In April 2007, the Arizona Geological Survey (AZGS) opened its first branch office in Phoenix; one of America’s fastest growing cities. This marks an important step forward in the Survey’s continuing effort to better serve the two-million residents of the Phoenix metropolitan area. The AZGS Phoenix branch is located at 1502 W. Washington, in the home of our sister agency, the Arizona Department of Mines and Mineral Resources.

Like most communities, Phoenix owes its existence in large part to its geologic setting; a setting rife with geologic hazards that threaten Phoenixians, their property and infrastructure. Surrounded by a wall of rugged mountains to the north and east, and by sparse mountain ranges to the south and west, Phoenix is watered by two perennial river systems, the Salt and Gila Rivers; flood control along the Gila River has reduced it to an ephemeral stream. Through countless floods over several million years, the two river systems deposited rich, fertile soils across the Valley of the Sun.

Geohazards
These fertile soils, so highly priced by ancient and modern farmers alike, are rich in absorbent clays that expand when wet. As a result, some of the valley’s soils swell and shrink seasonally, presenting special problems for engineers, builders, and homeowners. Modern farmers draw some irrigation waters from subterranean aquifers, which leads to sediment compaction and in some areas subsidence. The end result: earth fissures! And, of course, monsoonal flash floods and rarer regional floods threaten parts of Phoenix and environs.

Other geologic phenomenon that could adversely impact people and property – particularly those situated near mountainous terrain – include landslides, debris flows, and even earthquakes.

The AZGS Phoenix staff is ready to assist county and municipal authorities in identifying, assessing, and mitigating geologic hazards in the Phoenix metropolitan area and environs. Currently, the AZGS team is mapping earth fissures and identifying best practice protocols for the community. But rapid population growth and steady expansion into areas comprising shrink and swell soils, or prone to debris flows, flash floods, earth fissures and landslides, means that geologic hazards will be an important and potentially disruptive force in the valley for generations.

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