Imaging the architecture of the Critical Zone at Boulder Creek Critical Zone Observatory, Rocky Mountains Front Range of Colorado, USA

Boulder Creek Critical Zone Observatory functions as a nucleus for different scientific disciplines to study the development of the Critical Zone (CZ) along an altitudinal gradient. Three catchments represent different landscape types along this gradient. Green Lakes Valley is a typical alpine tundra area at around to 3600 m a.s.l., whereas Gordon Gulch (2700 m a.s.l.) represents a subalpine area. The lower montane area is represented by the watershed of Betasso (1900 m a.s.l.). We present results from all three catchments using various shallow geophysical methods such as ground penetrating radar (GPR), electric resistivity tomography (ERT) and party shallow seismic refraction (SSR) together with soil-geomorphological studies and results. The three study sites enormously differ in their geomorphological, hydrological, biological and pedological parameters within the Critical Zone of which we present the major differences along the altitudinal gradient which include variations in thickness, composition and layering of the sediments and soils along the slopes within the CZ. We further give first dating results by optical stimulated luminescence (OSL) of the slope sediments in order to elaborate a chrono-stratigraphy of the hill slope sediments. We find layered slope sediments in various compositions in the three different catchments dating back to glacial times where geli-solifluction must have been a major process for sediment production and therefore for the development of the critical zone.