What are lahars and how do they pose risks to populations?

Lahars are volcanic mudflows that pose risks to populations through destruction of infrastructure and loss of life.

Lahars, derived from the Indonesian term for volcanic mudflows, are a significant volcanic hazard. They are typically triggered by volcanic eruptions, but can also occur due to heavy rainfall or rapid snow and ice melt on the slopes of a volcano. Lahars consist of a mixture of water, volcanic ash, rock fragments, and other debris, which can flow rapidly down the slopes of a volcano and into surrounding valleys and river channels.

The risks posed by lahars to populations are considerable. Firstly, due to their high speed and large volume, lahars can cause widespread destruction of infrastructure. This includes homes, roads, bridges, and other structures, which can be completely buried or swept away. This not only results in significant economic damage, but also disrupts essential services and transport links, making emergency response and recovery efforts more difficult.

Secondly, lahars pose a direct threat to human life. People living in the path of a lahar may have little warning and limited time to evacuate, particularly if the lahar is triggered by a sudden volcanic eruption. Even if people are able to evacuate, they may still be at risk if the lahar changes course or if secondary lahars are triggered. In addition, lahars can also contaminate water supplies and agricultural land, leading to longer-term health risks and food shortages.

Despite these risks, many people continue to live in areas vulnerable to lahars, often due to economic necessity or lack of awareness about the risks. Therefore, effective lahar hazard management is crucial. This includes monitoring of volcanic activity and weather conditions, land use planning and restrictions, construction of lahar defences, and public education and warning systems. However, these measures can be challenging to implement and maintain, particularly in developing countries with limited resources.