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Post-glacial landscape response to climate variability in the southeastern San Juan Mountains of Colorado, USA

Published online by Cambridge University Press:  20 January 2017

Bradley G. Johnson ,
Martha Cary Eppes ,
John A. Diemer ,
Gonzalo Jiménez-Moreno  and
Anthony L. Layzell
Bradley G. Johnson*
Affiliation:
Environmental Studies Program, Davidson College, Box 7056, Davidson, NC 28035-7056, USA
Martha Cary Eppes
Affiliation:
Department of Geography and Earth Sciences, University of North Carolina Charlotte, McEniry 324, 9201 University City Blvd, Charlotte, NC 28223–0001, USA
John A. Diemer
Affiliation:
Department of Geography and Earth Sciences, University of North Carolina Charlotte, McEniry 324, 9201 University City Blvd, Charlotte, NC 28223–0001, USA
Gonzalo Jiménez-Moreno
Affiliation:
Departamento de Estratigrafía y Paleontología, Facultad de Ciencias, Universidad de Granada, Avda. Fuente Nueva S/N, 18002 Granada, Spain
Anthony L. Layzell
Affiliation:
Department of Geography, University of Kansas, Lawrence, KS 66045, USA
*
⁎Corresponding author. E-mail address:bradley_g_johnson@hotmail.com (B. G. Johnson).
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Abstract

Geomorphic mapping in the upper Conejos River Valley of the San Juan Mountains has shown that three distinct periods of aggradation have occurred since the end of the last glacial maximum (LGM). The first occurred during the Pleistocene–Holocene transition (~ 12.5–9.5 ka) and is interpreted as paraglacial landscape response to deglaciation after the LGM. Evidence of the second period of aggradation is limited but indicates a small pulse of sedimentation at ~ 5.5 ka. A third, more broadly identifiable period of sedimentation occurred in the late Holocene (~ 2.2–1 ka). The latest two periods of aggradation are concurrent with increases in the frequency of climate change in the region suggesting that Holocene alpine and sub-alpine landscapes respond more to rapid changes in climate than to large singular climatic swings. Soil development and radiocarbon dating indicate that hillslopes were stable during the Holocene even while aggradation was occurring in valley bottoms. Thus, we can conclude that erosion does not occur equally throughout the landscape but is focused upslope of headwater streams, along tributary channels, or on ridge tops. This is in contrast to some models which assume equal erosion in headwater basins.

Keywords

San Juan MountainsLandscape evolutionHillslope response to climate changePost-glaical climate variabilityHolocene terracesHolocene alluvial fans
Type
Research Article
Information
Quaternary Research , Volume 76 , Issue 3 , November 2011 , pp. 352 - 362
Copyright
University of Washington

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