Understanding the architecture of the deep critical zone in the Rio Icacos watershed (Luquillo Critical Zone Observatory, Puerto Rico) using a combination of hydrogeophysical methods.

Abstract:

The Rio Icacos watershed in the Luquillo Mountains (Puerto Rico) is characterized by rapid weathering rates and the accelerated development of a regolith mainly originated from the alteration of quartz diorite bedrock. Regolith materials create a blanket on top of the bedrock with a thickness that depends on its spatial distribution along the watershed (i.e. proximity to the river nickpoint in the southermost part of the watershed). Furthermore bedrock along the watershed is characterized by a system of heterogeneous fractures that apparently drive the formation of corestones and associated spheroidal fracturing and rindlets. In this study we used a combination of geophysical methods to better understand changes in regolith thickness and how the spatial distribution and density of fractures varies with topography and proximity to the nickpoint. Indirect and non-invasive geophysical methods included ground penetrating radar, GPR, terrain conductivity, and electrical resistivity imaging, ERI, and were constrained with direct methods (i.e. boreholes) already available from previous studies. Geophysical methods were consistent in imaging lateral changes in regolith distribution and fracture density along the watershed and showed the potential of multi-method approaches to better understand critical zone processes at multiple scales of measurement and high spatial resolution.