Global Volcanism Program | Image GVP-04353
A cluster of rounded boulders was deposited on a river terrace by a lahar in the Río Chinchina valley, 59 km WNW of the summit of Colombia's Nevado del Ruiz volcano on 13 November 1985. The boulders were carried within the lahar and deposited against the tree that served as an obstruction to flow. Note the mudline on the tree that marks the upper flow surface of the lahar.
Photo by Tom Pierson, 1985 (U.S. Geological Survey).