Sinkholes

Earthquakes

Landslides

Radon

Disaster Preparedness

Geohazard News

Geospatial Data

 

Landslide Science and Types

Landslides on the Map

Landslide Hazards and You

Alabama Landslides

Historical AL Landslides

References

 

 

LANDSLIDE SCIENCE AND TYPES

 

A landslide is defined as a perceptible downward and outward movement of slope-forming soil, rock, and vegetation under the influence of gravity. Landslides can be triggered by both natural and human-induced changes in the environment. These changes may result from a variety of causes such as:

§      Weaknesses in composition or structure of the rock or soil

§      High precipitation

§      Changes in ground-water level

§      Seismic activity

§      Construction or mining activity

§      Over-steepening of slopes

§      Changes in surface water runoff

§      Heavy loads on slopes

 

To see how landslides can be so dangerous, click the National Geographic movie to the right.

 

……………………………….…

 

 …………………………………….…

 

 

Landslide Types

There are several types of landslides and other downhill mass movements. The most common ones seen in Alabama include creep, slides, and rockfalls.

Creep (right) is an imperceptible, slow downward movement of soil or rocks on slopes. Along the creep slope, objects can display signs of this slow movement. Leaning utility poles, trees, retaining walls or offset fences can be signs that an area is undergoing creep.

 

 

 

   

Photo of surface rupture.

Photo of landslide scarp.

 

 

Slides (above) are movements of soil or rock along a distinct surface of rupture which separates the slide material from the more stable underlying material. At the top of the slide is a cracked portion of the hill slope referred to as the scarp (above left photo and center diagram). Near the bottom of the slide (the toe), material mounds up creating a bulge in the topography (the lower half of the above right photo).

 

 

Rock falls (left) are rapid movements of bedrock characterized by free-fall, bouncing, and rolling. These are most common in areas of very steep or near-vertical slopes such as roadcuts.

 

For more information on landslide types and processes, click here to download the U.S. Geological Survey factsheet “Landslide Types and Processes.” Or click here to download a more detailed document that goes more in depth (25.8 MB).

 

Areas Generally Prone to Landslides

 

Due to differences in geology, slope, and moisture, some areas are more prone to landslides than others. Areas more susceptible to slope failure include areas that are:

 

§      Near existing old landslides.

§      On or at the base of slopes.

§      In or at the base of minor drainage hollows.

§      At the base or top of an old fill slope.

§      At the base or top of a steep cut slope.

§      Developed hillsides where leach field septic systems are used.

 

   Thumbnail and link to USGS factsheet 2004-3072.

 

For more general info on landslide types and processes, click here to download USGS factsheet 2004-3072.

   Thumbprint and link to USGS Circular 1325.

 

For more in depth detailed information, click here to download USGS Circular 1325 (25.8 MB).

 

 

 

LANDSLIDES ON THE MAP

 

 

Topographic Maps

 

Larger landslides can be seen on topographic maps and have a characteristic curvature. The steepest slope occurs at the main scarp (see rotational landslide diagram above). Contour lines will appear curved concave toward the direction of the slide. The contour lines down the slope will also appear curved, with decreased slope, and convex toward the slide direction.

 

In the example to the right, the scarp is the close East-to-West contours near the center of the image. The material of the slide is south of the scarp through Stone Hollow and the toe of the slide is at the end of the “e” of “Stone.”

 

To read more about maps used for landslide exploration and research, click here to download the USGS Circular 1325 The Landslide Handbook—A Guide to Understanding Landslides Appendix B (Introduction to Landslide Evaluation Tools - Mapping, Remote Sensing, and Monitoring of Landslides). Or click here to see the full publication  and other appendices.

 

Area on a topographic map showing a landslide. 

 

Landslide area south of Lewis Mountain in the Maysville 7.5-minute topographic quadrangle in Madison County, Alabama.

 

Map of the US showing landslide susceptibility.

Incidence and Susceptibility Maps

 

Landslide incidence is defined as the number of landslides that have occurred in a given geographic area. Landslide susceptibility is defined as the probable degree of slope failure. The map units are split into three incidence categories according to the percentage of the area affected by landslides. High incidence means greater than 15 percent of a given area has experienced landslides; medium incidence means that 1.5 to 15 percent of an area has; and low incidence means that less than 1.5 percent of an area has been involved. High, medium, and low susceptibility are delimited by the same percentages as the incidence. Susceptibility is not indicated where it is the same as or lower than incidence.

