Earthflow

An earthflow (earth flow) is a downslope viscous flow of fine-grained materials that have been saturated with water and moves under the pull of gravity. It is an intermediate type of mass wasting that is between downhill creep and mudflow. The types of materials that are susceptible to earthflows are clay, fine sand and silt, and fine-grained pyroclastic material.[1]

When the ground materials become saturated with enough water, they will start flowing (soil liquefaction). Its speed can range from being barely noticeable to rapid movement. The velocity of the flow is dictated by water content: the higher the water content is, the higher the velocity will be.[1] Because of the dependency on water content for the velocity of the flow, it can take minutes or years for the materials to move down the slope.

Features and behavior

Earthflows are just one type of mass movement that can occur on a hill slope. It has been recognized as its own type of movement since the early 20th century.[2] Earthflows are one of the most fluid types of mass movements. Earthflows occur on heavily saturated slopes like mudflows or a debris flow. Though earthflows are a lot like mudflows, overall they are slower and are covered with solid material carried along by flow from within.[3] Earthflows are often made up of fine-grained materials so slopes consisting of clay and silt materials are more likely to create an earthflow.

As earthflows are usually water-dependent, the risk of one occurring is much higher in humid areas especially after a period of heavy rainfall or snowmelt.[4] The high level of precipitation, which saturates the ground and adds water to the slope content, increases the pore-water pressure and reduces the shearing strength of the material. As the slope becomes wet, the earthflow may start as a creep downslope due to the clay or silt having less friction. As the material is increasingly more saturated, the slope will fail, which depends on slope stability. In earthflows, the slope does not fail along a clear shear plane and is instead more fluid as the material begins to move under the force of gravity as friction and slope stability is reduced.[5]

Velocity

Earthflows vary in velocity of flow depending partly on the consistency of the flow for the speed of the entire movement, usually meaning how much water is in the material of the hill slope before the slope fails. Though water is often the key factor in slope failure, triggering an earthflow, there can also be dry granular flows made up of granular material.[6] The speed also depends on the angle of slope as earthflows can happen on moderate or steep slopes.[4] Because earthflows are usually water-dependent, they can take many years or just minutes to move a significant amount. An earthflow may affect as few as several square meters or up to several hectares in either time frame.

Effects

Earthflows can have sudden impacts on the amount of sediment that is deposited into a river system, which can have effects on the life in and around the river itself. They can also cause damage to roads and constructions built near the slope. One of the best mitigation techniques to avoid serious earthflow and landslide damage is properly draining the slope of water, especially in places of high levels of precipitation.[6]

Areas of risk

The areas most at risk for earthflows are:

  • Slopes that have been undercut or loaded with more sediment for human construction
  • Slopes that have been undercut by rivers or stream beds
  • Areas that receive heavy rainfall or snowmelt
  • Hill slopes made up of clay, silt, or other fine-grained materials
  • Areas with limited vegetation on hill slopes
  • Areas with evidence of past earthflows

See also

References

  1. ^ a b Easterbrook, D: “Surface Processes and Landforms”, page 78-79. Prentice-Hall, Inc, 1999
  2. ^ Baum, R.L., and W.Z. Savage, and J. Wasowski.(2003) Mechanics of Earth Flows. Proceedings of the International Conference FLOWS. Sorrento, Italy. Mechanics of Earth Flows. Archived 2015-12-22 at the Wayback Machine
  3. ^ Petersen, James (2011). Physical Geography. Cengage Learning. pp. 441–443. ISBN 111142750X.
  4. ^ a b Bierman, Paul (2014). Key Concepts in Geomorphology. New York: W.H. Freeman and Company Publishers. ISBN 1464152985.
  5. ^ Ward, Andy (2003). Environmental Hydrology. CRC Press. ISBN 1566706165.
  6. ^ a b "Landslide Types and Processes" (PDF). USGS. Archived (PDF) from the original on 2016-04-05.

External links

1663 Charlevoix earthquake

The 1663 Charlevoix earthquake occurred on February 5 in New France (now the Canadian province of Quebec), and was assessed to have a moment magnitude of between 7.3 and 7.9. The earthquake occurred at 5:30 p.m. local time and was estimated to have a maximum perceived intensity of X (Extreme) on the Mercalli intensity scale. The main shock epicentre is suggested to have occurred along the Saint Lawrence River, between the mouth of the Malbaie River on the north and the mouth of the Ouelle River on the south. A large portion of eastern North America felt the effects. Landslides and underwater sediment slumps were a primary characteristic of the event with much of the destruction occurring near the epicentral region of the St. Lawrence estuary and also in the area of the Saguenay Graben.

