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Luke Zoet

 
 
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I'm Lucas (Luke) Zoet an Assistant Professor in the Department of Geoscience, and I hold an appointment in Geological Engineering, and the American Indian Studies Program at the University of Wisconsin-Madison. 

Glaciers significantly contribute to sea-level rise, but there is still large uncertainty in estimates of their likely future contributions. One of the primary reasons for this uncertainty originates from an incomplete understanding how glaciers slip over their bases.  This same lack of understanding about slip also results in the inaccuracy of landscape evolution models, which heavily depend on glacier sliding speed to estimate glacial erosion. 

My research largely focuses on understanding the physics of glacier motion through field observation, laboratory experiments, and theoretical analysis. My work largely sits at the intersection of glaciology and glacial geology. I use a variety of geophysical and geological methods to explore glacial processes by traveling to modern day glaciers. I also use the geologic landforms left behind by Pleistocene glaciers to understand how past glaciers interacted with the solid earth in efforts to determine dominant glacier processes.  Wisconsin is a world class location to study a glacial deposits left by the Late Pleistocene Glaciers. 

Recently, I have also began working on coastal processes in the Great Lakes region using state of the art newly designed and developed instruments to monitor bluff stabilty proccesses . 

Contact Information

256 Weeks Hall

Madison WI 53706

ph: 1.608.262.1921

email: lzoet@wisc.edu

 

Appointments:

Present, Assistant Professor, Geoscience Department, University of Wisconsin- Madison

2012-2015 Postdoc, Iowa State University, Department of Geological and Atmospheric Sciences

2006 – 2006 Chevron Corporation

2005 – 2005  Lawrence Livermore National Laboratory

 

Education:

2012: PhD Penn State, Geosciences Department (focus geophysics)

2009: M.Sc. Penn State, Geosciences Department (focus geophysics) 

2005: B.S. Michigan State University, Geology Degree from Lyman Briggs School (focus geophysics)


 

News

 

I'm seeking two creative and quantitatively minded graduate students 1) Would work on coastal bluff's landslide studies 2) Would work with Shaun Marcott and myself on subglacial slip and erosion.   If you have interest in any of the projects on the Research page, or to similar projects please contact me.

 

Grad student Jacob Woodard and I joined collaborators from Iowa State University (Neal Iverson and Anna Thompson) to collect Terrestrial LiDAR Scanner (TLS) data and structure-from-motion data from the forefield of Castlegaurd glacier in Canada.  Along the way we sucessfully deployed a network of 6 passives seismic instruments on the surface of Saskatchewan glacier.  This work was done as part of an NSF funded project.  The pictures below were from the latest field season.  Next summer this project will continue with scanning forefields in the Swiss Alps for three weeks.  

Publications

 

Zoet, L.K., and Iverson N.R., (2016), Rate-weakening drag during glacier sliding. Journal of Geophysical Research - Earth Surface

 

Ívar Örn Benediktsson, Sverrir A. Jónsson, Anders Schomacker, Mark D. Johnson, Ólafur Ingólfsson, Lucas Zoet, Neal R. Iverson, Johann Stötter. (2016), Progressive formation of modern drumlins at Múlajökull, Iceland: stratigraphic and morphological evidence, Boreas.

 

Reba G. McCracken, Neal R. Iverson, Ívar Ö. Benediktsson, Anders Schomacker, Lucas K. Zoet, Mark D. Johnson, Thomas S. Hooyer, Ólafur Ingólfsson (2106). Origin of the active drumlin field at Múlajökull, Iceland: new insights from till shear and consolidation patterns. Quaternary Science Reviews

Iverson, N.R, and Zoet, L.K., Experiments on the dynamics and sedimentary products of glacier slip. Geomorphology (2015)

 

Zoet, L. K., and Iverson, N. R., Experimental determination of a double-valued drag relationship for glacier sliding. Journal of Glaciology (2015) 61

 

Zoet, L. K., Carpenter, B., Scuderi, M., Alley, R. B., Anandakrishnan S., Marone, C., & Jackson, M. The effects of entrained debris on the basal sliding stability of a glacier. Journal of Geophysical Research (2013). DOI: 10.1002/jgrf.20052

 

Zoet, L. K., Alley, R. B., Anandakrishnan, S. & Christianson, K. Accelerated subglacial erosion in response to stick-slip motion. Geology 1–21 (2012).doi:10.1130/G33624.1

 

Zoet, L. K., Anandakrishnan, S., Alley, R. B., Nyblade, A. A. & Wiens, D. A. Motion of an Antarctic glacier by repeated tidally modulated earthquakes. Nature Geoscience 5, 623–626 (2012). 
 


In Preparation  
Zoet, L. K., Scuderi, M., Carpenter, B., Alley, R. B., Anandakrishnan S., Marone, C., & Jackson, M. A laboratory study of unstable sliding at the base of glaciers

Zoet, L. K., Alley, R. B., & Anandakrishnan S. A new mechanism for seismicity of calving events at Thwaites Glacier, Antarctica

 

Research

The primary focus of my research is examining processes associated with glaciers by working at the intersection of glaciology and glacial geology. I am focused on resolving processes and use experimental, observational and theoretical analysis to investigate glaciers. 

