Groundwater-surface water interactions in Chadron Creek
The goal of Joe’s research is to understand how groundwater and surface water interact in the bed of Chadron Creek. To do this, Joe decided to map the diurnal (day/night) cycles of temperature in the streambed. Stream water is heated during the day and cools at night. In a normal reach (or in a losing reach) the change in temperature will penetrate the streambed through a process known as hyporheic exchange. In a reach where groundwater is discharging into the stream (a gaining reach) this temperature cycle will be subdued, or shallow, due to the constant temperature of incoming groundwater. By deploying a digital thermometer array in the streambed of Chadron Creek, Joe was able to analyze this diurnal temperature data to locate gaining and losing reaches of the stream as well as additional temperature and substrate trends. Making use of the principles of heat diffusion and a greater knowledge of streambed exchange and temperature distribution, he also hopes eventually to be able to measure discharge and additional stream characteristics.
Using lineaments to map faults in the Pine Ridge
Ever since there have been aerial photos, people have noticed straight and curved lines on the landscape. These are called lineaments and geologists suspected that some might be faults. Jennifer Balmat decided to study lineaments in the Pine Ridge of Nebraska to see if there might be a connection to faults in the rock below. She identified 1147 lineaments on satellite and radar images. A forest fire in the Nebraska National Forest south of Chadron during the summer of 2006 removed vegetation and exposed previously covered rock outcrops suitable for geologic study. A total of 31 faults were mapped in rocks on the north-south oriented ridge immediately south of Chadron. Using statistics of both lineament and fault orientation and location, she determined that there is a significant correlation between faults and lineaments. Jennifer is now confident that we can use surface lineaments to infer the location of faults in the rock below.
Evidence of recent earthquakes in the Pine Ridge
A circular depression in the Pine Ridge south of Chadron, NE, bears a curious similarity to "sand blows," features that form due to the sudden expulsion of water and sand during an earthquake. This feature, about 40m in diameter and with raised rims on 3 sides, lies on a south-facing slope, with bedrock exposed on the uphill side. A clastic dike approximately 1 cm thick containing sandy sediments cuts the bedrock. The dike sediments are laminated parallel to the dike walls, indicating that the sand flowed under pressure into the fracture. Age of the depression is not yet determined to acceptable precision, but T.J. counted rings in a Ponderosa pine growing in the bottom of the depression and showed that the tree germinated around 1880. The clastic dike, which establishes the maximum age, cuts late Miocene Arikareean Monroe Creek formation bedrock (ca. 23-25 Ma) but not the modern soil. Therefore the depression formed before 1880 but after 25 million years ago. The fact that these soft sediments are still present in the landscape, however, suggests that this feature’s age is much closer to the minimum age, possibly during historic time.
Ground water flow through faults in western Nebraska
Faulting has been shown to have effects on movement of groundwater. This study measured chemical characteristics of groundwater south of Chadron, NE, to determine if there was any mixing among shallow and deep aquifers. Water transfer along faults has implications for water supply and quality. Faults were identified using remote sensing, seismic data, and field observations. Water was sampled from 24 wells in a southeast to northwest transect across a fault and tested for alkalinity and conductivity using titrations and a solution analyzer. Preliminary data trends show increased alkalinity and conductivity levels along the fault compared with water from surrounding wells. This suggests possible aquifer mixing within the fault plane.
Mapping faults in the soft rocks of the Pine Ridge of Northwestern Nebraska
The Pine Ridge in northwestern Nebraska is a dissected north-facing escarpment of Eocene through Miocene age rocks. There are few faults mapped, but recent studies of lineaments point to many more unmapped geologic structures. This study was inspired by the apparent association of gravel deposits with lineaments. Gravel deposits are probably correlated with the sediment from fault ruptures and drainage control in the Pine Ridge area. The studied deposit stands out because it is at the intersection of two flat bottom, steep sided valleys. Flat bottomed, steep sided valleys have been recognized as features of fault controlled drainage. Closer examination showed a zone of extensive jointing and faulting of the Oligocene Sharps formation with low displacement listric faults and open joints. Joint attitudes were recorded at 4 sites in a 100 meter region of a fault-controlled canyon. Joints strike N 50 degrees E and dip 46 degrees SE. Another set 25 m away strikes S 18 degrees E and dips 47 degrees NE. The joints are highly systematic. The heavily jointed area is located at the intersection of the two valleys offset with strike-slip displacement. Greater understanding of this area’s structural geology can lead to advancements in economic practices of mining and groundwater flow, while additionally contributing to our understanding of the origin of the Pine Ridge.
Fossil horses from the Roswell, New Mexico, area
An assemblage of Late Pleistocene age fossils found at Chaves County, New Mexico, in the 1960’s was donated to Chadron State College in the summer of 2010 by collector Walter Harbach. The Six Mile Buckle locality, west of Roswell, New Mexico, is interpreted as a fissure filling of tectonically-controlled karstic fractures. Re-excavation of the site in 2012 revealed fossils in a sandy matrix, similar to that adhering to the specimens in the Harbach collection. Screen sifting of collected matrix samples expanded the collection with small bones including those of rabbit, snake, and rodents. Larger fauna in the assemblage include Stockoceros, several carnivores, including a bear, and over 100 horse teeth. Identifications of Equus conversidens and E. niobrarensis were made by comparison with horses at other late Pleistocene localities. The minimum number of horse individuals is 10. A high proportion of both young and old individuals indicates a classic attritional assemblage with a bias toward inexperienced and less healthy horses and rules out a death event that sampled a cross section of the population.
Preserving fossil footprints using digital technology
Toadstool Park, near Crawford, Nebraska, is the site of one of the world’s best preserved vertebrate trackways of Oligocene age. Systematic comparison of photogrammetric images of latex peels created at outcrops in 1995 with similar datasets made from the same outcrops in 2007 yields a wealth of information about ichnology as well as information about how this important data is being lost. Many vertebrate trackways from the outcrops offer evidence about the geologic environment in which the tracks were created. Track morphology is a good indicator of substrate and environmental conditions. This information can also support interpretation of the general behavior of the track-makers. Since Toadstool Park is currently undergoing rapid erosion, these trackways are threatened by natural processes and other threats including vandalism and public use. The method of digital documentation we are using ensures that the trackways will not be lost and will be available for study in a form resembling their current state even long after they have succumbed to erosion in the field.