Forcing of large-scale cycles of coastal change at the entrance to Willapa Bay, Washington     

Robert A. Morton  H. Edward Clifton  Russell L. Peterson 《Marine Geology》2007,246(1):24-41

Anomalous morphological features within large estuaries may be: (1) recorders of external forces that periodically overwhelm the normal morphodynamic responses to estuarine energy fluxes, and (2) possible predictors of cycles of future coastal change. At the entrance to Willapa Bay, Washington, chronic beach erosion and frequent coastal flooding are related to the historical northward channel migration that destroyed the protective sand spits of Cape Shoalwater. Northward channel migration since the late 1800s conforms to the long-term net sediment transport direction. What requires explanation is periodic southward relocation of the trunk channel by as much as 5 km, and attendant construction of moderately large sand spits on the north side of the bay such as Kindred Island, Tokeland Peninsula, and Cape Shoalwater.Both autocyclic and allocyclic processes may have been responsible for trunk channel realignment and associated spit deposition. Channel recycling may occur when the main channel becomes overextended to the north and the tidal flow is inefficient because of its decreased gradient and increased susceptibility to shoaling by the growth and migration of tidal sand ridges. Under those conditions trunk channel relocation would be facilitated by increased wave heights and water levels of El Niño winter storms. However, co-seismic subsidence is the most likely mechanism for abruptly increasing sand supply and longshore transport that would favor discrete periods of channel relocation and spit deposition. Unless external forcing changes sand supply and predominant sediment transport directions in the future, the relative rise in sea level, frequent winter storms, and local deficit in the sand budget assure that beach erosion will continue at the mouth of this large estuary.  相似文献   

Variations in solar emission at 3.3 mm wavelength and their relation to flares     

Earle B. Mayfield  John Higman  Clifton Samson 《Solar physics》1970,13(2):372-388

An investigation of variations in solar radio emission at 3.3 mm wavelength as observed with an antenna of half-power beamwidth of 2.8 arc-min indicates the existence of hot stable regions associated with sunspots. These regions are enhanced from 240 K (4%) to more than 3200K (50%) over the quiet center of the disk temperature of 6 600K. Positions of maximum enhancement occur near the neutral lines of primarily bipolar magnetic fields as determined from magnetograms of the longitudinal component of the field. Fourteen of the 113 regions studied were observed to produce flares reported as importance class 2 or greater during the period from mid-February through mid-August 1967. Eleven of the regions which flared had an enhancement of 8.5% or greater and a temperature gradient of 0.5%/deg or greater.  相似文献   

REGIONAL SHIFTS IN CHINA'S INDUSTRIAL OUTPUT     

Clifton W. Pannell 《The Professional geographer》1988,40(1):19-32

China's industrial output is large and has grown rapidly since 1950. The communist government which took power in 1949 sought to decentralize industry to the interior. Analysis of gross provincial industrial output data based on information statistics indicated a period of increasing industrial concentration from 1952–1957. Thereafter gross industrial output decentralized. Specific industries, however, displayed different spatial patterns. Steel, for example, has become more concentrated, whereas chemical fertilizers and cement showed remarkably dispersed patterns. The patterns reflect a dual structure of industrial production comprised of large, modern, efficient plants and small, less efficient plants producing for local consumption.  相似文献   

Influence of Dissolved Oxygen Convection on Well Sampling     

Don A. Vroblesky  Clifton C. Casey  Mark A. Lowery 《Ground Water Monitoring & Remediation》2007,27(3):49-58

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Heavy-mineral distribution in modern and ancient bay deposits,Willapa Bay,Washington, U.S.A.     

Gretchen Luepke  H. Edward Clifton 《Sedimentary Geology》1983,35(4):233-247

Analysis of heavy-mineral distribution in modern sediments of Willapa Bay, Washington, indicates a dominance of two mineralogic assemblages, one with approximately equivalent amounts of hornblende, orthopyroxene and clinopyroxene, the other dominated by clinopyroxene. The hornblende-orthopyroxene-clinopyroxene suite is derived from the Columbia River, which discharges into the ocean a short distance south of the bay. The clinopyroxene suite is restricted in modern sediments to sands in rivers flowing into the bay from the east. The heavy-mineral distributions suggest that sand discharged from the Columbia River, borne north by longshore transport, and carried into the bay by tidal currents accounts for most of the sand within the interior of Willapa Bay.Three heavy-mineral assemblages are present in the surrounding Pleistocene deposits; two of these are identical to the modern assemblages described above. These heavy-mineral assemblages reflect the relative influence of tidal and fluvial processes on the Late Pleistocene deposits; their relative influences are consistent with those inferred on the basis of sedimentary structures and stratigraphic relations in about two-thirds of the samples examined. The anomalies can be explained by recycling of sand from older deposits. The persistence of the two heavy-mineral assemblages suggests that the pattern of estuarine sedimentation in Late Pleistocene deposits closely resembled that of the modern bay.The third heavy-mineral suite, dominated by epidote, occurs in a few older Pleistocene units. On the north side of the bay, the association of this suite with southwest-directed foresets in crossbedded gravel indicates derivation from the northeast, perhaps from an area of glacial outwash. The presence of this suite in ancient estuarine sands exposed on the east side of the bay suggests that input from this northerly source may have intermittently dominated bay deposition in the past.  相似文献