Sink holes in Arizona

Ever since the tragic story of a Florida man being dropped into a sink hole while sleeping, there have been inquiries to the Arizona Geological Survey about sink holes in Arizona – and there are many sink holes here.

In 2010, I posted a story about the seven sink holes surrounding Sedona. That story shows diagrams on how sink holes form.

The Arizona Geological Survey has a publication, “A review and bibliography of Karst Features of the Colorado Plateau, Arizona” That URL links to the full report (20.8Mb) which contains photos, maps, and explanatory text.

“Karst is the name applied to topography that develops on land underlain by soluble rocks such as limestone, gypsum, and salt. Karst terrain is characterized by solution features such as caves, sinkholes, depressions, enlarged joints and fractures, and internal drainage. The name was derived from the Karst region of Slovenia (part of the former Yugoslavia), which is underlain by limestone.”

“The Colorado Plateau, with extensive areas underlain by limestone, gypsum, and salt (Figure 1), has potential for property damage and severe water quality problems related to dissolution of these soluble rocks. Karst features are particularly abundant south of Interstate 40 from the Snowflake-Taylor area northwest to Winslow, and in the Grand Canyon region north of Flagstaff to the Utah border.”

In Arizona, there are three main types of Karst features and sinkholes:

Breccia pipes developed mainly in the Redwall Limestone 200- to 300 million years ago when the climate was warm and humid. Caves developed as deep as 3,200 feet below the present surface and as the roofs collapsed, the caves turned into pipe-like structures filled with rock debris. Many reached the surface. The Sedona sinkholes are this type. On the Colorado Plateau, many of these breccia pipes concentrated uranium and copper minerals from groundwater about 141 million years ago. Over 1,300 breccia pipes have been identified on the Colorado Plateau.

Surficial Karst has developed in areas underlain by limestone and gypsum. “The most common features are enlarged joints and shallow sinks formed by near-surface dissolution of gypsum, and to a lesser extent limestone, in the Permian Kaibab Formation.” Surficial Karst may be an indication of cave formation deeper in the rock. In my travels, I have noticed these features in Southern Arizona near Benson, Bisbee, and Tombstone where the Escabrosa Limestone crops out.

The third type is related to salt deposits. This feature “results from the dissolution of salt beds in the Permian-age (245-286 m.y.) Supai Formation, with collapse propagating upward through the overlying Coconino Sandstone and Kaibab Formation. More than 500 fissures and sinkholes have been identified in the area between Springerville and Winslow….On topographic maps, large karst features appear as sinkholes or as basins that have internal drainage and commonly contain small lakes.” Some locations are shown in the map below:

For more details, see the AZGS report: http://repository.azgs.az.gov/uri_gin/azgs/dlio/134

Although rare, sink holes can also develop over lava tubes, the hollowed out areas that once contained rivers of lava within a flow. There are several lava tubes in the Flagstaff area.

If you plan to build anything in areas susceptible to sink holes, it would be wise to get a geological hazards assessment first. Check out information from the Arizona Geological Survey on earth fissures, landslides, and debris flows.