pg(s) 187-194 The
Holbrook Basin located in east-central Arizona is home to more
than 500 evaporite-karst depressions. The Arizona Department of
Water Resources (ADWR) recently acquired, processed, and
interpreted archived Interferometric Synthetic Aperture Radar
(InSAR) data to evaluate historical deformation patterns in the
Holbrook Basin in preparation for monitoring potential future
subsidence related to planned potash mining activities around
the Petrified Forest National Park. Three active land
subsidence features were identified by ADWR using InSAR data
from the European Space Agency's ERS 1 and 2 satellites between
1992 and 1997. Continued subsidence in two of the three
features was also identified by ADWR using InSAR data from the
Japan Aerospace Exploration Agency's ALOS satellite collected
from 2006 to 2011. In June 2012 Arizona Geological Survey
(AZGS) and ADWR staff visited one of the more prominent
subsidence features identified using InSAR. Numerous
steep-walled evaporite-karst sinkholes were observed en route
to the field site. These roughly circular collapse features
ranged in size from 40-130 m across and 10-30 m deep. The
subsidence features identified through InSAR are much more
extensive, up to 1,100 m across; are not as deep, up to 15 m;
and do not have steep walls. Local subsidence has resulted in
broad closed basins with drainage reversals and numerous
expanded joints in the Coconino Sandstone exposed at the
surface. A thin sandy soil above the Coconino covers the basin
floor except where collapsed into open joints. Expansion along
both joint orientations was observed. Which orientation was
expanded depended on location relative to ongoing subsidence.
Based on field observations and comparison with other collapse
features in the region, these three subsidence features are
relatively young, constitute different collapse morphology than
nearby sinkholes, and warrant further study. InSAR will remain
a critical remote-sensing tool for monitoring land subsidence
in the Holbrook Basin.
13TH SINKHOLE CONFERENCE NCKRI SYMPOSIUM 2 187 different collapse morphology than nearby sinkholes, and warrant further study. InSAR will remain a critical Introduction and is predominantly composed of halite with lesser amounts of anhydrite, gypsum and sylvite interbedded with dolomite, sand, and shale in the Corduroy Member body underlies more than 9,000 km 2 of eastern Arizona between the towns of Winslow, Sanders, Springerville, 2 (Figure 1). Salt up to 200 m thick has been measured south of salt body has become the focus of much interest from investors and mining companies due to the presence of up to 2.5 billion metric tons of potash (sylvite) near the top of the evaporite deposits. Due to the potential for land subsidence related to possible future potash mining, ADWR has begun collecting InSAR data for the region surrounding the limits of the potash deposit. Through evaluation of InSAR interferograms it was determined subsiding today or have been in the last 20 years. Geologic Setting by Permian Coconino Sandstone, Kaibab Limestone, and Coconino Sandstone is the most laterally extensive exposed bedrock at the surface throughout the study Abstract The Arizona Department of Water Resources (ADWR) recently acquired, processed, and interpreted archived Interferometric Synthetic Aperture Radar (InSAR) data to evaluate historical deformation patterns in the future subsidence related to planned potash mining by ADWR using InSAR data from the European Space Continued subsidence in two of the three features was collected from 2006 to 2011. and ADWR staff visited one of the more prominent InSAR are much more extensive, up to 1,100 m across; are not as deep, up to 15 m; and do not have steep walls. Local subsidence has resulted in broad closed basins with Coconino Sandstone exposed at the surface. A thin sandy expanded depended on location relative to ongoing with other collapse features in the region, these three subsidence features are relatively young, constitute MONITORING EVAPORITE KARST ACTIVITY AND LAND USING INTERFEROMETRIC SYNTHETIC APERTURE RADAR (INSAR) Brian D. Conway Arizona Department of Water Resources, 3550 N .Central Ave, Phoenix, AZ 85012 USA, email@example.com Joseph P. Cook Arizona Geological Survey, 416 W. Congress St, Suite 100, Tucson, AZ 85701 USA, firstname.lastname@example.org
NCKRI SYMPOSIUM 2 13TH SINKHOLE CONFERENCE 188 1, Neal et al., 1998), but isolated depressions do exist in undeformed beds above evaporite deposits to the northeast. Many of the depressions along the from the dissolution flexure are often much more m deep. Dissolution of Permian salt and associated Basin has likely been occurring since the Pliocene (Neal et al., 1998). Using modern remote sensing monitoring, it is possible to determine whether area. Thin beds of Kaibab Limestone are present near the western boundary of the salt body, but pinch out to the east. Isolated thin exposures of red Moenkopi sands mantle the lighter tan, distinctly crossbedded Coconino Sandstone elsewhere. has resulted in more than 500 sinkholes, expanded geomorphic changes including drainage captures and near the southwest margin of the salt body (Figure Figure 1. Location map of Holbrook Basin, study area extent, and distribution of existing evaporite karst sinks relative to the extent of the Holbrook salt body and anticline.
