Sakurajima is in the 25 km (15 mi)-wide Aira caldera, which formed in an enormous "blow-out-and-cave-in" eruption around 22,000 years ago.

[8] Several hundred cubic kilometres of ash and pumice were ejected, causing the magma chamber underneath the erupting vents to collapse.

[11] Volcanic activity at Kita-dake ended around 4,900 years ago: later eruptions have been centered on Minami-dake.

[8] Almost all residents had left the island in the previous days; several large earthquakes had warned them that an eruption was imminent.

[14][8] Lava flows filled the narrow strait between the island and the mainland, turning it into a peninsula.

[8] During the last stages of the eruption, emptying of the underlying magma chamber sank the centre of the Aira Caldera by about 60 cm (24 in).

Thousands of small explosions happen each year, throwing ash to heights of up to a few kilometers above the mountain.

The city conducts regular evacuation drills, and a number of shelters have been built where people can take refuge from falling volcanic debris.

[17] Sakurajima is part of the Kirishima-Yaku National Park, and its lava flows are a major tourist attraction.

[19] An eruption occurred from the Minami-dake summit crater at 5:38 on Sunday, August 9, 2010, sending debris up to 5000 m (16,000 ft).

[21] Photographer Martin Rietze captured a rare picture of lightning within the ash plume in January 2013 during a magma ejection, which was a NASA astronomy pic of the day in March 2013.

[22] On August 18, 2013, the volcano erupted from Showa crater and produced its highest recorded plume of ash since 2006, rising 5,000 metres high and causing darkness and significant ash falls on the central part of Kagoshima city.

[23] In August 2015, Japan's meteorological agency issued a level 4 emergency warning, which urges residents to prepare to evacuate.

[33] People in a 2-km radius were sent a warning by the local weather observatory against pyroclastic flows and falling rocks.

[35] Sakurajima is the title of a 1946 short story, written by the Japanese writer Haruo Umezaki, about a disillusioned Navy officer stationed on the volcano island towards the end of World War II as American air force planes bomb Japan.