Special Sessions
Sponsored by the Geomorphology Specialty Group
Association of American Geographers 103rd Annual Meeting
San Francisco, California, April 17-21.

Geomorphology - Works in Progress and Preliminary Results

Interactive Short Paper Session 2102
Wednesday, 4/18/07, from 8:00 AM - 9:40 AM

Sponsorship(s):

Geomorphology Specialty Group

Organizer(s):

Martin Lafrenz - Portland State University
Lisa Davis - University of Alabama

Chair(s):

Martin Lafrenz - Portland State University

Abstract(s):

• 8:00 AM Author(s):
  *Martin Lafrenz - Portland State University
  

  Abstract Title: Working With Middle School Science Students to Conduct Stream Channel Assessment.

  
  

  This project tests the accuracy and repeatability of visual stream channel assessments conducted by community volunteers and middle school science students from the Reynolds School District in Troutdale, OR. In the fall of 2006, a stream reachesin the Fairview Creek watershed, in east Multnomah County, was surveyed by the principal investigator (Lafrenz), using standard scientific stream channel survey techniques and equipment, in order to characterize stream habitat condition. The same stream reach was surveyed by two different middle school science classes and community volunteers, using similar geomorphic assessment techniques. This project seeks to establish whether stream condition, as determined by the middle school students, is similar or dissimilar to the condition quantified by the PI, as well as to test whether their visual assessments are similar or dissimilar to each other. The stream reach will be re-surveyed by each middle school class in the winter and spring of 2007 and by the PI in spring 2007 to quantify any changes in stream habitat condition during the study period and to test if the students' assessments detected similar changes in stream channel condition.

  Keywords: fluvial geomorphology, geomorphic techniques, science education

  
  
• 8:20 AM Author(s):
  *Dennis Dahms - University of Northern Iowa
  John Gosse - Dalhousie University
  

  Abstract Title: Early- to Mid-Pleistocene Cosmogenic Exposure Ages for Moraines, Table Mountain, Wyoming.

  
  

  Preliminary 10Be/26Al ages from moraine boulders on Table Mountain, Wyoming suggest the deposit may provide evidence for an early-to-middle Pleistocene glaciation in the Wind River Range. Cosmogenic nuclide exposure age-analyses of six granitic boulders on the same deposit generated ages that range from 270 to 736 ka (using estimated boulder erosion rate of 0.2-to-0.22 cm/kyr). Many of the generated ages are too young for the apparent age of the deposit, relative to adjacent moraines; this suggests that our erosion estimates are too low. One sample, however, could not have a higher erosion rate and still have amount of 10Be that was measured. Thus, it is obvious that some of the boulders were once buried and that we must consider not only the boulder erosion rate, but the rate of erosion of the moraine sediments as well. An accurate age estimate for this deposit then depends on at least three parameters: (1) how deep the boulders were buried in the moraine, (2) how long it took for the buried boulders to be uncovered by erosion (sediment erosion rate), and (3) what is a realistic erosion scenario for granitic boulders in this environment? These results suggest that the diamicton in which the boulders are imbedded was deposited between O-isotope stages 16 and 6. Final age determination must wait until the above erosion systematics can more clearly be estimated.

  Keywords: Middle Pleistocene, moraines, Wind River Range

  
  
• 8:40 AM Author(s):
  *Jose Roa-Lobo - University of Maryland - College Park
  

  Abstract Title: The Geomorphological, Multi-criteria Evaluation and Statistical approaches in a regional landslide susceptibility mapping. A comparative study.

  
  

  This paper explores a comparative analysis of three approaches used to achieve landslide susceptibility mapping: the Geomorphological, Statistical and Multi-criteria. The Geomorphological approach rather than traditional is still the battle line of the Geomorphological community in the practice of landslide hazard zonation however, the need for faster and GIS / remote sensing related procedures has prompted researchers to survey the capacities of methodologies based on different frameworks as the statistical and multi-criteria evaluation approaches. These three methods are founded upon different conceptual models. The Geomorphological depends intensively on the researcher's experience and familiarity with the study area via fieldwork, which is circumvented in the statistical one where the role of each factor causing slope instability is determined on the basis of the observed relations of the past/present landslide distribution to a full set of related geomorphic variables via weights of evidence. On the other hand, the Multi-criteria Evaluation divides the landsliding process into a number of simpler compounds related to geographical factors that form a decision hierarchy in order to be combined utilizing knowledge-based user preferences to identify and rank areas that are suitable to landslides without necessarily the input of a landslide inventory map. From these methods three subsequent landslide susceptibility maps are compared to the study area landslide inventory map using a success rate curve, which allows a more objective assessing of the landslide predictability accuracy of these approaches. The study area is located in a tropical mountain environment of the Venezuelan Andes.

  Keywords: Venezuela-Andes, landslides, slope-instability, tropical mountainnatural Hazards

  
  
• 9:00 AM Author(s):
  *Jonathan J Butler - University of Edinburgh
  *Michael Summerfield - University of Edinburgh
  Christoph Schnabel - Scottish Universities Environmental Research Centre
  Stewart Freeman - Scottish Universities Environmental Research Centre
  Rachel Walcott - University of Edinburgh
  

  Abstract Title: Bedrock channel erosion rates from cosmogenic isotope data: the Augrabies Falls system of the Orange River, South Africa.

  
  

  Quantifying rates of bedrock channel incision is fundamental to understanding rates and modes of long-term landscape development, yet the acquisition of such data has been problematic given the episodic nature of the high magnitude flood events that are likely to be responsible for most bedrock channel erosion. The development of cosmogenic isotope analysis now provides a means of quantifying rates of bedrock channel incision over time scales that are sufficiently long to integrate the effects of high magnitude - low frequency flood events. This approach has been applied to the Augrabies Falls system, the major knickpoint of the Orange River that forms the regional base level for the upper ~650 000 km2 of the Orange Basin. As a result of very low base flows (100 m3 s- 1 or less, compared with flood peaks of 10,000 m3 s-1 or more) a range of components of the complex landscape of the Augrabies Falls system are accessible for sampling, including the beds of anabranches above the main falls, the rock surfaces of subsidiary falls, interfluves between channels, exposed rock bars in the middle of the main channel and tributary channels below the main falls. Concentrations of in-situ?produced cosmogenic 10Be and 26Al in quartz from the granite-gneiss bedrock give rates of incision of ~60 mm ka-1 in channels above the main falls, while the channel in the gorge below the falls is downcutting at a rate of ~6 mm ka-1. Interfluve denudation rates are ~5 mm ka-1.

  Keywords: Geomorphology, cosmogenic isotopes, South Africa

  
  
• 9:20 AM Author(s):
  *Lisa Davis - University of Alabama
  J.P. Benstead - University of Alabama
  A.D. Huryn - University of Alabama
  

  Abstract Title: Geomorphic Constraints on Mussel Habitat, Bogue Chitto Creek, AL.

  
  

  Many rivers located in the state of Alabama provide habitat to freshwater mussels. Bogue Chitto Creek located in central Alabama provides habitat to an exceptional diversity of mussels, hosting at least 15 species of mussels in its bedload. The research being presented consists of ongoing research efforts aimed at identifying geomorphologic variables significant to the establishment and maintenance of the high diversity of mussel species observed in Bogue Chitto Creek.

  Keywords: mussels, geomorphology

  
  

Session Description: This Interactive Short Paper (ISP) Session allows for five-minute paper presentations involving a maximum of ten PowerPoint slides per presentation, which summarize initial research results or introduce research in progress in any aspect of geomorphology.