Araiyasushige · CC BY-SA 4.0 · Wikimedia Commons
Mountain in Nagasaki Prefecture, Japan
Mount Unzen is a volcano in Japan. Its summit stands 1,486 m above sea level.
From the lowest point within 5 km (108 m), it rises 1,378 m. The steepest side is the south-east face: 32° on average over the first kilometre. In places the ground near the top reaches 48° — terrain for climbers, not walkers.
The nearest town is Unzen, 5 km away at 546 m: 940 m below the summit.
Scores
Two scores out of 10, built only from open data — every part is shown. They describe what the mountain offers, not how safe it is.
Hiking & mountaineering
4.5/10
Difficulty to the top
Hike
Most path sections around the top are T1 on the SAC hiking scale.
Indicative only — never a safety assessment. Conditions change: ask local guides and check the forecast.
Ski score
—
No ski runs within 12 km in OpenStreetMap.
Ski (where OpenStreetMap has skiing within 12 km): up to 4 points for the length of downhill runs (300 km or more = 4), 1.5 for the number of lifts (40+), 1.5 for the vertical between lift stations (1,500 m) and 3 for the snow season — a month counts when the estimated mean temperature at the height of the ski area is −1 °C or lower and snow falls or lies there (NASA POWER, 2001–2020). Hiking & mountaineering: up to 2.5 for waymarked routes and paths, 1.5 for huts, 2 for the ascent from the valley (2,000 m), 1.5 for prominence (3,000 m), 1.5 for the season (months with summit afternoons above −5 °C) and 1 for via ferratas, climbing and glaciers. OpenStreetMap is built by volunteers: where few things are mapped, a score can be lower than reality.
Plan your visit
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Snow
At the summit, snow from December to April. Month by month below, at different heights on the way up.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Summit1,486 msnow from December to April | Snow on the ground all month | Snow on the ground all month | Snow on the ground all month | Snow on the ground all month | No snow | No snow | No snow | No snow | No snow | No snow | No snow | Snow on the ground all month |
Halfway up1,016 msnow from January to February (some years from December to February) | Snow on the ground all month | Snow on the ground all month | No snow | No snow | No snow | No snow | No snow | No snow | No snow | No snow | No snow | Snow some of the time |
Unzen546 mno snow | No snow | No snow | No snow | No snow | No snow | No snow | No snow | No snow | No snow | No snow | No snow | No snow |
Estimate for a normal year: average temperature and precipitation from NASA POWER, carried to each height, in a simple model of snow building up and melting. In a given year snow can come earlier or stay longer. It does not replace the local snow and avalanche bulletin.
Summit weather
Not a forecast: long-term averages (1991–2020), carried up to the summit. The orange line is where an average afternoon reaches 0 °C; above the dashed blue line it freezes even at dawn.
On an average August afternoon the summit reaches about 22 °C; on January nights it falls to about -6 °C. Afternoons at the top are above freezing in every month of the average year. In August the 0 °C line climbs to about 4,790 m, above the summit: the top thaws on an average afternoon. Across the region, January is the driest month (71 mm) and July the wettest (352 mm).
| Month | Summit high °C | Summit low °C | Unzen high °C | 0 °C line (m) | Rain & snow (mm) | Wet days | Sun h/day |
|---|---|---|---|---|---|---|---|
| January | 0 | -6 | 6 | 1,520 | 71 | 10 | 3.2 |
| February | 2 | -6 | 8 | 1,780 | 99 | 10 | 3.9 |
| March | 5 | -3 | 11 | 2,240 | 131 | 12 | 5.1 |
| April | 10 | 1 | 16 | 2,960 | 167 | 11 | 5.9 |
| May | 14 | 5 | 20 | 3,650 | 186 | 11 | 6.1 |
| June | 17 | 10 | 23 | 4,100 | 333 | 16 | 4.1 |
| July | 20 | 14 | 26 | 4,590 | 352 | 17 | 4.8 |
| August | 22 | 15 | 28 | 4,790 | 225 | 16 | 6.3 |
| September | 18 | 11 | 24 | 4,270 | 201 | 13 | 5.1 |
| October | 13 | 6 | 19 | 3,500 | 117 | 8 | 5.3 |
| November | 8 | 1 | 14 | 2,690 | 103 | 10 | 4.3 |
| December | 2 | -4 | 8 | 1,820 | 92 | 10 | 3.2 |
Estimate: the NASA POWER climate of a ~55 km cell (average height 116 m), adjusted to the summit by −6.5 °C per 1,000 m. Rain, wet days and sunshine are those of the region. Mountain weather changes fast — always check a local forecast. ★ = mildest months at the top.
Relief
Two cuts through the summit, 16 km long, from the 30 m Copernicus elevation model. Heights drawn 2× taller than lengths, so the shape can be seen.
Average slope of the first kilometre from the summit. The orange petal is the steepest side.
Around the mountain
Counted around the summit in OpenStreetMap, the map anyone can edit. The satellite plate shows 14 × 14 km.
N
5 km
Sentinel-2 cloudless 2016 (EOX, CC BY 4.0), 14 × 14 km, north up. Points © OpenStreetMap contributors.
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20 path sections within 5 km, by SAC hiking scale (T1 easy walk … T6 difficult alpine).
OpenStreetMap is built by volunteers: a low number may just mean nobody has mapped it yet. Places © OpenStreetMap contributors (ODbL).
Photos
Recent years
Afternoon high at the summit (estimate). The first row is the reference, the 1991–2020 average in °C; the years show only the difference.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1991–2020 average | 0 | 2 | 5 | 10 | 14 | 17 | 20 | 22 | 18 | 13 | 8 | 2 |
| 2020 | +2.5 | +1.7 | +1.2 | −1.9 | +0.2 | +1.0 | −1.8 | +0.8 | −1.0 | −0.6 | +1.1 | −0.3 |
| 2021 | +0.7 | +1.7 | +2.9 | +1.2 | −0.1 | +1.2 | +0.7 | −1.1 | +0.7 | +1.5 | −0.3 | +0.4 |
| 2022 | +0.3 | −2.4 | +1.7 | +1.3 | +0.3 | +0.5 | +1.4 | +0.3 | +0.6 | −0.1 | +2.4 | −1.2 |
| 2023 | +0.7 | +1.2 | +2.6 | +0.9 | −0.2 | +0.2 | +0.5 | +1.1 | +1.9 | −0.2 | +0.6 | +1.0 |
| 2024 | +1.6 | +1.9 | +0.4 | +2.5 | +0.1 | −0.1 | +0.6 | +1.8 | +3.9 | +2.3 | +1.4 | −0.4 |
| 2025 | −0.1 | −2.8 | +0.3 | +0.3 | −0.8 | +1.0 | +2.7 | +0.7 | +2.4 | +2.3 | +0.5 | +1.8 |
+1 warmer than usual −1 cooler than usual
Nearby
| Names, elevation, prominence | Wikidata (Q620860) · CC0 |
|---|---|
| Relief, 3D view, profiles | Copernicus DEM GLO-30 · © DLR e.V., © Airbus Defence and Space GmbH, Copernicus/ESA |
| Climate | NASA POWER, 1991–2020 · CC BY 4.0 |
| Around the mountain | © OpenStreetMap contributors · ODbL |
| Images | EOX Sentinel-2 cloudless 2016 · CC BY 4.0; Wikimedia Commons |
Every figure is an average, an estimate or a count from a public dataset. Licences and methods: data sources.
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