Ranco Lake is located in Ranco Province

Ranco Province

Ranco Province is one of two provinces of the southern Chilean region of Los Ríos . It is named after Ranco Lake shared by the communes of Futrono and Lago Ranco. The lake is drained by the Bueno River, on which basin lies most of the province...

 of Chile

Chile

Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

. It is the largest lake of Los Ríos Region

Los Ríos Region

The XIV Los Ríos Region is one of Chile's 15 first order administrative divisions. Its capital is Valdivia. Pop. 356,396 . It began to operate as region on October 2, 2007. It was created by subdividing the Los Lagos Region in southern Chile...

 and the fourth largest in Chile. Administratively Ranco Lake is split into three communes; La Unión

La Unión, Chile

La Unión is a city and commune of the Ranco Province in the Los Rios Region in Chile. It is situated approximately 40 km north of Osorno and 80 km south east of Valdivia. It covers an area of approximately 2136.7 km² and has a population of 39.447 of which 25,615 are considered part...

, Futrono

Futrono

Futrono is a city and commune in southern Chile administered by the Municipality of Futrono...

 and Lago Ranco

Lago Ranco, Chile

Lago Ranco is a town and commune in southern Chile administered by the Municipality of Lago Ranco. It is located in Ranco Province in Los Ríos Region...

. The lake host a series of islands of which Guapi Island is the largest. The western half of the lake is roughly circular while the eastern part has deep embayments. Geographically the lake lies in the Andean precordillera

Precordillera

Precordillera is a Spanish geographical term for hills and mountains lying before a greater range. The term is derived from cordillera meaning mountain range and applied usually to the Andes.Some places usually called Precordillera are:...

, the zone between the Chilean Central Valley

Chilean Central Valley

The Central Valley , Intermediate Depression or Longitudinal Valley is the depression between the Chilean Costal Range and the Andes Mountains. The central valley should not be confused with Central Chile that encompasses part of the valley...

 and the Andes

Andes

The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...

.

During the Miocene

Miocene

The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...

 the lake depression was connected to the Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

 as an embayment of it. During this period a series of marine fossilbearing sediments known as Estratos de Lago Ranco were deposited in the lake area. During the quaternary glaciations the lake depression was covered by a large glacier lobe

Glacier

A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...

 of the Patagonian Ice Sheet

Patagonian Ice Sheet

350px|thumb|right|Map showing the extent of the Patagonian Ice Sheet in the [[Strait of Magellan]] area during the [[last glacial period]]. Selected modern settlements are shown with yellow dots...

 which left semicircular moraine

Moraine

A moraine is any glacially formed accumulation of unconsolidated glacial debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past glacial maximum. This debris may have been plucked off a valley floor as a glacier advanced or it may have...

s around the lakes western shore.