National Parks · Hokkaido
Akan-Mashu National Park
阿寒摩周国立公園あかんましゅうこくりつこうえんAkan-Mashū Kokuritsu KōenVolcanoes, forest and caldera lakes in the Ainu heartland
Akan-Mashu National Park in eastern Hokkaido protects two volcanic calderas and their lakes: Akan, home of the marimo moss balls, and Kussharo with the famously clear Lake Mashu. One of Japan's first national parks, designated in 1934 as Akan National Park, it took its present name in 2017.
Overview
Akan-Mashu covers the volcanic highlands of eastern Hokkaido between Kushiro and the Sea of Okhotsk. It consists of two large volcanic systems. In the west, the Akan caldera holds Lake Akan, the twin cones of Meakan-dake and Oakan-dake and the smaller lakes Panke-tō, Penke-tō and Onneto. In the east lie the Kussharo caldera, the largest on land in Japan, with Lake Kussharo, the fuming Iō-zan (Atosanupuri) and, on its rim, the younger caldera of Lake Mashu.
Deep forests of Sakhalin fir, Yezo spruce and broadleaf trees cover much of the land, and the lakes are rich in hot springs: Akanko Onsen on the Akan shore, Kawayu Onsen at the foot of Iō-zan and the natural open-air baths on the shores of Lake Kussharo, where warm water rises through the sand.
The park was among the first batch of Japanese national parks in 1934. It was long called Akan National Park; in 2017 it was renamed Akan-Mashu to reflect the equal weight of its eastern half.
Landscape and formation
The Kussharo caldera, roughly 26 by 20 km, formed in a series of massive eruptions that ended some 30,000 to 40,000 years ago. Later activity built new volcanoes inside and on the rim: the lava domes of Iō-zan, still steaming with sulphur vents, and the Mashu volcano, whose summit collapsed some 7,000 years ago to form the steep-walled basin of Lake Mashu. Kamuishu, a small island in the lake, is the tip of a lava dome.
The Akan caldera is older and smaller. Oakan-dake later grew inside it and split the original lake into Lake Akan and the smaller Panke-tō and Penke-tō. Meakan-dake, on the southern rim, is one of Hokkaido's most active volcanoes, with frequent small phreatic eruptions. Hot springs, fumaroles and bubbling mud pools such as Bokke on the shore of Lake Akan show that the system is still alive.
Highlights
- 摩周湖Mashū-ko
A closed caldera lake of deep blue water, viewed only from its rim; the Ainu call it Kamuy-to, 'lake of the gods'.
- 阿寒湖Akan-ko
Forest-ringed caldera lake below Oakan-dake, home of the marimo and the hot-spring town of Akanko Onsen.
- 屈斜路湖Kussharo-ko
The largest caldera lake in Japan, with hot sands at Sunayu, open-air baths at Kotan and Wakoto Peninsula, and wintering swans.
Iō-zan (Atosanupuri)
硫黄山Iō-zanA barren, steaming lava dome near Kawayu Onsen with yellow sulphur vents at its foot.
Meakan-dake and Onneto
雌阿寒岳・オンネトーMeakan-dake, OnnetoThe park's highest peak (1,499 m), an active volcano, with the small lake Onneto at its foot, whose colour shifts with light and season.
Bihoro Pass
美幌峠Bihoro-tōgeA viewpoint on the western caldera rim looking across Lake Kussharo and its central island, Nakajima.
Nature
Ecology
The park lies in the transition between the conifer forests of northern Japan and the broadleaf forests further south. Sakhalin fir and Yezo spruce dominate around the lakes, with Mongolian oak and birch. Around Iō-zan, acidic volcanic soil supports an unusual low-altitude heath of Labrador tea and dwarf pine, plants normally found high in the mountains.
The lakes are the core of the park's biology: Lake Akan's marimo, the kokanee salmon (himemasu) native to Lake Akan and introduced elsewhere, and in winter the whooper swans that gather on the ice-free patches of Lake Kussharo kept open by hot springs.
Flora
Marimo
マリモmarimoBalls of the alga Aegagropila linnaei; Lake Akan is one of very few lakes worldwide where they grow into large spheres.
Labrador tea heath
イソツツジiso-tsutsujiWhite-flowering heath covering the slopes around Iō-zan at under 200 m, flowering in early summer.
Meakan kinbai and Meakan fusuma
メアカンキンバイ・メアカンフスマMeakan-kinbai, Meakan-fusumaAlpine plants named after Meakan-dake, growing on its volcanic scree.
Sakhalin fir and Yezo spruce forest
Dense conifer forest around Lake Akan, partly managed as a protected foundation forest since the early 20th century.
Fauna
Blakiston's fish owl
シマフクロウshima-fukurōThe endangered fish-eating owl lives along the park's forest rivers.
Whooper swan
オオハクチョウōhakuchōWinters on Lake Kussharo, especially at Sunayu and Kotan, where hot springs keep the water open.
Black woodpecker
クマゲラkumageraJapan's largest woodpecker inhabits the old forests of the park.
Brown bear and sika deer
Both are common in the forests; bears are encountered on mountain trails.
Kokanee salmon
ヒメマスhimemasuA landlocked sockeye salmon native to Lake Akan, from where it was introduced to Lake Shikotsu and other lakes.
