Remote Sensing of the Jeptha Knob Impact Crater, Kentucky

by

Chris Jung

ES 771 Remote Sensing, Emporia State University

Panoramic view of Jeptha Knob looking toward the northeast. Several antennas are located near the top of the knob. This panoramic was constructed using PTGui 6.0.3.


Abstract
Introduction
Aerial Overlays
Landsat
True Color Composite
False Color Composite
Conclusion
References


Abstract

Although hundreds impact craters have been discovered, there are perhaps thousands of others left unidentified. Many impact craters can be identified by their circular and steep outer rims; however, the majority of craters have undergone erosion, and their outer rims are no longer visible. The Jeptha Knob impact crater has been affected by heavy erosion but still has visible areas of faulting and uplifting that can be identified by remote sensing.

Return to the top


Introduction

William M. Linney discovered the Jeptha Knob structure in 1887. The disturbance was thought to be volcanic in origin until 1968 when data obtained from gravity and magnetic survey led Ronald Seeger (1969) to propose an impact origin. The impact crater is not officially known as a meteor impact because it is missing shatter cone impact structures. Shatter cones are distinctive impact features formed by shock metamorphism (Cressman, 1981). However, the lack of structural deformation in the basement rock indicates it was likely not caused by volcanism, and the high degree of faulting and presence of shock breccia make it reasonable (for the purposes of this project) to conclude that Jeptha Knob was caused by a meteor impact.

Geologic map of Jeptha Knob impact crater, Shelby County, Kentucky. Note the highly faulted areas.

The structure lies in the western part of the Bluegrass Region, at a latitude of 38 degrees 10 31 North and a longitude 85 degrees 07 13 West. The impact formed in a shallow coastal environment in the Late Ordovician to Early Silurian. The impacted area is approximately 4.27 kilometers in diameter with a 1.92 kilometer inner diameter. (Cressman, 1981) Topographic maps of the area reveal an elevated central peak. The outer rim of the crater has experienced heavy erosion and is no longer visible. The area consists of local farms and forestland.

Return to the top


Aerial Overlays

Searching for and reviewing aerial photos and topographic maps was the first step of the project. Arcview 3.2 was used to construct composite images detailing the topography, and an overlay was found that mapped the fault system within a reasonable degree of accuracy. Streams commonly follow faults or show displacement along active fault lines. Composite images were made from aerial photos, fault data, and stream data.

. Aerial, topographic, and fault/stream images. Note closely spaced contours on central peak of center image.

The topographic overlay clearly details the uplift of the central peak of the impact. A comparison of the streams in the area to fault lines yielded some questionable results. Many of the fault lines and streams run parallel to one another and are laterally offset. It is likely that the fault overlay represents a ruff interpretation of the true ground conditions and a more accurate fault map is required to make a substantial comparison.

Return to the top


Landsat

Landsat ETM+ (Enhanced Thematic Mapper) is a multispectral imager that is currently in orbit onboard Landsat 7. Landsat ETM+ has 7 bands that record energy in the visible, reflective-infrared, middle-infrared, and thermal infrared parts of the electromagnetic spectrum. The instrument has a swath width of 185 km and a spatial resolution of 15m, 30m, and 60m for various bands (Jensen, J., 2000).

.Band 4-Band, 4 3X3 Edge Enhancement, Band 4 7X7 Edge Enhancement

Band 4 was chosen for image enhance by using the Laplacian Edge Enhancement filter. Landsat band 4 records reflective infrared from the spectral wavelength of 0.75 to 0.90 mm. The Laplacian filter was chosen for its ability to expose linear features. Comparing the edge enhanced images with the stream photos reveal a circular trace of what could be the outer rim of the crater.


True Color Composite

A True color composite was generated for analyzing the site prior to the false color composite images. True color composite images most closely resemble the range of vision of the human eye. The image is a hazy blue because blue light is easily scattered by atmospheric conditions.

click on the images to enlarge

Return to the top


False Color Composite

Several false color composites were generated using Landsat data and IDRISI to enhance the visibility of the surface features. The composite of bands 4, 5, and 7 (RGB) proved to be the best for analysis of the central uplift and what might be the remnants of the outer rim.

457 (RGB), 235 (RGB)

Composites of bands 654 and bands 743 were created so that faulting could be found due to increases in soil moisture. The images met with varying degrees of success. The faults were diffcult to observe due to the vegetative cover and lack of exposures.

654 (RGB), 743 (RGB)

Return to the top


Conclusion

The uplift in the crater center was relatively easy to interpret through remote sensing. The fractured area could be more efficiently analyzed through a comparison of remotely sensed images and extended field reconnaissance that was not within the limited scope of this project. The use of other remote sensing techniques such as Synthetic Aperture Radar (SAR) may have also been helpful in penetrating the dense vegetation. A larger impact sites with outer rims that are less eroded that the Jeptha Knob site would have likely yielded better imaging data.

Return to the top


References

Akhir, J.M., Abdullah, I., 1997. Geological Applications of LANDSAT Thematic Mapper Imagery Mapping and Analysis of Lineaments in NW Penisula Malaysia: Universiti Kebangssan Malaysia, pp. 3

Clark Labs. Geographic Analysis and Image Processing Software. http://www.clarklabs.org/

Cressman, E. R. 1981. Surface geology of the Jeptha Knob Cryptoexplosion Structure, Shelby County, Kentucky: U.S. Geological Survey Professional Paper 1151-B, 16 p.

Cressman (1975) Geologic map of the Shelbyville Quadrangle, Shelby County, Kentucky: U.S. Geological Survey Geological Quadrangle Map, GQ-1258.

Cressman (1975) Geologic map of the Waddy Quadrangle, central Kentucky: U.S. Geological Survey Geological Quadrangle Map, GQ-1255.

Global Land Cover Facility Web Site. http://landcover.org/index.shtml Retrieved on 11/26/06.

Jensen, J.R. 2000. Remote Sensing of the Environment. Prentice Hall, pp. 192-194

Seeger, C.R., 1969. Origin of the Jeptha Knob Structure, Kentucky Kentucky Geological Survey, 631 p.

Return to the top


This web page was created to fulfill the requirements for ES 771 Remote Sensing at Emporia State University.
Return to student webpages.
This page was created on 12/07/06.