The Arizona Department of Water Resources has an excellent program to monitor a somewhat unique geologic hazard – land subsidence. Caused by compaction of valley sediments in areas of declining groundwater table, it can create significant problems for infrastructure such as drainage facilities, flood control works, and gravity flow utilities such as sewer lines. It can also induce a secondary geologic hazard, earth fissures. The ADWR has been using InSAR data supplemented with GPS surveying and other data since 1997 to monitor a number of land subsidence areas in Arizona. This is the first of what I presume will be a series of comprehensive reports on their program. [Source: Read the PDF report from the ADWR. Image: ADWR Land Subsidence Page]
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Arizona Geologic Survey Releases Earth Fissure Maps
Yesterday the Arizona Geologic Survey (AZGS) released the first two of their 1:12,000 series earth fissure maps to the general public. The mapping program, perhaps the first of its kind in the country, came about after an earth fissures opened up in 2005 near Queen Creek, AZ, southeast of metropolitan Phoenix received much media attention. As a result, the Arizona Legislature passed House Bill 2639 of the 2006 Legislative Session that tasked the AZGS with mapping earth fissures and providing the data to the State Land Department for eventual delivery to property owners in Arizona. More after the break. (At left, the Apache Junction study area map, AZGS)
Landslide on Arizona SR 87 Closes Highway
On March 21, 2008 a landslide caused the closure of Arizona State Route 87 between Payson and Phoenix near mile post 224. So far there are no official estimates as to the size, but based on aerial photos, it appears to be at least 50,000 sq-ft in plan. The offset at the head scarps was approximately 2-meters (6.6-ft) according to AZGS Geologists on site. It appears to have been a rotational slide as the toe of the landslide heaved the southbound roadway up by as much as 1-meter (3.3 ft). There was an existing soil-nail retaining wall on the slope that was destroyed by the slide as well. Lateral deformations can be seen in photos of the median barrier and the roadway striping. The deformations extended into the northbound lanes as well. More photos and links after the break. (Photo by ADOT)