Tephra occurrence in Alaska: a map-based compilation of stratigraphic tephra data

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Frequently anticipated questions:

What does this data set describe?

Title:
Tephra occurrence in Alaska: a map-based compilation of stratigraphic tephra data
Abstract:
The principal hazard associated with future explosive eruptions of Alaska volcanoes is the generation of volcanic ash clouds which are explosively blasted high into the atmosphere and then drift away from the volcano with the wind. The fragments in the ash cloud (tephra) vary in size and the heavier particles fall near the source while finer particles travel downwind. This transported tephra will fall out of the cloud and accumulate on surfaces and structures, contaminate water sources, and infiltrate electronics and motors. The weight of significant accumulations may collapse structures and cause other damage. Chronic exposure to ash may be a significant public health hazard. This publication presents the frequency and location of tephra fall throughout Alaska and into the Yukon Territory of Canada, resulting from eruptions of Alaska volcanoes from the Pleistocene to the present. The tephra occurrence map facilitates better visualization of areas in Alaska with past occurrences of ashfall. The map is a useful indicator of regional potential ashfall hazards. All files can be downloaded free of charge from the DGGS website (<http://doi.org/10.14509/30059>).
Supplemental_Information: 
AK_Coast:    Alaska coastline in NAD 83 datum	
Alaska Tephra Footprints:    Polygons representing the maximum spatial distribution of tephra for each eruption. Note that this is only available for those deposits with existing published information on distribution.	
DEM_NAD83_300m:    NAD 83 datum Digital Elevation Model (DEM). Digital image used in USGS Map I-2585 derived from digital elevation model 300m mosaic for Alaska.	
Populated_Places:    Point feature class of cities, towns, and other populated places in Alaska.	
Spatial_Frequency_Grid:    Gridded polygon feature class containing information about the number of tephras overlapping within each 10x10 km grid square. Reports Sum Footprints for each grid square.	
Stations:    Point feature class providing the location of the station, information about the publications that data were derived from, a count of tephra occurrence at each station, as well as any age data and subsequent calculations of recurrence intervals
  1. How should this data set be cited?

    Worden, A.K., Schaefer, J.R., and Mulliken, K.M., 2018, Tephra occurrence in Alaska: a map-based compilation of stratigraphic tephra data: Miscellaneous Publication MP 165, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 19 p.

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -179.999999
    East_Bounding_Coordinate: -104.060291
    North_Bounding_Coordinate: 70.091875
    South_Bounding_Coordinate: 48.106410

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 1964
    Ending_Date: 2018
    Currentness_Reference: ground condition

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: digital data

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      This is a point data set.

    2. What coordinate system is used to represent geographic features?

      The map projection used is Alaska Albers.

      Projection parameters:
      Standard_Parallel: 55.0
      Standard_Parallel: 65.0
      Longitude_of_Central_Meridian: -154.0
      Latitude_of_Projection_Origin: 50.0
      False_Easting: 0
      False_Northing: 0

      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.0000000030536018158500163
      Ordinates (y-coordinates) are specified to the nearest 0.0000000030536018158500163
      Planar coordinates are specified in meters

      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is GRS 80.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257222101000025.

  7. How does the data set describe geographic features?

    AK_Coast
    Alaska coastline in NAD 83 datum; file type: (Source: <http://www.asgdc.state.ak.us/#56> (2018))

    Alaska Tephra Footprints
    Polygons representing the maximum spatial distribution of tephra for each eruption. Note that this is only available for those deposits with existing published information on distribution.; file type: (Source: Mulliken and others (2018))

    DEM_NAD83_300m
    NAD 83 datum Digital Elevation Model (DEM). Digital image used in USGS Map I-2585 derived from digital elevation model 300m mosaic for Alaska.; file type: (Source: https://agdc.usgs.gov/data/usgs/erosafo/300m/300m.html (2018))

    Populated_Places
    Point feature class of cities, towns, and other populated places in Alaska.; file type: (Source: <http://www.asgdc.state.ak.us/#14> (2018))

    Spatial_Frequency_Grid
    Gridded polygon feature class containing information about the number of tephras overlapping within each 10x10 km grid square. Reports Sum Footprints for each grid square.; file type: (Source: Derived from Mulliken and others (2018))

