78-2 Sinkholes on the Mogollon Rim and near Flagstaff, Arizona: working toward a statewide sinkhole database

Session: New Frontiers in Cave and Karst Science

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Abstract:

Sinkholes are common in portions of Arizona where soluble geologic units lie at or beneath the surface. Sinkhole collapse or subsidence poses a possible hazard to infrastructure and existing sinkholes may serve as contaminant pathways to aquifers or pose a danger to the public. The abundance of sinkholes in Arizona has been underestimated due to forest cover concealing many of the features. The recent availability of high-resolution topographic data derived from LiDAR throughout much of the state as part of the USGS 3D Elevation Program (3DEP) has revealed previously undocumented sinkholes.

As a first step toward an inventory of sinkholes in Arizona, we chose two study areas with known sinkholes. The first study area surrounds Flagstaff, Arizona, where several documented sinkholes are known. The second study area is atop the Mogollon Rim east of Payson, Arizona, a high-use recreation area with documented sinkholes.  We mapped sinkhole features in ArcGIS Pro using slope maps, aspect maps, hillshades, and 1-m contour lines derived from 1-m-resolution digital terrain models. We mapped sinkhole boundaries using FGDC standard symbology for geologic contacts. We generated polygons of sinkhole areas from the mapped boundaries and categorized the sinkholes as “certain”, “probable”, and “possible” to indicate our confidence in the sinkhole identification.

In the greater Flagstaff study area, we identified and delineated over 75 sinkholes ranging in size from ~16 m² to 1.9 km². Several mapped sinkholes are adjacent to major roadways, although most are within more remote regions of Coconino National Forest. In the Mogollon Rim study area, we mapped over 130 sinkhole features, some which are aligned along major geologic structures. Several sinkholes in this study area are adjacent to highways and forest service roads and within popular recreation areas.

Sinkhole morphologies suggest a range in the age of sinkhole features, and/or differing processes of sinkhole genesis, i.e. solution vs collapse. This mapping represents a first step toward a statewide sinkhole database. Next steps involve: 1) compiling maps and GIS data from previously mapped sinkholes throughout Arizona, 2) identifying and mapping sinkholes in other regions of Arizona, and 3) displaying the mapped sinkhole features on the Arizona Geological Survey Natural Hazard Viewer to make the data available to land-use planners and the public.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10831

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