"But it cleared up and we hiked up," Elizabeth Gore of the United Nations Foundation tells PEOPLE by satellite phone. "The climb is really tough, but I'm proud to say no one has turned back."
After seven hours of climbing, the group reached 13,600 feet and settled in for an evening of singing and dancing. Grammy-nominated musician Kenna and rappers Lupe Fiasco and Santigold joined 200 locals for a singing contest between two teams of climbers. "We had two groups singing and dancing back and forth," says Gore. "When you have these great African voices and the likes of Kenna and these other musicians, it was pretty awesome. It was really, really fun."
After months of training, Biel seems to be handling the climb well. "She's kicking butt," says Gore. "She's doing just great. She and I are throwing jokes at each other back and forth every 10 steps. Then we'll switch back to talking issues. She is doing awesome. Awesome."
To keep their energy up, the group of climbers – which also includes Alexandra Cousteau, granddaughter of ocean explorer Jacques Cousteau, and Kick Kennedy, environmentalist and granddaughter of Robert F. Kennedy – snacks on dried fruit and popcorn popped over an open fire.
The group plans to reach the summit on Jan. 12. Next up is a trip to UNHCR refugee camp in Ethiopia for a first-hand look at the water crisis followed by a visit to the village where Ethiopian-born Kenna's family grew up and where his uncle died of a waterborne illness.
To follow the expedition and see photos, videos and Tweets, visit www.summitonthesummit.com