Dr. Jonathan D. Stock
Research Geologist, Western Geology & Geophysics Team, U.S. Geological Survey, 345
Middlefield Road, MS973, Menlo Park, CA, 94025, (650) 329-4968, jstock@usgs.gov
Jonathan Stock is a Research Geologist in the Western Geology & Geophysics
Team, USGS, Menlo Park. He investigates the role of geomorphic processes in shaping
Earth’s surface by combining new mapping technologies with field-based monitoring and
measurements, and theoretical modeling. He uses the mapping to delineate the extent of
different geomorphic processes, the field measurements and monitoring to quantify their
rates, and the modeling to generalize these local results for both environmental and
hazard applications. The goal of his research is to understand the processes that produce
and transport sediment in steeplands at a level at which their transport rates can be
forecast. His current projects include high-resolution landslide mapping using LiDAR in
Ventura area, a process model for sediment supply to the reef in Molokai, near real-time
landslide monitoring sensors in the San Francisco Bay Area, use of bathymetric LiDAR
to assess sediment supply on the Klamath River, and use of new environmental sensors
and repeat LiDAR to assess post-wildfire hazards in Southern California. He
communicates this science at invited academic talks here and abroad, but also at gradeschool and community meetings in his fieldsites. He was educated at U.C. Santa Cruz
(B.Sc., 1992), University of Washington (M.Sc., 1996) and University of California,
Berkeley (Ph. D., 2003).
Title: Linking the Ridge to the Reef: Adventures in Hawaiian Geomorphology
Abstract
In tropical watersheds, hillslope changes are producing increasing amounts of fine
sediment that can be quickly carried to reefs by channels. Suspended sediment
concentrations off the reefs of Molokai, Hawaii, chronically exceed a toxic level of 10
mg/L, threatening reef ecosystems. We hypothesize that historic overgrazing converted
watershed erosion from soil creep to overland flow, increasing both the magnitude and
frequency of sediment flooding adjacent reefs. We combined surficial and ecological
mapping, hillslope and stream gages, and novel sensors to locate, quantify and model the
generation of fine sediments polluting the Molokai reef. We find that small areas of
intense soil erosion (~ 1 cm/year) are active between 8-10 hours every year with large
storms whose rainfall intensities exceed 10 mm/hour. These hot-spots erode at rates that
are at least 100-fold greater than long-term rates of 0.13 mm/year. High modern rates
appear to depend on the availability of loose particles, which are refreshed annually by
intense weathering of unvegetated soil. When summed up over the catchment, predicted
hot-spot erosion nearly balances that observed at the catchment mouth. A small portion
(< 3%) of the landscape appears to be responsible for the majority of the sediment
pollution to the reef. Expansion of these hotspots as climate change alters vegetation
cover or storm characteristics could increase sediment pollution of the reef dramatically.