Skip to main content
U.S. flag

An official website of the United States government

Terrigenous sediment provenance from geochemical tracers, south Molokai reef flat, Hawaii

August 26, 2010

Land-derived runoff is one of the greatest threats to coral-reef health. Identification of runoff sources is an important step in erosion mitigation efforts. A geochemical sediment provenance study was done in uplands and across the adjacent fringing reef on the southeast shore of Molokai, Hawaii, to determine whether sediment runoff originated from hillsides or gulches. Source-region identification was based on geochemical differences between alkalic basalt, which outcrops on hillsides, and tholeiitic basalt, which outcrops in gulches. In Kawela watershed, copper to iron ratios (Cu/Fe) were distinct in hillside soil versus gulch sediment and suggest that hillside erosion is the predominant mechanism of sediment delivery to the nearshore. This suggests that runoff-mitigation efforts should take steps to reduce hillside erosion. Cadmium to thorium ratios (Cd/Th) in nearshore sediment suggest that there is a high-Cd source of runoff east of Kamalo Gulch. This compositional difference is consistent with the predominance of tholeiitic basalt on the eastern end of Molokai.

Citation Information

Publication Year 2010
Title Terrigenous sediment provenance from geochemical tracers, south Molokai reef flat, Hawaii
DOI 10.3133/ofr20101155
Authors R.K. Takesue
Publication Type Report
Publication Subtype USGS Numbered Series
Series Title Open-File Report
Series Number 2010-1155
Index ID ofr20101155
Record Source USGS Publications Warehouse
USGS Organization Pacific Science Center