三宅島の面積は？
The island is a stratovolcano with a granitic composite cone, dating from the late Pleistocene period, between 10,000 and 15,000 years ago. The island has a roughly circular coastline, 38.3 kilometers in length, with an average diameter of eight kilometers. The highest elevation is an active volcano with a height of 775.1 meters. The mountain has been recorded to have erupted numerous times throughout history, and is mentioned as far back as Nara period written records. Over the past 500 years, it has erupted 13 times, including five times since the start of the Meiji period. A lava flow in 1940 killed 11 people, and other eruptions occurred in 1962 and 1983.
On July 14, 2000, Mount Oyama began another series of eruptions, and by September, the island was completely evacuated. After a four-year period of volcanic emissions, residents were allowed to return permanently on February 1, 2005. After the eruption, there has been a constant flow of sulfur dioxide gas coming from Mount Oyama.
The residents of the island are required to carry gas masks with them at all times, but they do not need to be worn constantly. Alarms go off if there is a dramatic increase in the levels of toxic gases in the air. Volcanic gas emissions from this volcano are measured by a Multi-Component Gas Analyzer System, which detects pre-eruptive degassing of rising magmas, improving prediction of volcanic activity.
38.3 kilometers in length, with an average diameter of eight kilometers