(CNN) Cyclonic fire-tornadoes, also known as "firenados," are tearing across parts of southern Australia, adding to the apocalyptic scenes playing out amid one of that nation's worst fire seasons on record.

The firenados, triggered by explosive pyrocumulonimbus clouds reaching up to 16 kilometers (10 miles) high, are making conditions even more dangerous and unpredictable than usual.

One firefighter died when his truck was overturned in a fire tornado earlier this week.

Pyrocumulonimbus clouds form when the intense heat from a blaze forces air to rise rapidly as smoke billows in a massive, anvil-shaped tower.

These fierce clouds -- called flammagenitus -- produce erratic dynamics and bring quick, unpredictable changes, making the work of firefighters ever more dangerous, Bureau of Meteorology spokesman Neil Bennett told Australia's ABC.

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