Lake San Cristobal is a

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

in the

U.S. state In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its sove ...

Colorado Colorado (, other variants) is a state in the Mountain states, Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the wes ...

. Located in the

San Juan Mountains The San Juan Mountains is a high and rugged mountain range in the Rocky Mountains in southwestern Colorado and northwestern New Mexico. The area is highly mineralized (the Colorado Mineral Belt) and figured in the gold and silver mining industry ...

at an elevation of , the freshwater lake is long, up to deep, has a surface area of , and holds about of water. The town of Lake City, a few miles to the north, is named after Lake San Cristobal. The name ''San Cristóbal'' means Saint Christopher in the

Spanish language Spanish ( or , Castilian) is a Romance language of the Indo-European language family that evolved from colloquial Latin spoken on the Iberian peninsula. Today, it is a global language with more than 500 million native speakers, mainly in th ...

. Many old silver mines are near the lake and it is very clean and well kept, and stocked with Rainbow Trout.

Geology

Lake San Cristobal was formed about 700 years ago when the first

Slumgullion Earthflow The Slumgullion Earthflow in the San Juan Mountains in Hinsdale County, Colorado has been a National Natural Landmark since 1983. It is also a Colorado Natural Area and an Area of Critical Environmental Concern. The earthflow, a slow-moving la ...

, a natural landslide, created a

dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...

across the Lake Fork of the

Gunnison River The Gunnison River is located in western Colorado, United States and is one of the largest tributaries of the Colorado River. Description The river flows east to west and has a drainage area of according to the USGS. The drainage basin of ...

. Natural

landslide dam A landslide dam or barrier lake is the natural damming of a river by some kind of landslide, such as a debris flow, rock avalanche or volcanic eruption. If the damming landslide is caused by an earthquake, it may also be called a quake lake. Some ...

s are usually short-lived, but some have been known to fail after long periods—131 years in the case of Lake Yashinkul in the former

Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...

. This prompted the

United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...

to investigate the possibility that the Lake San Cristobal dam might fail. Based on its non-

porous Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...

composition and the fact that part of the dam's natural

spillway A spillway is a structure used to provide the controlled release of water downstream from a dam or levee, typically into the riverbed of the dammed river itself. In the United Kingdom, they may be known as overflow channels. Spillways ensure th ...

is actually cut into bedrock and not the material deposited by the landslide, the USGS concluded the dam is stable.

Sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

s washing down via the Lake Fork and Slumgullion Creek are slowly filling in the lake, but are not expected to affect the dam's stability. If sedimentation continues at the past rate, the lake will have completely filled with sediment in about 2,500 years.

Development

In the 1950s, the USGS studied Lake San Cristobal as a possible site for an artificial embankment dam. Such a dam would have been built near the present outlet and spanned the entire valley. This was rejected out of the concern that the upper, active part of the Slumgullion Earthflow could one day reach the dam site, and the possibility that the added

pore pressure Pore water pressure (sometimes abbreviated to pwp) refers to the pressure of groundwater held within a soil or rock, in gaps between particles ( pores). Pore water pressures below the phreatic level of the groundwater are measured with piezometer ...

of the deeper water could reactivate the lower part of the slide. Minor adjustments to the lake level have been made over the years. Hinsdale County constructed a small rock and wooden dam at the lake outlet in 1954, but it began to deteriorate by the 1970s. As of 2009, the water level is controlled by the seasonal addition and removal of boulders at the lake outlet. The county has proposed a modification of the outlet structure which would allow the controlled storage and release of up to water. According to an analysis submitted to the county, this will have a similar effect on the lake level as the previous practice.

References

{{authority control San Cristobal Bodies of water of Hinsdale County, Colorado San Cristobal San Juan Mountains (Colorado)