Field Guide to Earth Fissures and other Land Subsidence Features in Picacho Basin

This field trip focuses on subsidence features caused by removal of groundwater at rates greater than natural recharge in the Picacho basin. Land subsidence is common in Arizona's alluvial basins, where extensive groundwater withdrawal has lowered water tables by as much as six hundred feet. The water pressure (weight) of groundwater produces a subsurface buoyancy force. Removal of groundwater and the associated buoyancy force results in compaction of basin sediments, reduction of pore space, and subsidence at the Earth's surface. Subsidence has occurred in every basin in Arizona where use of groundwater has significantly lowered water levels. Earth fissures typically appear at the margins of subsiding basins and accommodate subsidence of the basin interior relative to basin margins and flanking bedrock. Multiple, extensive earth fissures have developed around the Picacho basin, an agricultural area where groundwater is being depleted. This field trip includes a visit to an area where an earth fissure system has developed that is over one mile long. The fissure system displays most of the features typical of earth fissures around the state.Documents in the AZGS Documents Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact azgs-info@email.arizona.edu