Part of the show Peruvian Mummies, Ancient Environments and the Sahara
Ian in Northampton asked:
I come from Dorset and there's a hill with a pond up there. The strange thing is that it never dries out. Why is this?
It's possibly a dew pond. These have been constructed through much of the South Downs and counties in the south of England. They're built on the top of hills so when the warm air rises, it condenses. The ponds are lined with clay and the clay cools down. This also helps when the air sinks to leave moisture behind. This forms a pond which farmers use to give water to their animals.