Using various techniques to study the ice-bed interface of glaciers I aim to characterize the mechanisms by which glaciers deform, slide, erode and deposit.  Using a variety of geophysical techniques (radar, seismic, GPS, and satellite observations), either from direct access to the base through subglacial tunnels or indirectly from surface measurements, I have investigated a range of processes active within and beneath glaciers.  Also, the inspection of deposits left behind by glacier provide valuable insight into the mechanics active at the base of not only modern glaciers, but also paleo glaciers. The combination of geophysical observations and glacial deposit analysis are crucial to identifying the full spectrum of mechanisms present within glaciers, but both need to be coupled with experimental and numerical modeling to fully explore the intricacies at work. 

 
 
 

Glacial Seismicity

Glaciers are some of the noisiest environments in the world, at least if you listen with a seismometer.  A big reason for the large amount of seismic energy is that glaciers are continually moving a high rates of speeds, effectively creating a constantly slipping fault between the glacier sole and the underlying bed.  The rate and magnitude of the seismicity is tied to many aspects of glacier dynamics; ice-bed properties, tides, subglacial hydrology.  Through the use of passive seismic techniques, we can learn about the properties that regulate glacier slip and deformation.  

We put out passive seismic instruments on glaciers around the world but one of our main focus is to better understand the glacial slip through precisely monitoring seismic behavior.  We are currently analyzing passive datasets from Thwaites Glacier in Antarctica and the North East Greenland Ice Stream (NEGIS) in Greenland with Penn State Collaborators.  We have been developing a new method do full waveform back projection in order to better constrain the temporal and spatial patterns of slip. This project has been headed by graduate student Ian McBrearty

 

We have 8 geophone based seismometers that can be quickly deployed on ice surfaces.  We have used these devices to collect a passive seismic dataset from Saskatchewan glacier in Banff national park in 2017.  

 

Glacier Erosion

Glacial erosion is one the most powerful geomorphic processes on the surface of the Earth.  The rates at which glacier erode are orders of magnitudes larger then rivers by basin size.  Glaciers primarily eroded through two processes 1) Abrasion 2) Quarrying.  Abrasion is like sand paper rubbing against the underlying rock where Quarrying occurs when a block of rock is detached in one segment from the bedrock.  The mechanics of these processes under a stably sliding glacier have been the focus of study for the past 30 years, but are still being improved upon today.  Though work we have done indicates that a potential mechanism for greatly increasing the rates of glacier erosion occurs when glaciers do not slide stably, but rather move in spurts, often referred to as stick-slip.  Stick-slip movement can drastically reduce water pressure in subglacial cavities (Figure) as cavities are forced to rapidly expanded when the glacier rapidly slips forward a few millimeters in milliseconds. A decrease in water pressure causes large gradients in subglacial water pressure over short distances that can effectively hydro-fracture bedrock.  Abrasion rates can also greatly increase in a stick-slip type glacier because the static shear stress imparted on the bed during the stick phase is higher than the dynamic shear stress imparted on the bed in a stably sliding glacier.  This increase in shear stress results in a nonlinear increase in abrasion and quarrying rates.

 

Glacial Calving

Marine terminating glacier calve large blocks off into the ocean.  In Antarctica calving is the primary way ice is discharged into the ocean.  As ice bergs are calved off the terminus they begin the roll and slide past other blocks of ice, and it doing so produce a seismic signal.  Using these seismic signals we can better constrain the stress that is constraining these blocks.  We have developed a new analytic model to help us understand how this might occur and are coupling it with high resolution satellite imagery to better constrain the motion of these rotating blocks.  We hope to produce a model that is capable of estimating the stress in the ice mélange in front of the blocks based on the magnitude and nature of the seismic energy that is produced.  We have located seismicity emanating from rotating blocks in Thwaites glacier’s Ice-shelf that are the basis for this work.  This work is done with colloborators at Penn State Univeristy 

 

Ice Deformation

Most of the ice near the base of glaciers contains debris (up to 40% by volume), but the mechanics of the debris laden ice’s deformation are poorly constrained.  This is part due to the fact that once ice is near 0 C liquid water lies at the grain boundaries of the ice and next to debris particles.  This liquid water along with the debris complicates the dislocation mechanics of the ice.  

