2011


Calvin Johnson

Calvin Johnson


Years participated in RESESS:
2011


POSTER
Download full-res PDF [6.9 MB] »


An Overview

Academic Affiliation: Fort Valley State University

Science Research Mentor: Burke Minsley, USGS
Writing and Communication Mentors: Jonathan Caine, USGS, David V. Fitterman, USGS, & V.J.S. (Tien) Grauch, USGS
Coach: Nic Flores, UNAVCO
Peer Mentor: Aaron Piña, SOARS


Biography

Calvin grew up in Warner Robins, Georgia, where he graduated with honors from Northside High School. He decided to pursue a degree in Mathematics at Fort Valley State University, Georgia. He will then work towards a dual degree in geophysics at the University of Texas in Austin. His passion for geoscience was sparked by his first geology course. Calvin enjoys reading, going to the mall, watching movies, or relaxing and reflecting on life.


Abstract

Delineation of aquifer heterogeneities using transient electromagnetic soundings in the Great Sand Dunes National Park

During the Pleistocene epoch a laterally extensive aquitard composed of clay was deposited in the bed of Lake Alamosa throughout San Luis Valley (SLV), southern Colorado, including what is now Great Sand Dunes National Park and Preserve. Despite the lateral continuity of the “blue clay,” as it is colloquially known, hydrological and geophysical evidence suggests that there are heterogeneities in the depth and thickness of the clay within the siliciclastic aquifer system. These heterogeneities can cause variations in the confining pressure affecting groundwater flow and complicating the monitoring of groundwater resources. Transient electromagnetic (TEM) soundings were used to delineate the continuity of the blue clay near Antelope Springs. TEM data were collected along profiles by inducing electrical currents into the ground. Resistivities of litho- logical features were modeled using mathematical inversion and were used to develop a cross section of the subsurface. In the interpreted cross section, the top of the blue clay unit has a 50 m decrease in depth over a distance of approximately 1400 m along the profile and then terminates at the interpreted shoreline of the ancient Lake Alamosa. Preliminary analysis suggests that subsurface elevation of the top of the blue clay unit exhibits an anomalous decrease to the west, and post-depositional faulting is unlikely because of the shallow and gradual slope. Additional data acquisition and analysis are needed to further investigate whether the heterogeneity in the blue clay is related to pre-depositional faulting, sedimentary processes, or both.