Two Records, Fifty Years Each
Japan's agencies have been counting things for a long time, and they publish the counts as machine-readable files that almost nothing written in English ever opens. Two of them decide whether a trip works: how often Sakurajima erupts, and how much ice reaches the Sea of Okhotsk. They point in opposite directions.
Sakurajima: the year matters, the month does not
The Kagoshima observatory has counted eruptions at Sakurajima every month since October 1955, and explosions separately. That is eight hundred and fifty-three months in one file, updated every week.
| Decade | Eruptions per year |
|---|---|
| 1980s | 346 |
| 1990s | 259 |
| 2000s | 152 |
| 2010s | 792 |
| 2020s | 242 |
Japan Meteorological Agency, Kagoshima Local Meteorological Observatory · monthly counts since October 1955, updated weekly · file as of 2026/09/07 · decade averages ours. The agency counts only eruptions whose plume rises roughly 1,000 m above the crater rim, so every figure here is a floor.
The mountain does not trend. It swings. In 2011 it erupted 1,355 times and 996 of those were explosive, which is 2.7 explosions a day for a year. In 2024 it managed 99. Someone who came in 2013 and someone who came in 2024 saw different mountains, and neither of them chose.
The month you pick barely moves the odds. Averaged across the forty-five years the count exists, January to March run about 35 eruptions a month and June and July about 22. That is a real difference, and it is nothing next to a decade that multiplies the number by five.
What the record does tell you is that nothing is not unusual. Forty-five months since 1955 recorded no eruption at all, nineteen of them in the 2000s alone, and the most recent blank month was March 2026. If you are building a holiday around watching a volcano erupt, that is the number to know.
The Okhotsk ice: it is going, and the record shows how fast
The Meteorological Agency has measured the greatest extent the sea ice reaches in the Sea of Okhotsk every winter since the 1970-71 season. Fifty-six seasons, one file.
| Decade | Maximum extent (10⁴ km²) |
|---|---|
| 1970s | 131.3 |
| 1980s | 123.2 |
| 1990s | 114.0 |
| 2000s | 115.5 |
| 2010s | 105.8 |
| 2020s | 98.3 |
Japan Meteorological Agency, Sea of Okhotsk sea ice series · maximum extent each season since 1970-71 · decade averages ours.
The first ten seasons average 131.3. The last ten average 103.2. That is a fall of 21 per cent inside one lifetime and, unlike the volcano, it does not swing back.
Last season came in at 75.84, the second smallest of the fifty-six, behind only 2014-15. The largest on record was 1977-78 at 152.25, twice last winter's figure.
The spread matters as much as the slope. A season can land at 70 or at 150, so a single February tells you nothing on its own; the drift only shows across decades. But the drift is there, and it runs one way.
Why put these two side by side
Both are public records kept for half a century by the same agency, and both are the kind of thing a visitor would want to know before booking. They give opposite advice.
The volcano's numbers say you cannot plan around it. The decade you happen to visit in decides what you see, and no one gets to pick their decade. The ice numbers say the opposite: the thing you came for is measurably smaller than it was when the record started, and the direction has not changed in fifty years.
One is a lottery. The other is a queue.
Where the numbers come from
- Eruption and explosion counts: Japan Meteorological Agency, Kagoshima Local Meteorological Observatory. Monthly since October 1955, updated weekly. The agency counts only explosions, and eruptions whose plume rises roughly 1,000 m above the crater rim; smaller ones are left out. The published figure is a floor, not a ceiling.
- Sea ice maximum extent: Japan Meteorological Agency, Sea of Okhotsk series, from the 1970-71 season.
- Both files are public under the Japanese government's standard terms of use. The decade averages, the rankings and the comparisons on this page are ours, not the agency's.