Satellites and Soil Chemistry Reveal Hidden Sinkhole Threat Beneath a Penn State Golf Course

Sinkholes have long been the stuff of nightmare stories for golf course managers across the United States. In Illinois, a man survived an 18-foot fall into one at Annbriar Golf Course in 2013. Workers dropped 14 feet into another at Georgia Tech’s golf facility two years later. In Lancaster County, Pennsylvania, the Evergreen Golf Course closed its doors in 2025 after six decades of operation, defeated by the collapse-prone ground beneath it. Now, a team of researchers at Pennsylvania State University has turned an unusual combination of satellite radar, optical imaging, and water chemistry loose on a sinkhole-prone course of its own, and the results reveal how everyday course maintenance may be quietly reshaping the ground underfoot.

The study, led by R. C. Bussard of Penn State’s Department of Geosciences and published in Environmental Earth Sciences, focused on the Blue and White Golf Course at Penn State’s State College campus. The course traces its origins to 1924, when a predecessor known as the Campus Course was built on land that today hosts two eighteen-hole layouts, the Blue Course and the White Course. The entire region sits atop dolomite and limestone bedrock in Pennsylvania’s Nittany Valley, part of the broader Ridge and Valley Province. These carbonate rocks dissolve slowly in weakly acidic water, carving out the caves, springs, and sinkholes that define karst terrain. In the mid-2000s, a large sinkhole opened east of the Blue Course’s Hole 15, a reminder that the hazard is not hypothetical.

To map the hidden threat, the researchers combined two very different satellite perspectives. They processed 250 scenes from the Sentinel-1 C-band radar satellite spanning 2017 to 2025 using interferometric synthetic aperture radar, or InSAR, a technique that detects millimeter-scale ground movement by comparing the phase of radar signals from repeat passes. After rigorous quality filtering that retained 1,002 interferograms across 232 dates, they produced an average vertical velocity map validated against a continuous GNSS station. The result was striking: broad subsidence across the golf course, with rates exceeding 1 centimeter per year in the south and southwest portion of the Blue Course, while nearby campus infrastructure to the east remained essentially stable.

Complementing the radar data, the team analyzed 63 cloud-free Landsat 8 and 9 scenes from the same eight-year window to calculate the Normalized Differenced Moisture Index, a measure of vegetation and soil moisture derived from near-infrared and shortwave-infrared bands. The golf course showed consistently higher NDMI values than the surrounding landscape, frequently exceeding 0.15 along the fairways, indicating persistently wetter near-surface conditions than the area around it. The researchers also checked whether soil moisture fluctuations could be contaminating the InSAR signal itself, a known artifact in radar interferometry, and found no strong correlation between moisture variability and phase noise, giving them confidence that the deformation was real.

The field component of the study brought the investigation underground. The team installed soil pore water samplers at four locations within the golf course and two control sites outside its boundaries, each placed roughly 30 centimeters below the surface to avoid the root zone. Deployed for 72 hours during a late-July storm that delivered nearly 4 centimeters of rain, the samplers yielded water samples whose pH and conductivity were measured within an hour of collection. The findings were telling: pore water beneath the golf course averaged a pH of 6.50, noticeably more acidic than the 7.15 measured at control sites, while conductivity values were broadly similar across all samples.

That modest difference in acidity carries significant implications. Weakly acidic water is precisely what dissolves carbonate rock. Rainfall percolating through soil picks up carbon dioxide from the atmosphere and from soil respiration, forming carbonic acid that eats away at limestone and dolomite. The researchers suggest that fertilizer application and elevated soil carbon dioxide at the course may be enhancing this natural acidification, creating thermodynamic conditions more favorable for calcite dissolution beneath the fairways than beneath the surrounding suburbs. They are careful, however, to note the limitations: the sample size was small, and carbonate saturation cannot be determined from pH alone without alkalinity and dissolved inorganic carbon measurements.

What makes the situation particularly interesting is what the data ruled out. Many documented sinkhole crises worldwide stem from large-scale groundwater extraction, such as the water table declines exceeding 50 meters in Saudi Arabia’s Jouf region between 2009 and 2011, or the acceleration of sinkhole formation in Turkey’s Konya Basin over two decades. Extreme recharge events can also trigger collapse, as happened when Tropical Storm Debby’s rains spawned more than 200 sinkholes across Florida. Yet at the Blue and White Golf Course, groundwater records from a nearby USGS observation well show repeated seasonal and interannual fluctuations rather than sustained regional decline, and subsidence timing does not correlate with rainfall patterns either. The ground is sinking without any obvious regional driver.

The answer, the researchers argue, lies in local factors. When they compared ground deformation at pixels containing mapped karst features with pixels lacking them, the mean subsidence rate was substantially higher where features existed: 0.75 centimeters per year versus 0.41 centimeters per year. Pre-existing cavities and preferential recharge pathways appear to concentrate deformation along specific corridors, particularly where a cluster of karst features sits southwest of the course near a drainage ditch. Meanwhile, the estimated 75,000 cubic meters of water a typical golf course applies annually through irrigation may be creating localized recharge hotspots that feed water into those vulnerabilities even in the absence of regional decline or extreme storms.

The time series data add further nuance. Some sample sites showed step-wise deformation, with bursts of rapid subsidence interspersed with periods of stability, while others moved linearly or barely at all over the eight-year record. Site one, which was among the most acidic and showed the most variable NDMI, displayed the most erratic displacement history. Control sites outside the course showed minimal deformation despite sitting on similar geology, underscoring that the golf course’s management practices, rather than its underlying rock alone, distinguish it from its surroundings.

The researchers caution that shallow processes such as mechanical compaction from equipment traffic and organic matter decomposition cannot be fully excluded as contributors. But the convergence of evidence, wetter soils, more acidic pore water, faster subsidence near known karst features, and stability everywhere else, paints a coherent picture in which modest but repeated land-use modifications interact with pre-existing karst susceptibility to produce localized ground loss. Given that the region near Hole 15 already produced a sinkhole once, the southwest Blue Course could see more in the future, particularly if climate change brings heavier rainfall. For a golf industry worth $102 billion in the United States alone, the message is clear: understanding which drivers of sinkhole formation can be mitigated through smarter irrigation, fertilization, and monitoring may determine whether courses stay open for another six decades or become the next cautionary headline.

Subject of Research: Sinkhole hazard assessment at a karst golf course using remote sensing and field geochemistry

Article Title: Assessing sinkhole hazard at the blue and white golf course, state college, using a combined remote-sensing and field methods approach

Article References: Bussard, R. C., Housego, R., Wauthier, C., Marqeuz, M., & Miller, J. (2026). Assessing sinkhole hazard at the blue and white golf course, state college, using a combined remote-sensing and field methods approach. Environmental Earth Sciences, 85(15), Article 403. https://doi.org/10.1007/s12665-026-13134-6

Image Credits: AI Generated

DOI: 10.1007/s12665-026-13134-6

Keywords: sinkhole, karst, InSAR, remote sensing, groundwater, carbonate dissolution, golf course, Landsat, soil moisture, pore water, subsidence, Pennsylvania