『Abstract
To constrain the spatial distribution of erosion rates in Waimea
river watershed, on the western side of the island of Kauai, Hawaii,
we calculate the frequency distribution of cosmogenic 3He
concentrations ([3He]c) from helium
isotopic measurements in olivine grains from a single sample of
river sediment. Helium measurements were made in 26 aliquots of
〜30 olivine grains each. The average [3He]c
from the 26 aliquots was used to estimate a basin-wide average
erosion rate of 0.056 mm/yr, a value that is similar to erosion
rates obtained from geochemical analyses of river sediments from
tectonically stable landforms. However, forward models of cosmogenic
nuclide production and sediment generation rates are inconsistent
with the hypothesis that the observed [3He]c
frequency distribution is the result of a homogeneous, basin wide,
erosion rate. Instead, a distribution of erosion rates, from 〜0
to 4 mm/yr, may account for the observed frequency distribution.
The distribution of erosion rates can be modeled by both non-linear
slope- and curvature-dependent erosion rates with power law exponents
ranging from 2.0 to 2.5. However, the spatial distribution of
cosmogenic nuclides for slope- and curvature-dependent erosion
rates are distinct, and we propose strategies to test further
the extent to which erosion rates are controlled by the macroscale
topographic features. These results demonstrate that the observed
frequency distribution of cosmogenic nuclide concentrations in
river sediments, combined with numerical modeling of erosion rates,
can provide constrains on both the spatial variability of erosion
rates in a drainage basin and the form of parameterized erosion
laws.
Keywords: cosmogenic nuclides; erosion laws; frequency distribution;
helium; Hawaii; topography 』
1. Introduction
2. Geological setting, sampling strategy, and measurement techniques
3. Cosmogenic 3He and constraints on basin-wide erosion
rates
4. Observed frequency distribution and the spatial variability
of erosion rate
4.1. Frequency distribution model using a constant erosion
rate in the drainage area
4.2. Frequency distribution model using slope- and curvature-dependent
erosion functions
5. Implications
6. Conclusions
Acknowledgements
References