GSA North Central Section meeting in Madison, WI: 5/2015

Just prior to graduation I submitted an abstract entitled, “Interpretation of a Paleo-Inlet’s Depositional History: A Ground Penetrating Radar Investigation, Grand Island, MI.” I presented this research using power point as a medium.  A previous analysis of a 50MHZ Ground Penetrating Radar (GPR) subsurface profile of the entire Grand Island Tombolo revealed a depositional feature displaying channel fill reflection patterns near the center of the tombolo and beneath the modern strandplain.

100MHZ GPR profile of paleo-inlet
Common radar stratigraphic terms

This author hypothesized that this feature could be a Paleo-inlet which existed prior the deposition of the modern strandplain and formation of the tombolo.  A higher resolution (100MHZ) GPR profile of this feature was collected to allow for a more detailed analysis.  The content presented in Madison displays evidence pointing to the existence of channel like conditions in the proposed paleo-inlet through the use of radar stratigraphic analysis.

Paleo-inlet facies (B1-4) were identified using radar stratigraphic analysis.  The facies are bounded by the modern strandplain above (A) and prograding sand spits below (C).
Paleo-inlet facies (B1-4) were identified using radar stratigraphic analysis. The facies are bounded by the modern strandplain above (A) and prograding sand spits below (C).

A paleo-geographic reconstruction of the Grand Island Tombolo was created based on the authors understanding of lake level chronology, regional geology, and and applied radar stratigraphy.  This reconstruction is meant to provide a base illustration which I hope will foster future discussion, decomposition of current hypothesis, and construction of new hypothesis.

During the Nippising high stand a cuspate foreland is present sub aerially and a straight exists between the East and West bedrock lobes.
During the Nippising high stand a cuspate foreland is present sub aerially and a straight exists between the East and West bedrock lobes.
Longshore  drift moves sediment through the straight until it reaches a lower energy regime by the cuspate foreland.   Two separate sand spits develop. The larger spit progrades north and east away from the cuspate foreland.   The second smaller spit progrades north and west away from the eastern bedrock lobe of Grand island.
Longshore drift moves sediment through the straight until it reaches a lower energy regime by the cuspate foreland.
Two separate sand spits develop.
The larger spit progrades north and east away from the cuspate foreland.
The second smaller spit progrades north and west away from the eastern bedrock lobe of Grand island.
The sand spits do not merge in the middle. Strong northeast storm winds open sequential inlets allowing sediments to move south through the sand spits and be deposited on the lee side. Complex channel fill patterns are deposited in the inlet during calm weather.
The sand spits do not merge in the middle.
Strong northeast storm winds open sequential inlets allowing sediments to move south through the sand spits and be deposited on the lee side.
Complex channel fill patterns are deposited in the inlet during calm weather.
Eventually a tombolo is formed as sediment fully chokes the lee side of the inlet.   A modern strand plain progrades north into Trout Bay forming the sequence of dune ridges observed on the tombolo today.
Eventually a tombolo is formed as sediment fully chokes the lee side of the inlet.
A modern strand plain progrades north into Trout Bay forming the sequence of dune ridges observed on the tombolo today.

My full PowerPoint presentation can be accessed below.  Enjoy!

“Interpretation of a Paleo-Inlet’s Depositional History: A Ground Penetrating Radar Investigation, Grand Island, MI.”

My research partner and co-author, Sean Morrison, is currently working on a paper regarding this topic in addition to studying as a master’s student at University of Waterloo in Canada under the direction of John Johnston.  Future research by this author will be released on this blog.

Advertisements

Life after Phillips Hall

This past December I completed my undergraduate degree and received a bachelors in science with a comprehensive geology major and a minor in mathematics.  I’ve made a lot of friends in Phillips hall: I couldn’t ask for a better group of classmates and faculty. I can’t believe this is it but I know it’s the right time to move on.

During my time here I have:

  • Tutored in the math lab – thank you Dr. Swanson for keeping that place running, it’s assistance to students is enormous
  • Traveled all over the country with the geology department:  NM, AR, WI, MN, SD, WY… the best geologists have seen the most rocks.
  • Formed lasting friendships with my classmates…  blood runs thicker than water
  • Participated in incredible coastal ground penetrating radar research with Sean Morrison and Dr. Harry Jol.   Their contributions to my education are probably immeasurable.  I will always want to return to Munising MI and Pictured Rocks National Lake shore
  • Found a degree advisor that half carried me through my last year in the program so I could get the requirements needed for graduation in a timely manner.  Thank you so much Katherine Grote, the department is really gonna miss you
  • Expanded my horizons to encompass the world outside of UW-Eau Claire.  GSA in Vancouver was incredible.

Next up is hard to tell.  But I have applied for Missouri State in the Geospatial sciences in geology and geography masters program and hope to attend in the fall.  Otherwise I am open to beginning my career in earth sciences in a position that could lead me down a path to my ultimate goal of working at an environmental consulting firm.

