Geologic studies at the FRF have included surface sediment texture, box and vibracoring, subbottom profiling, and side-scan sonar mapping. These studies are unique because of the availability of complementary nearshore dynamics and survey data that can be used to put the geologic data into time and process context. On this page you will find descriptions and links to several of the geologic data sets and analyses.
The subaerial beach and shallow nearshore at the FRF are primarily composed of a bimodal mixture of medium quartz sand and small pebbles. Sediment size decreases offshore and becomes unimodal. Upper shoreface sediments consist of fine and very fine sand. Further offshore, sediments are moderately well sorted, mainly very fine sand and fine sand. Less than 10% of the surficial sediments are silts, though silts exist in the area.
This variation in grain-size cross-shore and with depth is shown in the figures below (Click image for larger view).
From 20 March 1984 to 6 September 1985, surface grab samples were collected along the two shore-normal transects routinely surveyed by the CRAB (Profile lines 62 & 188). Approximately 17 samples were collected along each line during 21 surveys although the coverage of each line differed. A total of 318 samples were collected along line 62, and 182 along line 188. Samples were sieved to 1/4 phi intervals using a sonic sifter. Line 62 samples were reported on in: Stauble, D. K., 1992, "Long-Term Profile and Sediment Morphodynamics: Field Research Facility Case History," US Army Corps of Engineers, Coastal & Hydraulics Laboratory, TR-CERC-92-7, Vicksburg, MS.
The data are available in two tab-delimited text files - These text files are 52 columns wide. Each row includes complete information about each sample including sample location, analysis statistics, and 1/4 phi size distribution. These are good for opening into a spreadsheet or a matrix processing program like MATLAB. Each file includes 5 lines of column header information. Line188Sediment1984-1985.txt (52K) Line62Sediment1984-1985.txt (99K).
Forty nine oriented vibracores were collected in July 1993 along two shore-normal transects extending from the beach out to ~8 m water depth. Close vibracore spacing and detailed hierarchial sedimentologic analysis enabled high-resolution definition of the textural and structural architecture of the shoreface prism which was then compared with biweekly survey data collected with the CRAB representing a 12+ year period.
The Results of this study are published in: Schwartz, R. K., Cooper, D. W., and Etheridge, P. H., 1997, "Sedimentologic Architecture of the Shoreface Prism, Relationship to Profile Dynamics, and Relevance to Engineering Concerns: Duck, North Carolina," US Army Corps of Engineers, Waterways Experiment Station, TR-CHL-97-19, Vicksburg, MS. This report includes detailed analysis along with core logs. The cores were epoxy peeled, x-rayed, and photographed. They are currently stored at the Department of Geology, Allegheny College.
During DUCK94, daily beach profiles and sediment samples were collected along three cross-shore transects during 18 days in October 1994. Conditions ranged from near calm to full storm conditions followed by 2 days of beach recovery. Sediment grain-size distributions vary in the cross-shore direction, with medium size grains on the upper foreshore, coarse gravel deposits on the lower foreshore and progressively finer sands in the offshore direction. After the storm, the foreshore and bar/trough samples were coarser with little change in the nearshore sediment distributions.
The results of this study were published in: Stauble & Cialone, 1997, "Sediment Dynamics and Profile Interactions, DUCK94", Proceedings of the 25th International Conference on Coastal Engineering, Vol 4
1994 – 1997 Nearshore Boxcores
From 1994 to 1997 several boxcore samples were collected in order to monitor the evolution of the seabed during storms. This study presents some of the first field results of nearshore cores collected where the seabed elevation and hydrodynamic forcing are continuously measured by instrumentation during storms. Continuous measurements of seabed elevation changes were made at 3 locations in 5.5, 8, and 13 meter water depth. The dissertation of Rebecca Lenel Beavers for her Doctor of Philosophy in the Department of Geology in the Graduate School of Duke University focuses on this topic. The following link provides access to her work along with photographs of the boxcore samples.
During the SandyDuck nearshore experiment, sediment samples were collected in the surf zone using short diver-collected tube cores. These samples were collected near instruments where the locations were known and repeatable. Foreshore grab samples were also collected along the same instrument lines. The samples were sieved using a sonic sifter at quarter-phi intervals, ranging from -3 phi (8.0 mm) to 4.25 phi (0.53 mm), and weight percentages for each interval were computed. These data are available in several formats.
Page created: April 2000 by WAB