The Arizona Geological Survey has been busy mapping the many earth fissures in Arizona. Most earth fissures occur in the corridor between Tucson and Phoenix, and from Phoenix west along interstate 10 (see map below).

Earth fissures develop from soil compaction associated with extensive pumping of groundwater. The fissures range in width from a few inches to tens of feet. Length of the fissures ranges from hundreds of feet to miles.

These fissures pose danger to cattle, wildlife, and unwary humans. The presence or possibility of a fissure-prone area also has implications for municipal planners, developers, highways, and railroads. And, because they tend to develop perpendicular to surface drainage, they can capture runoff and develop into large gullies.

The gateway to the Survey’s many maps and reports is the Earth Fissure Viewer, an interactive map that allows you to zoom in on areas and get detailed maps. Maps, reports, and photos are also available at the Survey’s Earth Fissure Center.

The City of Sedona is surrounded by seven sinkholes. That is the subject of a new report by geologist Paul Lindberg published by the Arizona Geological Survey.  The spectacular red rock country near Sedona, Arizona, hides an unusual and potentially hazardous geologic feature.

Sinkholes are collapse features that form when surface, and near-surface rocks subside into the cavernous Redwall Limestone, which lies more than 600 feet below the surface. Gradual collapse of the roof of the cave results in a breccia pipe that extends upward from the Redwall Limestone to the floor of the sinkhole, situated up to 100 feet, below the exposed rim of the sinkhole. See cross-section below.

The Devils Kitchen sinkhole is the most active of the seven, with historic collapses in the 1880s, 1989, and 1995. The other sinkholes are in various stages of collapse, some beginning as early as the end of the last ice age, about 10,000-years ago. Structures like this on the north rim of the Grand Canyon host uranium deposits.

The following graphic (from the Devil’s Canyon report, cited below) shows how sinkholes develop.

The Sedona sinkholes range in size from about 225 feet in diameter by 100 feet deep at Red Canyon, to Sinkhole 4543, which is 13 feet in diameter and about 3 feet deep. Devils Kitchen, the most well known of the sinkholes, has an opening 150 feet by 90 feet, with the floor situated 35 to 70 feet below the rim. Lindberg estimates that caverns in the Redwall Limestone, could have volumes on the order of 1.3 million cubic feet (a cave roughly 100 feet high and 130 feet in diameter).

According to the report, the groundwater of the Middle Verde watershed, which fills the Redwall caverns, began as precipitation on the Colorado Plateau, near the western flank of the San Francisco Peaks above 6,900 feet. Groundwater passes beneath Sedona at a flow rate of approximately 15 million gallons per day.

Lindberg notes, “While the danger of future collapse is minimal to humans, unregulated septic leakage into hidden sinkhole breccias within the town limits could contaminate groundwater being tapped for municipal use ….” A second hazard, which could threaten hikers and sightseers, are the presence of sandstone overhangs at several sinkholes that could collapse without warning in the near future.

The arcuate patterns as shown in the photo above represent a place where the rock has been stressed enough to break, but the rock has not yet collapsed. This may be the site of a future sinkhole.

(I wonder if arcuate patterns such as shown above might have given rise to the legend of vortexes near Sedona?)

Lindberg’s reports include pictures, maps, and schematic, to-scale drawings of each sinkhole. A pdf copy of the full report is available at the Geological Survey’s publications page in the Contributed Reports section: http://www.azgs.az.gov/publications_online.shtml

The general report on Sedona sinkholes (21 Mb) can be downloaded from:

http://www.azgs.state.az.us/publications_online/contributed_reports/cr10c.pdf

A report specific to the Devil’s Canyon sinkhole (24 Mb) can be downloaded from :

http://www.azgs.state.az.us/publications_online/contributed_reports/cr10b.pdf

The Arizona Geological Survey has just received an $18 million grant from the Department of Energy to lead a coalition of 46 state geologic surveys and universities to study the geothermal resources of the United States. The study is scheduled to last three years.

According to a press release by AZGS, “Over the next 3 years, data relevant to geothermal exploration and development will be digitized and published online from 46 states in a web-based, distributed, interoperable National Geothermal Data System (NGDS).

The Arizona Geological Survey was chosen as lead agency because it was already working toward the goal of collation and integration of spacial data, in conjunction with the U.S. Geological survey. The AZGS is a national leader in constructing a framework for geo- spacial data integration. Such a geo-spacial framework will be a valuable tool for other sciences also. It can, for instance, help integrate information on mineral deposits, vegetation patterns, wildlife occurrence and habitats, groundwater supply, and land use. It will allow scientists of many states and countries to share data. The AZGS program is also partnering with 21 European countries for spacial integration of scientific data.

There is already quite a bit of information about Arizona geothermal potential available online from the Arizona Geological Survey: http://www.azgs.state.az.us/geothermal_ngds.shtml Most of the geothermal research in Arizona was done in the late 1970s and early 1980s when there was an oil shortage.

The survey says “Geothermal energy abounds in the US, ranging from low-temperature, ground-source heat that can be extracted to cool homes in the summer and heat them in the winter; to direct use of low- to moderate-temperature water (68 F to 302 F) for homes, industry and commercial uses; to high-temperature systems capable of driving turbines and generating electricity.”

This program will give us a good assessment of the potential for geothermal energy as an alternative energy source, and provide a framework for integration of other resource studies.