    Stations
    Point feature class providing the location of the station, information about the publications that data were derived from, a count of tephra occurrence at each station, as well as any age data and subsequent calculations of recurrence intervals; file type: (Source: Alaska Division of Geological & Geophysical Surveys (DGGS) and Alaska Volcano Observatory)

    CitationID
    Citation ID assigned to the publication in the AVO reference database, GeoDIVA. Data from unpublished sources was assigned a NULL value. (Source: this report)

    Integer

    Author
    The author of the publication used for the data. This is not necessarily the geologist who visited the section. (Source: this report)

    String

    StationID
    Unique ID number assigned to the station for reference in AVO's GeoDIVA database. Null values indicate that the station could not be located or that the tephra layers described in the publication were not identified from a single continuous stratigraphic section. (Source: this report)

    Integer

    Lat_nad83
    Latitude of station in decimal degrees, NAD 83 datum. Null values indicate that the station could not be located or that the tephra layers described in the publication were not identified from a single continuous stratigraphic section. (Source: this report)

    Double

    Long_nad83
    Longitude of the station in decimal degrees, NAD 83 datum. Null values indicate that the station could not be located or that the tephra layers described in the publication were not identified from a single continuous stratigraphic section. (Source: this report)

    Double

    Location
    Information on how the location of the station was obtained. If the station was queried from GeoDIVA, coordinates are as found in GeoDIVA. If the station did not previously exist in GeoDIVA, the location is either from specific coordinates given in the text or derived by georeferencing a location map included in the publication. (Source: this report)

    String

    Station
    Station name as represented in GeoDIVA or in the preliminary publication. (Source: this report)

    String

    TephraNumb
    Number of discrete tephra deposits within a stratigraphic section. In some cases with very high tephra counts (and often very thin tephras), the number of discrete tephras was obtained from the text of the publication. This is considered a minimum number of events, as erosion and other natural processes can sometimes destroy deposited tephra layers. (Source: this report)

    Integer

    Thickness
    Denotes (yes or no) whether stratigraphic thickness information was included in the source publication (not necessarily corresponding to a tephra layer). No numerical thickness data has been compiled at this time. (Source: this report)

    String

    LowerAge
    This field contains the initial ages taken directly from the publication. These ages may be calibrated (if so, the age remains the same when moved to the appropriate field). Information from this column is parsed into the appropriate age column in the spreadsheet. Numbers in parentheses refer to a calendar year. Numbers not in parentheses are yr BP. If the value is null, it indicates that there is no reported tephra at the station. If the value is "unspecified", it indicates that there is tephra recorded at the station, but no age data. (Source: this report)

    String

    OldestDate
    If the oldest tephra in the sequence is the result of a specific historic eruption, the date of that event is entered here. These dates are entered in years C.E. (Source: this report)

    Integer

    OldestAge
    Reported ages for the oldest (lowest) tephra in the section, in yr BP. (Source: this report)

    String

    AgeYrBPmax
    For ages with an error margin, this field is the maximum (oldest) age for the lowest tephra. (Source: this report)

    Integer

    AgeYrBPmin
    For ages with an error margin, this field is the minimum (youngest) age for the lowest tephra. (Source: this report)

    Integer

    Confidence
    Some calibrations report a percentage confidence interval, typically 1-2 sigma. (Source: this report)

    Double

    MedLowAge
    For radiocarbon ages that were calibrated as part of this work, the calculated median age of the oldest/lowest tephra is presented here in yr BP. (Source: this report)

    MedLowAge

    Method
    Indicates dating method for reported oldest ages. * indicates ages calibrated for this study. (Source: this report)

    String

    Recurrence
    The minimum recurrence interval indicates the average number of years between tephra fall events (yrs/1 tephra). This is calculated by dividing the oldest age of tephra by the number of tephras in the section. This is a minimum recurrence interval because the number of tephra layers in a section is considered a minimum number of events. (Source: this report)

    Recurrence

    FreqTephra
    The frequency of tephra occurrence, calculated by dividing the number of tephra layers by the maximum tephra age. This is reported in tephra/1000 years. This field is based on ages provided in publication. (Source: this report)

