20260128 12541200 1.0 TRUE 150000000 5000 FGDC 20260129 000000 ArcGIS Metadata 1.0 USFS, R10 TNF, Tongass Forest Supervisor's Office Please call the phone number 907-225-3101 for the front desk. Ketchikan AK 99901 US 907-225-3101 dataset USA Tongass Landslide Initiation 2026-03-10T11:18:25 USDA Forest Service 2026-03-10T11:18:25 Landslide inventory of the Tongass National Forest Proclamation Boundary. This layer is updated yearly or as new imagery or field data becomes available. Last updated in August 2025. <DIV STYLE="text-align:Left;"><DIV><P><SPAN>This feature class is a polygon landslide inventory of the Tongass National Forest. The digital version of this inventory was started in the year 2000 and the once-over inventory was completed in 2017. The feature class is updated annually or as new imagery becomes available. Both field and photo interpreted landslides are included. The inventory includes all mass wasting features--including talus slopes, snow avalanche fields, and snow avalanche chutes. Therefore, it may be necessary to exclude some mass wasting features prior to analysis depending on the intended use of the data. Each of these are coded differently in the attributes. Most of the landslide polygons were digitized on the 1998 to 2010 ortho photos in GIS, although some were digitized using imagery taken more recently. All the landslides have been age bracketed within the available photo data sets to estimate date of occurrence. Many of them were age bracketed using air photos back to the 1929 Navy Trimegon photos. All landslides have been dated before or after 1948 imagery and before or after the 1996 to 1998 imagery. There is an associated point feature class that contains the landslide initiation zone approximations. These points only exist for true landslides--debris avalanches, debris torrents, combination debris avalanches/torrents, slumps, rotational failures, and rock fall-initiated failures. The 2023 update included new slides from 2020 imagery on Chichagof Island. The 2024 update included new slides from 2023 imagery of Admiralty, Kupreanof, Mitkof, and Wrangell Islands as well as part of Kuiu Island. The 2025 update included additional slides on Mitkof, Wrangell, Etolin and Revilla Islands and adjacent mainland. The 2025 update also revised fields and some previous entries to record imagery sources and more precise dates of occurrence.</SPAN></P></DIV></DIV> SM.FS.data@usda.gov USFS, R10 TNF, Tongass Forest Supervisor's Office Please call the phone number 907-225-3101 for the front desk. Ketchikan AK 99901 US 907-225-3101 Avalanche;Landslides;Mass Wasting;Soil;economy;economy;elevation;elevation;environment;environment;geoscientific​Information;geoscientific​Information;location;location;planning​Cadastre;planning​Cadastre;structure;structure;transportation;transportation;utilities​Communication;utilities​Communication ISO 19115 Topic Categories elevation; environment; planning​Cadastre; economy; geoscientific​Information; transportation; structure; utilities​Communication; location <DIV STYLE="text-align:Left;"><DIV><P><SPAN>The USDA Forest Service makes no warranty, expressed or implied, including the warranties of merchantability and fitness for a particular purpose, nor assumes any legal liability or responsibility for the accuracy, reliability, completeness or utility of these geospatial data, or for the improper or incorrect use of these geospatial data. These geospatial data and related maps or graphics are not legal documents and are not intended to be used as such. The data and maps may not be used to determine title, ownership, legal descriptions or boundaries, legal jurisdiction, or restrictions that may be in place on either public or private land. Natural hazards may or may not be depicted on the data and maps, and users should exercise due caution. The data are dynamic and may change over time. The user is responsible to verify the limitations of the geospatial data and to use the data accordingly.</SPAN></P></DIV></DIV> The U.S. Forest Service makes no warranty, express or implied, nor assumes any liability or responsibility for the accuracy, reliability, completeness, or utility of these geospatial data or for the improper or incorrect use of those data. The data are dynamic and may change over time. The user is responsible for verifying the limitations of the geospatial data and for using the data accordingly. Aerial and satellite imagery has become increasingly available in the past 10 years. As of 2025, satellite imagery from Maxar GEGD is accessible to all employees who support a U.S. government mission. Maxar imagery is taken several times a year throughout Southeast Alaska and allows for improved time constraints on recent landslides. Planet satellite imagery is also used and is taken up to several times per week. Research on precipitation-landslide relationships relies on narrow time windows of landslides. Some slides might be attributable to specific storms using the landslide inventory in the future, but only if dates (instead of years only) are entered. Faculty from the University of Oregon have confirmed that inputting dates, when available, will be useful to landslide researchers (Josh Roering, pers. comm.). 