Landslide impact on the archaeological site of Mitla, Oaxaca

Abstract

Some large landslide deposits are recognized within and around the Mitla archaeological site, which is located in a very seismically active region cut by the Tehuacan-Oaxaca fault system. Previous studies have shown that this fault system has produced coseismic ruptures and associated earthquakes in the past. Our work on the Mitla landslide deposits clearly demonstrates that their morphology and nature are typical of dry-rock avalanches. Thus, collapses of rock already weakened by alteration and/or weathering, and unstably mobilized by intense rainfall, are discarded as possible triggers of the avalanche events. We instead propose that the landslides were triggered by earthquake activity. Moreover, our data indicate that part of the original Mitla settlement lies buried under a large rock-avalanche deposit produced sometime during the post-Classic period (900–1520 AD). At that time, the city of Mitla was inhabited by over 10,000 people as estimated from archaeological reconstructions. This devastating landslide almost entirely obliterated Mitla, which at the time of the Spanish arrival still existed as a city, but much reduced in area and populations.