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

Periglacial and Feeze/Thaw Processes

Paper Session 2124
Wednesday, 4/18/07, from 8:00 AM - 9:40 AM

Sponsorship(s):

Cryosphere Specialty Group
Mountain Geography Specialty Group
Geomorphology Specialty Group

Organizer(s):

Forrest D. Wilkerson - Minnesota State University

Chair(s):

Forrest D. Wilkerson - Minnesota State University

Abstract(s):

• 8:00 AM Author(s):
  *Forrest D. Wilkerson - Minnesota State University
  Ginger L. Schmid - Minnesota State University
  

  Abstract Title: Fifteen years of periglacial research in the White Mountains, California.

  
  

  Since 1991 detailed studies have been conducted on a variety of periglacial landforms in the White Mountains of California. The landforms range from large-scale sorted patterned ground and boulder streams to small-scale sorted patterns or frost boils. Activity rates have varied widely between the types of landforms studied, primarily along an elevational gradient from 3225m to over 4300m. Methods employed have ranged from high-resolution surveying techniques to low-resolution dowels and surface markers. Activity among the large-scale landforms has not been detected in any landforms below 4100m. However, landforms above 4100m are very active with horizontal movements in many cases exceeding 10.0cm per year. Smaller-scale landforms show progressively higher rates of activity with increased elevation. At the lowest elevations, only horizontal surface movement has been detected and is thought to be primarily the result of needle ice movement. Above 3800m frost penetration is deeper and distinct horizontal and vertical components were noted. Wooden dowels placed in landforms above 3800m routinely have heave rates averaging greater than 15cm per year and surface plots average noticeable movement within two thirds of the markers. Above 4100m all landforms are highly active and include a solifluction component that is audible on calm days in late summer. The most recent investigations concern geomorphic activity rates, primarily periglacial activity, surrounding GLORIA sites in the White Mountains of California.

  Keywords: periglacial activity, geomorphology, California

  
  
• 8:20 AM Author(s):
  *Frederick E. Nelson - University of Delaware
  Michael T. Walegur - University of Delaware
  Kim J. Park Nelson - University of Minnesota
  

  Abstract Title: Periglacial Appalachia: Paleoclimatic and Geocryological Implications of Blockfield Elevation Gradients, Eastern U.S.A.

  
  

  Locational data were obtained for 96 periglacial blockfields in the Appalachian Mountains of eastern USA using "TerraServer," a Virtual Globes (VGs) resource for viewing air-photo and satellite imagery. The elevation of Appalachian blockfields south of the Last Glacial Maximum border parallels regional gradients of contemporary mean July, summer, and annual temperature. July temperature reductions inferred from paleoecological studies indicate that the median elevation of blockfields throughout the Appalachians lay at or above timberline during the Last Glacial Maximum (LGM). Paleotemperatures calculated using known Appalachian lapse rates and published LGM temperature departures indicate that most blockfields in the study area were formed in association with permafrost. Allochthonous blockfields appear to be constituent elements of periglacial "form communities" developed under severely cold conditions, and are useful indicators of Pleistocene permafrost conditions. Internet-based VGs can be used to create generalized reconnaissance-level data bases of large-scale periglacial landforms and hillslope features over large areas. Complementary use of Virtual Globes technology and spatial-analytic techniques holds considerable potential for addressing the broad-scale problems with which traditional climatic geomorphology is concerned.

  Keywords: Appalachian Mountains, blockfield, periglacial, permafrost, Quaternary, Virtual Globes

  
  
• 8:40 AM Author(s):
  *Alexander Brenning - University of Waterloo
  Michael Grasser - Friedrich-Alexander-Universität Erlangen-Nürnberg, Institut für Geographie, Erlangen, Germany
  Donald A Friend - Minnesota State University
  

  Abstract Title: Quantifying the Significance and Modeling the Distribution of Rock Glaciers in the San Juan Mountains, Colorado, USA.

  
  

  The quantitative significance of rock glaciers is assessed and their spatial distribution patterns are analyzed in the San Juan Mountains, Colorado/USA (2874 km² above 3400 m a.s.l.). Statistical estimation techniques and generalized additive models are used to efficiently evaluate a set of 2933 surface points obtained by random sampling and air photo interpretation. Results show that active and inactive rock glaciers in the study area occupy an estimated area of 70 km², which corresponds to a water equivalent of 0.50-0.76 km³, and estimated rock glacier debris volumes imply postglacial denudation rates (vertical lowering rates) of 0.5-1.1 mm per year within the talus sheds of rock glaciers. The generalized additive model, which is able to represent both linear and nonlinear effects, is based on topographic attributes derived from digital elevation models of the Shuttle Radar Topography Mission (SRTM). The model structure indicates that the covariables of local slope, slope of the contributing area, local curvature and size of the contributing area are among the main factors controlling rock glacier distribution. The predictive capabilities of the models for mapping rock glaciers regionally are further improved by combining terrain attributes and Landsat Enhanced Thematic Mapper (ETM) remote sensing data.

  Keywords: generalized additive modeling; rock glacier; terrain analysis

  
  
• 9:00 AM Author(s):
  *David William Hedding - North West University
  

  Abstract Title: A First Inventory of Periglacial Features in Western Dronning Maud Land, Antarctica.

  
  

  Due the remoteness of Southern Circumpolar Region, particularly Antarctica, and the perceived absence of ice-free areas on the Antarctic continent, it has received significantly less attention from the scientific community with regard to periglacial studies when compared to the Northern Hemisphere. Few data have, thus, been published on periglacial features in the Southern Circumpolar Region, specifically continental Antarctica, even though substantial ice-free areas exist (~280,000 km2), which are all underlain by permafrost. A need, therefore, exists to create an inventory of the periglacial features of Western Dronning Maud Land, Antarctica. This paper documents periglacial geomorphology found on the Robertskollen, Vesleskarvet, Valterkulten and some nunatuks in the Borge Mountains. Detailed measurements describing the characteristics of patterned ground, depth of sorting, and the existence of permafrost are presented.

  Keywords: Antarctica, periglacial, patterned ground, permafrost

  
  

Session Description: This session involves the role of freeze/thaw processes in the development of patterned ground and other periglacial landforms in both mountainous and non-mountainous environments.