Lake San Cristobal
Encyclopedia
Lake San Cristobal is the second largest natural lake
in the U.S. state
of Colorado
. Located in the San Juan Mountains
at an elevation of 9003 feet (2,744.1 m), the freshwater
lake is 2.1 miles (3.4 km) long, up to 89 feet (27.1 m) deep, has a surface area of 0.52 square miles (1.3 km²), and holds about 11000 acre.ft 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
.
, created a dam
across the Lake Fork
of the Gunnison River
. Natural landslide dam
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
. This prompted the United States Geological Survey
to investigate the possibility that the Lake San Cristobal dam might fail. Based on its non-porous
composition and the fact that part of the dam's natural spillway
is actually cut into bedrock
and not the material deposited by the landslide, the USGS concluded the dam stable. Sediment
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.
. 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
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 960 acre.ft water. According to an analysis submitted to the county, this will have a similar effect on the lake level as the previous practice.
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
in the U.S. state
U.S. state
A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...
of Colorado
Colorado
Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
. Located in the San Juan Mountains
San Juan Mountains
The San Juan Mountains are a high and rugged mountain range in the Rocky Mountains in southwestern Colorado. The area is highly mineralized and figured in the gold and silver mining industry of early Colorado. Major towns, all old mining camps, include Creede, Lake City, Silverton, Ouray, and...
at an elevation of 9003 feet (2,744.1 m), the freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
lake is 2.1 miles (3.4 km) long, up to 89 feet (27.1 m) deep, has a surface area of 0.52 square miles (1.3 km²), and holds about 11000 acre.ft of water. The town of Lake City
Lake City, Colorado
The Town of Lake City is a Statutory Town that is the county seat of, and the only incorporated municipality in, Hinsdale County, Colorado, United States. The town population was 375 at the U.S. Census 2000...
, a few miles to the north, is named after Lake San Cristobal. The name San Cristóbal means Saint Christopher
Saint Christopher
.Saint Christopher is a saint venerated by Roman Catholics and Orthodox Christians, listed as a martyr killed in the reign of the 3rd century Roman Emperor Decius or alternatively under the Roman Emperor Maximinus II Dacian...
in the Spanish language
Spanish language
Spanish , also known as Castilian , is a Romance language in the Ibero-Romance group that evolved from several languages and dialects in central-northern Iberia around the 9th century and gradually spread with the expansion of the Kingdom of Castile into central and southern Iberia during the...
.
Geology
Lake San Cristobal was formed about 700 years ago when the first Slumgullion Earthflow, a natural landslideLandslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
, created a dam
Dam
A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...
across the Lake Fork
Lake Fork Gunnison River
Lake Fork Gunnison River or Lake Fork is a tributary of the Gunnison River in Colorado. The river's source is Sloan Lake near Handies Peak in the San Juan Mountains of Hinsdale County. Lake Fork flows through Lake San Cristobal and Lake City before a confluence with the Gunnison River in Blue...
of the Gunnison River
Gunnison River
The Gunnison River is a tributary of the Colorado River, long, in the Southwest state of Colorado. It is the fifth largest tributary of the Colorado River, with a mean flow of 4320 ft³/s .-Description:...
. Natural landslide dam
Landslide dam
A landslide dam, debris dam, or barrier lake is a natural damming of a river by some kind of mass wasting: landslide, debris flow, rock avalanche or volcano. If it is caused by earthquake, it may also be called a quake lake. Some landslide dams are as high as the largest existing artificial dam...
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
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
. This prompted the United States Geological Survey
United States Geological Survey
The United States 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, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...
to investigate the possibility that the Lake San Cristobal dam might fail. Based on its non-porous
Porosity
Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0–1, or as a percentage between 0–100%...
composition and the fact that part of the dam's natural spillway
Spillway
A spillway is a structure used to provide the controlled release of flows from a dam or levee into a downstream area, typically being the river that was dammed. In the UK they may be known as overflow channels. Spillways release floods so that the water does not overtop and damage or even destroy...
is actually cut into bedrock
Bedrock
In stratigraphy, bedrock is the native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil...
and not the material deposited by the landslide, the USGS concluded the dam stable. Sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
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 damEmbankment dam
An embankment dam is a massive artificial water barrier. It is typically created by the emplacement and compaction of a complex semi-plastic mound of various compositions of soil, sand, clay and/or rock. It has a semi-permanent waterproof natural covering for its surface, and a dense, waterproof...
. 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
Pore water pressure refers to the pressure of groundwater held within a soil or rock, in gaps between particles . Pore water pressures in below the phreatic level are measured in piezometers...
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
Hinsdale County, Colorado
Hinsdale County is the least densely populated of the 64 counties of the State of Colorado of the United States. The county population was 790 at U.S. Census 2000. The county seat and the only municipality in the county is the Town of Lake City. Hinsdale County is named for George A. Hinsdale, a...
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 960 acre.ft water. According to an analysis submitted to the county, this will have a similar effect on the lake level as the previous practice.