New two-mile-long earth fissure discovered in southern Pinal County

Figure 1. Appearance of Tator Hill fissures in December 2014 Google Earth imagery. Red arrows point to the new fissure; blue to an older, previously mapped fissure. Note sharp, unvegetated appearance of new earth fissure compared to old fissure.  (Photo by B. Gootee)

Figure 2. New earth fissure trending north-south in the center of the frame. The sharp contrast in fissure geometry, from open, with a width and depth of 10s of feet, to a closed, crack-like feature, is apparent. (Photo by B. Gootee). 

A fresh, ~ 2-mile long earth fissure occurs 10 miles south-southwest of Picacho Peak State Park on Arizona Trust Land in southern Pinal County (Figure 1a & b.). This new fissure, which is oriented roughly north-south, parallels other fissures in the Tator Hills Earth Fissure Study area. Fissures at Tator Hills were first observed in 1977, and by 2009 over 11 miles of fissures were mapped there.

The width and depth of the new fissure varies dramatically along its length; from a narrow, inch-wide crack to a shallow crevice up to 10 feet wide and 25- to 30-feet deep. At 1.8 mile in length, this newest fissure is more than a ½-mile longer than other area fissure. Unlike older fissures in the Tator Hills, this fissure is free of vegetation, commensurate with having formed over just the past several years.

Comparing dated Google Earth imagery, AZGS Earth Fissure program manager, Joe Cook, determined the fissure began to form between Mar. 2013 and Dec. 2014. The onset of fissuring began in the north before extending southward and may have coincided with heavy rains in fall 2014. The southern portion of the fissure postdates the Dec. 2014 imagery.

Fissure Drone Video. On 19 Jan. 2017, AZGS’ Brian Gootee and Joe Cook, along with Arizona Dept. of Water Resources’ Brian Conway, captured the first drone video of a fresh earth fissure in Arizona (Figure 2, VIDEOS URL). The two videos illustrate the variable geometry (width and depth) and overall fresh appearance of the fissure.

Fissures videos at AZGSweb Youtube channel:

https://www.youtube.com/watch?v=9xdAnftBKvY (2.75 minutes)

https://www.youtube.com/watch?v=Rbd1sWPTxyk (1.75 minutes)

Geohazard! In urban areas earth fissures pose a substantial threat to infrastructure – homes, building, roads and bridges. In rural areas, fissures threaten roaming livestock and individuals recreating in off-road and 4-wheel drive vehicles. Fissure sidewalls are precipitous, unstable, and prone to sudden collapse that could snare an unwary observer standing on the collapsing edge (Figure 3).

Figure 3. AZGS geoscientists Brian Gootee, drone operator, and Joe Cook, earth fissure mapping program director launching the first drone-fissure exercise. Photo by B. Conway (ADWR).

Origin of Earth Fissures in Arizona. Earth fissures result from basin subsidence
 that accompanies extensive ground water withdrawal in the Sonoran Desert. In Arizona, fissures first appeared near Eloy in 1929 and are now identified and mapped in basins in Cochise, La Paz, Maricopa, Pima and Pinal Counties; the Natural Hazards in Arizona viewer,

Online Resources

Arizona Geological Survey, 2009, Earth Fissure Map of the Tator Hills Study Area: Pinal County, Arizona: Arizona Geological Survey Digital Map - Earth Fissure Map 11 (DM-EF-11), map scale 1:24,000.

Natural Hazards in Arizona Viewer: an interactive map tool illustrating the distribution of earth fissures in south-central and southeastern Arizona.

Arizona Land Subsidence Group, 2007, Land Subsidence and Earth Fissures in Arizona: Research and Informational Needs for Effective Management: Arizona Geological Survey Contributed Report CR-07-C, 29 p.

Slaff, S., 1993, Land Subsidence and Earth Fissures in Arizona. Arizona Geological Survey Down-to-Earth #3, 30 p.

 

4 New Geologic Map Quadrangles in Arizona

Map showing approximate location of maps

AZGS just released four (4) new geologic map quadrangles for western and southeastern AZ, (see map for approximate locations). The maps are free to download at our online document repository - 'Recent Submissions' at http://repository.azgs.az.gov/ (bottom of the page).

