MODEL RELEASED. Volcanologist wearing a gas mask to protect him from the potentially poisonous gases seen swirling around him. Volcanoes produce several poisonous gases, such as sulphur and hydrogen sulphide. The helmet is intended to protect him from the large chunks of rock that can be ejected to, and fall from, great heights during a volcanic eruption. This is Niri Mbwelesu Taten, a crater in the Ambrym caldera. Ambrym is a volcanic island, one of the most active of the New Hebrides Trench, an underwater volcanic zone in the south-western Pacific Ocean that has formed many volcanic islands, including the Vanuatu group of which Ambrym is part. Photographed in 2000.