The material which makes up the avalanche is snow, and snow is frozen water.
Water symbolizes your emotions, the unconscious, and, at times, life itself.
Therefore, this dream is about rapidly and violently descending emotions and thoughts.
Emotions which may have been repressed have finally been unlocked and may be overwhelming you.
You may have this dream during emotionally turbulent times of your life, or in your dreams you may be remembering and reliving some difficult emotional experiences.
To watch in avalanche in a dream is to see obstacles coming and have no way to avoid those obstacles.
An avalanche is usually a warning, and can be avoided in real life if one is careful and changes a plan or a detail or two.
In a prophetic dream if you are buried under an avalanche oddly enough is considered a good sign and you will likely receive a spectacular stroke of good luck!
If you dream of others being buried under this avalanche then a change of surrounding is likely to occur.