AT&G
- Spotila's active tectonics and geomorphology research
Role of glaciers in the
development of the active Chugach-St. Elias Range, Alaska
Photo of Yaga Peak (~8300') at the western end of the Guyot
Glacier, west of Icy Bay, taken from helicopter
in August, 2001.
Scope: To test whether rapid glacial erosion
influences the partitioning of plate motion and deformation in a high-latitude
mountain belt, we are studying the geomorphology and exhumation history of the
Chugach/St. Elias Range in southeast Alaska. This began with a project in collaboration with Andrew Meigs
at Oregon State University, which resulted in publication of the first
low-temperature thermochronometry across much of the St. Elias Range in Geology
in 2004. The main goals of the
initial work were to document the patterns of exhumation to see whether
climatic patterns (e.g. precipiation, glacial equilibrium line altitude) are
related, as well as to make a first-order measurement of the million-year time
scale erosional efflux from the range.
The results showed a clear correlation between exhumation and climatic
trends, and also suggest a potential link between climatic variables and where
active structures occur. In
addition, we very loosely measured the volumetric efflux and found that within
large error bars, it could match the volumetric tectonic influx of the accreting
Yakutat microplate. As a result, a
steady-state flux may be possible, which is consistent with an idea that
glaciers are effecient agents of erosion that can limit the topographc of
mountain belts (the "glacial buzz saw hypothesis"). Andrew Meigs also conducted studies of
individual erosional processes, including impact of bedrock landsliding during
deglaciation on total erosion.
The second phase of this study has begun as a new project of
the Continental Dynamics program at NSF known as STEEP, or St. Elias Erosion
Tectonic Project. This is a large
collaborative project (see list of participants below) that will take a much
broader look at the dynamics of the same orogenic belt. In this case, several lines of
investigation will attempt to quantify different aspects of the plate boundary,
such as a GPS study to document crustal motions and isolate the strain
accumulating on individual faults, an offshore seismic study to better
constrain the characteristics of the microplate indentor (Yakutat terrane) and
test whether its oceanic component may be an oceanic plateau, as well as
detailed models, rooted in new data, on glacial erosion and the interaction of
erosion and crustal strain. The
combination of large new data sets and modeling will make a tremendous
contribution to understanding the interaction of tectonics, erosion, and
climate in this orogenic setting.
The Virginia Tech component of STEEP is to continue with
thermochronometry. We will
collaborate with Peter Zeitler (Lehigh U.) to measure upwards of 50 new apatite
bedrock and detrital helium ages, as well as a large number of zircon helium
ages. In collaboration with John
Garver (Union College) and Richard Stewart (U Wash.), apatite and zircon
fission-track ages will also be measured on bedrock and detrital samples. Currently there are two new students
working on this project at Virginia Tech.
Aaron Berger is working towards his Ph.D. and will be studying the large
exhumation history of the core of the orogen, using both existing and new samples
to be collected in upcoming field seasons. Aaron may also perform detailed studies of active faults in
the Wrangell Mountains during these field seasons. Ryan McAleer is an M.S. candidate and will work on the
exhumation of the Fairweather Range.
In particular, he is interested in the denudation driven by
transpressive deformation along the Fairweather fault, where reconnaissance
dating implies rapid exhumation.
There is also more room for additional work on this project - if
interested in graduate studies, please contact me!
Personnel: Jamie Buscher (M.S., 2003)
and collaborator Andrew Meigs (Oregon State
University) worked on the first stage of the project. This project is continuiing as part of STEEP (see below for
funding and list of participants), with graduate students Aaron Berger (Ph.D
candidate) and Ryan McAleer (M.S. candidate).
Funding: Tectonics program of the National
Science Foundation award EAR0001239, 6/00-7/03 (with Andrew Meigs). Newly funded NSF Continental Dynamics
program; a large, five-year, collaborative project organized by Terry Pavlis
(see links to participants below) entitled the ST. Elias Erosion/Tectonics
Project or STEEP;
EAR0409224, 9/04-8/09.
Links Wrangell/St. Elias National Park. Here's a proposal
to make southeast Alaska a special study site for glacial erosion in the Margins,
NSF program. Here's a very useful science plan (whitepaper) from a
workshop organized by Sean Guilick and Jeff Jaeger and sponsored by NSF-CD and
JOI on future research directions in the area, held May 2003; Interplay of
Collisional Tectonics and Late Cenozoic Glacial Climate in Alaska. Here are links to all the participants
of the Continental Dynamics project STEEP: Terry
Pavlis (UNO), Bernard
Hallet (UW), Sean
Gulick (UTIG), Jeff
Freymueller (UA Fairbanks), Gail Christenson (UTIG),
Peter Koons (U.
Maine), Ron Bruhn (Utah), Richard
Stewart (UW), Ken Ridgeway
(Purdue), Peter Zeitler
(Lehigh), John
Garver (Union College), and Gary Pavlis
(Indiana U.). Links to some other
folks doing geology in the Chugach/St. Elias Range include Andrew Meigs (Oregon
State), Jinny Sisson (Rice), Jeanne
Sauber (NASA), Sarah
Roeske (UC Davis), Peter Haeussler
(USGS), and John Jaeger (U
Fla.).
Follow
this link for photos from the 2001 field excursion. Note that
this leads to a very extensive set of photos!
Comments to: spotila@vt.edu