A Lahar is a devastating volcanic hazard consisting of a mudflow of ash, rock debris and water. These flows occur when heavy rain, melting glaciers or displaced crater lakes mix with loose volcanic material. Lahars move at high speeds down river valleys, possessing the consistency of wet concrete and can bury entire towns located far from the volcano. ANSWER: (B) Volcanic mudflows (ash + water)
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A lahar is a specific geographical hazard where water and volcanic fragments combine to form a high-speed slurry. These mudflows are often triggered by the sudden melting of snow and ice during an eruption or by intense rainfall on unstable ash deposits. Because they follow existing drainage patterns like river valleys, they can impact communities dozens of miles away from the eruptive site. Lahars are incredibly destructive due to their high density and velocity; they can carry boulders and destroy bridges. The 1985 eruption of Nevado del Ruiz in Colombia remains a tragic example of the lethal power of lahars.