Pete Oxford / Geothermal activity as evidenced by bubbles eminating from the seabed, Roca Redonda and eroded volcano in mid ocean north of Isabela Island, Galapagos Islands, Ecuador, South America

Doug Perrine / Hot molten pillow lava erupts from an underwater lava tube at ocean entry of Kilauea Volcano on Hawaii Island, Hawaii

Tui De Roy / Cerro Azul caldera with lake and tufa cone at 5,900 feet, Cerro Azul Volcano, Isabella Island, Galapagos Islands, Ecuador

Doug Perrine / Shimmering heat waves distort the image of diver as he samples erupting pillow lava at ocean entry of Kilauea Volcano, Hawaii Island.

Doug Perrine / Videographer filming pillow lava erupting underwater at Kilauea Volcano, Hawaii.

Doug Perrine / Diver shaping erupting pillow lava by hand to form underwater lava sculptures at ocean entry from Kilauea Volcano, Hawaii.

Doug Perrine / Diver sampling red hot pillow lava at underwater eruption of Kilauea Volcano, Hawaii.

Michel Roggo / Underwater view of Blue Lake, lake in an extinct volcano, Mount Gambier, South Australia, Australia. March 2015. Photographed for The Freshwater Project

Michel Roggo / Underwater view of Blue Lake, lake in an extinct volcano, Mount Gambier, South Australia, Australia. March 2015. Photographed for The Freshwater Project

Michel Roggo / Underwater view of Blue Lake, lake in an extinct volcano, Mount Gambier, South Australia, Australia. March 2015. Photographed for The Freshwater Project

Franco Banfi / Mesmerising dancing volcanic sands and multicoloured sediments leaping from the bottom at Litlaa 'Little River', northern Iceland

Franco Banfi / Split level view of volcanic crack Nesgja, in Asbyrgi National Park, northern Iceland