Landslides in Arizona
Landslides in Arizona are common; far more common than most people think. 'Landslide' is a generic term referring to the downslope movement of rock, soil, and detritus driven by gravity. Landslides frequently start on the moderate to steep slopes of Arizona's mountains, plateaus, mesas, and buttes before spilling out into her canyons and valley floors. In the U.S., landslides rival floods as the deadliest and costliest natural hazard, causing dozens of fatalities and ~$2–3 billions of damage to infrastructure, roads, buildings and homes annually (Source: NOAA National Weather Service Flood Loss Data, http://www.nws.noaa.gov/hic/).
- Landslide features appear on the Natural Hazards in Arizona Viewer
- More than 6,000 landslide features are identified in Arizona
- Landslides velocities range from in/yr to miles/hr
- Landslides occur in all 15 Arizona Counties
- ~ 50% of landslides occur on Tribal Lands
A wide array of landslides occur in Arizona. Ranging from fast-moving debris flows, rockfall, and topple to slow-moving creep, and from larger volume rotational landslides and debris avalanches to smaller volume earthflow. Landslides result from disturbances in the natural stability of a slope. Frequently, they accompany heavy rains, earthquakes, or volcanic eruptions.
Principally associated with mountainous areas, landslides can occur in areas of low relief, as well. Common landslide triggers include heavy rain, rapid snow melt, earthquakes, volcanic eruptions, and freeze and thaw cycle. Channelized debris-flows are common in Arizona's mountains and frequently accompany intense rainfall. Flows may occur hours after the period of the heaviest rain in a storm and miles from the storm center.
Landslide Snapshot Video
Photographs of recent landslide deposits in Arizona.
Impacts on People, Property, and Infrastructure
As of August, we have identified more than 6,300 landslide features and 1,400 debris flow deposits in Arizona. Debris flow events are severely underrepresented due to the difficulty in distinquishing between discrete debris flow events in Arizona's rugged canyons and drainages. The collective footprint of landslide deposits is more than 770 sq. miles (2,000 sq. kilometers); an area equivalent to that of Phoenix and Tucson combined.
Historic landslides have destroyed homes, damaged roads, utilities, and infrastructure, and resulted in death. As recently as 15 July 2017, a post-fire debris flow in the Tonto National Forest devolved into a flash flood that swept over and killed 10 people in the Cold Springs swimming hole north of Payson. Channelized debris flows and associated flash floods are responsible for most landslide-related deaths in Arizona.
Signs of possible impending slope failure or landslide:
- Structural deformation such as large foundation cracks, misaligned doors and windows, tilted floors, or sagging decks
- Large, open cracks in driveways, curbs, and roads
- Failing retaining walls
- Arc-shaped cracks in the ground
- New cracks or bulges in the ground
- Leaning telephone poles, trees or fences
To reduce the risk of landslides direct water away from steep slopes and into storm drains or natural drainages and avoid undercutting steep or unstable slopes.
Geoscience at Work for Arizona - Landslide Database
In 2014, on the heels of deadly landslides in Washington and Colorado, the AZGS initiated its first landslide hazard program. Working hand-in-hand with the Arizona Division of Emergency and Military Affairs (DEMA), we landed a grant of ~$170,000 from the Federal Emergency Management Agency (FEMA) Pre-Disaster Mitigation program to build Arizona’s first statewide landslide inventory database (AzSLID) documenting historic, Holocene and Pleistocene landslide events.
Why AzSLID? A 250-foot section of US 89 near Page, Arizona, was swept away by a landslide in Feb. 2013. No one was killed or injured, but Page, principally accessible via US 89 saw its tourism industry sink beneath the waves of nearby Lake Powell. Two years later in March 2015, US 89 was returned to service - at a cost approaching $50+ million.
AzSLID provides county, tribal, and city planners, land management agencies, and the emergency management community with a powerful tool for reconnoitering existing landslide features with an eye towards managing development to mitigate the impact of landslide-prone slopes on the people, property and infrastructure of Arizona. AzSLID could well save lives and millions of dollars in damaged or destroyed buildings and infrastructure.
Building AzSLID. From 2014 to 2017, AZGS’ Ann Youberg and Joe Cook combed through geologic maps, reports, dissertations and theses to identify all previously documented landslides. At the same, we examined aerial photographs and imagery served by Google Earth to reconnssainase mountain slopes, canyons, and the perimeters of plateaus, mesas and buttes to explore for heretofore undiscovered landslide features.
Parameters of each landslide feature – landslide type, location, footprint, age, volume, and notes among other things – were compiled in the AzSLID database, which now includes more than 6,300 landslide features and 1,400 debris flow points. The database and a graphical representation of the entire data suite are available at the Natural Hazards in Arizona Viewer.