Qualibou, also known as the Soufrière Volcanic Centre is a 3.5 X 5 km wide caldera on the island of Saint Lucia that formed approximately 32-39,000 years ago. This eruption also formed the Choiseul Tuff which covers the south east portion of the island. The Pitons are two large lava domes that formed 200-300,000 years ago, some time before the formation of the caldera and since then other domes have filled the caldera floor. More recently, there was a phreatic eruption in 1766 that deposited ash over a wide area.