The cause of the fires was weather conditions and dry vegetation. Even under normal conditions, fire spreads rapidly in eucalypt woodlands, due to the oil contained in the trees, and the amount of woody litter on the ground. Because of a drought in 1982 the woodlands were severely dried out, leading to extreme fire danger areas. Only a month before the fires, the weather was abnormally hot and dry. In Adelaide after a year in which there was only 60% of the average rainfall, it had rained for only three days that month. By the mid-morning of Ash Wednesday the temperature was up to 40 degrees and the wind gusted at 50km/h. In these types of conditions, little could be done to prevent the outbreaks of fires.
Four fires started by the middle of the day. By the mid-afternoon, twelve people had died. At about 3.30pm the Northerly wind had suddenly changed, and was now at least 10 degrees cooler. Before the full effects of the fires were known, volunteer fire-fighters emerged from the fire areas with descriptions of fire balls racing across open areas, houses exploding with fire and trees bursting into flames hundreds of meters ahead of the main fire. Aluminium wheel trims on cars were found completely melted from the intense heat. People who obeyed instructions from authorities to stay in their cars as the fire passed were incinerated.