The Corona de Tucson map includes the northern portion of the Santa Rita Mountains, an area of interest to the copper mineralization industry.

1. Geologic map of the Dome Rock Mountains SW 7 ½' Quadrangle, La Paz County, Arizona

2. Geologic map of the Mule Wash 7 ½' Quadrangle, La Paz County, Arizona and Riverside County, California

3. Geologic map of the Mount Nutt 7½' Quadrangle, Mohave County, Arizona.

4. Geologic map of the Corona de Tucson 7 ½' Quadrangle, Pima County, Arizona.

New Leadership at Arizona Geological Survey

Dr. Phil Pearthree

AZGS has a new director and Arizona a new State Geologist. University of Arizona Dean of Science, Dr. Joaquin Ruiz, confirmed that Phil Pearthree, Ph.D., is the new director of the Arizona Geological Survey. As part of his duties, Dr. Pearthree assumes the role of Arizona State Geologist. Phil follows former State Geologist Lee Allison who died tragically in a fall in Aug. 2016.

Phil received his B.S. at Oberlin College, and M.S. and Ph.D. at the University of Arizona. He joined AZGS in 1988 and was chief of the Environmental Geology section for more than a decade. As an AZGS research geologist, Phil has authored or co-authored more than 100 geologic reports and maps over the past 29 years.

In 2013, Phil and two co-authors received the prestigious Kirk Bryan Award from the Geological Society of America’s Quaternary Geology and Geomorphology Division for their report, 'Stratigraphic evidence for the role of lake-spillover in the inception of the lower Colorado River in southern Nevada and western Arizona'.

Dr. Pearthree mapping surficial deposits in the Organ Pipe Cactus National Park

History of the Morenci Mining District, Greenlee County, Arizona

Smelter of the Detroit Copper Mining Co., ca. 1896.

The definitive mining history of Arizona's iconic Morenci mining district by geologist David Briggs is now available online at http://repository.azgs.az.gov/uri_gin/azgs/dlio/1695.  This 76-p manuscript with 41 illustrations exhaustively examines  mining activity in the Morenci area from 1870 to 2015.

From DISCOVERY 1863-1872

'During the early 1870s, prospectors who first ventured into the area that would become the Morenci mining district found evidence of primitive excavations at the site. Although Native Americans did not attempt to smelt the colorful copper-bearing oxides extracted from these ancient mine workings, it appears they used these minerals as pigments in their pottery and for other decorative purposes (Colquhoun, 1924).

The first record of copper mineralization near Morenci appears in a report prepared by soldiers of General Carleton's Regiment of California Volunteers, who camped near the junction of Chase Creek and San Francisco River for a few days in January 1863 (Watt, 1956). While there, they noted the presence of strong copper oxide staining on numerous outcrops that lined the slopes along Chase Creek and named the area Copper Mountain. Scouting parties also discovered placer gold along tributaries of the Rio Prieta, now known as Eagle Creek, in concentrations that ran as high as "forty cents (i.e. 0.02 troy ounces) to the pan" (Cogut and Conger, 1999a).

After learning of this discovery, Henry Clifton, the recorder of the Hassayampa mining district near Prescott, Arizona led a prospecting party to search for gold along the Gila and San Francisco rivers during 1864. Although the party also noted the presence of copper along Chase Creek, the remote location and hostilities with Apaches made further development imprudent at that time. '

Posted 11/29/2016 MC

Small Magnitude Earthquakes in NW Arizona 22-25 Nov 2016

Three (3) small magnitude earthquakes occurred in northwestern Arizona over the past week. The largest event was M 2.2, ~ 22 miles south of Colorado City, AZ, on 22 Nov. at 7:31 pm. USGS estimates the focus (depth) at 13.3 km.

On the included map, yellow circles represent earthquake epicenters.

M 1.5, 40 miles SE of Littlefield, Arizona, Depth ~ 5 miles, 2016-11-25 - 6:05 (MST)
M 1.1, 9 miles SSW of Colorado City, Arizona, Depth ~ 7.5 miles, 2016-11-23 – 15:23 (MST)
M 2.2, 22 miles S of Colorado City, Arizona, Depth ~ 8.5 miles, 2016-11-22 – 19:31 (MST)

Source: US Geological Survey

Posted 11/28/2016 MC