The event occurred during the early European settlement of North America and some of the best recorded first hand accounts were from Catholic missionaries that were working in the area. These records were scrutinized to help determine the scale of damage and estimate the magnitude of the quake in the absence of abundant records from that time period.

Aiken Canyon Preserve

Aiken Canyon Preserve is a 1,621-acre (6.56 km2) Nature Conservancy-managed state property in Colorado. It is named after Charles Aiken, a U.S. surveyor and ornithologist. There is a four-mile (6 km)-loop hiking trail.Aiken Canyon is one of the state's Natural Areas and one of The Nature Conservancy protects, an effort that began more than 50 years ago. Its mission is to "preserve the plants, animals and natural communities that represent the diversity of life of Earth by protecting the lands and waters they need to survive."

Blue goo

Blue goo is a sticky, plasticky, blueish-grey, clay-textured soil derived from a highly weathered serpentinite mélange. The name derives from the soil's color; a result of undergoing anaerobic conditions and becoming gleyed. A greyer variation is called "grey goo". Blue goo is primarily found along the Northern California coast.

Colorado Natural Areas Program

Colorado Natural Areas Program is a program of Colorado Parks and Wildlife that identifies and protects public, and in some cases private, areas with at least one unique or high-quality natural feature of statewide significance. It was established in 1977 by statute. There are 93 designated sites that in total protect more than 250 endangered, rare, or threatened species. Land management agreements are made with landowners concerning private property.

Colorado Parks and Wildlife

Colorado Parks and Wildlife manages the state parks system and the wildlife of the U.S. State of Colorado. The division currently manages the 41 state parks and 307 wildlife areas of Colorado.

The Colorado Natural Areas Program has 93 designated sites that in total protect more than 250 endangered, rare, or threatened species.

Lake San Cristobal

Lake San Cristobal is a lake in the U.S. state of Colorado. Located in the San Juan Mountains at an elevation of 9,003 feet (2,744 m), the freshwater lake is 2.1 miles (3.4 km) long, up to 89 feet (27 m) deep, has a surface area of 0.52 square miles (1.3 km2), and holds about 11,000 acre feet (14,000,000 m3) 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. Many old silver mines are near the lake and it is very clean and well kept, and stocked with Rainbow Trout.

Landslide

The term landslide or less frequently, landslip, refers to several forms of mass wasting that include a wide range of ground movements, such as rockfalls, deep-seated slope failures, mudflows, and debris flows. Landslides occur in a variety of environments, characterized by either steep or gentle slope gradients, from mountain ranges to coastal cliffs or even underwater, in which case they are called submarine landslides. Gravity is the primary driving force for a landslide to occur, but there are other factors affecting slope stability that produce specific conditions that make a slope prone to failure. In many cases, the landslide is triggered by a specific event (such as a heavy rainfall, an earthquake, a slope cut to build a road, and many others), although this is not always identifiable.

Landslide classification

There have been known various classifications of landslides and other types of mass wasting.

For example, the McGraw-Hill Encyclopedia of Science and Technology distinguishes the following types of landslides:

fall (by undercutting)

fall (by toppling)

slump

rockslide

earthflow

rockslide that develops into rock avalanche

List of Colorado Natural Areas

The U.S. State of Colorado has designated 93 natural areas of the state for special protection. The Colorado Natural Areas Program was established in 1977 to preserve and protect special areas of the state with distinctive flora, fauna, ecological, geological, and paleontologic features.

List of National Natural Landmarks in Colorado

The National Natural Landmarks in Colorado include 15 of the almost 600 National Natural Landmarks (NNLs) in the United States; fourteen fully within Colorado and one shared with Wyoming. They cover areas of geological, biological and historical importance, and include lakes, mountains, rock formations and numerous fossil sites. The landmarks are located in 13 of the state's 64 counties. Four counties each contain all or part of two NNLs, while two landmarks are split between two counties. The first two designations, Slumgullion Earthflow and Summit Lake, were made in 1965, while the most recent designation, the West Bijou Site, was made in 2016. Natural Landmarks in Colorado range from 60 to 380,000 acres (24.3 to 153,780.5 ha; 0.1 to 593.8 sq mi) in size. Owners include private individuals and several municipal, state and federal agencies.The National Natural Landmarks Program is administered by the National Park Service, a branch of the Department of the Interior. The National Park Service determines which properties meet NNL criteria and, after notifying the owners, makes nomination recommendations. The Secretary of the Interior reviews nominations and, based on a set of predetermined criteria, makes a decision on NNL designation or a determination of eligibility for designation. Both public and privately owned properties can be designated as NNLs. Owners may object to the nomination of the property as a NNL. This designation provides indirect, partial protection of the historic integrity of the properties via tax incentives, grants, monitoring of threats, and other means.

