2:45 PM - 3:05 PM
[O06-04] The Ogasawara Islands as a World Heritage Site: Geology of Chichijima and Nishinoshima
★Invited Papers
Keywords:andesite, boninite, continent, sea floor
The Ogasawara Islands (Mukojima Islands, Chichijima Islands, Hahajima Islands, Nishinoshima Island, Kita-Iwo-To Island, Minami-Iwo-To Island) were added to the World Heritage List in 2011 as Japan's fourth natural heritage site. The Japanese government nominated the islands based on three criteria: topography and geology, ecosystem, and biodiversity. However, the International Union for Conservation of Nature (IUCN), an advisory body to the World Heritage Committee, reviewed the islands and found that the outstanding universal value of the islands was not recognized for their topography and geology or biodiversity, but only the value of their ecosystem. Topography and geology are World Heritage Site registration criteria (viii), which states that a site represents a major stage in the Earth's history. As of February 2025, there are no Japanese heritage sites that meet this criteria.
The goal of the Ogasawara Islands is to add them to the World Heritage List with new scientific findings after 2011 (i.e., to add criterion (viii) to the Ogasawara Islands World Heritage Site). Chichijima is an island formed by the uplift of lava (an andesite with a high magnesium content called boninite) created by undersea volcanic activity 46 to 48 million years ago. Nishinoshima is an active volcano that resumed eruptions in 2013, and the summit of the submarine volcano became an island and is spewing andesite magma. The andesite of Chichijima indicates the beginning of plate subduction, while the andesite of Nishinoshima suggests the birth of a continent. I will explain what this means and what it indicates in the history of the Earth. I will also review the differences between Chichijima and Nishinoshima not only in terms of the chemical composition of the andesite, but also in terms of crustal structure and eruption forms, and discuss what is lacking in the criteria for World Heritage registration (viii) and what is needed in the future.
The goal of the Ogasawara Islands is to add them to the World Heritage List with new scientific findings after 2011 (i.e., to add criterion (viii) to the Ogasawara Islands World Heritage Site). Chichijima is an island formed by the uplift of lava (an andesite with a high magnesium content called boninite) created by undersea volcanic activity 46 to 48 million years ago. Nishinoshima is an active volcano that resumed eruptions in 2013, and the summit of the submarine volcano became an island and is spewing andesite magma. The andesite of Chichijima indicates the beginning of plate subduction, while the andesite of Nishinoshima suggests the birth of a continent. I will explain what this means and what it indicates in the history of the Earth. I will also review the differences between Chichijima and Nishinoshima not only in terms of the chemical composition of the andesite, but also in terms of crustal structure and eruption forms, and discuss what is lacking in the criteria for World Heritage registration (viii) and what is needed in the future.