Avalanches are mass of snow that slides very fast down an inclined slope such as a mountainside. They are usually caused by precipitation, rapid temperature changes, or human activity. Especially in mountainous terrains, they are serious hazards to hikers. There are two main types of triggers for avalanches- natural and artificial (as mentioned above). 

1. Natural
   1. Usually on slopes, snow is piled up and supported by snow-pack. It keeps snow from falling down all the time. However, avalanches happens when the snowpack start to weaken and become unstable and allow the build of snow to be released. Small avalanches are usually made of ice, snow, air. The larger ones are of rocks, trees, debris. The amount of snow in an avalanche will differ based upon many factors such as temperature. 
2. Artificial
   1. Contrary to popular belief, avalanches can also be provoked by human activities. Humans have contributed to the start of many avalanches. For example, a person's weight can cause an avalanche too. The sudden addition of weight can cause a fracture in weakly-bonded snow layers.