At least two giant volcanic debris-avalanche deposits are associated with the Colima Volcanic Complex located in the western part of the Trans-Mexican volcanic belt. One avalanche originated from Volcán de Colima (3820 m), probably 4300 yr ago. A much larger avalanche originated from Nevado de Colima (4240 m) 18500 yr ago; it traveled more than 120 km from its source and covered an area of at least 2200 km2, almost twice the area of any previously described avalanche deposit. This older debris avalanche is the second largest (by volume) known, has the longest travel distance yet reported, and has one of the lowest height/length ratios (0.04). The avalanche material was probably hot during emplacement and, after initial slope failure, may have behaved similarly to a pyroclastic flow. Such large long-runout landslides from volcanic or nonvolcanic constructs present a serious geologic hazard that must be considered in risk assessment.