GSA 2014 Vancouver Poster Presentation

In 2013 a classmate of mine, Sean Morrison, completed a preliminary ground penetrating radar (GPR) investigation on Grand Island in the upper peninsula of Michigan with professor and mentor Harry Jol under the sponsorship of the UW -Eau Claire Summer Research Experiences for Undergraduates (SREU) program.  In February 2014 Sean and I co-authored a proposal to SREU for funding to allow us to further the same research during Summer 2014.

Research was carried out between July 26th-30th 2014 with the invaluable assistance of Henry Loope, retired member of the National Parks Department.

An abstract was accepted for the Geomorphology and Quaternery Geology Division of the GSA 2014 Vancouver convention.  A poster detailing the accomplishments of our GPR research was presented at the convention in mid October.  A full copy can be viewed here as a PDF.

GSA2014

 

We expect to continue research in the coming years.

GPR Analysis at UW-Eau Claire

During spring of 2014 I participated in a Ground Penetrating Radar (GPR) class led by Dr. Harry Jol of the UW-Eau Claire Department of Geography and Anthropology.  The course focused upon the applications, analysis, and interpretation of GPR subsurface data.

The final goal of the coarse was to collect new GPR data at the Eau Claire municipal well field, analyze and interpret the data, and present the finding in poster format for faculty and students at UW-Eau Claires 2014 annual Celebration of Excellence in Research and Creative Activity (CERCA).  Valuable experience using GPR equipment and data as well as experience gained discussing my findings with faculty will be applied towards further work assessing the shallow sub-surface using GPR techniques.

Abstract

Traditionally, aquifer characterization is conducted by extrapolating stratigraphy between boreholes and producing a fence diagram. However, the point-source nature of boreholes can produce inaccurate models so a better methodology is needed. Ground penetrating radar (GPR) is a geophysical method using electromagnetic signals and provides a non-invasive way to image the subsurface. Our project’s goal is to improve characterization of the aquifer supplying the Eau Claire municipal well field by correlating borehole data with GPR profiles to produce stratigraphic models at a higher degree of accuracy than traditional methods. Using a pulseEKKO 100 system, GPR data was collected across a 150 m and two 50 m transects to a depth of 12 m using a frequency of 100 MHz with a 0.5 m step size and 1 m antennae separation. The results show two facies representing a migrating sidebar and an expanding floodplain. Borehole data was collected to a depth of 30 m revealing grain size ranging between medium sand to gravel. Combining these data will ultimately lead to more accurate models than those produced using only point-source data. This method is effective in many geologic settings and can provide hydrogeologists with an accurate, cost-effective way to characterize aquifers without relying on costly point-source data.

Municipal Well Field
Eau Claire Municipal Well Field. Pump House 21 on the right.

Methods

Our data collection methodology was three-fold: 1) to collect and analyze data from secondary sources addressing the hydrogeologic aspects of the Eau Claire municipal well field (ECMWF), 2) to collect primary source GPR data on site, and 3) to process the data and assess their viability in characterizing groundwater flow. 1) Initially we contacted the drilling companies responsible for installing the high-capacity wells supplying the ECMWF to acquire drill logs from the borings. Upon analysis the geologic data for Well log 21 was determined to be the best available and so we chose its location as our target area. We were also given a tour of the ECMWF and information about the aquifer (e.g. water table depth, water quality, water removal rates); (Greene, 2014).  2) To begin on site data collection, we measured a 150 m transect (R1) and two 50 m transects (C1 and C2) perpendicular to R1 and recorded GPS coordinates at the transects’ endpoints.

Transect Map of EC Municipal Wel Field
Transect Map of EC Municipal Wel Field

Using a Topcon laser level and surveying rods we recorded elevation differences every two meters to calibrate our subsurface reflections with the area relief (Jol and Bristow, 2003). Using a pulseEKKO 100 GPR system we first recorded a common midpoint (CMP) centered at the 75 m mark of the R1 transect to determine the subsurface velocity; this technique is necessary to convert our electromagnetic wave travel time measurements to depth.

CMP Survey Results: Speed of groundwave was 0.105 meters/nanosecond
CMP Survey Results: Speed of groundwave was 0.105 meters/nanosecond

Following the CMP survey data was collected across the R1, C1, and C2 transects using a frequency of 100 MHz with a 0.5 m step size and 1 m antennae separation (Jol and Bristow, 2003). We also collected data along the C2 transect at 50 MHz with a 1 m step size and 2 m antennae separation and at 200 MHz with a 0.10 m step size and 0.5 m antennae separation to determine the most effective resolution for imaging reflections in the study area (Jol and Bristow, 2003).

