Document Type


Journal/Book Title/Conference

2011 Geological Society of America Annual Meeting, Minneapolis, MN

Publication Date



The critical zone is the zone within which meteoric water, atmospheric gases, soil, and bedrock interact, encompassing the zone of soil formation (Anderson et al., 2007). The concentrations of various pedogenic compounds at a given location indicate the degree of weathering that has taken place in the Critical Zone. Among the products of chemical weathering are secondary phyllosilicate minerals (clays) and iron (Birkeland, 1999). At stable sites, chronosequence studies have shown that the amount of pedogenic iron oxide and clay increase as soils become older (McFadden and Hendricks, 1985).

Meteoric ¹⁰Be is a cosmogenic nuclide produced from oxygen and nitrogen in the atmosphere. It reaches the surface in rain water and dust and then binds to soil particles. As a soil profile evolves, so does its meteoric ¹⁰Be inventory due to soil formation and mixing processes. Given a steady state hillslope, the peak concentration of meteoric ¹⁰Be is expected in one horizon (Jungers et al., 2009). Concentration then decreases with depth, and the inventory is expected to increase downslope, creating a profile with a bulge. Given a young and eroding hillslope profile, the highest concentration of meteoric ¹⁰Be will still be in a single layer but erosion prevents this concentration from moving to depths beyond near-surface (Graly et al., 2010). The geochemistry of soils provides useful insight into soil character and development, and when applied to steep, active hillslopes, aids in the analysis of evolving topography. The addition of meteoric ¹⁰Be to soil analysis, combined with well-constrained delivery rates, allows for the dating of evolving soils and calculation of downslope soil transport.

This study examined hillslopes in Gordon Gulch, a 2.75 km² catchment with locally exposed bedrock and one of three focus areas of the Boulder Creek Critical Zone Observatory. Gordon Gulch is located downslope and to the east of the modern alpine environment and late Pleistocene glacial limit and generally upslope and to the west of the deeply incised landscape that characterizes the lower portion of Front Range rivers. Gordon Gulch may be affected by both upstream-migrating rejuvenation from the lower portion of the range and/or alpine environmental processes (i.e. periglacial activity).


This work made publicly available electronically on March 8, 2013.