The author has identified the following significant results. Water truth observations, NASA aerial photography from an altitude of 60,000 feet, and ERTS-1 imagery made off the South Texas coast showed a mutually consistent pattern of water turbidity in the Gulf of Mexico. At the time of the measurements, plumes of turbid water were being formed by ebb-tidal discharges from the bays through tidal passes and were being diverted southward by the coastwise drift. The occurrence of the bands of turbid and relatively clear water suggests the existence of large scale helical circulation cells having axes almost parallel to shore with the outer turbid band probably being a zone of surface divergence and bottom water upwelling. The impingement of a turbid water mass onto the shoreline suggests that some, and perhaps most, of the suspended sediment in nearshore waters may not have been stirred up from the nearshore sea floor but may have traveled long distances in the water mass, perhaps even having remained in suspension from the time of its entry into the Gulf tidal inlets such as Aransas Pass.
ABSTRACT A flume study indicates that grainflow on slipfaces accounts for most cross-strata formed in unidirectional, shallow-water flows. The slipfaces studied were on small megaripples and delta-like steps (0.06-0.28 m high). During intermittent avalanching, at relatively low flow velocities, periods between avalanches were marked by grainfall onto the slipface, the intensity of which was greatest near the brink of the slipface and increased with current velocity. Nearly all grainfall deposits, however, were incorporated into subsequent grainflows. Grain flow cross-strata were made up of relatively distinct layers, at least near the base of the slipface. Continuous avalanching at high flow velocity was marked by a steady stream of grains forming more poorly defined cross-strata. Although the fundamental cause of grain flow is the gradual buildup of sediment on the upper slipface to the angle of initial yield, four other processes were recognized as promoting avalanching: 1) migration of superimposed bedforms to the brink, 2) generation of turbulent pulses upstream of the brink, 3) lee-eddy impingement on the lower slipface, and 4) extension of the lee eddy above the brink. The lee eddy proved very significant in slipface processes by redistributing grainfall sediments and both promoting and impeding grainflow. Regression analyses showed that the slipface advance per avalanche, Sa, is strongly correlated with the slipface height, H, expressed approximately by Sa = 0.060H. In addition, Sa is a direct function of the rate of slipface advance, Vb. The relationship among Sa, H, and Vb can be expressed as Sa/H = 0.0385[1 - 0.134 (min/cm) Vb]-1. Cross-strata dip angles between 28° and 34° show no systematic relation to H and Vb, but dip angles greater than 34° occurred only when both H and Vb were small, and dip angles less than 28° occurred only when both H and Vb were large.
Research Article| March 01, 1985 Storm-controlled oblique dunes of the Oregon coast: Discussion and reply: Reply RALPH E. HUNTER; RALPH E. HUNTER 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar BRUCE M. RICHMOND; BRUCE M. RICHMOND 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar TAU RHO ALPHA TAU RHO ALPHA 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Author and Article Information RALPH E. HUNTER 1U.S. Geological Survey, Menlo Park, California 94025 BRUCE M. RICHMOND 1U.S. Geological Survey, Menlo Park, California 94025 TAU RHO ALPHA 1U.S. Geological Survey, Menlo Park, California 94025 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1985) 96 (3): 410. https://doi.org/10.1130/0016-7606(1985)96<410:SODOTO>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation RALPH E. HUNTER, BRUCE M. RICHMOND, TAU RHO ALPHA; Storm-controlled oblique dunes of the Oregon coast: Discussion and reply: Reply. GSA Bulletin 1985;; 96 (3): 410. doi: https://doi.org/10.1130/0016-7606(1985)96<410:SODOTO>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract No Abstract Available. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Pleistocene Shoreline and Shelf Deposits at Fort Funston and Their Relations to Sea-Level Changes–Latest Cretaceous Eartly Tertiary Systems of the Northern Diablo Range, California Depositional Facies of Sedimentary Serpentinite: Selected Examples from the Coast Ranges, California
Abstract The outcrops described in this report are in the vicinity of Cape Sebastian, Curry County, Oregon (Fig. 1). The principal outcrop (Point A, Fig. 2) is in the Cape Sebastian Sandstone as restricted by Bourgeois (1980), at the south tip of the Cape Sebastian headland. Visitors can most easily reach the outcrop by a 1.2-mi-long (2 km) foot trail that leads down to the south tip of the headland from the parking area at the south end of the road through Cape Sebastian State Park (Point B, Fig. ). The entrance to the state park is on U.S. 101, 6 mi (10 km) south of Gold Beach, Oregon. The outcrops of the Hunters Cove Formation of Dott (1971) are located along the shore of Hunters Cove and can most easily be reached by walking northward along the beach from the parking area alongside U.S. 101 just south of the cove (Point C, Fig. ).
