National Geographic : 2011 Apr
Clouds of toxic gas and frequent tremors were two of the challenges faced by a team of scientists led by Dario Tedesco and Ken Sims (top left) as they studied Nyiragongo's crater. All the team's food, water, and gear had to be hauled to the summit rim by porters, many of them local women (bottom left), and then lowered by pulley into the caldera (above). The biggest threat was falling rocks, Sims says. "The caldera is continually collapsing on itself."