geologic hazards

Geoscience and Arizona

Via the Arizona Geological Survey: The American Geosciences Institute (AGI) has just released Geoscience and Arizona regarding the impact of geoscience on the Arizona economy. You can download the fact sheet at:

Arizona’s first online Natural Hazard Viewer

The Arizona Geological Survey & Arizona Division of Emergency Management have announced release of an online interactive hazards viewer.

The interactive Natural Hazard Viewer focuses on four hazards common to Arizona—geologic faults and earthquakes, earth fissures, floods and wildfire. Each hazard is described in detail and displayed as a layer on a map. Moreover, the natural hazard information is dynamic; site updates will occur as new or revised hazard data becomes available.

You can make maps with several layers on a road-map base or an air-photo base.  The maps are scalable from region-wide to as detailed as 1″=1,000 feet.  You can use the “Find Local Hazards” search tool to identify hazards existing within a three mile radius of a specific address. You can print the interactive maps, and supporting data can be downloaded.

The new Natural Hazard Viewer of Arizona website,, was developed by the Arizona Geological Survey (AZGS) in partnership with the Arizona Division of Emergency Management (ADEM).  Give it a try.  Below two screen shots, one with the roadmap base, showing faults in the state, and another showing the flood potential near Tucson on an air photo base.


Age of young volcanic field near the Palo Verde nuclear power plant

The Arizona Geological Survey has a new report on the age of young volcanic rocks near the Palo Verde nuclear power plant.  The report was produced over concern of geologic hazards near the generating station.

You can download the full report here and a video abstract here.

The report concerns the Sentinel – Arlington volcanic field which extends over about 50 miles from Sentinel volcanic field west of Gila Bend northeastward to Arlington volcano west of Buckeye.  That puts it within 6 miles of the power plant.

Arlington Volcano is located 6 miles southeast of the power plant. Six potassium-argon radiometric dates of basalt rock samples from Arlington volcano range from 1.28- to 3.28 million years old.  Although there is a two-million-year spread in the age dates, AZGS notes that the Arlington “volcano is geologically simple, consisting of a single, small, low-relief volcano with no soil horizons between flows.  Most likely it was erupted in a single volcanic episode of short geologic duration (<10,000 years), …about 2.1 million years ago.

Gillespie volcano occurs about 12 miles south of the Palo Verde Nuclear Generating Station.  It is a morphologically similar low shield volcano without soil horizons or multiple eruptive centers. Four of five potassium-argon dates range from 2.67- to 3.6 million years, suggesting an age of 3 million years. AZGS infers that this eruption temporarily dammed the Gila River.

The report goes on to discuss other volcanoes more distant from the Palo Verde nuclear station.  The AZGS report concludes with a caveat:

“The Sentinel – Arlington volcanic field produced extensive, low relief basalt lava flows and small, gently sloping basalt shield volcanoes. Available geochronologic data suggest that the Sentinel – Arlington volcanic field has erupted intermittently over the past 1.1-3.5 Ma, with no clear migration of volcanic activity within the field. Although there is no geochronologic evidence for eruptions during the past one million years, the large range of geochronologic dates from the Sentinel volcanic field, the uncertainties inherent in many of the older potassium-argon dates, and the large number of eruptive centers, allow for the possibility of more recent activity that is as yet undocumented.”


See also:

Young Volcanic Fields of Arizona

Yellowstone Super Volcano

Where the Next Big American Earthquake and Tsunami Might Occur

Earthquake videos from Arizona Geological Survey

Most earthquakes in Arizona are low magnitude and go unnoticed.  However, there is  potential for a big one.  The Arizona Geological Survey has several videos featuring earthquakes in and near Arizona.  The newest is a time-lapse animation of the Brawley earthquake swarm that occurred on 26-29, August, 2012. Brawley is in southern California, just south of the Salton Sea.

To see this video go to:

That link also contains several other earthquake-related videos (4 to 6 minutes long) so scroll down the page and you will see:

Earthquakes in Arizona

Time-lapse video animation of earthquakes in and around Arizona from 1852 to 2011. The apparent increase in seismic events in the latter part of the 20th century and early 21st century stems from improved seismic monitoring.  It is interesting to see where the most earthquakes occur.

Lake Mary Fault

The Lake Mary Fault, located immediately south of Flagstaff, Arizona, represents the greatest earthquake hazard to the more than 70,000 people of Flagstaff and environs. Dr. David Brumbaugh, Arizona Earthquake Information Center (AEIC) at Northern Arizona University, narrates the, “Lake Mary Fault — Potential Earthquake Threat to Flagstaff, Arizona.”

Little Chino Fault and Big Chino Fault

Filmed on location in Chino Valley, two separate  six minute videos describe the geometry and timing of seismic activity on these faults. This is an active fault area with a moderate recurrence rate on the order of tens of thousands of years. It is capable of yielding earthquakes in the range of magnitude 6 to 6.5 and presents a hazard to residents of Chino Valley and nearby Prescott, Arizona.

Earthquake Monitoring in Arizona, the role of the Arizona Integrated Seismic Network

Arizona has earthquakes. Geologist Dave Brumbaugh and seismic technician Lisa Linville, both of the Arizona Earthquake Information Center (Northern Arizona University), describe the role of the Arizona Integrated Seismic Network in monitoring earthquake activity in the Grand Canyon State. And Lisa deconstructs one of the broadband seismic stations that form the backbone of the system.