2026-03-10 1 485113.4472 1049910.8615 922256.707500003 316299.997199997 R10 Tongass NF 0 Contributors to the landslide inventory have corrected errors in the tabular data as they are identified during annual updates. The search method involves the use of a grid at 1:15000 to reduce the number of landslides missed. Landslide intiation point spatial accuracy is related to the accuracy of source imagery used to digitize the slides. Source imagery has not been orthorectified in all cases. Data completeness of Tongass Landslide Initiation feature class reflects the frequency and quality of the imagery used to locate the landslides. For example, 19 years elapsed between the 1929 imagery and the next available imagery in 1948. Frequency and quality of imagery have improved over time. The most recent landslides may not be digitized as they continue to occur. Regional landslide inventories are ultimately unable to capture every landslide. However, the manual identification of landslides used in this dataset is typically more accurate than machine learning or artificial intelligence methods to identify landslides as of 2025. Data spatial accuracy is related to the accuracy of the imagery used to digitize the landslide boundaries. When compared with orthorectified imagery, polygons are generally accurate within 10 meters. Some exceptions are likely, however. Recent landslides were generally digitized using more spatially accurate imagery than older landslides. Initiation point locations are inferred based on the landform and landscape position observed in imagery and digital elevation models. Initation points are usually located within 10 meters of the highest elevation of the landslide scar. Retrogressive scarp movement , which can occur after the main pulse of debris mobilization, is therefore not accounted for. Most landslides are identified using aerial or satellite imagery but field data is occassionally used. When using imagery, a search area is selected each year and scanned for landslides at a scale of 1:15000 along a grid. Field-identified landslides are recorded using GPS or other location-enabled services. Polygons are delineated around the boundary of each landslide based on the imagery or on field-derived GPS data. Landslide dates are entered using aerial imagery flight dates or dates of satellite image captures. Initiation point locations are inferred based on the landform and landscape position observed in imagery and digital elevation models. For example, if a gully intersects the highest landslide scar elevation, the initiation point might be inferred within the deepest part of the gully where water is concentrated. Initation points are usually located within 10 meters of the highest elevation of the landslide scar. 2026-03-10 withheld withheld withheld 14509 Polygon ESRI GIS Dictionary S_USA.Tongass_Landslide_Initiation Polygon 14509 OBJECTID Internal feature number. Esri Sequential unique whole numbers that are automatically generated. OBJECTID OID 4 10 0 TNF_LS_NO Every landslide is assigned a unique number in this attribute. This number can be used to relate Landslide Areas to Landslide Initiation point data. US Forest Service Unique landslide number TNF_LS_NO Short 0 5 0 INVENTORY This attribute describes the inventory campaign that is associated with each landslide and initiation point. The current dataset is an aggregate of many inventory campaigns. US Forest Service Name of inventory campaign INVENTORY String 4 0 0 LATEST_DATE_NOT_SEEN This is the latest date a landslide was not observed in imagery. If an imagery source has low temporal precision, January 1 was selected as the default date. This is intended to express the earliest possible date that a landslide could have occurred given limited information. US Forest Service Date (MM/DD/YYYY) LATEST_DATE_NOT_SEEN Date 0 0 0 NOT_SEEN_SOURCE This is the imagery source used to populate "latest_date_not seen". Imagery sources are Google Earth / Maxar AHAP / Maxar G-EGD / Planet Explorer / Tongass_NF_MultiRes_2016_RGB. US Forest Service Source of Imagery NOT_SEEN_SOURCE String 255 0 0 FIRST_DATE_SEEN This is the first date a landslide was observed in imagery. If an imagery source has low temporal precision, December 31 was selected as the default date. This is intended to express the latest possible date that a landslide could have occurred given limited information. US Forest Service Date (MM/DD/YYYY) FIRST_DATE_SEEN Date 0 0 0 SEEN_SOURCE This is the imagery source used to populate "first_date_seen". Imagery sources are Google Earth / Maxar AHAP / Maxar G-EGD / Planet Explorer / Tongass_NF_MultiRes_2016_RGB. US Forest Service Source of Imagery SEEN_SOURCE String 255 0 0 CONFID_DAT This is the date of occurrence (MM-DD-YYYY) preceeded by a code to indicate whether it is known (K) or estimated (E). The “E” or “K” must be entered and the month and day may be omitted if unknown. When the date is different than "first_date_seen" and "latest_date_not_seen", "confid_dat" is derived from a date of a storm or reported date of a landslide. Value is NULL when dates taken from