Lone Mesa State Park

Lone Mesa State Park is a closed-access state park in Colorado. It is currently undergoing development and planning. The only allowed use is limited hunting with special permits.

Rockslide

A rockslide is a type of landslide caused by rock failure in which part of the bedding plane of failure passes through compacted rock and material collapses en masse and not in individual blocks. While a landslide occurs when loose dirt or sediment falls down a slope, a rockslide occurs only when solid rocks are transported down slope. The rocks tumble downhill, loosening other rocks on their way and smashing everything in their path. Fast-flowing rock slides or debris slides behave similarly to snow avalanches, and are often referred to as rock avalanches or debris avalanches.

Slumgullion

Slumgullion may refer to:

Carson Hill, California, formerly called Slumgullion

Slumgullion Pass

Slumgullion Earthflow

An alternative name for American goulash

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 landslide, crawled down the valley about 700 years ago creating the 4 miles (6.4 km) long and 2,000 feet (610 m) wide mass. The earthflow lies a few miles south east of Lake City. The landmark site covers 1,291 acres (522 ha) and is owned by the US Forest Service and the Bureau of Land Management. It is "a striking example of mass wasting (the movement of large masses of earth material)." Lake San Cristobal was dammed by the earthflow. A second earthflow has been moving continuously for about 300 years over older stable rock. It moves at a rate of about 7 meters (23 feet) per year.The area is a habitat for elk and deer. It is crossed by Colorado Highway 149, the principal highway of the area connecting Lake City, Colorado with Creede.

Slumgullion Pass

Slumgullion Pass (elevation 11,530 ft (3,510 m)) is a mountain pass in southwestern Colorado traversed by State Highway 149 east of Lake City. The north side has the steepest grade of any continuously paved road in Colorado (9%), but the pass does not close often in winter because snowplows clear the route regularly during this season. It has a few switchbacks and tight spots, but other than that, most travelers will find it an easy, scenic route.

Technically speaking, the current highway does not traverse the true Slumgullion Pass, which lies just off the highway on the ridge between Cebolla Creek and the Lake Fork of the Gunnison River, at an elevation of about 11,300 ft (3,400 m). As a result of a realignment several decades ago (evident by comparing USGS topographic maps of different vintages), the road now takes a shorter but somewhat higher route as it travels east and south from this spot toward Spring Creek Pass. The road sign at the high point refers to Slumgullion Summit rather than Slumgullion Pass in order to reflect this. This is analogous to the usage of the terms Donner Summit and Cajon Summit in California. However, in all three cases, the more familiar but slightly inaccurate name is routinely used.

Slump (geology)

A slump is a form of mass wasting that occurs when a coherent mass of loosely consolidated materials or rock layers moves a short distance down a slope. Movement is characterized by sliding along a concave-upward or planar surface. Causes of slumping include earthquake shocks, thorough wetting, freezing and thawing, undercutting, and loading of a slope.

Translational slumps occur when a detached landmass moves along a planar surface. Common planar surfaces of failure include joints or bedding planes, especially where a permeable layer overrides an impermeable surface. Block slumps are a type of translational slump in which one or more related block units move downslope as a relatively coherent mass.

Rotational slumps occur when a slump block, composed of sediment or rock, slides along a concave-upward slip surface with rotation about an axis parallel to the slope. Rotational movement causes the original surface of the block to become less steep, and the top of the slump is rotated backward. This results in internal deformation of the moving mass consisting chiefly of overturned folds called sheath folds.

Slumps have several characteristic features. The cut which forms as the landmass breaks away from the slope is called the scarp and is often cliff-like and concave. In rotational slumps, the main slump block often breaks into a series of secondary slumps and associated scarps to form stairstep pattern of displaced blocks. The upper surface of the blocks are rotated backwards, forming depressions which may accumulate water to create ponds or swampy areas. The surface of the detached mass often remains relatively undisturbed, especially at the top. However, hummocky ridges may form near the toe of the slump. Addition of water and loss of sediment cohesion at the toe may transform slumping material into an earthflow. Transverse cracks at the head scarp drain water, possibly killing vegetation. Transverse ridges, transverse cracks and radial cracks form in displaced material on the foot of the slump.

