Mudslides, or debris slides, claim several lives each year and destroy property and infrastructure. They often occur during intense rainfall on sloped soil that is already saturated. The clearing of land for agriculture or housing, or as a result of forest fires, is often blamed for these tragic occurrences. Some mudslides are triggered by volcanic eruptions.
Mudslides can accelerate to speeds up to 35 mi (56 km) per hour.
A series of mudslides in western Japan in 2018 killed over 170 people.
Debris slides—known as pyroclastic flows—from certain volcanic eruptions can reach temperatures as hot as 1,500 ˚F and reach speeds of 100 mi (160 km) per hour to 150 mi (240 km) per hour.
A huge pyroclastic surge from the US’s Mt. St. Helens destroyed an area of 230 square mi (368 square km) in 1980.
A lahar, a volcanic mudslide composed of rock, mud, and water, can rush down slopes at 20 to 40 mi (32 to 64 km) per hour.
Lahars can travel more than 50 mi (80 km).
Looking like a flowing river of wet cement, a lahar may have a rock content up to 90% of its weight. Lahars are a serious threat to communities downstream from glacier-clad volcanoes.
Lahars have killed more than 44,000 people worldwide since 1600, about 20% of volcano-related deaths.
– Source: US Geological Survey, Department of the Interior