    String

    AgeComment
    Additional information about the ages of samples, including dating techniques, calibration details, tephra identification, source eruptions, and chronologic sequences. (Source: this report)

    String

    GenComment
    General comments about the station or specific layers within a stratigraphic column. Some age or identifying information may also be included here. (Source: this report)

    String

    Reference
    Reference for the publication containing original station, sample and age data. (Source: this report)

    String

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

    As a compilation of previously published data, this project is built on a foundation of work done by other scientists. The list of authors whose work contributed to this database would be too extensive to cite here, but each is credited in the reference table of the dataset. We would like to thank Patricia Gallagher (DGGS), Mike Hendricks (DGGS), and Kristi Wallace (USGS-AVO) for their review of this publication. This project was partially funded through DGGS cooperative agreements with the USGS Volcano Hazards Program, grant number G16AC00165. The Alaska Volcano Observatory is a joint program of the U.S. Geological Survey, the Geophysical Institute of the University of Alaska Fairbanks, and the State of Alaska Division of Geological & Geophysical Surveys.

  3. To whom should users address questions about the data?

    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK 99709-3707
    USA

    (907)451-5020 (voice)
    (907)451-5050 (FAX)
    dggspubs@alaska.gov

    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays

Why was the data set created?

Tephra fall (volcanic ash) studies are a key component to understanding the frequency and magnitude of volcanic eruptions and conducting volcano-hazard assessments. In addition, many interdisciplinary studies rely on tephra fall deposits as time-stratigraphic markers. Information on tephra deposits in Alaska has previously been dispersed amongst hundreds of publications that span numerous research disciplines. The tephra occurrence map facilitates better visualization of areas in Alaska with past occurrences of ashfall. The map is a useful indicator of regional potential ashfall hazards.

How was the data set created?

  1. From what previous works were the data drawn?

    DGGS Staff and Cameron, C.E., 2004 (source 1 of 2)
    Staff, DGGS, and Cameron, C.E., 2004, Alaska GeoSurvey News - The geologic database of information on volcanoes in Alaska (GEODIVA): a comprehensive and authoritative source for volcanic information: Newsletter NL 2004-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 8 p
    Type_of_Source_Media: digital data
    Source_Contribution: data compilation

    Mulliken, K.M. and others, 2018 (source 2 of 2)
    Mulliken, K.M., Schaefer, J.R., and Cameron, C.E., 2018, Geospatial distribution of tephra fall in Alaska: a geodatabase compilation of published tephra fall occurrences from the Pleistocene to the present: Miscellaneous Publication MP 164, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 46 p
    Type_of_Source_Media: digital data
    Source_Contribution: Spatial Frequency Grid

  2. How were the data generated, processed, and modified?

    Date: 2018 (process 1 of 3)
    Data compilation - The stations dataset within the geodatabase presents the synthesis of over 1200 stratigraphic columns located throughout Alaska and parts of the Yukon Territory of Canada, originally published in 140 references. Unpublished tephra count data by Alaska Volcano Observatory (AVO) staff is also included for the Dutch Harbor/Unalaska region (Makushin volcano, J. Schaefer, written commun.) and the Lower Cook Inlet region (K. Wallace and K. Mulliken, written commun.). Although some stations and basic information were queried from the Alaska Volcano Observatory's (AVO) Geologic Database of Information on Volcanoes in Alaska (GeoDIVA) (Cameron, 2004), an additional 604 stations were added from original references. Primary source documents were also used to compile stratigraphic information not already present in GeoDIVA, including tephra count, stratigraphic section age information, and age calculations, and this new compilation has been entered into the larger GeoDIVA database. See accompanying report for additional information about the data compilation methodology and a comprehensive bibliography of data sources.

    Data sources used in this process:

    • DGGS Staff and Cameron, C.E., 2004

    Date: 2018 (process 2 of 3)
    Recurrence interval and frequency calculations - Tephra relative or direct ages and age dating methods were compiled from publications that included age data. For each station with reported age information, an average minimum recurrence interval was calculated. The recurrence interval represents the average number of years elapsed between tephra depositions. Similarly, a tephra frequency was calculated and reports the number of tephra layers per 1000 years.

