Sector collapse of the SW flank of Volcán de Colima, México: The 3600 yr BP La Lumbre–Los Ganchos debris avalanche and associated debris flows

Some 3600 years ago the SW flank of Volcán de Colima collapsed, generating a debris avalanche that travelled 25 km to the Armería River and stopped against the Cerro Grande limestone escarpment. The debris avalanche deposit covers an area of 48 km2, has an average thickness of 35 m, and a volume of 1.7 km3, with an H/L ratio of 0.13. Along the La Lumbre ravine, the deposit forms a series of flat terraces up to 65 m thick. A pyroclastic flow deposit overlies the debris avalanche deposit, suggesting that the Colima collapse was accompanied by a magmatic component. The debris avalanche deposit dammed the Armería River, forming a temporary lake that accumulated a water volume of ∼ 0.19 km3. The subsequent breaking of the dam formed a debris flow that travelled at least 20 km along the Armería River, emplacing 15–70 m thick deposits. The debris flow deposits cover a surface of 6.4 km2 and have a volume of ∼ 0.2 km3. The avalanche deposit contains fragments of carbonized wood that where dated at 3600 ± 120 yr. BP by Komorowski et al. (1997). This deposit underlies a younger debris avalanche (2505 ± 45 yr BP), and a debris flow deposit with pottery shards and charcoal dated at 1940 ± 90 yr BP. These pottery shards likely related to the Capacha people (820–300 yr BC) indicating that the region has been inhabited during the last 3000 years. A future collapse of Volcán de Colima in the same direction may affect several towns for a total population of circa 40,000.