I believe the person you are thinking of is Haroun Tazieff (pictured below) who tried to lower himself into the lava lake at Mount Nyiragongo.
Wikipedia has this stub on him:
He was featured in a 1973 National Geographic special called “The Violent Earth.”
Tazieff later served in French Prime Minister Laurent Fabius’ cabinet as secretary of state for the prevention of natural and technological disasters in 1984. There’s a lot of general information about him around the internet, but I don’t think there’s an official page.
This is what the lava lake at Nyiragongo looks like…. The level of the lake rises and falls significantly over time in the crater… I’m not sure I’d want to repel down that cliff face…