Research Article| December 01, 1983 Storm-controlled oblique dunes of the Oregon coast RALPH E. HUNTER; RALPH E. HUNTER 1U. S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar BRUCE M. RICHMOND; BRUCE M. RICHMOND 1U. S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar TAU RHO ALPHA TAU RHO ALPHA 1U. S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1983) 94 (12): 1450–1465. https://doi.org/10.1130/0016-7606(1983)94<1450:SODOTO>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation RALPH E. HUNTER, BRUCE M. RICHMOND, TAU RHO ALPHA; Storm-controlled oblique dunes of the Oregon coast. GSA Bulletin 1983;; 94 (12): 1450–1465. doi: https://doi.org/10.1130/0016-7606(1983)94<1450:SODOTO>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The large (mean height 25 m, spacing 300 m), relatively straight-crested dunes of the central Oregon coast migrate an average of 3.8 m/yr toward an azimuth of 26°. The dunes are transverse to the strong, south-southwesterly winter storm winds that are responsible for their basic form, orientation, and migration. The dry, moderate, north-northwesterly summer winds modify the dune form but not the dune trend.Comparison of the sand transport calculated from wind data and the transport measured from dune migration indicates that the actual transport by the wet southerly winds is only one-third of the amount calculated assuming dry conditions. The resultant (vector-mean) transport rate, as recalculated by comparison of the measured and initially calculated rates, is 34 m3/m·yr toward an azimuth of 45°. The dunes are thus oblique by our definition of an oblique dune (angle between dune trend and resultant transport direction between 15° and 75°).The internal structures of the dunes confirm northward migration during wet conditions. Evidence for deposition during wet conditions includes slipface deposits deformed mostly by sliding and various structures formed by the adhesion of sand grains to wet surfaces. Most summer deposits are not preserved, but those on the basal apron (the gentle north slope at the base of the winter slipface) have a high preservation potential. A depositional model based on dune climbing predicts that the preserved record of oblique dunes formed by an obtuse-bimodal wind regime would consist of tabular sets of crossbeds in which the dip angles increase upward from the base of each set. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
This report analyzes various depositional environments in three archaeologically significant areas of the Colorado River corridor in Grand Canyon. Archaeological features are built on and buried by fluvial, aeolian, and locally derived sediment, representing a complex interaction between geologic and cultural history. These analyses provide a basis for determining the potential influence of Glen Canyon Dam operations on selected archaeological sites and thus for guiding dam operations in order to facilitate preservation of cultural resources. This report presents initial results of a joint effort between geologists and archaeologists to evaluate the significance of various depositional processes and environments in the prehistoric formation and modern preservation of archaeological sites along the Colorado River corridor in Grand Canyon National Park. Stratigraphic investigations of the Palisades, Lower Comanche, and Arroyo Grande areas of Grand Canyon yield detailed information regarding the sedimentary history at these locations. Reconstruction of past depositional settings is critical to a thorough understanding of the geomorphic and stratigraphic evolution of these three archaeologically significant areas. This examination of past sedimentary environments allows the relative significance of fluvial, aeolian, debris-fan, and slope-wash sedimentary deposits to be identified at each site. In general the proportion of fluvial sediment (number and thickness of flood deposits) is shown to decrease away from the river, and locally derived sediment becomes more significant. Flood sequences often occur as 'couplets' that contain a fluvial deposit overlain by an interflood unit that reflects reworking of fluvial sediment at the land surface by wind and local runoff. Archaeological features are built on and buried by sediment of various depositional environments, implying a complex interaction between geologic and cultural history. Such field analysis, which combines geological and archaeological information and techniques, can provide a basis for future determination of the effects of Glen Canyon Dam operations on selected areas of the river corridor. This knowledge is essential to the development of preservation strategies for cultural resources in Grand Canyon.
