This website is the digital version of the 2014 National Climate Assessment, produced in collaboration with the U.S. Global Change Research Program. For the official version, please refer to the PDF in the downloads section.
Lahars move rapidly down valleys like rivers of concrete. If you are on the floor of a valley that leads from a volcano and become aware of an oncoming lahar, seek high ground. Lahar is an Indonesian term that describes a hot or cold mixture of water and rock fragments that flows down the slopes of a volcano and typically enters a river valley.
Some simulated lahars can propagate for 15 km or reach combined flow depths of 2 m and speeds of 5â10 m/s, even over flat terrain. Probabilistic multi-hazard frameworks like the one presented here can be invaluable for volcanic hazard assessment worldwide.