imagery are the best available dates. The following are examples of valid entries: E00001990 – The slide is estimated to have occurred in 1990. K10071992 – The slide is known to have occurred on October 7, 1992. K00001987 – The slide is known to have occurred in 1987 but the exact date is unknown US Forest Service Certainty of date expressed as known (K) or estimated (E) followed by date (MMDDYYY) CONFID_DAT String 9 0 0 ESTIM_YEAR The average year between the last date the slide was not seen and the first date the slide was seen. This attribute was formerly the average of years. US Forest Service Year (YYYY) ESTIM_YEAR Integer 4 10 0 TREATMENT This indicates whether or not a slide has been treated for erosion control. US Forest Service Yes / No TREATMENT String 1 0 0 RD_INITIATED Signifies whether an initiation point is within 100 feet of a road. Note: Dennis Landwehr, former soil program manager, personally used the 100 foot metric and taught it to others when inputting inventory data (Jenny Richter, pers. comm.). US Forest Service Yes / No RD_INITIATED String 1 0 0 FAIL_TYPE Type of landslide or mass failure observed. Appendix D - Starting at page 168 - "Geomorphic definitions and codes" of the "Terrestrial Ecological Unit Inventory Technical Guide: Landscape and Land Unit Scales." US Forest Service Combination debris avalanche and debris torrent SOAR-DEFL-FLOW - Source Area-Debris Flow-Flow US Forest Service Debris avalanche field MASC-UNDI-SLID - Main Scarp-Undifferentiated Slide-Slide US Forest Service Rock fall inititiated failures SOAR-ROFA-COMP - Source Area-Rock Fall Avalanche-Complex US Forest Service Talus slopes DEPO-FAPS-FALL - Deposit (Talus)-Fall-Prone Slope-Fall US Forest Service Slump SLEF-COMP - Slump-Earth Flow-Complex US Forest Service Snow avalanche chute TRZO-SNAS-FLOW - Transport Zone (Chute)-Snow Avalanche Slope-Flow US Forest Service Debris avalanche SOAR-DEAV-FLOW - Source Area-Debris Avalanche-Flow US Forest Service Debris torrent TRZO-DEFL-FLOW - Transport Zone-Debris Flow-Flow US Forest Service Rotational slide ROSL-SLID - Rotational Slide-Slide US Forest Service Snow avalanche field SOAR-SNAS-FLOW - Source Area-Snow Avalanche Slope-Flow US Forest Service FAIL_TYPE String 14 0 0 EXAMINER Examiner who entered data for the landslide. US Forest Service Name ( First Last) EXAMINER String 50 0 0 SLOPE_PER This is the slope gradient of the initiation zone measured in percent gradient. A value is entered only if it is based on a field measurement. US Forest Service Percent slope gradient SLOPE_PER Short 0 5 0 SLOPE_SHA Slope shape is described in two directions. The first code describes the up-and-down slope (perpendicular to the contour) and the second code describes the shape across the slope (along the horizontal contour). It is based on the slope shape at the zone of initiation. A value is entered only if it is based on a field measurement. US Forest Service LL Linear Linear US Forest Service LV Linear Convex US Forest Service LC Linear Concave US Forest Service VL Convex Linear US Forest Service VV Convex Convex US Forest Service VC Convex Concave US Forest Service CL Concave Linear US Forest Service CV Concave Convex US Forest Service CC Concave Concave US Forest Service SLOPE_SHA String 2 0 0 BDRK_F_ZON This is the type of bedrock at the initiation zone. A value is entered only if it is based on a field measurement. 3 character NASIS code that appears on pages 1-18 and 1-19 of “The Field Book for Describing and Sampling Soils". NRCS Various; see pages 1-18 and 1-19 of “The Field Book for Describing and Sampling Soils". BDRK_F_ZON String 3 0 0 PM_F_ZONE This is the type of parent material at the initiation zone. A value is entered only if it is based on a field measurement. 3 character NASIS code that appears on pages 1-16 and 1-17 of “The Field Book for Describing and Sampling soils.” NRCS Various; see pages 1-16 and 1-17 of “The Field Book for Describing and Sampling soils.” PM_F_ZONE String 3 0 0 LANDSLIDE_NAME A landslide name is assigned if a name is commonly used in verbal or written communication. US Forest Service Name LANDSLIDE_NAME String 50 0 0 LANDWEHR_N Landslides have a Landwehr number (landwehr_n) if they are present in the Landwehr landslide inventory. This number is used to relate the two inventories. US Forest Service Number LANDWEHR_N String 3 0 0 GROUPED_SL This field indicates whether a landslide is part of a complex of several slides. US Forest Service Yes / No GROUPED_SL String 2 0 0 RECURRENCE This field indicates whether a different landslide has occured in the same location (Yes/No). The date of the previous landslide is included if known. US Forest Service Yes / No RECURRENCE String 9 0 0 ACRES Total acres of the landslide polygon. US Forest Service Number ACRES Double 8 38 8 GLOBALID A type of UUID (Universal Unique Identifier) in which values are automatically assigned by the geodatabase when a row is created. Esri A type of UUID (Universal Unique Identifier) in which values are automatically assigned by the geodatabase when a row is created. GLOBALID globalid 0 0 0 EPSG 6.12(3.0.1) FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998