Meeting/Event Information

Technical Talks: The Minnesota Section of AIPG holds technical talks September through May, generally the first Tuesday of the month. The talks are designed to fulfill 1 Professional Development Hour (PDH). Professional Geologists, as licensed in the State of Minnesota, are required to complete 24 PDHs every biennium licensing period, including 2 PDHs of ethics.  The technical talks feature important subjects of interest to professional geologists.

The cost includes a buffet lunch and is $21 for non-members, $16 for members, and $0 for students when registering in advance.  We have limited same-day registration for $25. 

*During the pandemic, we are webcasting our Technical Talks.  The cost is $10 for non-members and $5 for members. You must register by 11 AM the day of the talk to be sent the login link/information. Students may attend free of charge. Fees go toward supporting the online meeting platform and the Education Fund. Your contribution to the Education Fund helps support many activities, please see our Giving Back page.

As always, non-members and non-geologists are welcome to attend!


American Engineering Testing, Inc.

Apr 2021 Meeting - Till: spatially variable, complex and dense!

April 06, 2021
11:45 AM - 1:00 PM

MS Teams - details included in registration receipt & emailed before the meeting

Registration for the AIPG MN Section's Tuesday, April 6, 2021 technical talk is now open online!

Meetings are webcast-only for the next few months.

The cost is $10 for non-members and $5 for members when registering before Tuesday, April 6, 2021 at 11:00 AM Central Time. Students may attend free of charge. 

You must register by 11:00 AM Central Time the day of the talk to be sent the login link/information. The meeting link information is also included in your receipt.

As always, non-members and non-geologists are welcome to attend!   

Fees go toward supporting the online meeting platform and the Education Fund. Your contribution to the Education Fund helps support many activities, please see our Giving Back page.

 

Till: spatially variable, complex and dense (or to quote Dr. H.E. Wright, Jr., “It’s all very complex.")

by Carrie E. Jennings, PhD, PG, Freshwater Society

 

Presentation Abstract

Till is sediment that is the product of erosion, transport and direct deposition by ice. But because glacial processes are highly spatially and temporally variable, till can be variable, both vertically and horizontally, in composition, structure, fabric and therefore hydrologic properties. Tills in Minnesota may have also been subject to several glacial and interglacial cycles over the last two million years. Therefore, to best predict the possible degree and scale of variability of till, four classification strategies can be simultaneously deployed:

  • Lithological classification—grain-size distribution and matrix and clast lithology
  • Stratigraphic position—to help understand the potential impact of periglacial and non-glacial processes such as weathering, soil development and erosion.
  • Mode of deposition—links glacial processes with facies characteristics
  • Engineering behavior

 

In the areas mapped by through County Geologic Atlas program, the first two and often three are adequately described. The last category lies in the arena of hydrogeologic and geotechnical investigations, primarily at the site scale.

Lithologically, tills in Minnesota range from fine-grained, matrix-dominated, exotic tills of ice lobes (e.g. New Ulm Formation) to silty, coarse-grained tills of more local derivation (e.g. Boundary Waters Formation). These vary in their hydrologic and engineering properties because of the nature the matrix and concentration of clasts. 

However, it is also possible to have tills with the same lithologic and textural composition but distinctly different hydrologic and engineering properties. The temperature and effective pressure at the glacier bed strongly control the density, fabric and strength of a till. The subglacial environment varies from low to high effective pressure with varying amounts of total strain. This affects the consolidation state of till and the macro- and microscopic orientation of its grains.

Stratigraphic setting imparts an understanding of chemical and physical changes associated with weathering and soil formation such as leaching, oxidation and the addition of carbon. Geochemical changes can alter the concentration and mobility of certain elements. The presence of fractures and development of soil structure alters preferred pathways.

The scale of spatial variability is best anticipated by accurately defining the depositional environment. Facies associations and landforms, where preserved, can help determine if a till was deposited in a subglacial or supraglacial setting. Supraglacial tills are lower density, more variable because they may have been remobilized and sorted.

Tills of obscure depositional setting are best described by testing key properties at an appropriate scale. Carefully reconstituting tills to the same density in a lab may be important for some engineering applications where strength is key. Whereas, the average variability of an in situ till at a regional scale may be more important for interpreting hydrogeologic conditions.

 

Biography

Carrie E. Jennings, PhD, PG has taught glacial geology at the University of Minnesota for 25 years, following in the footsteps of her PhD advisor, H.E. Wright. She also has an MS from the U of M in glaciology (Roger LeB. Hooke) and a B.A. in geology from Northwestern University in Evanston, Illinois.

She furthered her understanding of glacial sediment during a 24-year mapping and research career, 22 with the Minnesota Geological Survey and two with the DNR, Division of Lands and Minerals. She was also Science Reports Lead for the hydrogeologic portion of the County Geologic Atlas program at the DNR for two years.

Carrie has built and funded collaborative, interdisciplinary teams of scientists to address the impacts of land management and drainage practices compounded by changing rainfall patterns on river and hillslope processes.

Carrie joined Freshwater as Research and Policy Director in 2016. There, she applies her understanding of glacial geology and landscape evolution to bridge the gaps between what science provides and what a policy maker, watershed district, local government official or citizen needs to know. She helps shape state and local approaches to manage surface water and groundwater, avoid hazards, and use geologic resources wisely.

Carrie and her husband live on a 120-acre farm which is primarily in a permanent conservation easement through the Dakota County Farmland and Natural Areas Program. She has twice been elected town board supervisor and served on the planning commission for Eureka Township.

 

Tickets

$5.00 AIPG MN Section Member Ticket

$10.00 Non-Member Ticket

$0.00 Student Ticket