Exploring Arizona earth fissures: An anthropogenic geologic hazard

ABSTRACT Earth fissures are tensile surface cracks exposed at Earth’s surface. In Arizona, such fissures are predominantly found in the central and southeastern regions of the state, where they form in response to subsidence driven by groundwater pumping. Growth and erosion of these fissures often occurs during large monsoon storms, resulting in slumping and collapse of the fissure walls, propagation of the fissure head, as well as the development of gully networks out from the main fissure stem. Fissure initiation and propagation threaten existing infrastructure, can cause property damage, and increase the potential for groundwater contamination from surface pollutants. It is exceedingly important that these hazards be well understood, documented, and monitored. The Arizona Geological Survey (AZGS) founded the earth fissure program in 2007 to systematically identify, map, and monitor earth fissures in Arizona. Data are released through an interactive viewer (https://uagis.maps.arcgis.com/apps/webappviewer/index.html?id = 98729f76e4644f1093d1c2cd6dabb584), which is regularly updated to show new fissures and growth of existing ones. Additionally, beginning in November 2018, repeated surveys of a series of large earth fissures in Apache Junction, Arizona, (50 km east of Phoenix) have been done using UAV-SfM (unmanned aerial vehicle–structure from motion) to better elucidate the processes controlling the short-term evolution of this geologic hazard. This field trip will take us to two fissure locations in the greater Phoenix metropolitan area. The first will be the Apache Junction earth fissure area, where we will be able to observe the large, dramatic scale of these features, as well as highlight the important role large monsoon storms have on fissure propagation and geomorphological changes. Furthermore, we will show how high-resolution topographic surveys provide a means for significant improvements to current mapping and monitoring efforts for assessing hazards related to earth fissures. The second site will be a fissure location just to the southwest of Apache Junction in Chandler Heights, Arizona, which we refer to as the “Queen Creek” earth fissure area. At this field-trip stop, we will show how fissure initiation and growth threaten human development, as well as describe the role the AZGS earth fissure program plays in identifying and monitoring these hazards.