Avalanches, which are natural forms of erosion and often seasonal, are usually classified by their content such as a debris or snow avalanche. Speeds can reach over 200 mi per hr (300 km per hr). They are triggered by such events as earthquake tremors, human-made disturbances, or excessive rainfall on high gradient slopes, often where materials are loosely consolidated or weathered.
From this passage, you can conclude:
The author specifies in the passage how avalanches can be classified, such as debris or snow avalanche. The other options are incorrect.