Covariation of climate and long-term erosion rates across a steep rainfall gradient on the Hawaiian island of Kaua'i

Abstract

Erosion of volcanic ocean islands creates dramatic landscapes, modulates Earth's carbon cycle, and delivers sediment to coasts and reefs. Because many volcanic islands have large climate gradients and minimal variations in lithology and tectonic history, they are excellent natural laboratories for studying climatic effects on the evolution of topography. Despite concerns that modern sediment fluxes to island coasts may exceed long-term fluxes, little is known about how erosion rates and processes vary across island interiors, how erosion rates are influenced by the strong climate gradients on many islands, and how modern island erosion rates compare to long-term rates. Here, we present new measurements of erosion rates over 5 yr to 5 m.y. timescales on the Hawaiian island of Kaua'i, across which mean annual precipitation ranges from 0.5 to 9.5 m/yr. Eroded rock volumes from basins across Kaua'i indicate that million-year-scale erosion rates are correlated with modern mean annual precipitation and range from 8 to 335 t km-2 yr-1. In Kaua'i's Hanalei River basin, 3He concentrations in detrital olivines imply millennialscale erosion rates of >126 to >390 t km-2 yr-1 from olivine-bearing hillslopes, while fluvial suspended sediment fluxes measured from 2004 to 2009 plus estimates of chemical and bed-load fluxes imply basin-averaged erosion rates of 545 ± 128 t km-2 yr-1. Mapping of landslide scars in satellite imagery of the Hanalei basin from 2004 and 2010 implies landslide-driven erosion rates of 30-47 t km-2 yr-1. These measurements imply that modern erosion rates in the Hanalei basin are no more than 2.3 ± 0.6 times faster than millennial-scale erosion rates, and, to the extent that modern precipitation patterns resemble long-term patterns, they are consistent with a link between precipitation rates and longterm erosion rates. © 2013 Geological Society of America.