Exploring an active volcano and how fast does Santa’s sleigh travel?

The Democratic Republic of Congo is home to some of the most active volcanoes on Earth. Professor Chris Jackson and a team of scientists have been on a dangerous expedition to the country to investigate these rarely visited volcanoes and try to predict when they'll next erupt. Chris tells us more about his adventure, which was filmed for a programme on BBC Two called Expedition Volcano.

Plus, as it's close to Christmas, we check in with Santamory - the elf in charge of science and technology at the North Pole - who explains how fast Santa's sleigh has to travel to visit all the children around the world on Christmas Eve and we learn about polar bears in this week's Dangerous Dan.