Because ice near the bottom of the glacier undergoes the largest deformation and because it is in contact with the base it is likely the most important ice to know its mechanical properties. Due to the importance of debris laden basal ice we are currently building three ice deformation rigs with the specific intent of studying the stress vs. strain-rate properties of debris laden ice as a function of stress, temperature, and debris content.  The ice samples will be housed in a circulating bath within a cold room providing temperature control to within 0.01C while a stress is applied and strain is continually measured.  Ice will be thin sectioned for c-fabric and grain size analysis once strain is completed.  This project is being headed by Material Science undergraduate Alex Horvath

 

Bluff and Hill Slope Stability

Rising levels in Lake Michigan are causing destructive wave action to reach greater elevations on beaches and in some instances directly erode coastal bluffs.  Removal of material from the base of bluffs is resulting in recession of slope toes and an overall steepening of the bluffs.  Steepening of a bluff increases the probability of a slope failure, thus causing potential hazards for city utilities and citizens who live within close proximity. Once the lake levels have been elevated for an extended period of time, and the toes of slopes have been eroded, bluff failure is then controlled by the material properties of the slope (including strength, i.e., angle of internal friction and cohesion, and unit weight), slope geometry, stratigraphy, and groundwater level.  These properties are less well understood along the Great Lakes shoreline.

To measure these properties, we are installing a new instrument (BADGER in Figure) that was developed by us as part of a funded SEAGRANT projects in hopes to constrain the properties relevant to slope failure at the exact time of failure.  In this way we can better constrain what factors will lead to instability in the future.  We also have been using drones to build high resolution DEMs using structure-from-motion for use in hill slope stability models.  This project is being completed with Wisconsin Geologic and Natural History Survey Quaternary Geologist Elmo Rawling

 

GIS of Glacial Systems

 

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Using GIS to study glacial systems has been a popular tool for the past 20+ years, but only recently has wide spread high resolution LiDAR data become freely and publicly available for regions that were once glaciated.  Simply identifying the 2d geometry of glacial features is often insufficient for understanding the processes that formed them.  Because of this were are using various datasets with advanced spatial analysis scripts we've written in programs such as Python and MATLAB to scan across 10's of thousands of identified features to test the spatial and 3D significance.  We are looking for ways in which the landforms vary in statistically significant manners to help us better understand what might be controlling their distribution.  

We are currently mapping the 10,000+ drumlins and other elongated features that fall in the footprint of the Green Bay Lobe (GBL), so that we can systematically interrogate their 3D morphology in relation to parameters such as flow history of the GBL, local bed rock types, and composition.  Using advanced spatial analysis techniques of our own development we hope to use the distribution of the GBL's landforms to better infer the dynamics of the GBL during the Late Wisconsin glaciation.  This project is being headed by Geoscience undergraduate Nolan Barrette.

 

Subglacial Drainage

The Green Bay Lobe has numerous glacial geomorphic feature related to subglacial drainage events.  Probably the most striking are the large Tunnel Channels that drained the Western side of the Green Bay Lobe.  These large linear features (Figure above) are remnants of huge drainage events that vacated vast amounts of subglacially stored water from the base of the Laurentide Ice Sheet.  These channels can be 100's of meters wide and 10's of meters deep.  We have constructed glacial hydraulic models that indicate regions which are likely to have stored the subglacial water, and conducted a geophysical survey in Waushara county using active and passive seismic as well at GPR to better characterize the cross-cutting relationship between the Tunnel Channels and the local stratigraphy and bedrock.  This work is an done in an attempt to better constrain the timing and mechanics of the discharge events.  Large drainage events like this are likely analogs to current processes that are draining regions of Greenland. This project is being competed with Wisconsin Geologic and Natural History Survey Quaternary Geologist Elmo Rawling

 

Sliding Experiments

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A new ring shear device is being constructed and will be placed in a large freezer at UW-Madison to further empirically study the sliding mechanics of glaciers.  The new device will be capable of 400 kPa of effective stress, infinite displacement, and have walls made of transparent acrylic so that the ice bed processes can be directly observed. It should be completed by Fall 2017.  In addition a direct shear devices is housed in the freezer that is capable of testing rate and state friction of ice.  


Using the shear devices, we can slide ice over till  or till over till to simulate the slip mechanics present at the base of soft-bedded glaciers, like those along the Siple Coast of Antarctica or Thwaites glacier, Antarctica. Using the shear device pictured in the figure we shear only till, and through years of experimentation by collaborator Neal Iverson at Iowa State University it has become apparent that till behaves as a coulomb material.  But the question is whether an ice-till interface exhibits a purely coulomb response or if it has some component of rate dependence.  Using a new ring devices that are being designed and built at UW-Madison we will be able to measure properties in the till and at the ice-till interface during slip to better constrain what mechanism is facilitating displacement and how it is accomplished.

 

The sliding experiments are being conducted by PhD student Dougal Hansen.  

 

Instructor University of Wisconsin Madison

Geomorphology: Spring 2017

Glacial and Pleistocene Geology Seminar:  Spring 2016, Fall 2017

Matlab for Geoscience: Fall 2016

Glacial and Pleistocene Geology: Spring 2016, Spring 2017

Glacier Mechanics: Fall 2015 

 

Instructor, Iowa State University

Surficial Processes, Fall 2014

Independent Study Glacial Till Processes, Fall 2014

Computational Techniques for Geosciences, Fall 2013

Glaciers and Glaciations Graduate Seminar, Spring 2013

Independent Study Glacial Geophysics, Spring 2013