Avalanches initiated by this process are known as spontaneous avalanches. Other dangers include blizzards and avalanches. Furthermore, natural hazards are occurring more frequently, such as floods, avalanches, and landslides. Melting glaciers in the Alps caused avalanches and flash floods in Switzerland. They are a natural defence against landslides, avalanches, and flooding. Additional threats exist for rockfalls and avalanches. Steep coastal cliffs can be caused by catastrophic debris avalanches. Furthermore, avalanches and erosion from snowmelt can scour terrain of vegetation. Seismic activity may also trigger the failure in the snowpack and avalanches. Steep cliffs on the Cape Verde Islands have been caused by catastrophic debris avalanches. The largest avalanches form turbulent suspension currents known as powder snow avalanches or mixed avalanches. Throughout the climb, the four men were constantly threatened by snow avalanches and rock falls. Geologists now attribute its formation to submarine avalanches or strong turbidity currents. He also coauthored works with other volcanologists that focused on debris avalanches. The remainder of this article refers to snow avalanches.