Slash-and-Burn
It is a common practice of farming that refers to cutting and burning of woodlands and vegetation for clearing the land. Quite often, the slash-and-burn practice results in catastrophic wildfires.
# Lightning
Wildfires caused due to lightning occur at a frequency of three to five per year. Since lightning is usually associated with rain, such fires do not spread over large areas.
# Drought, Wind and Changing Weather Conditions
Extreme hot temperatures lead to drying up of the vegetation of that particular area and can aggravate a wildfire by fueling it all the more. Moreover, an already ignited fire can spread over large distances with wind as its medium.
# Volcanic Activity
Sometimes, volcanoes create a favorable condition for ignition of wildfires in the surrounding areas. They are also caused due to pyroclastic clouds (those containing rocks or ash from volcanic eruption), generated from active volcanoes.
# Underground Coal Fires
Underground coal fires are the slow and flameless forms of combustion, below the earth's surface. Such fires continue to burn for many years, resulting in the release of toxic fumes and destruction of vegetation and human property.
# Prescribed Fires
They are controlled fires meant to eliminate the elements which can aggravate a wildfire or a forest fire. Often, they are a part of wildland management. Sometimes, these prescribed fires are also not channelized properly and they lead to catastrophic infernos.
Read more at Buzzle: http://www.buzzle.com/articles/what-causes-wildfires.html