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<br />Ramsey County | Multi-Jurisdiction Hazard Mitigation Plan 61 <br />Common techniques for measuring and monitoring the extent of landslides include field surveys (e.g., <br />geological mapping, slope measurements), remote sensing (e.g., satellite imagery, aerial photography), <br />ground-based monitoring (e.g., GPS, inclinometers, extensometers), and Light Detection and Ranging <br />(LiDAR). <br />3.9.3.2 Land Subsidence <br />Subsidence can develop gradually or suddenly due to natural processes, such as karst sinkholes in areas <br />with soluble bedrock, or due to human activities. In the U.S., subsidence has affected over 17,000 <br />square miles across 45 states, with annual costs estimated at $125 million. The primary causes include <br />aquifer-system compaction, organic soil drainage, underground mining, hydro compaction, natural <br />compaction, sinkholes, and thawing permafrost. <br />Common techniques for measuring and monitoring the extent of land subsidence include geodetic <br />surveys (e.g., leveling surveys, GPS/GNSS monitoring), remote sensing (e.g., Interferometric Synthetic <br />Aperture Radar [InSAR], satellite imagery), borehole measurements (e.g., extensometers, piezometers), <br />and LiDAR. <br />3.9.4 HISTORY <br />Ramsey County has a moderate history of impactful geologic incidents. The MN Department of Natural <br />Resources (DNR) paper Historical Landslide Inventory for the Twin Cities Metropolitan Area was <br />consulted for incident records. <br />Table 15. Significant Geological Hazard Events in Ramsey County, MN <br />Est. Date Type Location Deaths/ <br />Injuries <br />Property <br />Damage <br />Description <br />May 13, <br />1879 <br />Landslide Saint Paul u/k u/k Rock and sediment <br />July 28, <br />1892 <br />Landslide Saint Paul u/k u/k Unknown <br />Winter <br />1969 <br />Landslide Saint Paul u/k u/k Sediment <br />July 24, <br />1987 <br />Landslide Saint Paul u/k u/k Glacial sediment. This was <br />a late-night event <br />associated with a slow- <br />moving thunderstorm. <br />April 8, <br />2011 <br />Landslide Saint Paul u/k u/k Rock. A boulder the size of <br />two minivans struck and <br />demolished a local bakery. <br />May 1, <br />2011 <br />Landslide Saint Paul u/k u/k Glacial sediment and fill <br />May 22, <br />2013 <br />Landslide Saint Paul 2/4 u/k Rock and sediment. A <br />rockslide killed two and <br />injured two fourth graders <br />at Lilydale Regional Park. <br />Two firefighters were also