ABSTRACT Springfield, Greene County, Missouri, is the third largest city in Missouri and is located within the Springfield Plateau, a subregion of the Ozark Physiographic Region of the United States. This region is underlain by the Burlington-Keokuk Limestone, which is highly susceptible to solution and is host to more than 2500 sinkholes within Greene County. Springfield, as well as the surrounding communities, has been growing in recent years. Prime areas for development are scarce, thus, leaving more areas that are vulnerable to sinkholes targeted for development. Development next to, and sometimes within, a sinkhole has exacerbated flooding problems, caused structural damage to homes and businesses, and is prone to increasing pollution into the underlying shallow aquifer. Control of stormwater in and around sinkhole areas typically involved the use of several standard approaches: concrete-lined channels draining into sinkholes; installation of pipes into the sinkhole “eye” (swallow hole); filling of sinkholes; elaborate drain or pump systems to remove stormwater from one sinkhole and discharge into another basin or sinkhole; and enlargement of swallow holes by excavation to increase drainage capacity. In an effort to remedy these issues, the City of Springfield adopted a Sinkhole Ordinance around 1990, requiring a permit if a development will encroach upon a sinkhole, sinkhole drainage area, or impact a sinkhole area. This field trip will review examples of pre-ordinance and post-ordinance practices of development in and around sinkholes and sinkhole areas, view recent investigations within this karst area, and discuss approaches to matching geologic knowledge with urbanization in a karst area.

ABSTRACT After the first saltwater disposal (SWD) wells associated with the development of the Fayetteville Shale became operational in April 2009, central Arkansas experienced an increase in the rate of earthquakes with M ≤4.7. This seismic activity in the Fayetteville Shale development area (FSDA) included both natural and induced earthquakes that often occurred in spatial and temporal clusters. The Center for Earthquake Research and Information (CERI) and the Arkansas Geological Survey (AGS) closely monitored the area using a permanent network of seismograph stations, augmented by portable real-time broadband stations, to focus on specific sites of suspected induced seismicity. Any concerns were communicated directly to the Arkansas Oil and Gas Commission (AOGC), the agency charged with regulating SWD wells in the state. The largest and most significant cluster of induced earthquakes in the FSDA occurred between August 2010 and July 2011, when thousands of earthquakes (M ≤4.7) occurred on the Guy-Greenbrier fault, which had not been mapped prior to the earthquakes. Since a 13-km-long fault can potentially produce a M 6 earthquake if it slips as a single event, CERI and AGS staff testified at an AOGC hearing in July 2011 that continued fluid injection into SWD wells near the fault could potentially trigger a damaging earthquake. Operators voluntarily shut down and plugged three nearby SWD wells. Another SWD well operator was ordered (by the AOGC) to shut down and plug their well. Earthquake activity dramatically decreased on the Guy-Greenbrier fault and ceased soon after shut-in, thus providing strong supporting evidence that the earthquakes were induced. The AOGC also established a moratorium that prohibited SWD well operations in the area surrounding the fault and rules governing proximity of new SWD wells to mapped faults and proximity of SWD wells to each other. When the price of natural gas rises to make development cost effective, we anticipate the new rules will help to minimize the occurrence of felt and potentially damaging earthquakes. Although the Guy-Greenbrier earthquake sequence ended in 2011, earthquakes still occurred within the FSDA. While some of these earthquakes were within 10 km of active SWD wells, many other earthquakes were not close to any SWD well. We identified 156 earthquakes M ≤3.4 from the regional catalog that occurred between 2012 and 2016 that were within 5 km of a natural-gas production well during the hydraulic fracturing window posted by the AOGC. This suggests that these earthquakes may have been induced by hydraulic fracturing.

Abstract This field trip provides an overview of geological features in southwestern Missouri that are related to the American Civil War and to human culture. This includes the geology and history of the Wilson’s Creek National Battlefield (where the second important battle of the American Civil War was fought on 10 August 1861), Zágonyi’s Charge (25 October 1861), the Battle of Springfield (8 January 1863), and the gravestones and monuments of the National Cemetery in Springfield in which many of those who fought at Wilson’s Creek and other Civil War conflicts are buried. Other stops include the Springfield Underground and the quarries and facilities at what was once the town of Phenix (which, along with Carthage, Missouri, was the home of some of the largest dimension-stone quarries west of the Mississippi River); and a reconstructed mill site in Point Lookout, just south of Branson. Most of the field trip involves outcrops, quarries, and bedrock composed of the Mississippian Burlington-Keokuk limestones (undivided), providing numerous chances to examine outcrops and products made of limestone and chert.