A lahar is a type of volcanic mudflow that consists of a mix of water, rocks, and volcanic debris. Lahars are formed when a volcano erupts and sends a mix of ash, pumice, and other materials down the side of the mountain, often in a fast-moving flow. They can also be triggered by heavy rains or the melting of snow and ice on the slopes of a volcano.
Lahars can be extremely destructive, as they can flow quickly and have the power to sweep away anything in their path, including houses, roads, and bridges. They can also cause landslides and create dams that block rivers and cause flooding. Lahars are particularly dangerous because they can occur with little warning and can move at speeds of up to 100 km/h.
Lahars are most common in areas with active volcanoes, particularly in Indonesia and the Philippines. They have also been known to occur in other parts of the world, including the United States (e.g., Mount St. Helens in 1980), South America, and Europe