How lakes form (origin)

Lakes and ponds form where water collects in a hollow. Classifying lakes by how that hollow formed gives their origin. This catalog uses the categories of the 4th National Survey on the Natural Environment, a nationwide lake survey carried out in 1991 by the Environment Agency of Japan (now the Ministry of the Environment).

Categories of origin

Definitions are translated from the report's glossary and survey guidelines. Lakes of unknown origin are marked Unknown.

Caldera lakes

Lakes that fill a caldera, a large bowl-shaped hollow formed when the ground collapsed through volcanic activity. Only 15 of the 478 lakes surveyed nationwide (3.1%) are caldera lakes, but their average area is large at 25.09 km², and many are deep.

The report notes that about half of caldera lakes are oligotrophic and a certain number are acidotrophic. This is thought to be because they lie at high elevations where few nutrients flow in, and because of the geology and soils created by volcanic activity.

Hokkaido has 7 caldera lakes: Lake Kussharo, Lake Shikotsu, Lake Toya, Lake Mashu, Lake Akan, Lake Kuttara, Naganuma Pond.

Volcanic lakes

Lakes formed in craters or crater floors; caldera lakes are a separate category. There are 59 nationwide (12.3%). They are sometimes called crater lakes, but the survey has no separate crater-lake category, so lakes in craters are counted as volcanic lakes. Hokkaido has 4.

Dammed lakes

Lakes formed when a river valley or hollow was blocked for various reasons (excluding lagoon-origin lakes). With 183 lakes (38.3%), this is the most common origin nationwide. According to the report, they are found both deep in the mountains and near populated areas, with no clear trend in nutrient level. Hokkaido has 16.

Lagoon-origin lakes

Lakes in what was once part of the sea. The report attributes them to the action of the sea, such as coastal currents building sandbars that close off the mouths of bays and inlets. There are 101 nationwide (21.1%), and the report notes that more than half of them are in Hokkaido. By total area, lagoon-origin lakes are the largest category, accounting for 43.6% of the nation's lake area.

Because they lie in lowlands, they are easily affected by human activity: half are eutrophic, and about 20% are dystrophic, fed by water from wetlands. Hokkaido has 60, the most common origin in this catalog, including Lake Saroma and Lake Notoro on the Okhotsk coast and Lake Furen in Nemuro.

Tectonic lakes

Lakes filling hollows created by fault movement. There are only 13 nationwide (2.7%), but their average area of 61.19 km² is the largest of any origin. The report notes that half are eutrophic. In Hokkaido, the only tectonic lake is Kumagaike Pond.

Other and unknown

Oxbow lakes left behind when rivers changed course, spring-fed ponds and similar lakes are classed as Other. Nationwide there are 62 (13.0%), plus 45 (9.4%) of unknown origin. In Hokkaido there are 22 Other and 17 Unknown.

Lakes by origin nationwide

National figures are from table III-1-1 of the report (1991 survey).