The Great 1914 Sakura-jima Eruption

Background

Sakura-jima is a stratovolcano in southern Japan. It sits in the tongue of ocean called Kagoshima Bay, named after the large industrial city across the bay from the volcano. The 1914 eruption of Sakura-jima was the biggest eruption in Japan this century. It taught volcanologists a number of lessons about how volcanoes work. And because the people quickly left the island, there were few deaths.

Sakura-jima as seen from Kagoshima City. Photo Copyrighted by Bob Decker

Sakura-jima is the latest stage of activity of a much larger volcanic system called Aira Caldera. This is a 15 mile (25 km) wide caldera formed about 22,000 years ago by a gigantic eruption that deposited volcanic ash over wide areas of southern Japan. The eruption removed magma from beneath the volcano and spread it all around the volcano, so naturally a giant collapse occurred, forming the caldera. Sakura-jima has grown up on the rim of the caldera and has had historic eruptions beginning in the years 708, 764, 1471, 1779, 1914 and 1946. Since 1955 Sakura-jima has entered a new stage of activity, having hundreds of small eruptions each year.

A new way to study volcanoes is to use radar - which transmits waves of energy to the target and then measures how much of the energy is refelcted back. This radar image of was taken from the Space Shuttle in 1994. It shows the stratovolcano Sakura-jima almost filling Kagoshima Bay. The orange colors on Sakura-jima are lava flows; the 1914 lava is visible on the bottom-left side of the volcano. If many more lava flows in the future erupt in that area a land bridge may be created to the mainland.

1914 Eruption

The 1914 eruption came after more than 100 years of inactivity at Sakura-jima. But eruptions at other Japanese volcanoes during the previous five years had led to a great public awareness of the danger of eruptions. Thus, when five strong earthquakes were felt around Sakura-jima on Jan. 10, 1914 and more than 250 occurred the next day, the 23,000 people who lived on the island did not wait for the government to tell them what to do. All available boats were used to evacuate everyone (and their farm animals) from the island. Because of the speedy actions of the people - and by the 12th the Japanese army and navy were helping, very few people were killed by the eruptions.

White plumes of steam were visible at the top of the volcano on January 11, and a great explosion occurred at 10:05 AM on the 12th. A black puff suddenly shot up from the flank of Sakura-jima. Quoting the geologist Jaggar (1945, p 71):

"First the jet from this west vent was upward and westward and a great pall of black sand and dust shot out laterally. Then it straightened up to a vertical column and churned, boiled up spirally, and swelled 30,000 feet into the sky, first club-shaped, then like a giant lily and finally the top bent majestically eastward in some upper wind which strewed the fine dust over all of central Japan."

The eruption continued all day and night from locations on both the east and west sides of the volcano. The view was awesome at night: there was a fiery red glow of hot rocks being thrown out of the volcano, swirling clouds of smoke and dust, and lightning crackling through it all!

View across Kagoshima on January 14, 1916 just as the lava flow reached the bay.

At 6:29 PM on the 12th, a strong earthquake (it broke the seismometer at Kagoshima) ripped through the area, killing 35 people and injuring hundreds of others. Thus, the earthquake caused many more deaths than did the eruption. Another earthquake on the 13th coincided with a change in volcanic activity. Previously, the eruption had consisted of violent explosion that rained down ash and boulders, and occasional pyroclastic flows, but added to that now was a flowing lava river. In Japan the magmas are so rich in volcanic gases that most eruptions just produce ash deposits, so the outbreak of massive lava flows was unusual. In fact, Prof. Koto who chronicled the eruption was amazed because he had never before seen flowing lava!

Lava streamed from vents on both the east and west sides of Sakura-jima burying fields and villages under tens of feet of rock. The lavas continued to flow for months, covering small islands near Sakura-jima and greatly shallowing Kagoshima bay. On the eastern side the lava crossed the narrow sea lane and connected Sakura-jima to the shore. What had been an island volcano was now a peninsula jutting out from the mainland. The narrowing and shallowing of Kagoshima Bay even changed the height of the spring tides. They were increased from 10.5 feet before the eruption to 12 feet afterwards. And the pouring of hot lava into the bay heated the water to temperatures of 1380F and more. Thousands of fish and other sea life were cooked alive in the bay.

Ash was so deep it buried buildings

Rafts of pumice floated in the bay, making it difficult for boats to pass through. The ash fell widely, especially to the east, where it was blown by west winds. The ash was so deep that it buried many homes at Kagoshima and elsewhere. Many houses collapsed due to heavy ash collecting on the roofs.By January 13 everyone had evacuated Kagoshima, going to outlying towns where they were sheltered and fed. Relief funds and supplies came from the government of Japan and from other nations. More than $19,000,000 worth of damage was done, including the destruction of 2,548 buildings and the burial of large amounts of farmland.

An unexpected discovery was that a broad region centered on the part of Kagoshima Bay north of Sakura-jima subsided after the eruption. The middle of the bay sunk by more than two feet. The sinking was probably due to the removal of magma during the Sakura-jima eruption. But because the subsidence was centered on the bay - the old Aira Caldera - that shows that Sakura-jima's magma came from under the old caldera. Sakura-jima is, as we said at the beginning of this essay, just the latest stage in the evolution of Aira Caldera.

For more information about current activity of Sakura-jima visit the Sakura-jima page of the Japanese Volcano Research Center. And use a World Wide Web search engine to find some of the other interesting Japanese homepages that show the problems of having a modern city only a few miles away from a volcano that erupts every couple of days.

Sources of Information:

Koto, Bundjiro (1916) The Great Eruption of Sakura-jima in 1914. Journal of the College of Science, Tokyo Imperial University, Japan; Vol. 38, Article 3.

Jaggar, T.A. (1924) Sakurajima, Japan's greatest volcanic eruption. National Geographic Vol. 45, No. 4 (April, 1924), p. 441-470.

Jaggar, T.A. (1945) Volcanoes Declare War, Paradise of the Pacific Press, Honolulu; pp 63-76.