Dr. Harry Jol
Dr. Harry Jol
50 MHZ GPR antennae oriented along transect C2.  Data Collection in progress.
50 MHZ GPR antennae oriented along transect C2.
Data Collection in progress.
In field interpretation of reflection data can indicate whether a survey was successful.
In field interpretation of reflection data can indicate whether a survey was successful.

Analysis

Based upon State records of well bore logs the subsurface at the ECMWF has been characterized by the Wisconsin Geological Survey (WGS).  These logs provide stratigraphic data which has been geospatially compiled by the WGS to map depth to bedrock within Eau Claire County (Johnson, 1993).  This map shows that the ECMWF straddles a deep (> 30 meters) bedrock valley between the Chippewa Rivers lowest terraces in northern Eau Claire (Johnson, 1993).

Bedrock Map of Northern Eau Claire, Wisconsin
Bedrock Map of Northern Eau Claire, Wisconsin

This bedrock valley contains glacial outwash sediments overlain by braided stream deposits that form a heterogeneous unconfined aquifer more than 30 meters deep from which up to 61 million liters of high quality water is pumped daily (Johnson, 1993; Greene, 2014).  The heterogeneity of the valley sediments in the locale of the ECMWF can be categorized into three stratigraphic facies based upon their depositional environment.  GPR images and the Well 21 drill log confirm an upper facies containing alluvial sediments from depths of 0 to 5 m that are deposited by aggradation of the Chippewa River floodplain and result in a relatively permeable and well sorted deposit above the middle facies (Roberts and Brevard, 1997). Our GPR investigation revealed a middle facies containing braided stream structures formed by the Chippewa River between depths of 3 to 12 meters (See results table) (Roberts and Brevard, 1997; Bridge and Lunt, 2006).  The lowest facies consist of well graded sands and gravels deposited during the end of the Wisconsin glaciation which reach thicknesses of up to 20 meters above the bedrock within the ECMWF (Johnson, 1993).

Stratigraphic Section of Well 21 sediment logs.
Stratigraphic Section of Well 21 sediment logs.

Summary of Results

Subsequent to on site data collection Sensors and Software, Inc.’s EKKOproject and Lineview software was used to compile elevation, CMP, and transect data to produce the images seen in the results section.

Reflections and their interpretations for both the C1 and C2 transects
Reflections and their interpretations for both the C1 and C2 transects

The data collected along R1 contained a significant amount of noise (likely emanating from FM radio waves or power lines) as well as many underground obstructions (e.g. pipes) which interferes with our image clarity and hinders interpretation (Jol and Bristow, 2003). Through the western portion of the R1 transect noise decreases and the quality of the image increases.  The C1 and C2 transects produced images which can be interpreted and are believed to be representative of the western portion of R1. Prominent reflections from C1 and C2 were geometrically characterized and formatted with Coreldraw to assist in interpreting sedimentary facies (Jol and Bristow 2003). C1 and C2 both illustrate a subtle change of sedimentary facies within the mixed sand and gravel not observed in the Well 21 bore log (Jol and Bristow, 2003). Two distinct facies are interpreted; aggrading floodplain deposits, shown as red traces, and braided stream deposits, shown as blue traces (Roberts and Bravard, 1997; Bridge and Lunt, 2006). The green traces in C1 are anomalous and represent an underground obstruction (e.g. pipe) (Jol and Bristow, 2003). A lower facies identified in the Well 21 drill log as a well graded glacial outwash exists below the depth of about twelve meters but could not be imaged with GPR due to signal attenuation caused by fine grained sediments (e.g. silts, clay) (Johnson, 1993).

Description of sedimentary facies based upon GPR Reflections.
Description of sedimentary facies based upon GPR Reflections.

The reflections which are interpreted as braided stream deposits and categorized as a middle facies is of interest during a hydrogeologic characterization of the aquifer because it contains adjacent well sorted sedimentary units of varying hydrogeologic properties; the type and spatial extent of these units control how water moves within the upper portions of the aquifer (Slater and Comas, 2009; Bridge and Lunt, 2006).

Acknowledgments

This was a project for an independent study through the University of Wisconsin: Department of Geography and Anthropology. We would like to extend our thanks to Dr. Harry Jol of the UWEC, for providing equipment and serving as our mentor through this project, and to Sean Morrison for his help and guidance as a field assistant. We would also like to thank Linda Richards of Mark J Traut Wells, Inc., for providing data for the drill core logs at well 21, and the people at Sensors and Software, Inc., for providing exceptional GPR processing software and advice. We would like to extend a special thanks to Tim Greene of the Eau Claire municipal well field for accommodating us and for his continued support for the UWEC Department of Geology.

References

A copy of the work done at the Eau Claire Municipal Well Field can be found as a PDF link below.

Aquifer Characterization through GPR and Borehole Analysis Eau Claire Municipal Well Field, Wisconsin

 

Add more detail- Be more concise