Mount Agung, a volcano on the Indonesian island of Bali, has erupted for the first time in more than 50 years. Sending ash more than 4000 metres in the air, the eruption has forced the closure of the island's busy airport and authorities have ordered the evacuation of 100,000 people near the volcano. Martyn Unsworth, Professor of Physics / Earth and Atmospheric Sciences at the University of Alberta, joins Danielle to explain how volcanoes affect the globe's atmosphere & weather patterns.