Slumps frequently form due to removal of a slope base, either from natural or manmade processes. Stream or wave erosion, as well as road construction are common instigators for slumping. It is the removal of the slope's physical support which provokes this mass wasting event. Thorough wetting is a common cause, which explains why slumping is often associated with heavy rainfall, storm events and earthflows. Rain provides lubrication for the material to slide, and increases the self-mass of the material. Both factors increase the rate of slumping. Earthquakes also trigger massive slumps, such as the fatal slumps of Turnagain Heights Subdivision in Anchorage, Alaska. This particular slump was initiated by a magnitude 8.4 earthquake that resulted in liquefaction of the soil. Around 75 houses were destroyed by the Turnagain Slump. Power lines, fences, roads, houses, and other manmade structures may be damaged if in the path of a slump.

The speed of slump varies widely, ranging from meters per second, to meters per year. Sudden slumps usually occur after earthquakes or heavy continuing rains, and can stabilize within a few hours. Most slumps develop over comparatively longer periods, taking months or years to reach stability. An example of a slow-moving slump is the Swift Creek Landslide, a deep-seated rotational slump located on Sumas Mountain, Washington.

Slumps may also occur underwater along the margins of continents and islands, resulting from tidal action or a large seismic event. These submarine slumps can generate disastrous tsunamis. The underwater terrain which encompasses the Hawaiian Islands gains its unusual hummocky topography from the many slumps that have taken place for millions of years.

One of the largest known slumps occurred on the south-eastern edge of the Agulhas Bank south of Africa in the Pliocene or more recently. This so-called Agulhas Slump is 750 km (470 mi) long, 106 km (66 mi) wide, and has a volume of 20,000 km3 (4,800 cu mi). It is a composite slump with proximal and distal allochthonous sediment masses separated by a large glide plane scar.

Thistle, Utah

Thistle is a ghost town in Spanish Fork Canyon in southeastern Utah County, Utah, United States. During the era of steam locomotives, the town's primary industry was servicing trains for the Denver and Rio Grande Western Railroad (often shortened to D&RG, D&RGW, or Rio Grande). The fortunes of the town were closely linked with those of the railroad until the changeover to diesel locomotives, when the town started to decline.

In April 1983, a massive landslide (specifically a complex earthflow) dammed the Spanish Fork River. The residents were evacuated as nearly 65,000 acre feet (80,000,000 m3) of water backed up, flooding the town. Thistle was destroyed; only a few structures were left partially standing. Federal and state government agencies have said this was the most costly landslide in United States history, the economic consequences of which affected the entire region. The landslide resulted in the first presidentially declared disaster area in Utah.U.S. Route 6 (US‑6), U.S. Route 89 (US‑89) and the railroad (now part of Union Pacific Railroad's Central Corridor) were closed for several months, until they were rebuilt on a higher alignment overlooking the area. The remains of Thistle are visible from a view area along US‑89 or from the California Zephyr passenger train.

Truttman Sink

The Truttman Sink is an earthflow within the Humboldt Lagoons State Park, along the coast of Humboldt County, California. It is located between Trinidad to the south and Orick to the north. It deposits materials into the northern end of Big Lagoon and the Pacific Ocean, especially during periods of heavy rain. The soil characteristics, geology, and vegetation along the slope of this mass-wasting feature suggest a combination of an earthflow movement and a rotational slump.

Uncompahgre Wilderness

The Uncompahgre Wilderness (formerly called the Big Blue Wilderness) is a U.S. Wilderness Area in southwest Colorado comprising 102,721 acres (415.70 km2). Elevation in the Wilderness ranges from 8,400 feet (2,600 m) to 14,309 feet (4,361 m), at the summit of Uncompahgre Peak.Managed by the Uncompahgre National Forest, it is located approximately 5 miles (8.0 km) northwest of the town of Lake City and some 10 miles (16 km) east of the town of Ouray.

The area is named for Uncompahgre Peak, which at 14,309 feet (4,361 m) is the highest peak in the San Juan Mountains. The Wilderness includes one other prominent fourteener, Wetterhorn Peak at 14,015 feet (4,272 m).

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