French firefighters face 'pyrocumulonimbus' for first time

• Such a formation, also called a cumulonimbus flammagenitus cloud, can be seen during volcanic eruptions -- or, as in this case, when a wildfire roasts the air near the ground, causing it to rise quickly.
• The rising air cools and becomes a cloud, or fire cloud: a turbulent mass that can generate its own winds that worsen fires.
• If it becomes very large it can even generate lightning.