Lahar is one of the effects of volcanic eruptions and is composed of water and pyroclastic material. It is a type of mudflow, which flows down the slope of a volcano. It is most common along the river valleys, as they get a proper course to follow. Lahars can be very destructive for the vegetation surrounding the volcanic mountain. They can become solid when the temperature lowers down, while in case of high temperatures they are extremely fluid. The origin of the term Lahar is in the country of Indonesia where it first occurred.

Lahars can be very dangerous if they are of great density and speed and have the capacity to flow for a long distance and cover a large area. They can gather the momentum if they fall down a steep slope and travel above 12 meters per second. One of the most devastating lahars in the recent past occurred in 1953 when the lahars from the Nevado Del Ruiz eruption in Colombia killed above 21,000 people.

Causes of Lahar

There can be two possible causes of Lahar:

• During a pyroclastic flow if the snow and glaciers are melted then it results in lahars.
• Flooding from glacier break down can also result in lahars
• Typhoons resulting in gushes of volcanic ash and rock along with water

Effects of Lahar

Lahars can be extremely dangerous if they are not forewarned. They have the capability to engulf the entire population which comes in it way.

To avoid such a situation there is Lahar Warning System at Mount Ruapehu in New Zealand.