, combined with triggering factors like earthquakes, heavy rainfall, or human activities such as mining or construction. Once initiated, these events can travel long distances at high speeds, sometimes exceeding 100 kilometers per hour, and can cover vast areas, posing significant hazards to infrastructure and human life.

Rock avalanches are often preceded by signs of instability, such as cracks in rock faces or slow deformation of slopes. Monitoring techniques, including remote sensing and ground-based instruments, help assess risks and predict potential events. Mitigation strategies may include rockfall barriers, slope stabilization, or controlled blasting to reduce instability before a catastrophic failure occurs.

Notable historical examples of rock avalanches include the 2002 Hunga landslide in Papua New Guinea, which triggered a tsunami, and the 2014 rockslide in Washington State, USA, which buried a portion of the State Route 503. These events highlight the destructive potential of such phenomena and the importance of understanding their mechanics for hazard management.