To dream of a landslide symbolizes emotions you have been pushing back for a while. These emotions continue to build up and may soon manifest in an emotional overload. Your pent-up emotions might take the form of a violent outburst.
The landslide in your dream may also represent the anxieties, worries, and responsibilities you carry in life.... Dream Symbols and Analysis
If the dreamer is witnessing the landslide as it happens, then sudden and unexpected events, which he really should be prepared for, will take him totally by surprise.
The dream is warning him to be prepared. Other symbols in the dream may reveal exactly what the events will entail, and what he should do about it.
If the landslide has already taken place and the rocks are lying in the middle of the road, then the dreamer faces obstacles ahead that will need to be removed before he or she can move on and accomplish whatever it is that needs to be done.... Dream Explanations of Astro Center