 

For more information on the map to the left, click here.

 

Read More About Landslide Areas

§      Recent landslides around the world

§      Underwater landslides

§      Landslide conferences

§      Landslide bibliographic database

§      USGS Landslide Hazards Program

§      Talk to USGS National Landslide Info Center

 

 

 

 

LANDSLIDE HAZARDS AND YOU

 

 

According to the USGS, landslides in the country cause an excess of $1 billion in damages and about 25 - 50 deaths annually.

 

To learn more about what you can do if you live near steep slopes, click here to download the USGS Fact Sheet FS-071-00 “Landslide Hazards” (o para Español, aquí).

 

Thumbnail and link to the USGS Factsheet FS-071-00.

 

Landslide Warning Signs

 

§      Springs, seeps, or saturated ground in areas that have not typically been wet before.

§      New cracks or unusual bulges in the ground, pavement, or sidewalks.

§      Soil moving away from foundations.

§      Ancillary structures such as decks and patios tilting and/or moving relative to the main house.

§      Tilting or cracking of concrete floors and foundations.

§      Broken water lines and other underground utilities.

§      Leaning utility poles, trees, retaining walls or fences.

§      Offset fence lines.

§      Sunken or down-dropped road beds.

§      Sticking doors and windows, and visible open spaces indicating jambs and frames out of plumb.

§      Note, some of the above warning signs may also be indicative of sinkhole or mine subsidence. Click here to read more on those topics.

Before a Landslide

 

§   Do not build near steep slopes, close to mountain edges, near drainage ways, or natural erosion valleys.

§   Get a ground assessment of your property.

§   Contact local officials, state geological surveys or departments of natural resources, and university departments of geology. Ask for information on landslides in your area, specific information on areas vulnerable to landslides.

§   Watch the patterns of storm-water drainage near your home, and note where runoff water converges, increasing flow in channels. These are areas to avoid during a storm.

§   Learn about the emergency-response and evacuation plans for your area. Develop your own emergency plan for your family or business.

§   Consider planting ground cover on slopes and/or building retaining walls to help minimize hazards on your property.

Evaluating the Hazard

 

Thumbnail and link to the USGS Circular 1325, Section II.

 

Section II of USGS Circular 1325: Evaluating and Communicating Landslide Hazard

Mitigation Approaches

 

Thumbnail and link to the USGS Circular 1325, Section III.

 

Section III of USGS Circular 1325: Mitigation Concepts and Approaches

 

After a Landslide

§      Stay away from the slide area. There may be danger of additional slides.

§      Watch for flooding, which may occur after a landslide or debris flow.

§      Check for injured and trapped persons near the slide, without entering the direct slide area and direct rescuers to their locations.

§      Look for and report broken utility lines and damaged roadways and railways to appropriate authorities.

§      Check the building foundation, chimney, and surrounding land for damage.

§      Replant damaged ground as soon as possible since erosion caused by loss of ground cover can lead to flash flooding and additional landslides in the near future.

§      Seek advice from a geotechnical expert for evaluating landslide hazards or designing corrective techniques to reduce landslide risk.  A local phone directory will have contact information for geologic or geotechnical engineers who can help.

 

 

 

 

LANDSLIDES IN ALABAMA

 

Landslides in Alabama have occurred around the state previously and are related to both geology and natural slopes as well as human-influenced topography. Geologic units most prone to landslides include shales and soft clay or sands on moderate to steeply sloped areas. Weakly cemented rocks are also susceptible to landslides if on steeper slopes. For a list of geologic units and their rock types in Alabama, click here, or to read more in depth about rock types and stratigraphy in Alabama, click here to download GSA Circular 140 PDF (17.7 MB). To read more about factors influencing landslide susceptibility, continue reading.

 

 

 

Rock Strength

 

Geologic map of Alabama.

Rock strength influences landslide susceptibility. Physical properties of geologic units (left) influence rock strength and rock strength (right) is categorized  based on the below criteria.

