Evaluation of Sediment Dynamics and the Mobility of Heavy Minerals on a Linear Sand Shoal
Two instrumented tripoda were deployed in summer and fall, 1987, at Smith Island Shoal a coast-parallel sand ridge near the 10-meter depth contour just north of the Chesapeake Bay entrance on the Virginia inner shelf. Previous studies of the shoal have noted a high abundance of heavy minerals (up to...
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Journal of Coastal Research
1991
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ftfloridaojojs:oai:journals.flvc.org:article/78623 2023-05-15T18:20:01+02:00 Evaluation of Sediment Dynamics and the Mobility of Heavy Minerals on a Linear Sand Shoal Boon, John D. Berquist, Jr., C. R. 1991-10-12 application/pdf https://journals.flvc.org/jcr/article/view/78623 eng eng Journal of Coastal Research https://journals.flvc.org/jcr/article/view/78623/76028 https://journals.flvc.org/jcr/article/view/78623 Journal of Coastal Research; Vol 7 No 4 (1991): Journal of Coastal Research 0749-0208 info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion Peer-reviewed Article 1991 ftfloridaojojs 2020-11-14T19:12:57Z Two instrumented tripoda were deployed in summer and fall, 1987, at Smith Island Shoal a coast-parallel sand ridge near the 10-meter depth contour just north of the Chesapeake Bay entrance on the Virginia inner shelf. Previous studies of the shoal have noted a high abundance of heavy minerals (up to 16 percent by weight) contained within the surficial sediments (fine to very-fine sands) on its flanks, as compared to much lower concentrations elsewhere. Measurements of near-bottom current, wave-orbital velocity, wave height and optically-sensed suspended sediment concentration within a meter of the seabed show that the flank areas of the shoal frequently experience wave-induced, bottom orbital velocities well in excess of the critical level needed to produce grain motion. During periods of moderate wave activity (Hmo = 0.81-1.0 m, T = 8.5-9.5 s) bottom orbital velocities were "groupy" in their distribution, reaching maximum values as high as 60 cm/s. Pronounced resuspension of bed material occurred within a meter of the bottom and was strongly modulated at wave-group periods of 100 to 200 seconds. Samples of suspended material show approximately the same mineral composition as that of the local bed material but with some indication of height-dependent mineral sorting. Wave induced resuspension of heavy minerals is thus indicated during all but fair weather conditions, with near-bottom currents generally slow and erratic. This suggests that the potential for selective mineral sorting is restricted to grains moving in suspension. Article in Journal/Newspaper Smith Island Florida Online Journals (FloridaOJ) Smith Island ENVELOPE(-62.520,-62.520,-62.981,-62.981) |
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Open Polar |
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Florida Online Journals (FloridaOJ) |
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ftfloridaojojs |
language |
English |
description |
Two instrumented tripoda were deployed in summer and fall, 1987, at Smith Island Shoal a coast-parallel sand ridge near the 10-meter depth contour just north of the Chesapeake Bay entrance on the Virginia inner shelf. Previous studies of the shoal have noted a high abundance of heavy minerals (up to 16 percent by weight) contained within the surficial sediments (fine to very-fine sands) on its flanks, as compared to much lower concentrations elsewhere. Measurements of near-bottom current, wave-orbital velocity, wave height and optically-sensed suspended sediment concentration within a meter of the seabed show that the flank areas of the shoal frequently experience wave-induced, bottom orbital velocities well in excess of the critical level needed to produce grain motion. During periods of moderate wave activity (Hmo = 0.81-1.0 m, T = 8.5-9.5 s) bottom orbital velocities were "groupy" in their distribution, reaching maximum values as high as 60 cm/s. Pronounced resuspension of bed material occurred within a meter of the bottom and was strongly modulated at wave-group periods of 100 to 200 seconds. Samples of suspended material show approximately the same mineral composition as that of the local bed material but with some indication of height-dependent mineral sorting. Wave induced resuspension of heavy minerals is thus indicated during all but fair weather conditions, with near-bottom currents generally slow and erratic. This suggests that the potential for selective mineral sorting is restricted to grains moving in suspension. |
format |
Article in Journal/Newspaper |
author |
Boon, John D. Berquist, Jr., C. R. |
spellingShingle |
Boon, John D. Berquist, Jr., C. R. Evaluation of Sediment Dynamics and the Mobility of Heavy Minerals on a Linear Sand Shoal |
author_facet |
Boon, John D. Berquist, Jr., C. R. |
author_sort |
Boon, John D. |
title |
Evaluation of Sediment Dynamics and the Mobility of Heavy Minerals on a Linear Sand Shoal |
title_short |
Evaluation of Sediment Dynamics and the Mobility of Heavy Minerals on a Linear Sand Shoal |
title_full |
Evaluation of Sediment Dynamics and the Mobility of Heavy Minerals on a Linear Sand Shoal |
title_fullStr |
Evaluation of Sediment Dynamics and the Mobility of Heavy Minerals on a Linear Sand Shoal |
title_full_unstemmed |
Evaluation of Sediment Dynamics and the Mobility of Heavy Minerals on a Linear Sand Shoal |
title_sort |
evaluation of sediment dynamics and the mobility of heavy minerals on a linear sand shoal |
publisher |
Journal of Coastal Research |
publishDate |
1991 |
url |
https://journals.flvc.org/jcr/article/view/78623 |
long_lat |
ENVELOPE(-62.520,-62.520,-62.981,-62.981) |
geographic |
Smith Island |
geographic_facet |
Smith Island |
genre |
Smith Island |
genre_facet |
Smith Island |
op_source |
Journal of Coastal Research; Vol 7 No 4 (1991): Journal of Coastal Research 0749-0208 |
op_relation |
https://journals.flvc.org/jcr/article/view/78623/76028 https://journals.flvc.org/jcr/article/view/78623 |
_version_ |
1766197449703030784 |