13TH SINKHOLE CONFERENCE NCKRI SYMPOSIUM 2 189 evaluate land subsidence associated with any of the existing possible future land subsidence related to proposed potash SAR data were downloaded from the ASF which allowed InSAR data (Figure 2). sink was as high as 5 cm and 26 cm, respectively. This pairs. The spatial extent and magnitude of land subsidence of the new land subsidence features was consistent across all the other interferograms. To better understand the historical activity of the new land subsidence features, ADWR ordered archived SAR data 456 were downloaded from ESA which allowed ADWR to create 27 interferograms. The historical dataset from Land Subsidence Monitoring using InSAR ADWR has been collecting, processing, and analyzing InSAR data for monitoring land subsidence throughout produced invaluable results and end products that are used not only by ADWR but also other state, county, and local agencies, universities, and private companies for their own monitoring, modeling, mitigation, planning that transmits a pulsed microwave signal towards the earth and records both the amplitude and phase of the is a technique that utilizes interferometric processing that compares the amplitude and phase signals received during geographic area at different times. InSAR techniques, scale vertical resolution. Changes in land elevation are detected through the change in phase of the radar signal. InSAR is used to detect surface motion along active faults, on volcanoes, landslides, sinkholes, and other geologic ADWR has compiled an extensive historical InSAR with InSAR in Arizona. Most data sets cover time periods between 1992 to 2000, 2004 to 2010, 2006 to than 25 land subsidence features in Arizona, collectively ADWR has used InSAR not only for monitoring land subsidence but also seasonal deformation (uplift and tool for geological mapping and investigations, locating mitigation and land subsidence modeling. InSAR Results ADWR collected InSAR data from the Alaska Satellite Facility (ASF) and the Japanese Aerospace Exploration northeastern Arizona. The InSAR data were collected to Figure 2. ALOS-1 12/06/2006 to 02/01/2011 Interferogram.
NCKRI SYMPOSIUM 2 13TH SINKHOLE CONFERENCE 190 Active Sink Morphology The thickness of salt below the western and northern of approximately 240 m and 225 m, respectively. Salt located approximately 5 km north of the eastern feature. dataset (Figure 2). The reasons why the northern land subsidence feature subsidence at the northern feature is episodic or complete. the western, eastern, and northern subsidence features, respectively. Continued InSAR monitoring of this area will help constrain subsidence rates and patterns. Figure 5. Example of a compression ridge within the eastern subsidence feature. Broken bedrock along this ridge follows a sinuous east-west trend. Bedrock slabs in the background are pushed against and above one another. Figure 6. Example of an expanded joint within the eastern subsidence feature. Figure 3. Eastern Land Subsidence Sink and InSAR Profile. Figure 4. ERS-1/2 11/24/1992 to 03/07/1997 Interferogram.
