Lawn Lake Dam was an earthen 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...

 in Rocky Mountain National Park

Rocky Mountain National Park

Rocky Mountain National Park is a national park located in the north-central region of the U.S. state of Colorado.It features majestic mountain views, a variety of wildlife, varied climates and environments—from wooded forests to mountain tundra—and easy access to back-country trails...

, United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 that failed on July 15, 1982 at about 6 a.m. The sudden release of 220 million US gallons (830,000 m³) of water resulted in a flash flood that killed three people camping in the park and caused $31 million in damage to the town of Estes Park, Colorado

Estes Park, Colorado

Estes Park is a town in Larimer County, Colorado, United States. A popular summer resort and the location of the headquarters for Rocky Mountain National Park, Estes Park lies along the Big Thompson River. Estes Park had a population of 5,858 at the 2010 census...

 and other downstream areas.

Lawn Lake was originally a natural lake with a surface area of 16.4 acres (66,000 m²) located at an altitude of approximately 11,000 feet (3,400 m) in the Rocky Mountains

Rocky Mountains

The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...

. In 1903 a group of farmers from Loveland

Loveland, Colorado

Loveland is a Home Rule Municipality that is the second most populous city in Larimer County, Colorado, United States. Loveland is situated north of the Colorado State Capitol in Denver. Loveland is the 14th most populous city in Colorado. The United States Census Bureau that in 2010 the...

 built a dam to increase it to 48 acres (190,000 m²) for the purpose of providing water for irrigation in Loveland.

Over the years the road that had been cut to permit construction of the dam fell into disrepair and ceased to exist. Because of the dam's remote and difficult location, inspection and repairs lapsed. The Colorado State Engineer determined that the probable cause of the dam failure was deterioration of lead caulking on the joint between the outlet pipe and the gate valve leading to internal erosion of the earth-fill dam.

When the dam failed the waters rushed down the Roaring River

Roaring River (Colorado)

The Roaring River is a tributary of the Fall River in Larimer County, Colorado. The river's source is Crystal Lake in the Mummy Range of Rocky Mountain National Park The river flows through Lawn Lake before a confluence with the Fall River in Horseshoe Park. The collapse of the Lawn Lake Dam in...

 valley, which falls 2500 feet (762 m) in 6 miles (9.7 km), at a peak rate of 18,000 cubic feet per second (510 m³/s), scouring a large gully out of the mountain stream and killing one person camping alongside it. At this rate, the lake emptied in about a minute. When the waters reached the broader valley of Fall River

Fall River (Larimer County, Colorado)

The Fall River is a tributary of the Big Thompson River in Larimer County, Colorado. The river's source is near the Alpine Visitor Center in Rocky Mountain National Park. It flows down a canyon and over Chasm Falls before a confluence with the Big Thompson in Estes Park....

 at Horseshoe Park they spread out and slowed down, leaving behind a large alluvial fan

Alluvial fan

An alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain. A convergence of neighboring alluvial fans into a single apron of deposits against a slope is called a bajada, or compound alluvial...

 of debris. The flood continued down Fall River and hit the Cascade Dam which stored water to run a hydroelectric

Hydroelectricity

Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...

 plant about a mile (2 km) downstream. Cascade Dam failed from the onslaught and added its waters to the flood. The Aspenglen campground was destroyed and two campers who returned to recover camping gear lost their lives although rangers had been able to give advance warning. The flood entered the town of Estes Park and caused severe damage to the downtown shops. In Estes Park the flood joined the Big Thompson River

Big Thompson River

The Big Thompson River is a tributary of the South Platte River, approximately 78 miles long, in the U.S. state of Colorado.- Course of the river :...

 and flowed into Lake Estes on the eastern edge of the city. Olympus Dam, part of the Colorado-Big Thompson Project

Colorado-Big Thompson project

The Colorado-Big Thompson Project is a water diversion project in Colorado designed to collect West Slope mountain water from the headwaters of the Colorado River and divert it to Colorado's Front Range and plains...

, there withstood the deluge and the flood was halted.
The scar left by the scouring of Roaring River and the alluvial fan at Horseshoe Park are still very apparent 30 years later and will remain for a very long time. Twenty-five years after the accident, the extent of the former reservoir is still clearly evident, and at the mouth of the lake, the start of the Roaring River flows through the location of the former dam.

As a consequence of the dam failure, aging dams at Pear Reservoir, Bluebird Lake and Sandbeach Lake in the park were demolished and removed.