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Open-File Report 2009-1051

Transient Electromagnetic Soundings Near Great Sand Dunes National Park and Preserve, San Luis Valley, Colorado (2006 Field Season)

By David V. Fitterman and Oderson A. de Sozua Filho

Abstract

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Time-domain electromagnetic (TEM) soundings were made near Great Sand Dunes National Park and Preserve in the San Luis Valley of southern Colorado to obtain subsurface information of use to hydrologic modeling. Seventeen soundings were made to the east and north of the sand dunes. Using a small loop TEM system, maximum exploration depths of about 75 to 150 m were obtained. In general, layered earth interpretations of the data found that resistivity decreases with depth. Comparison of soundings with geologic logs from nearby wells found that zones logged as having increased clay content usually corresponded with a significant resistivity decrease in the TEM determined model. This result supports the use of TEM soundings to map the location of the top of the clay unit deposited at the bottom of the ancient Lake Alamosa that filled the San Luis Valley from Pliocene to middle Pleistocene time.

First posted April 13, 2009

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Suggested citation:

Fitterman, D.V., de Sozua Filho, O.A., 2009, Transient electromagnetic soundings near Great Sand Dunes National Park and Preserve, San Luis Valley (2006 Field Season), Colorado: U.S. Geological Survey Open-File Report 2009-1051



Contents

Abstract

Introduction

Description of Transient Electromagnetic Soundings

Sounding Locations and Elevation

Data Quality and Averaging Procedure

Inversion of Transient Electromagnetic Measurements

Interpretation of Results

Conclusions

References Cited

Appendix A Description of TEM Data Processing

Appendix B Voltage Units and Apparent Resistivity

Appendix C Description of TEM Data Files

Appendix D TEM Sounding Report Files

Appendix E TEM Sounding Plots and Descriptions


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