Okama Crater Lake (Zaō)

Interesting facts

The lake's depth has swung dramatically with volcanic activity: about 50 m in 1908, 35 m in 1937, then back to 63 m during the unrest of 1939.

Volcanologists suggest that if the volcano fell completely quiet, the crater could eventually fill with sediment and the lake would disappear.

No stream visibly leaves the lake; its water is thought to seep out underground into the Nigori River, eventually reaching the Pacific.

Apart from rain, the only inflow is snowmelt until about July, carried by a seasonal stream that has built a small delta on the shore.

Chemistry drives the colour changes: oxidising iron can tint the water reddish, and iron sulphide formed in the lake can make it look almost black.

Water clarity once reached 5.7 m in a quiet year, 1928, but fell to just 1.5 m when the volcano stirred in 1939.

Gas vents on the lake floor still release volcanic gas, and the water warmed noticeably during the unrest around 1939.

From the early 1930s scientist Anzai Toru studied the lake from a boat for over 20 years, winters included, though some locals saw boating on it as sacrilege.

The lake fills an explosion crater about 400 m wide in Goshiki-dake, a cone that grew inside a caldera whose eastern wall collapsed into a horseshoe.

Roughly 300,000 people a year come up to look down into the crater.

Why it is worth it

Okama — "the cauldron" — is the crater lake at the heart of the Zaō volcanic range in northern Honshu, lying at about 1,550 metres on the border of Miyagi and Yamagata prefectures. It fills the crater of Goshiki-dake, the central volcanic cone of the range, and it is almost perfectly round: roughly 325 metres across in both directions, about a kilometre around, and up to 27.6 metres deep. Steep, bare walls of grey and ochre volcanic debris drop straight to the water on every side, so the lake is seen from above, like a jewel set in a rough stone bowl.

Its colour is the reason people climb up to look at it. On a calm day in quiet volcanic periods, the water is an intense milky turquoise, often compared to jade or lapis. But it changes: with the angle of the sun, the weather and the season, it shifts through emerald, blue and grey, and when the volcano stirs the water can cloud to white or darker tones. That variability gave it its other name, Goshiki-numa, the five-coloured pond. The water is strongly acidic, with a pH around 3.5, and almost nothing but a few microscopic organisms lives in it — which is part of why it keeps such an unreal clarity of colour.

Around the lake the landscape is stark and wind-scoured: slopes of volcanic sand and rock, the summit of Karita-dake at 1,758 metres rising just above. Because the colour depends so much on light and weather, the same lake can look entirely different to two visitors an hour apart.

Getting there

The crater lake is reached by the Zaō Echo Line (Yamagata–Miyagi Prefectural Route 12), a mountain road crossing the range between the two prefectures, and then the Zaō High Line spur to the parking area near the summit of Karita-dake, from where a short walk leads to the rim; a lift also climbs to the top from a lower car park. Yamagata city is about 13 km away as the crow flies, and the nearest airport is Yamagata Airport (GAJ), about 31 km away.

From the encyclopaedia

Okama, meaning an honourable cauldron, is the inactive volcanic crater on top of Mount Zaō, located in Kawasaki, Miyagi, on the border with Yamagata, Japan. While local people call it affectionately Okama, the visitors tend to call it Goshiki-numa, meaning "Five Color Pond", because its color changes depending on the time of the day, the weather, or the season of the year.

Wikipedia · CC BY-SA 4.0

Okama Crater Lake (Zaō)

Interesting facts

Why it is worth it

Getting there

Plan your visit

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From the encyclopaedia