Map showing inventory and regional susceptibility for Holocene debris flows and related fast moving landslides in the conterminous United States: Raster data

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Frequently anticipated questions:

What does this data set describe?

Map showing inventory and regional susceptibility for Holocene debris flows and related fast moving landslides in the conterminous United States: Raster data
Debris flows, debris avalanches, mud flows and lahars are fast-moving landslides that occur in a wide variety of environments throughout the world. They are particularly dangerous to life and property because they move quickly, destroy objects in their paths, and can strike with little warning. The purpose of this map is to show where debris flows have occurred in the conterminous United States and where these slope movements might be expected in the future.
(This should ONLY contain information that does not fit in any other section.)
  1. How might this data set be cited?
    Brabb, E.E., Colgan, J.P., and Best, T.C., 1999, Map showing inventory and regional susceptibility for Holocene debris flows and related fast moving landslides in the conterminous United States: Raster data: U.S. Geological Survey Miscellaneous Field Studies Map 2329, U.S. Geological Survey, Menlo Park, CA.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: 172
    East_Bounding_Coordinate: -66
    North_Bounding_Coordinate: 72
    South_Bounding_Coordinate: 18
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 1928
    Ending_Date: 1999
    All of the data on this map were compiled from reports published or field work conducted after the year 1928. No distinction was made between debris flow scars, made shortly after the events and debris flow deposits, which may be thousands of years old. We believe that all of the debris flows described in this report formed during the past 10,000 years (Holocene), but some of them could be older.
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: map
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Raster data set. It contains the following raster data types:
      • Dimensions 4152 x 7230, type Grid Cell
    2. What coordinate system is used to represent geographic features?
      The map projection used is Lambert Azimuthal Equal Area.
      Projection parameters:
      Longitude_of_Projection_Center: -100.00
      Latitude_of_Projection_Center: 45.00
      False_Easting: 0.0
      False_Northing: 0.0
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 1.0
      Ordinates (y-coordinates) are specified to the nearest 1.0
      Planar coordinates are specified in METERS
      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is GRS1980.
      The semi-major axis of the ellipsoid used is 6378206.4.
      The flattening of the ellipsoid used is 1/294.98.
  7. How does the data set describe geographic features?
    Debris-flow susceptibility grid cell
    Any of the data elements in the debris-flow susceptibility file (Source: author)
    Debris-flow susceptibility grid cell value
    The value refers to color of the raster cell in the tiff file. The various shades of pink represent areas that are susceptible to debris flows, and the shades of gray represent areas that are likely not at high risk for debris (Source: author)
    Range of values

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Brabb, E.E.
    • Colgan, J.P.
    • Best, T.C.
  2. Who also contributed to the data set?
    We are grateful to several state geologists and members of their staff who kindly reviewed a preliminary copy of the map and the bibliography and provided new information. We are particularly grateful to M. Lee Allison, State Geologist for Utah, and members of his staff who contributed a digital database of debris flow locations for Utah. We also wish to thank Stephen Ellen, Russell Campbell, Gerald Wieczorek, and David Howell for their reviews and help during various phases of the work.
  3. To whom should users address questions about the data?
    Steve Kambly
    U.S. Geological Survey
    561 National Center
    Reston, VA

    703-648-5094 (voice)

Why was the data set created?

These data are intended for geographic display and analysis at the national level, and for large regional areas. It is not intended for hazard evaluation or other site-specific work, and should not be used for such. It can be used to determine where debris flow processes may be a problem and where additional information and investigation are warranted. Although the digital form of the data removes the constraint imposed by the scale of a paper map, the detail and accuracy inherent in map scale are also present in the digital data. The fact that this database was edited at a scale of 1:2,500,000 means that higher resolution information is not present in the data. Plotting at scales larger than 1:2,500,000 will not yield greater real detail, and it may reveal fine-scale irregularities below the intended resolution of the database. Similarly, where this database is used in combination with other data of higher resolution, the resolution of the combined output will be limited by the lower resolution of these data. No responsibility is assumed by the U.S. Geological Survey in the use of these data.

How was the data set created?

  1. From what previous works were the data drawn?
    DEM (source 1 of 1)
    National Oceanic and Atmospheric Administration, 1991, United States 30-second DTM: National Oceanic and Atmospheric Administration, Washington, DC.

