French thermonuclear test "Licorne", Moruora - July 3rd, 1970. From a photoset at Flikr by Pierre J.
The Licorne shot was a hydrogen bomb suspended by a balloon at 500m. The yeild was 914 kilotons. Low for a hydrogen weapon. The French Canopus test in 1968 was 2.6 megatons. Although it looks like the explosion is right in front of you, it is actually 25 kilometers away. My guess is that the fireball is about 1,500 meters in diamater and the entire mushroom cloud is 5,000 meters. By six minutes after the explosion, the cloud had risen to 25,000 meters or 78,000 feet.
I find this really beautiful as a visual spectacle. Some may not be able to get over the content. Just remember it was a test and nobody got hurt.
Here is a page about the 1970 French test series.
