Tens of thousands of people have been evacuated from Bordeaux’s surrounding region of Gironde, as France continues to fight against wildfires being stoked by an unprecedented “pyrocumulonimbus” or fire clouds.

Scientists sometimes describe these clouds as a fire-generated thunderstorm because the fire itself provides the energy needed to build the cloud.

The huge amount of heat generated by wildfires makes the air above the fire rise rapidly, carrying smoke, ash and water vapour high into the atmosphere.

As the air rises, it cools and the water vapour condenses into a cloud.

If the fire is powerful enough and the atmosphere is unstable, that cloud can grow into a towering cumulonimbus – the same type of cloud associated with thunderstorms.

Turbulent winds created by the fire clouds can send embers shooting off in all directions, making wildfires unpredictable and harder to fight. Lightning strikes can also spark more blazes.