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An evacuation route sign in case of volcanic eruption or lahar.

Several mountains in the world, including Mount Rainier in the US, Mount Ruapehu in New Zealand, and Galunggung in Indonesia, are considered particularly dangerous due to the risk of lahars. Several towns in the Puyallup River valley in Washington state, including Orting, are built on top of lahar deposits that are only about 500 years old. Lahars are predicted to flow through the valley every 500-1,000 years, so Orting, Sumner, Puyallup, Fife, and the Port of Tacoma face considerable risk. The USGS has set up lahar warning sirens in Pierce County, so that people can flee an approaching debris flow.
A lahar warning system has been set up at Mount Ruapehu by the New Zealand Department of Conservation and hailed as a success after it successfully alerted officials to an impending lahar on 18 March 2007.Preventative measures by the Philippine government did not stop over 20 feet (6.1 m) of mud from flooding many villages around Mount Pinatubo from 1992 through 1998.



Nevado del Ruiz

The lahar from the 1985 eruption of Nevado del Ruiz that wiped out the town of Armero in Colombia.

In 1985, the volcano Nevado del Ruiz erupted. As pyroclastic flows erupted from the volcano's crater, they melted the mountain's glaciers, sending four enormous lahars down its slopes at 60 kilometers per hour (40 miles per hour). The lahars picked up speed in gullies and coursed into the six major rivers at the base of the volcano; they engulfed the town of Armero, killing more than 20,000 of its almost 29,000 inhabitants. Casualties in other towns, particularly Chinchiná, brought the overall death toll to 23,000. Footage and photographs of Omayra Sánchez, a young victim of the tragedy, were published around the world. Other photographs of the lahars and the impact of the disaster captured attention worldwide and led to controversy over the degree to which the Colombian government was responsible for the disaster. A banner at a mass funeral in Ibague read, "The volcano didn't kill 22,000 people. The government killed them."



 Mount Pinatubo

Before and after photographs of a river valley filled in by lahars from Mount Pinatubo

The 1991 eruption of Mount Pinatubo caused lahar flows: the first eruption itself killed only six people, but the lahar flows killed more than 1500. The eye of Typhoon Yunya passed over the volcano during its eruption on June 15, 1991. The rain from the typhoon triggered the flow of volcanic ash, boulders, and water down the rivers surrounding the volcano. Angeles City was damaged by the volcano's sticky mud when Sapang Balen Creek and the Abacan River became the channel for the lahar and carried it to the heart of the city. Over 20 feet (6 m) of mud destroyed or damaged Castillejos, San Marcelino, Botolan, Porac, Mabalacat, Tarlac City, Capas, Concepcion, and Bamban. The mud flow down the Sacobia Bamban River scoured all structures in its path, including the bridges and dikes by the Parua river in Concepcion. The Tarlac River in Tarlac City was inundated by over 20 feet (6 m) of lahar, causing the river to lose the ability to hold water.

On the morning of October 1, 1995, pyroclastic material which clung to the slopes of Pinatubo and surrounding mountains rushed down because of heavy rain, and turned into a 25-foot (8 m) lahar. The mudflow killed hundreds of people in Barangay Cabalantian in Bacolor. The Philippine government under former president Fidel V. Ramos ordered the construction of the FVR Mega Dike in an attempt to protect people from further mudflows.