Understanding the architecture of the deep critical zone and its relation to knickpoint evolution in the Rio Icacos watershed (Luquillo Critical Zone Observatory, Puerto Rico) using hydrogeophysical methods.

Tuesday, 25 July 2017: 11:00 AM
Paul Brest West (Munger Conference Center)
Xavier Comas1, William J Wright2, Mario J Job2, Neil Terry3, Dimitrios Ntarlagiannis4, Finn Whiting5, Scott A Hynek6, Susan Brantley7 and Raymond C Fletcher8, (1)Florida Atlantic University, Geosciences, Boca Raton, FL, United States, (2)Florida Atlantic University, Boca Raton, FL, United States, (3)Rutgers University, Department of Earth & Environmental Sciences, Newark, NJ, United States, (4)Rutgers-Newark, Department of Earth & Environmental Sciences, Newark, NJ, United States, (5)Florida Atlantic University, Geosciences, Davie, FL, United States, (6)Pennsylvania State University Main Campus, University Park, PA, United States, (7)Pennsylvania State University, State College, United States, (8)Pennsylvania State University Main Campus, Department of Geosciences, University Park, PA, United States
The Rio Icacos in the Luquillo Mountains of Puerto Rico is characterized by a sharp knickpoint associated to changes in relative baselevel during isostatic uplift, that define the front of a slow-moving wave of erosion that propagates upstream. Previous studies have shown differential rates of denudation across the watershed associated with the positioning of the knickpoint, with slower rates of erosion at higher relict positions above the knickpoint when compared to areas below the knickpoint. Furthermore, bedrock along the watershed has been characterized by a system of heterogeneous fractures that apparently drive the formation of corestones and associated spheroidal fracturing and rindlets. However, how the near-surface critical zone architecture (i.e. spatial patterns in regolith thickness or fracture distribution) may dictate changes in weathering rates and potential knickpoint migration, has not been properly characterized and is mainly based in a few cores scattered within the watershed. In this study we used an array of near-surface geophysical methods (including ground penetrating radar, terrain conductivity, electrical resistivity imaging and induced polarization, capacitively-coupled resistivity, and shallow seismic, constrained with direct methods from previous studies) to better understand spatial variability of the critical zone architecture. These methods were combined with stress modeling to: 1) image changes in regolith thickness within the watershed; and 2) understand how the spatial distribution and density of fractures varies with topography and proximity to the knickpoint, showing increased dilation of fractures with proximity to the knickpoint. Our results are consistent at showing the potential of geophysical methods for imaging the architecture of the critical zone and its relation to knickpoint migration.