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.
Bibliographical noteFunding Information:
Funding was provided by USGS EDMAP grant # 07HQAG0051 (MCE, BGJ). Additional funding was provided by the Geological Society of America Student Grant program (BGJ), The Colorado Scientific Society (BGJ), the University of North Carolina —Charlotte Geology Scholars Award (BGJ), UNC Charlotte Faculty Research Grant (MCE, JAD) and the Chama Institute of Arts and Sciences . Field assistance was provided by Catherine Arrington, Jake Armour, Jessica Jelacic, and Joshua Link. Thanks to Olav Slaymaker, Jim Knox, and an anonymous reviewer for comments that significantly improved the manuscript.
Copyright 2011 Elsevier B.V., All rights reserved.
- Hillslope response to climate change
- Holocene alluvial fans
- Holocene terraces
- Landscape evolution
- Post-glaical climate variability
- San Juan Mountains