Culture
The Akan and Kussharo region is part of the Ainu homeland, and Ainu place names cover the map: Mashu, Kussharo (kutchar, 'throat', the outlet of the lake), Kotan ('village'). Akanko Ainu Kotan, a community of craft workshops on the shore of Lake Akan, is one of the main centres of living Ainu culture in Hokkaido, with a theatre for traditional dance, which is inscribed on UNESCO's intangible heritage list.
The Marimo Festival, begun in 1950 to protect the marimo from over-collection, has become an Ainu ceremony each October in which marimo are welcomed and returned to the lake. Lake Mashu, perpetually veiled in fog, entered popular culture through the 1966 song Kiri no Mashu-ko (Lake Mashu in the Mist).
Akanko Ainu Kotan
阿寒湖アイヌコタンAkanko Ainu KotanAinu village and craft street at Akanko Onsen, with the Ikor theatre for traditional dance.
Marimo Exhibition and Observation Center
Facility on Churui Island in Lake Akan where marimo can be observed in tanks; reached by lake cruise.
Kotan open-air bath
コタンの湯Kotan-no-yuA free-flowing rock bath on the shore of Lake Kussharo, separated only by a rock from the lake.
History
c. 40,000–30,000 years ago
The last great eruptions of the Kussharo caldera end.
c. 7,000 years ago
The summit of the Mashu volcano collapses, forming the caldera of Lake Mashu.
1897
The botanist Kawakami Takiya finds the algal balls in Lake Akan and gives them the name marimo.
1931
A transparency of 41.6 m is measured in Lake Mashu.
1934
Akan National Park is designated on 4 December, among Japan's first national parks.
1950
The first Marimo Festival is held at Lake Akan.
1952
The marimo of Lake Akan are designated a Special Natural Monument.
2005
Lake Akan is listed as a Ramsar wetland.
2017
The park is renamed Akan-Mashu National Park.
Through the seasons
Spring
Ice leaves the lakes in April and May; forests green late, and mountain trails remain snowy into June.
Summer
Cool summers with frequent fog at Lake Mashu; the main season for lake cruises, hiking and canoeing on the Kushiro River, which flows out of Lake Kussharo.
Autumn
Maple and birch colour the caldera walls from early October; the Marimo Festival takes place on Lake Akan.
Winter
Temperatures drop far below freezing. Lake Akan freezes solid for ice fishing and winter festivals; swans gather at Kussharo, and frost flowers form on the ice.
Routes and trails
Meakan-dake
A half-day climb from Meakan Onsen or Onneto to the crater rim with views of the fuming craters and Lake Akan; subject to volcanic alert levels.
Oakan-dake
A steep forest climb from the Lake Akan side to a summit overlooking both Akan lakes and the Panke-tō and Penke-tō lakes.
Mashu-dake (Kamui-nupuri)
A ridge walk from the first Mashu observation deck along the caldera rim to the summit of the old volcano.
Bokke nature trail
A short forest walk at Akanko Onsen to the bubbling mud pools on the lakeshore.
Kushiro River canoe
Canoeing from the outlet of Lake Kussharo down the clear upper Kushiro River through forest.
Practical notes
- The park is reached from Kushiro airport (about an hour to Lake Akan) and Memanbetsu airport; JR Mashu and Kawayu Onsen stations lie on the Senmō Line.
- Distances are long and public transport is limited; most visitors travel by car or on seasonal sightseeing buses.
- Meakan-dake and Iō-zan are monitored active volcanoes; check the Japan Meteorological Agency's alert level before hiking.
- Bears inhabit the whole park; carry a bell or spray on trails.
- Removing marimo from Lake Akan is prohibited.
Frequently asked questions
What are marimo?
Marimo are spherical colonies of a green alga that roll on the bed of Lake Akan and can grow larger than a football. Lake Akan's population is a Special Natural Monument, and the Ainu Marimo Festival is held on the lakeshore each autumn.
Why is Lake Mashu so often invisible?
Lake Mashu lies in a steep caldera about 200 m below its rim, and summer sea fog from the Pacific frequently fills the basin, giving it the nickname 'lake of mist'. There is no public access to the shore; it is viewed from observation decks on the rim.
Is Lake Mashu really one of the clearest lakes in the world?
In 1931 a transparency of 41.6 m was measured, a world record at the time. Clarity has decreased since, but the lake, with no inflowing or outflowing rivers, remains exceptionally clear.
Where can Ainu culture be experienced in the park?
Akanko Ainu Kotan on the shore of Lake Akan is one of the largest Ainu communities in Hokkaido, with craft shops, a theatre for traditional dance and performances.
Can you climb the volcanoes?
Yes. Meakan-dake, Oakan-dake and Mashu-dake have marked trails. Meakan-dake is an active volcano, and access to its summit area may be restricted depending on its alert level.
Related
Sources
- 1.阿寒摩周国立公園 (opens in a new tab) — 環境省
- 2.国立公園の概要 (opens in a new tab) — 環境省
- 3.Akan-Mashu National Park (opens in a new tab) — Ministry of the Environment, Japan
- 4.Ramsar Sites Information Service (opens in a new tab) — Ramsar Convention Secretariat