The following story is part of the R4 Solar Climate Change form 15th - 17th June...
Plumes of smoke and ash are continuing to rise from Colombia's Nevado del Ruiz volcano.
People living on its slopes said they had heard "strong, strange noises" coming from the summit of the 5,346m-high mountain on Friday and Saturday.
Officials say an orange alert first declared three weeks ago is still in place for areas near the summit.
More than 25,000 people died in a mudslide caused by Nevado del Ruiz in its last eruption in 1985.
Officials have distributed 30,000 face masks to residents living in areas affected by ash from the volcano.