They were taken on a flight from Canberra to Melbourne
While on a flight from Canberra to Melbourne Merrin Macleod had an excellent view of pyrocumulus clouds over very active bushfires. She said on Twitter, “The country looks like ten or fifteen volcanoes have gone off.”
If the pilot had taken the most direct route to Melbourne they would have flown over many very active fires. The photos are used here with her permission.
Below is actual flight path for her 50-minute flight. About 16 minutes after takeoff the aircraft was 36,000 feet over the NSW/Victoria border.
A pyrocumulus cloud is produced by the intense heating of the air over a fire. This induces convection, which causes the air mass to rise to a point of stability, where condensation occurs. If the fire is large enough, the cloud may continue to grow, becoming a cumulonimbus flammagenitus which may produce lightning and start another fire.