Japan is substantially prone to earthquakes, tsunami and volcanoes because of its location along the Pacific Ring of Fire. It has the 15th highest natural disaster risk as measured in the 2013 World Risk Index. Japan has 108 active volcanoes, which are primarily the result of large oceanic movements occurring from the mid-Silurian to the Pleistocene as a result of the subduction of the Philippine Sea Plate beneath the continental Amurian Plate and Okinawa Plate to the south, and subduction of the Pacific Plate under the Okhotsk Plate to the north. Japan was originally attached to the Eurasian continent; the subducting plates opened the Sea of Japan around 15 million years ago. During the twentieth century several new volcanoes emerged, including Shōwa-shinzan on Hokkaido and Myōjin-shō off the Bayonnaise Rocks. Destructive earthquakes, often resulting in tsunami, occur several times each century. The 1923 Tokyo earthquake killed over 140,000 people. More recent major quakes are the 1995 Great Hanshin earthquake and the 2011 Tōhoku earthquake, which triggered a large tsunami.