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Carl Renshaw

Hydrology and Structural Geology

 

 

Contact Information:

 
Dartmouth College
Department of Earth Sciences
6105 Fairchild Hall
Hanover, NH 03755
 
Email: carl.renshaw@dartmouth.edu
Office: 208 Fairchild
Office Phone: 603-646-3365
Office Fax: 603-646-3922
Lab: 211 and 212 Fairchild
 

 

Please click HERE to see Carl's person website for up-to-date information.

Overview of Research :

My research interests span two separate, but related disciplines; hydrogeology and advanced structural geology. Ultimately, I am interested in how water and contaminants move through watersheds. This information is of critical importance for understanding the impact of pollution on our environment.

The movement of contaminants is fundamentally controlled by two factors; the geometry of the pathways the contaminant takes and the geochemical interactions that occur as the contaminant travels along these paths. My research focuses on both these issues.

Once water and contaminants reach crystalline bedrock, their flow paths are governed by the geometry of the fractures and faults that form the subsurface plumbing of these systems. My research in Advanced Structural Geology is focused on how these fractures and faults form. Our approach combines a variety of methods from high resolution in situ mapping of the three dimensional geometry of fracture networks in the field, to careful laboratory studies of rock mechanics during failure, to physically-based numerical simulations of the failure process. Our objective is to determine ways in which information collected by structural geologists and hydrogeologists can be used to constrain the plumbing of fractured rock. Here the question is not only what information is useful, but also how can it be translated into a form useful for understanding flow and transport?

As contaminants travel along these pathways, they will interact with the rock and soil. These interactions can dramatically affect not only the rate, but also the type of contamination leaving the watershed. For example, we are showing that the input of organic waste into a watershed can result in the release of naturally-occurring arsenic. An important question that our research asks is to what extent can we determine where a contaminant has been and what it has interacted with by monitoring levels of the contaminant reaching a stream.

Finally, even after contaminants enter a stream they may still may interact with the permeable bed of the stream. In many cases, stream bed sediments can trap and store large amounts of contaminants for a very long time. What makes this storage so interesting is that the stream bed itself is not fixed; floods will completely rework a stream channel, releasing many of the stored contaminants. However, the natural reworking of stream sediments has been dramatically affected by dams. Much of our understanding of how dams affect streams comes from studies on western U.S. dams, but New England is much more impacted by dams; New England has more dams per square area than any other region in the U.S. Compared to the western U.S., our understanding of how dams have affected the eastern U.S. remains very limited.

Current Projects

Watershed Hydrology

Can groundwater remediation cause arsenic contamination? We are showing that the natural attenuation of organic contamination - the leading approach for remediating this type of waste - can result in the release of naturally occurring arsenic and create a potentially more lethal and long term contamination problem. This is a collaborative study with Benjamin Bostick .

Are eastern Dams unique? Unlike the massive dams of the western U.S., eastern watersheds typically have a larger number of smaller dams. While previous studies have focused on the impact of a single dam on a single stream, we're looking at how multiple small dams interact to impact the movement of sediment and contaminants and how these impacts affect the riparian ecosystem. This is a collaborative study with Frank Magilligan , and Brian Dade .

Can structural geology help constrain hydrogeologic models of fractured rock? We know fractures strongly control flow and transport in the subsurface, but how can the data that structural geologists collect help us build better hydrogeologic models? This study combines high resolution field mapping and testing will innovative approaches for converting this data into information useful for flow and transport studies.

What do streams tell us about groundwater? As groundwater and contaminants move through a watershed, they interact with the soil and bedrock, changing both the form and rate of movement of the contaminants. These changes provide valuable information about how watersheds work. We are using high resolution monitoring of stream quantity and quality to test possible models for how groundwater and contaminants move and interact through a watershed. This is a collaborative study with Xiahong Feng .

Advanced Structural Geology

What can ice tell us about rock? Ice has a major advantage over rock with regard to understanding how crystalline materials fail; namely, it is transparent. In using ice as a model material for ice we can observe in great detail how fractures and faults form. This has lead to new understanding of the formation of fractures and faults in both ice and rock that would be nearly impossible to obtain using only rock. This is a collaborative project with Erland Schulson .

How can we map the three dimensional geometry of fractures? We're using high resolution ground penetrating radar to non-destructively map, for the first time, the in situ, outcrop scale geometry of fracture networks. These maps are invaluable for understanding how fractures interconnect to form permeable networks.

What happens when a fracture reaches a bedding layer? Whether or not a fracture propagates across a bedding layer dramatically affects the interconnectedness of fracture networks. We're using innovative experiments to observe the growth of fractures in the lab as a guide for interpreting field data. This is a collaborative study with Stephen Brown .

 

Selected Recent Publications:

  1. Renshaw, C.E., Myse, T.A., Brown, S.R., Role of heterogeneity in elastic properties and layer thickness in the jointing of layered sedimentary rocks, Geophysical Research Letters , in press, 2003.

  2. Bursik, M.I., Renshaw, C.E., McCalpin, J., Berry, M., A volcanotectonic cascade: Activation of range front faulting and eruptions by dike intrusion, Mono Basin-Long Valley Caldera, California, Journal of Geophysical Research , 108(B8):2393, doi10.1029/2002JB002032, 2003.

  3. Feng, X. H., Taylor, S., Renshaw, C. E. & Kirchner, J. W. Isotopic evolution of snowmelt - 1. A physically based one-dimensional model. Water Resources Research 38 (2002).

  4. Renshaw, C. E. & Schulson, E. M. Universal behaviour in compressive failure of brittle materials. Nature 412 , 897-900 (2001).

  5. Renshaw, C. E., Dadakis, J. S. & Brown, S. R. Measuring fracture apertures: A comparison of methods. Geophysical Research Letters 27 , 289-292 (2000).

  6. Renshaw, C. E. Connectivity of joint networks with power law length distributions. Water Resources Research 35 , 2661-2670 (1999).

  7. Schulson, E. M., Iliescu, D. & Renshaw, C. E. On the initiation of shear faults during brittle compressive Failure: A new mechanism. Journal of Geophysical Research-Solid Earth 104 , 695-705 (1999).

 

 

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