 

A (blue). Strongly Cemented Rocks – crystalline rocks and well-cemented sandstone.

 

B (yellow). Weakly Cemented Rocks and Soils - sandy soils and poorly cemented sandstone.

 

C (red). Argillaceous Rocks - shales, clayey soil, existing landslides, poorly compacted fills.

 

Rock strength categories A, B, and C are based on Wieczorek (1985) and match the categories used in HAZUS software for modeling landslide potential during earthquake shaking.

 

Rock strength map of Alabama.

 

Slope

 

Slope map of Alabama.

Slope is also a determining factor in landslide susceptibility. While most of Alabama’s topography is relatively low slope (left), areas such as the Valley and Ridge, Piedmont, and Cumberland Plateau have a number of steeper slopes. In addition to this, steep slopes in Alabama can also be found along river bluffs and roadcuts.

 

The map to the left shows slope with warmer colors representing steeper slopes (based on USGS National Elevation Data). The map to the right shows slope broken into categories relative to landslide susceptibility modeling. Warmer colors represent slope categories with higher susceptibility. Blues have the lowest susceptibility. The palest blue represents areas with the least slope.

Slope category map of Alabama.

 

Additional Factors

 

Map of select historical landslides in Alabama.

In addition to geology and slope, mapping known historical landslides is also important in helping assess where landslides may occur in the future. Areas with known historical slides (left) are likely to have future slides. Points on the map at the left indicate places with historical landslides as indicated in previous documents and maps by Pomeroy (1982), and Rheams (1982), and Thomas (1979, 1982).

 

Rainfall (right) is also a contributing factor. In general, steep slopes that receive more annual rainfall are more susceptible to landslides. The map to the right shows annual rainfall averages (darker blue represents higher rainfall) from 1961 to 1990 (source information).

Map of annual precipitation in Alabama.

Landslide Susceptibility in Alabama

 

Click here for a pdf poster of landslide susceptibility in Alabama. The poster “Susceptibility to Landslides in Alabama” contains geology, rock strength, slope categories, landslide incidence, and landslide susceptibility maps.

 

* Please note that the map to the right and the downloadable poster above is not intended for site planning or site selection.

 

To download associated GIS data, please visit our Geospatial Hazards Data page.

 

Landslide susceptibility across Alabama.

Susceptibility Documentation

 

Landslide susceptibility is based on estimates of rock strength and terrain slope. In general, landslide susceptibility increases with slope and in weaker rocks. Very high landslide susceptibility, classes VIII, IX, and X, includes very steep slopes in hard rocks and moderate to very steep slopes in weak rocks. Categories I - X are based on Wilson and Keefer (1985) where I is the least susceptible and X is the most susceptible.

 

Landslide susceptibility data was categorized for use with HAZUS for earthquake damage and loss modeling. For additional details on the categories and earthquake-induced landslides and modeling within HAZUS, see the HAZUS technical manual Chapter 4. To learn more about HAZUS software, click here.

 

 

 

 

HISTORICAL ALABAMA LANDSLIDES

 

A number of landslides have occurred throughout the state over the past several years. Below are just a few examples of Alabama landslides and information on clean-up costs and geology by county. The largest landslide in Alabama mentioned in historical literature was described in an article in The New York Times on January 30, 1886. This article (“A Big Landslide”) describes a large landslide (1 mile long as reported!) along the side of Bogan Mountain (formerly Scraper Mountain) in Cherokee County that temporarily dammed up the Chattooga River. While the slide is not apparent on the topographic maps,  the mountain does have steep slopes with a relatively high landslide susceptibility.

 

 

Autauga County

 

Near Prattville in Autauga County, County Road 47 was closed by a landslide in 2005. The problem stemmed from unconsolidated sediments that move underneath the road when it rains. A temporary repair was implemented which cost between $150,000 and $200,000 ($173,000 and $232,000 in 2010 dollars), and a more permanent repair is estimated to cost several million dollars, if feasible.

 

Baldwin County

 

Currently, in the City of Spanish Fort in, the bluffs located along the eastern shore of the Mobile Bay are slowly receding due to wave erosion causing a substantial threat to a number of homes along the bluff. The City of Spanish Fort and the State of Alabama applied for funds to stabilize the bluff to reduce future property and infrastructure damage that could be caused by a landslide in this area.