    Type_of_Source_Media: Online
    Source_Contribution: Digital elevation values
  2. How were the data generated, processed, and modified?
    Date: 1999 (process 1 of 4)
    A Digital Elevation Model (DEM) released by the National Oceanic and Atmospheric Administration (NOAA) provides convenient nationwide data for the preparation of a slope map. The database consists of ground-surface elevations at 30 arc-second (approximately 1 km by 1 km) grid cells. Apparently these data were derived from the Army Map Service 1:250,000 topographic maps. However, several slope maps were prepared from this database using ARC/INFO, a commercial GIS software program. To calculate the slope at each one-kilometer grid cell, the process fits a quadratic surface to the elevation values of a 3 cell by 3 cell box surrounding the grid cell for which the slope is to be calculated. The slope assigned to the middle cell is the maximum slope of the quadratic surface at that point. Data sources used in this process:
    • DEM
    Data sources produced in this process:
    • Slope map
    Date: 1999 (process 2 of 4)
    Brabb and others (1989) have discussed several problems with the database. One of these concerns the average value for the slope over a 9km square area. This figure is generally much flatter than the actual value for slopes within the selected area. Map values of one or two degrees may correspond to slopes steeper than the 25- degree value targeted for the susceptibility map. Because of this discrepancy, the map is referred to as a slope index map, giving relative slope rather than actual slope at any specific area. Several slope index maps were prepared to try to find slopes steeper than 25 degrees where debris flows might be expected in the future. The maps were adjusted by trial and error to incorporate the largest number of debris-flow points without including large, gently sloping areas where no debris flows are expected. We eventually adopted a map with a slope index steeper than 3 percent, which includes about 75 percent of the debris flows mapped. Only individual debris-flow locations were used to compute the percentage of debris flows in each slope category, because the locations of debris flows within the polygon areas are too uncertain for this purpose. The other debris flows may occur in areas where more gentle average slopes contain steep slopes of limited extent, such as cliffs along rivers and lakes that are too small to be detected in the one-kilometer grid cell. Alternatively, some features mapped as debris flows may not be debris flows. Data sources used in this process:
    • Slope map
    Data sources produced in this process:
    • Susceptibility map
    Date: 1999 (process 3 of 4)
    The susceptibility map was combined with a digital shaded-relief map to make the tiff image file for map display. This was done using the grid commands Data sources used in this process:
    • Susceptibility map
    • DEM
    Data sources produced in this process:
    • Shaded-relief susceptibility
    Date: 22-Jan-1999 (process 4 of 4)
    Creation of original metadata record Person who carried out this activity:
    Peg Rawson
    U.S. Geological Survey
    521 National Center
    Reston, VA

    703-648-4183 (voice)
  3. What similar or related data should the user be aware of?

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
  2. How accurate are the geographic locations?
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    This data set includes an inventory of debris flows and related fast-moving landslides for the conterminous United States, and a susceptibility map covering the same area. This inventory is up-to-date as of August 1999, but there undoubtedly exists a significant amount of information that is not included in this report.
  5. How consistent are the relationships among the observations, including topology?
    No additional checks for topological consistency were performed on this data set.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: None
None. Acknowledgment of the National Atlas of the United States of America and (or) the U.S. Geological Survey would be appreciated in products derived from these data.
  1. Who distributes the data set? (Distributor 1 of 1)
    USGS Information Services
    Box 25286
    Denver Federal Center
    Denver, CO

    1-888-ASK-USGS (voice)
    303-202-4693 (FAX)
  2. What's the catalog number I need to order this data set?
  3. What legal disclaimers am I supposed to read?
    Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made by the U.S. Geological Survey regarding the utility of the data on any other system, nor shall the act of distribution constitute any such warranty. No responsibility is assumed by the U.S. Geological Survey in the use of these data. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
  4. How can I download or order the data?

Who wrote the metadata?

Last modified: 23-Feb-2015
Metadata author:
Peter N Schweitzer
USGS Midwest Area
Collection manager, USGS Geoscience Data Clearinghouse,
Mail Stop 954
12201 Sunrise Valley Dr
Reston, VA

703-648-6533 (voice)
703-648-6252 (FAX)
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

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