Building a Statewide Inventory of Landslides in Arizona Ann M. Youberg, Joseph P. Cook, Laura M. Bookman, Brian F. Gootee, Philip A. Pearthree, Michael Conway Arizona Geological Survey, Tucson, Arizona
Landslides in Arizona Range from very disruptive and expensive… …to geologically interesting but isolated and inconsequential.
Hwy 89 Bitter Springs Landslide 2013
Diaz Peak Debris Flows 2008 Organ Pipe Cactus National Monument
So, Arizona has landslides, but how many, what types, where are they, and do they pose a risk? • Why create a statewide landslide inventory? • What do we mean by “landslides”? • How are we creating and populating the geodatabase? • What is the status of the project? • What are some of the challenges? • Do you have data to contribute?
• Moving forward: • How will the data be used?
• How will the public access the data?
Coronado National Memorial, 2006
Why create a statewide landslide inventory? • To address deficiencies in the Landslide Hazard profile of the 2013 State of Arizona Hazard Mitigation Plan: • Incomplete - only summarized some of more wellknown, recent landslide events. • From our own mapping it was clear there were many more documented landslides than identified in the plan. • Some types of landslides (e.g. post-fire debris flows) appear to be increasing in frequency. • DEMA and AZGS partnered to obtained funding from FEMA’s Pre-Disaster Mitigation Grant Program
• Funding Split: • 75% FEMA • 25% AZGS
Our Approach • Task 1: Create the database - design and build a GIS geodatabase. • Task 2: Populate the database - compile all documented (with a caveat or two) landslides from available maps and reports, map archives, and published journal articles.
• Task 3: Fill in some data gaps - work with our partner agency, DEMA, and with our stakeholders to identify and prioritize areas requiring new mapping of known but previously undocumented landslides. • Task 4: Update hazard mitigation plans - incorporate the new landslide information into the 2018 State of Arizona Hazard Mitigation Plan, and provide assistance for incorporating the data into local and tribal hazard mitigation plans. • Task 5: Get the word out - reach out to public and civil authorities with map tools identifying landslides.
Classes of Mass Movements (“Landslides”) Included in Database USGS Fact Sheet 2004-3072
Type of Material Rock (bed) Debris (crs) Earth (fn)
Complex (http://pubs.usgs.gov/fs/2004/3072/)
Rotational Landslides – Toreva Blocks • Large, tilt-block landslides • Very common in northern AZ • Smaller slides may form within the larger landslide mass
Bitter Springs landslides sits w/in larger landslide block
Figure from ADOT
Reiche, 1937, J. Geology, v 45, No 5
Rotational Landslides
Sunset Point, I-17
• Saturation , earthquakes, gravity • Areal – largest component of inventory • Often know general info but no details.
Translational Landslides • Typically shallow • Very common way for debris flows to initiate in saturated conditions
Photo: USGS
Rockfalls and Topples • Rockfalls: • Large rocks or blocks from cliffs break off and fall • quite common • Rock topples differ from rockfalls in that whole sections of cliffs or bluffs topple over • Saturation, temperature fluctuations, erosion of underlying layers, gravity
Verde Valley
Photo: G. Billingsley
Debris Flows • Debris flows are, unsteady, nonuniform, non-Newtonian, very poorly sorted, sediment-rich slurries
BAB Wash, Ft Bowie, 2006
• >~60% sediments by volume • Floods – Newtonian. Water based. Up to ~40% sediments by volume • Hyperconcentrated – Newtonian. ~40~60% sediments by volume
• Saturation induced • Runoff induced – wildfires
• Becoming our most-common landslide • Generated by very little rainfall (RIs <1+) Channelized Photo: J. Cook
Unchannelized
Debris Flows
Photo: USGS
Photo: USGS
Photos: AZGS
2006
2003
Arizona Statewide Landslide Inventory Database (AzSLID) – Creating the Database • Repository of identified landslides across Arizona. • Design and build a GIS database capable of: • accommodates diverse data from many sources, • utilizes a comprehensive metadata structure; versatile, easily updated, and • compatible with the US Geoscience Information Network (USGIN).