The 1887 Sonoran Earthquake

On 3 May 1887, a magnitude 7.2 earthquake rippled across Sonora, Mexico, and southern Arizona. Phil Pearthree, Chief of the Environmental Geology division of the Arizona Geological Survey, revisits that event in this video. The earthquake killed dozens of people and damaged or destroyed several hundred structures. A similar event today would disturb and disrupt population centers in northern Sonora and southeastern Arizona and New Mexico.

For more information on the 1887 earthquake, see my post: The Great Arizona-Sonora Earthquake of 1887

For more information on earthquakes and other geologic hazards, visit the AZGS Geologic Hazards Center:

The future of the Arizona Geological Survey

The Arizona Geological Survey is facing a normal sunset review in the Arizona legislature Monday, Oct. 17.  I urge the legislators to continue the survey because is provides many valuable services and maintains a repository of scientific knowledge about Arizona.

The statutory mission of AZGS is:

1. Serve as a primary source of geologic information in this state to enhance public understanding of the state’s geologic character, geologic hazards and limitations and mineral resources.

2. Inform, advise and assist the public in matters concerning the geological processes, materials and landscapes and the development and use of the mineral resources of this state.

3. Encourage the wise use of the lands and mineral resources of this state toward its development.

4. Provide technical advice and assistance in geology to other state and local governmental agencies engaged in projects in which the geologic setting, character or mineral resources of the state are involved.

5. Provide technical advice and assistance in geology to industry toward the wise development and use of the mineral and land resources of this state.

The Arizona Geological Survey is a leader among state surveys.  For instance, last year the Arizona Geological Survey 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.

In April of this year, the Arizona Department of Mines and Mineral Resources was deactivated and its duties transferred to the Arizona Geological Survey.  These duties include maintaining a repository of mineral and mining information, including databases, books, periodicals, individual mine files, mine map repository files, mining district data and an archive of mine data; and providing quality mining data, evaluation, and assistance relating to mineral development to the legislature, federal, state and local governmental agencies, industry, and the public.

An example of the Arizona Geological Survey’s direct value to citizens is its brochure: A home buyer’s guide to geologic hazards.  The Survey has published warnings to the public of the additional  consequences of our devastating forest fires: Forest fires create increased danger of destructive debris flows.  The Survey provides expertise in the realm of geology as applied to water law and regulation, for instance: San Pedro River Geology – Implications for water law.

You can voice your opinion by sending emails to the co-chairs of the hearing committee: John Nelson, and Kate Brophy-McGee, as well as to your own state representatives.

A Home buyer’s Guide to Geologic Hazards in Arizona

The Arizona Geological Survey has a 45-page booklet discussing some geologic hazards that home buyers should be aware of. You can download the booklet here. Subjects include floods, earthquakes, problem soils, mass movement, subsidence & fissures, radon, karst (caves), abandoned mines, and volcanic hazards.

“Our purpose is not to say that any particular parcel of land should not be developed. Rather, in those areas where geologic hazards or limitations are known to be present or where they may potentially exist, knowledge of their existence should help guide planning, design, construction, and maintenance. It remains up to property buyers or owners and local government to determine the level of acceptable risk from geologic hazards.”

In the desert, ironically, flooding is the most widespread, common, and damaging of all the geological hazards. This section explains floodplains and “100-year floods” and notes the areas most prone to this hazard.

“Over the past 150 years, more than 20 earthquakes having magnitudes greater than 5 have occurred in or near Arizona, and all of Arizona has experienced at least moderate earthquake shaking. The magnitude 7.4 Sonoran earthquake of 1887, which was centered about 40 miles southeast of Douglas, caused 51 deaths in Sonora and extensive property damage throughout southeastern Arizona. The Yuma area has experienced repeated damage from earthquakes that occurred in southern California or northern Mexico.” This section of the booklet shows maps which rate potential hazards.



















“Damage to structures in Arizona is commonly related to soil characteristics, with expansive (shrink/swell) soils and collapsing soils causing the most problems. Cracking of foundations, walls, driveways, swimming pools, and roads cost millions of dollars each year in repairs.” Such damage is related to the amount and type of clay in the soil.

The section on mass movement deals with landslides and debris flows which occur along mountain fronts and at the base of cliffs.

Land subsidence and earth fissures occur in areas in which groundwater is withdrawn faster than natural recharge.

“Radon gas is a radioactive element that is produced by the decay of uranium, which is present in virtually all rocks and soils, typically at concentrations of 1-4 parts per million.” The hazard is that radon can seep into buildings through cracks in the foundation. A sufficient concentration poses a health hazard. This section explains the danger and shows the areas of Arizona especially prone to radon emissions.

Karst terrain is developed in areas underlain by limestone, especially on the Colorado Plateau. Sinkholes may develop as cave systems mature.

 Old mine workings present a danger of toxic substances as well as falling in them.

Volcanic activity has occurred frequently in Arizona, some just 800 years ago (see ). The San Francisco volcanic field near Flagstaff is considered active. “Hazards associated with volcanic activity include ash and cinders that can overload the weight-bearing capacity of some roofs. Houses built in the Flagstaff area, where snow is routine, are already designed with loading in mind. Volcanic gases include carbon dioxide and sulfur gases that are sometimes at concentrations that may be harmful to breath.”

The AZGS booklet is well-illustrated with maps and other graphics showing the general locations of each hazard and what to expect.