GRINNELL GLACIER, MONTANA:
I am currently a co-PI on collaborative research in Glacier National Park between Bryn Mawr and Macalester Colleges. In Summer 2005, Kelly MacGregor (Macalester) and I led a research team of undergraduates from each school, with the goal of documenting ice motion of Grinnell Glacier by using differential GPS, snowmelt using an acoustic sensor and data logger, and sediment production by coring two lakes downstream of Grinnell Glacier. The resulting glacial data will be used to constrain numerical models of cirque-glacial erosion, allowing us to assess the sensitivity of cirque morphologies to climatic conditions. Melt-rate data that will constrain a numerical model of glacial retreat, a model that will be able to assess the approximate date in which 'Glacier National Park' will actually be 'Formerly Glaciated National Park.' The lake core data will be used to assess changing environmental conditions in Glacier National Park over the Holocene, including forest-fire frequency, floral diversity, and anthropogenic impacts on sedimentation rates. This research will form the basis of senior theses for several undergraduates and for at least three major publications (modeling of cirque erosion, modeling of glacial retreat, laboratory analyses of lake cores).

BENCH GLACIER, ALASKA:
Fieldwork conducted over two summers at the remote Bench Glacier, located in the Chugach Range, southcentral Alaska, has provided a unique meteorological, glaciological, hydrological and sedimentological data set with which to address some of these issues. I spent a total of four months in summers 1999 and 2000 instrumenting and monitoring the 7-km long temperate alpine glacier with the help of a small team of undergraduate and graduate students. I was partly responsible for field logistics, along with installing and maintaining a meteorological station and stream gauge, measuring water chemistry, suspended sediment, and bedload in the glacier outlet stream, installing and maintaining ablation stakes, and monitoring velocity stakes with optical surveying and GPS.

Several time series of data collected at the Bench Glacier suggest that a subglacial network of conduits develops over the melt season. Water discharge of the proglacial Bench Stream reflects increasingly efficient transmission of runoff from the glacier surface to the proglacial area toward mid- to late summer. Periodic floods, triggered by precipitation or high melt events, evacuate large amounts of sediment from the glacier sole. Hysteresis in the sediment load record indicates that the proglacial stream becomes sediment starved before flooding subsides. We infer that during flooding, the subglacial hydrologic network changes from an inefficient linked-cavity network to a more efficient system of conduits, enabling rapid mobilization of sediment stored at the glacier bed. Because the conduits persist after flooding, post-flood runoff is more directly transmitted across the glacier bed. Simple analytical and numerical modeling suggests that the variability of conduit position over annual to decadal timescales dictates the amount of change in subglacial sediment storage, and therefore, the relationship between glacial erosion and proglacial sediment load.

Publications:
Riihimaki, C. A., MacGregor, K. R., Anderson, R. S., Anderson, S. P., and Loso, M. G. (2005), Sediment evacuation and glacial erosion rates at a small alpine glacier, Journal of Geophysical Research, Earth Surface, 110, F03003, doi:10.1029/2004JF000189.

MacGregor, K. R., Riihimaki, C. A., and Anderson, R. S. (2005), Spatial and temporal evolution of sliding velocity on a small alpine glacier: Bench Glacier, Alaska 1999 and 2000, Journal of Glaciology, 51, 49-63.

Anderson, R. S., Anderson, S. P., MacGregor, K. R., Waddington, E. D., O'Neel, S., Riihimaki, C. A., and Loso, M. G. (2004), Self-defeating unsteady sliding of an alpine glacier, Journal of Geophysical Research, Earth Surface, 109, F03005, doi:10.1029/2004JF000120.

ROCKY MOUNTAINS, WYOMING AND COLORADO:
During the late Cenozoic, relief has dramatically increased in the Laramide ranges and intramontane basins at rates of up to ~100 m/Myr. Interpretations of the Cenozoic tectonic and climatic history of the entire western U. S. hinge on assumptions about Laramide landscape evolution, and yet the cause of recent relief production in this landscape is ill-understood. I seek to address quantitatively the significance, timing, and cause of relief production by fulfilling two critical needs in Laramide research: collecting new geochronologic data to augment temporal constraints on the development of key landforms that document major geomorphic episodes; and developing mechanistic, numerical models to interpret the sequence and spatial pattern of landscape feature formation.

Numerical modeling results indicate that relief production driven by tectonic uplift or climate change may have very different signatures in the landscape. The long-term pattern of tectonic uplift in our model tends to produce relief over 5-10 Myr, whereas dramatic changes in climatic forcing over the last 2 Myr of model runs generate the same amount of relief in only ~1 Myr. These results highlight the need for geochronologic data for 1-10 Ma to distinguish between the driving mechanisms of fluvial incision and range uplift. Our chemical analysis of stream deposits for ¹⁰Be and ²⁶Al during the next year should help fill this data gap.

Publications:
Riihimaki, C. A., Anderson, R. S., and Safran, E. B. (accepted), Impact of rock uplift on rates of late Cenozoic Rocky Mountain river incision, Journal of Geophysical Research, Earth Surface.

Riihimaki, C. A., Anderson, R. S., Safran, E. B., Dethier, D. P., Finkel, R. C., and Bierman, P. R. (2006), Longevity and progressive abandonment of the Rocky Flats surface, Front Range, Colorado, Geomorphology, 78, 265-278.

Stock, G. S., Riihimaki, C. A., and Anderson, R. S. (2006), Age constraints on cave development and landscape evolution in the Bighorn Basin of Wyoming, USA, Journal of Cave and Karst Studies, 68, 76-84.