The Huilo-Huilo is a waterfall

Waterfall

A waterfall is a place where flowing water rapidly drops in elevation as it flows over a steep region or a cliff.-Formation:Waterfalls are commonly formed when a river is young. At these times the channel is often narrow and deep. When the river courses over resistant bedrock, erosion happens...

 located in Huilo-Huilo Biological Reserve

Huilo-Huilo Biological Reserve

Huilo-Huilo Biological Reserve is a private natural reserve and ecotourism project in southern Chile. The reserve was created in 1999 and includes of native forest in Chile dedicated to wildlife conservation and tourism...

 in southern 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 lies next to Neltume

Neltume, Chile

Neltume is a Chilean town in Panguipulli commune, of Los Ríos Region. It lies along the 203-CH route to Huahum Pass into Argentina. The town's main economic activities are forestry and, more recently, tourism since the Huilo-Huilo Biological Reserve was created in 1999...

 in the international road to Huahum Pass

Huahum Pass

Huahum Pass is an international mountain pass in the Andes between Chile and Argentina. The pass takes its name from the Huahum River that flows from Argentina into Chile at the site of the border crossing. Even though the pass does not go through the continental divide, it crosses the highest...

, in the border to Argentina

Argentina

Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...

. The waters of the Huilo-Huilo Falls originates in Lácar Lake

Lácar Lake

The Lácar Lake is a lake of glacial origin in the . It is enclosed in a mountain range of the Andes, at 630 m above mean sea level, approximately at . The area around the lake is mostly uninhabited, except for the small city of San Martín de los Andes on its northeastern coast.The lake has a...

 in Argentina. During the summer it frequently dries, as consequence of low precipitation and subterranean runoff. As consequence of this infiltration a large aquifer

Aquifer

An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...

 is situated under Mocho-Choshuenco

Mocho-Choshuenco

Mocho-Choshuenco is a glacier covered compound stratovolcano in the Andes of Los Ríos Region, Chile. It is made of the twin volcanoes Choshuenco in the northwest and the Mocho in the southeast...

 volcano. Contact between the water of the aquifer and magma may have caused the explosive phreatic eruption

Phreatic eruption

A phreatic eruption, also called a phreatic explosion or ultravulcanian eruption, occurs when rising magma makes contact with ground or surface water. The extreme temperature of the magma causes near-instantaneous evaporation to steam, resulting in an explosion of steam, water, ash, rock, and...

s that created the Tumba del Buey crater on the western flank of the Mocho-Choshuenco.