Mudslides occur on steep slopes over 10°. They are defined by the rapid sudden movement of land due to periods of heavy rain. When there is not enough vegetation to hold the soil in place, saturated soil flows over impermeable sub-soil, causing great devastation and endangering lives.
On the Road
As there are hardly any plains among the mountains and rivers along the Tea Horse Road, many towns and villages are built on mountain slopes or tiny plains at river junctions, making them vulnerable to natural disasters such as mudslides. Tourists to Danba County in Sichuan province have been reported caught in devastating mudslides. However, the risk is much lower if you avoid the rainy reason (from July to September). At any rate, this shouldn't be much of a problem, as the best time to visit the gorgeous Danba valley is October. You can find more information about Danba by having a look at the features on Danba-Beauty Valley and Kingdom of One Thousand Castles.
(Definition of geographical terms are edited from bbc.co.uk/Photo Source: bbc.co.uk)