When most people think about volcanoes, the first thing that could be dangerous is lava. If you asked people what a lahar is they would have no idea. Unfortunately many lives have been taken do to these dangerous landslides.
A lahar is a volcanic mudflow composed of pyroclastic material and water that flows from explosive volcanoes. The name lahar came from the Javanese language in Indonesia. In order for a lahar to happen the conditions have to be right. First and foremost the lahar needs water to flow. When an explosive volcano blows up it spreads volcanic ash and debris. The lahar starts as a flow of water then collects the volcanic debris and starts a flow down the side of a volcano. As it flows down the volcano it gets bigger by collecting more debris and most lahars grow to ten times their starting size. The lahar acts like a lava flow and looks runny when moving but when standing still it has the consistency of concrete. Probably the most dangerous aspect of the lahar is its speed. When the lahar gets to the maximum amount of debris it can move up thirty feet per second but then they quickly die as they spread around the base of the volcano.
Lahars can only happen on explosive volcanoes so a lot of volcanoes never have lahars. Mt. Rainier in Washington has supposedly hade fifty-five lahars in its history. The last lahar Mt. Rainier had was about five hundred years ago. Since lahars occur about every five hundred to a thousand years, scientists believe Mt. Rainier will soon have a lahar. Some other volcanoes that have had lahars are Mt. Saint Helens and Mt. Redoubt in Alaska.
The threat of lahars is limited because of alarm systems set up to warn people of the lahars. The danger is still huge though because the lahars can happed with out warning. The best way to avoid a lahar though is to stay away from the volcanoes. LK3