    Date: 2018 (process 3 of 3)
    Spatial Frequency Grid - Tephra location, age, and recurrence calculations were compiled into an ArcGIS geodatabase and an ArcMap document. To assist in gauging tephra fall frequency for areas without stratigraphic sections, we used Mulliken and others (2018) publication to derive a spatial tephra frequency grid for the State of Alaska. The Spatial Frequency Grid polygon feature class contains identifying grid numbers and values for the sum of the footprints (Sum Footprints: reports the number of overlapping tephra footprints that fall within that grid square). This derived grid product contains only tephra-fall deposits and eruptions with existing published information on distribution and is, therefore, a minimum estimate of past tephra fall occurrence.

    Data sources used in this process:

    • Mulliken, K.M. and others, 2018

  3. What similar or related data should the user be aware of?

    Cameron, C.E., and Nye, C.J., 2014, Preliminary database of Quaternary vents in Alaska: Miscellaneous Publication MP 153, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 11 p
    Cameron, C.E., and Schaefer, J.R., 2016, Historically active volcanoes of Alaska: Miscellaneous Publication MP 133 v. 2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet

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

  1. How well have the observations been checked?

    This dataset is a compilation of data from numerous publications. Individual publications report geochronologic information in different ways, with no uniform standards, resulting in a variety of formats that make it difficult to design query-friendly age data fields. In addition, as eruption histories are refined with more study and improved dating techniques, so are the ages of specific tephra deposits. Ages listed in this dataset are meant to guide researchers, who are encouraged to refer to original publications for more detail on deposit geochronology. For each station with reported age information, an average minimum recurrence interval was calculated. The recurrence interval represents the average number of years elapsed between tephra depositions. This recurrence interval is both an approximation and a minimum value, as we only have a minimum count for the possible number of tephras that have fallen and subsequently been preserved in an area and the oldest age data is often not directly correlated to the lowest tephra layer (instead being attributed to layers found below the tephra). Smaller ash fall events can occur without preservation in the geologic record. Similarly, a tephra frequency was calculated and reports the number of tephra layers per 1000 years. This calculation uses the same information as described above and serves as an alternate method of displaying the expected frequency of tephra producing eruptions. See the accompanying report for additional discussion of data uncertainties.

  2. How accurate are the geographic locations?

    This dataset is a compilation of data from numerous publications and thus has limitations. The accuracy of tephra deposit contours is dependent on the original publications from which the tephra fall distributional data were digitized. Geospatial accuracy is particularly uncertain when locations were digitized from very small, manually georeferenced illustrations and map figures. Accuracy issues have been mitigated by using landmark cities, vent locations, major geographic features, geopolitical boundaries, roads, and rivers to better locate data points depicted in small illustrations and maps.

  3. How accurate are the heights or depths?

  4. Where are the gaps in the data? What is missing?

    Development of this database is ongoing. As new publications are released that contain tephra distribution data, this dataset compilation will become outdated. The GeoDIVA Alaska Tephra Database is continually updated. Therefore, the static station and samples exported from GeoDIVA on December 7, 2017, and incorporated in this database will eventually be non-comprehensive. We intend to update this dataset to incorporate new data as new datasets are published.

  5. How consistent are the relationships among the observations, including topology?

    not applicable

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints:
This report, map, and/or dataset is available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).
Use_Constraints:
Any hard copies or published datasets utilizing these datasets shall clearly indicate their source. If the user has modified the data in any way, the user is obligated to describe the types of modifications the user has made. The user specifically agrees not to misrepresent these datasets, nor to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys. The State of Alaska makes no express or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.

  1. Who distributes the data set? (Distributor 1 of 1)

    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK 99709-3707
    USA

    (907)451-5020 (voice)
    (907)451-5050 (FAX)
    dggspubs@alaska.gov

    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
  2. What's the catalog number I need to order this data set?

    MP 165

  3. What legal disclaimers am I supposed to read?

    The State of Alaska makes no expressed or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.

  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 19-Sep-2018
Metadata author:
Alaska Division of Geological & Geophysical Surveys
Attn: Simone Montayne
Metadata Manager
3354 College Road
Fairbanks, AK 99709-3707
USA

(907)451-5020 (voice)
(907)451-5050 (FAX)
dggspubs@alaska.gov

Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:

Generated by mp version 2.9.21 on Wed Sep 19 16:35:46 2018