Database Fields: Feature Type Data Source Movement Type Failure Mechanism Feature Age Total Cost
Tracking Identifier Movement Class Failure Depth Volume Notes
Black Canyon City, I-17
Creating the Database
Populating AzSLID Georeferenced scans of pre-GIS, non-AZGS geologic maps • Scans of older geologic maps georeferenced in ArcMap • Landslide units must be found manually (scrutinize scanned map) • Draw in landslide boundaries according to map, refine as needed using basemaps and imagery • Errors in original map and georectification must be addressed • Often coarse in scale, primary focus on bedrock mapping • May be compiled/superceded by more accurate GIS-based mapping
USGS Miscellaneous Field Studies MF-1138
Populating AzSLID AZGS geologic maps • Scans of older AZGS geologic maps have the same issues as other scanned maps • Many AZGS maps have GIS data available and the database format is familiar to current database architecture • Select landslide units from existing GIS database and import into new landslide database • Attribute imported polygons with available data • Mapped polygons often general landslide unit, no specific age data or information about mechanics of failure • Some scarp linework exists and has been imported AZGS Digital Geologic Map DGM-64
Populating AzSLID Import from other existing GIS data • Many USGS and other agency maps and data available in GIS formats • Database format may be dated and require import tools to make readable in current versions of ArcMap
• Spatial accuracy is good, much better than scanned maps although projections should be double-checked • Select landslide units from database using attribute selection tools, no manual scrutiny of all map polys • Attribute imported polygons with available data • Mapped polygons often general landslide unit, no specific age data or information about mechanics of failure • Some scarp linework exists and has been imported
USGS Scientific Investigations Map 3247
Populating AzSLID Aerial Photo Interpretation - Aravaipa Canyon, AZ • Several days of heavy rains in southern AZ in July, 2006 resulted in many new debris flows in steep terrains
• Comparison of 2005 and 2007 imagery yielded over 400 debris flows in the canyon • Hundreds more in other ranges throughout southern AZ attributable to same time period • Debris flow initiation or outlet points mapped as point features, flow paths as line features, and snouts and levees (deposits) as polygon features depending on scale and method of observation NAIP images of Aravaipa Canyon
Populating AzSLID Google Earth landslide mapping • Many large landslide complexes were spotted in Google Earth through a combination of aerial photo interpretation and panning/tilting the 3D surface • Rough approximation of unmapped landslide features • Best for larger features that show up in the DEM
• Great for adding landslide features in similar terrain/geology outside nearby mapped geologic quadrangles • Possible to draw landslide extent in Google Earth and accurately import to ArcMap using import tools • Historical imagery tool is useful for locating recent debris flows and rockfalls
Sycamore Mesa and Tank Creek Mesa landslides in the Prescott National Forest
Populating AzSLID Other AZGS studies and institutional knowledge • Most of the debris flows in this database are derived from other AZGS studies, many of which are associated with post-wildfire assessments (e.g. AZGS DI-44) • Additional debris flows are derived from informal reports and surveys of debris-flow events (e.g. 1983 debris flows in the Picacho Mtns from dissipating tropical storm Octave or the 2010 Orange Peel debris flow in the Tonto National Forest from a monsoon storm) Orange Peel debris flow near Roosevelt Lake, looking upstream and downstream
Status of AzSLID • Most identified and known landslide masses (~95%) have been added to the database (4,426 polys)
• Many identified debris flows or debris-flow basins (~80%) have been added to the database (1,379 points) • We are still searching for additional data documenting landslides so if your agency, company or other entity has data please contact us! • Starting the process to: • New mapping in critical areas identified by stakeholders • This is an opportunity for your organization to participate in identifying areas for new mapping.
Challenges of AzSLID • Designing a database that works well with broad data types and information • Data deficient areas (e.g. sparesly populated areas, Native American Reservations) • Many existing, historical geologic maps do not include mapping landslide features such as debris flows and rockfalls due to their abundance • Finding and obtaining data held by other agencies and stakeholders
Can see lots of landslides in Google Earth or know by institutional knowledge but not yet documented
Arizona Statewide Landslide Inventory Database (AzSLID) – Moving Forward… • Once completed the new landslide data will be incorporated the into the 2018 State of Arizona Hazard Mitigation Plan • Available to all tribes and government agencies for use in updating their own hazard mitigation plans. • The data will also be publically available through the Arizona Natural Hazards Viewer. http://data.azgs.az.gov/hazard-viewer/
Thank You! http://azgs.az.gov/
[email protected] [email protected]
Post-fire debris flow on the 2012 Gladiator Fire Photos: M. Massis, YCFC