 

 

Bullock County

 

Area on a topographic map of Union Springs, Alabama, showing a landslide.

 

Photo (below) of an active landslide in the backyard of a neighborhood in Union Springs, Bullock County, 2010. Scarp shown clearly in center of photo. The landslide’s scarp is in the Cusseta Sand Member of the Ripley Formation. Landslide topography can also be seen on the 1973 Union Springs 7.5-minute topographic map (left).

 

Landslide in Union Springs, Alabama.

(Photo from Francis Ashland, USGS)

 

Conecuh County

 

Landslide in Conecuh County, Alabama.

 

Landslide in Conecuh County in 1997. Photo above shows the scarp and upper portion of the slide.

DeKalb County

 

Landslide in DeKalb County, Alabama.

 

In 1998, a landslide in DeKalb County wiped out a portion of County Highway 81 on Lookout Mountain (above). The slide moved 117,527 cubic yards of rock and cost $1.7 million to repair. Other slides on Highway 35 between Rainsville and Fort Payne and on Highways 146 and 71 in Jackson County have cost between $1 and $2 million each to repair.

 

Etowah County

 

North of Gadsden in Etowah County, the southbound lane of Interstate 59 slid from its perch on a mountainside down into the valley below in 1972, resulting in $1.3 million ($7.2 million in 2010 dollars) in repairs and prolonged disruption of traffic.

 

Jefferson County

 

In Birmingham in 1988, a landslide destroyed apartment buildings during the construction of an adjacent Festival Center. Estimated damages were over $10 million ($19.5 million in 2010 dollars).

 

 

Marshall County

 

Landslide in Marshall County, Alabama.

 

This landslide occurred in the Guntersville Dam 7.5-minute topographic quadrangle in Marshall County, Alabama. The slide originated in the Mississippian age Pennington Formation, a geologic formation with weak rock strength and past history of landslides.

Tuscaloosa County

 

Landslide in Tuscaloosa County, Alabama.

 

Landslide on a deforested slope. Underlying geology is the unconsolidated sand of the Cretaceous Coker Formation of the Tuscaloosa Group.

 

 

 

 

READ MORE ON LANDSLIDES

 

Alabama

 

Alabama Emergency Management Agency, 2010, Landslides, Section 5.2.4, State Hazard Mitigation Plan 2010 Update, p. 5-32 – 5-36.

 

Pomeroy, J.S., 1982, Landslides and related features, Alabama and Tennessee: U.S. Geological Survey Open-file Report 82-181. Plates of maps used by Pomeroy in mapping.

 

Pomeroy, J.S., and Thomas, R.E., 1985, Geologic relationships of slope movement in northern Alabama: U.S. Geological Survey Bulletin 1649, 13 p.

 

Rheams, K. F., 1982,  Inventory of landslides, slope failures, and unstable soil conditions in Alabama: Geological Survey of Alabama Open-file Report, p. 8-35.

 

Thomas, R.E., 1979, Landslides and related features, Alabama, Georgia, and Tennessee: U.S. Geological Survey Open-file Report 79-944. Plates of maps used by Thomas in mapping.

 

Thomas, R.E., 1982, Landslides and related features, Alabama and Tennessee: U.S. Geological Survey Open-file Report 82-193. Plates of maps used by Thomas in mapping.

 

 

Regional

 

Wieczorek, G.F. and B.A. Morgan, 2008, Debris-flow hazards within the Appalachian Mountains of the Eastern United States: U.S. Geological Survey Fact Sheet 2008-3070, 4 p.

 

Wieczorek, G.F., Eaton, L.S., Morgan, B.A., Wooten, R.M., and Morrissey, M., 2009, An examination of selected historical rainfall-induced debris-flow events within the central and southern Appalachian Mountains of the Eastern United States: U.S. Geological Survey Open-File Report 2009-1155, 25 pp.

 

 

Sinkholes

Earthquakes

Landslides

Radon

Disaster Preparedness

Geohazard News

Geospatial Data

 

Geological Hazards Home

 

 

GSA Home