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.
The maximum flow depths are around 10 m in some proximal sectors where flows might get channelized. Maximum flow speeds can reach 25 m/s and be maintained around 10-12 m/s over proximal-medial sectors (up to ~4 km). On distal sectors (~4â6 km), the lahars slow down to speeds of 5 m/s or lower (Figures 9D,10A).