Tourists visit the volcano mouth on Laohei Mountain, the core zone of the Wudalianchi World Geopark, northeast China's Heilongjiang Province, Sept. 20, 2010. Reputed as "an open textbook on volcanoes", the geopark contains five connected volcanic barrier lakes formed by volcanic actions in the Quaternary period. It is not only of great importance to the history of ecological science, geography and physics, but also of unique aesthetic and applying value to natural aesthetics and environment medicine. [Xinhua]