Sakurajima

Background Information

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Sakurajima
View of Sakurajima from mainland Kagoshima, 2009
Elevation	1,117 m (3,665 ft)
Location
Sakurajima Kagoshima Prefecture, Japan
Coordinates	31°35′N 130°39′E Coordinates: 31°35′N 130°39′E
Geology
Type	Stratovolcano
Last eruption	2013 (continuing)

Sakurajima (桜島) is an active composite volcano ( stratovolcano) and a former island in Kagoshima Prefecture in Kyushu, Japan. The lava flows of the 1914 eruption caused the former island to be connected with the Osumi Peninsula.

The volcanic activity still continues, dropping large amounts of volcanic ash on the surroundings. Earlier eruptions built the white sands highlands in the region.

Sakurajima is a composite mountain. Its summit is split into three peaks, Kita-dake (northern peak), Naka-dake (central peak) and Minami-dake (southern peak) which is active now.

Today's Kita-dake is Sakurajima's highest, rising to 1,117 m (3,665 ft) above sea level. The mountain is located in a part of Kagoshima Bay known as Kinkō-wan. The former island is part of the city of Kagoshima. The surface of this volcanic peninsula is about 77 km² (30 sq mi).

Geological history

Sakurajima is located in the Aira caldera, formed in an enormous eruption 22,000 years ago. Several hundred cubic kilometres of ash and pumice were ejected, causing the magma chamber underneath the erupting vents to collapse. The resulting caldera is over 20 km (12 mi) across. Tephra fell as far as 1,000 km (620 mi) from the volcano. Sakurajima is a modern active vent of the same Aira caldera volcano.

Sakurajima was formed by later activity within the caldera, beginning about 13,000 years ago. It lies about 8 km (5 mi) south of the centre of the caldera. Its first eruption in recorded history occurred in 963 CE. Most of its eruptions are strombolian, affecting only the summit areas, but larger plinian eruptions have occurred in 1471–1476, 1779–1782 and 1914.

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

1914 eruption

Date	January 1914
Type	Peléan
VEI	4
Impact	Pre-eruption earthquakes killed at least 35 people; caused an evacuation and significant changes to the local topography.

The 1914 eruption was the most powerful in twentieth-century Japan. Lava flows filled the narrow strait between the island and the mainland, turning it into a peninsula. The volcano had been dormant for over a century until 1914. The 1914 eruption began on January 11. Almost all residents had left the island in the previous days, in response to several large earthquakes that warned them that an eruption was imminent. Initially, the eruption was very explosive, generating eruption columns and pyroclastic flows, but after a very large earthquake on January 13, 1914 which killed 35 people, it became effusive, generating a large lava flow. Lava flows are rare in Japan—the high silica content of the magmas there mean that explosive eruptions are far more common—but the lava flows at Sakurajima continued for months.

The island grew, engulfing several smaller islands nearby, and eventually becoming connected to the mainland by a narrow isthmus. Parts of Kagoshima bay became significantly shallower, and tides were affected, becoming higher as a result.

During the final stages of the eruption, the centre of the Aira Caldera sank by about 60 cm (24 in), due to subsidence caused by the emptying out of the underlying magma chamber. The fact that the subsidence occurred at the centre of the caldera rather than directly underneath Sakurajima showed that the volcano draws its magma from the same reservoir that fed the ancient caldera-forming eruption. The eruption partly inspired a 1914 movie, Wrath of the Gods, centering around a family curse that ostensibly causes the eruption.

Current activity

An image taken from the International Space Station showing Sakurajima and its surroundings on January 10, 2013

Sakurajima's activity became more prominent in 1955, and the volcano has been erupting almost constantly ever since. Thousands of small explosions occur each year, throwing ash to heights of up to a few kilometers above the mountain. The Sakurajima Volcano Observatory was set up in 1960 to monitor these eruptions.

Monitoring of the volcano and predictions of large eruptions are particularly important because of its location in a densely populated area, with the city of Kagoshima's 680,000 residents just a few kilometers from the volcano. The city conducts regular evacuation drills, and a number of shelters have been built where people can take refuge from falling volcanic debris.

In light of the dangers it presents to nearby populations, Sakurajima was designated a Decade Volcano in 1991, identifying it as worthy of particular study as part of the United Nations' International Decade for Natural Disaster Reduction.

Sakurajima is part of the Kirishima-Yaku National Park, and its lava flows are a major tourist attraction. The area around Sakurajima contains several hot spring resorts. One of the main agricultural products of Sakurajima is a huge basketball-sized white radish ( Sakurajima daikon).

On March 10, 2009, Sakurajima erupted, sending debris up to 2 km (1.2 mi). An eruption had been expected following a series of smaller explosions over the weekend. It is not thought there was any damage caused by the latest eruption.

In 2011 and 2012, Sakurajima experienced several significant eruptions; volcanic activity continues into 2013. 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.