13TH SINKHOLE CONFERENCE NCKRI SYMPOSIUM 2 191 present at the eastern sink as observed in more mature, portion of the eastern sink near the southern portion exposures exist near the northern and northwestern limits of the actively subsiding sink. The depth of the m relative to the top of surrounding sandstone slopes which is dramatically less than depths observed at many mature, inactive sinks to the west. Drainages near the southern limit of the eastern sink and 60 m thick at a depth of 245 m. For comparison, The overall shape of the eastern sink is that of a broad depression with gently sloping sides that gradually rise Coconino and Moenkopi sandstone outside the InSAR signature. While no vertical walls or steep sides are Figure 7. Subsidence-related geomorphic features of the eastern active sink. Aerial imagery from 2010 National Agricultural Imagery Program (NAIP).
NCKRI SYMPOSIUM 2 13TH SINKHOLE CONFERENCE 192 feature results in compression between subsiding blocks lower in the landscape. Compressional ridges have been Basin such as the McCauley Sinks, Richard Lake, and at ridges observed here are somewhat smaller than those described by Neal and others but some appear freshly slabs of rock precariously balanced against one another (Figure 5). The ridges observed in the eastern active more abundant in the northern portion of the subsidence feature immediately downslope from the cluster of wide of modern subsidence. InSAR Methodology sensors are processed using the same interferometric methodology. Interferometry is used to process the change in phase between each pair of satellite data. It is important to processed together due to the different sensors. InSAR (DEM) to remove the topography from the phase website ( ) was used to remove the topographic phase component. viewed as deformation contours when examining each feature. ADWR recently started collecting regularly InSAR data will provide ADWR with a critical tool for broken Coconino Sandstone litter the slopes. Portions of No water was present in the lowest point during any of runoff events. Rills, bar and swale channel deposits, and plant matter suspended in and around trees near channels indicate at channels leading to the lowest point of the sink. nearby Moenkopi outcrops, mantles much of the side slopes and bottom of the active sink. Occasionally this nearly continuous cover is broken by collapse wide and up to several meters deep. Joint width tapers Linear depressions in surface sands often parallel or obscured or plugged by overlying sand. Areas of exposed bedrock within the subsidence feature exhibit open to greater depths than those mantled by sediment. that are alternately expanded depending on orientation relative to tension from ongoing subsidence. In some at the northern and northwestern edge of the InSAR across, up to 10 m deep, with vertical offset up to 1 m between blocks. Successive vertical offset across open the edge of the active subsidence feature. Coconino outcrops beyond these exposures do not exhibit this subsidence indicates subsidence may have initiated somewhat farther to the north than indicated by recent InSAR data (Figure 7).
13TH SINKHOLE CONFERENCE NCKRI SYMPOSIUM 2 193 opportunity to observe the gradual processes that lead to sinkhole formation is an exciting prospect. In addition to continued subsidence monitoring observations, photos, and have installed eye bolts across to enable repeat measurement in the future. A benchmark near the most rapidly subsiding area within the eastern obtained to supplement future InSAR data and enable repeat surveying of subsidence within the feature. In an attempt to better understand the subsurface geometry monitoring ongoing land subsidence at these two new sinks as well as possible land subsidence associated National Park. Conclusions created a dynamic, geomorphically intriguing landscape. With recent interest in potash mining and continued that is the source of dissolution beneath hundreds of subsidence rates and mechanisms is important. Because Figure 8. Radarsat-2 InSAR frame used to monitor future land subsidence in the Holbrook Basin.
NCKRI SYMPOSIUM 2 13TH SINKHOLE CONFERENCE 194 and lithologic structure deep Refraction Microtremor conducted both within and outside the subsidence feature. Results of this investigation are pending and future visits to the eastern subsidence feature to collect as Richard Lake which most closely resembles the extent and morphology of the eastern active sink, are proposed. References derived ground displacements in hydrogeology. Neal JT, Colpitts R, Johnson KS. 1998. Evaporite Borchers JW, editor. Land Subsidence, Case Studies and Current Research. Belmont (CA):