An Ancient Sea Once Separated the Pacific and Indian Oceans

Because of the West’s scarce labor situation, hop growers early on recognized the need to hire workers from all walks of life, including men and women, old and young, and across racial and ethnic lines. From the beginning, the three-week hop harvest was a multicultural affair that revealed the diversity of the West. The first half of this chapter explains the English origins of the American harvest season, including the actual demands and the festiveness of the harvest that many called a paid vacation. The second half of the chapter explains the opportunities and challenges that American Indian and East Asian agricultural workers faced while working in the Pacific Northwest hopyards during the late nineteenth and early twentieth centuries.

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Phase change in subducted lithosphere, impulse, and quantizing Earth surface deformations

Solid Earth ◽

10.5194/se-6-1075-2015 ◽

2015 ◽

Vol 6 (3) ◽

pp. 1075-1085

Author(s):

C. O. Bowin ◽

W. Yi ◽

R. D. Rosson ◽

S. T. Bolmer

Keyword(s):

Angular Momentum ◽

Phase Change ◽

Spherical Harmonic ◽

Plate Tectonics ◽

Phase Changes ◽

Metallic Nickel ◽

Spherical Harmonic Degree ◽

The Pacific ◽

Seamount Chain ◽

Harmonic Degree

Abstract. The new paradigm of plate tectonics began in 1960 with Harry H. Hess's 1960 realization that new ocean floor was being created today and is not everywhere of Precambrian age as previously thought. In the following decades an unprecedented coming together of bathymetric, topographic, magnetic, gravity, seismicity, seismic profiling data occurred, all supporting and building upon the concept of plate tectonics. Most investigators accepted the premise that there was no net torque amongst the plates. Bowin (2010) demonstrated that plates accelerated and decelerated at rates 10−8 times smaller than plate velocities, and that globally angular momentum is conserved by plate tectonic motions, but few appeared to note its existence. Here we first summarize how we separate where different mass sources may lie within the Earth and how we can estimate their mass. The Earth's greatest mass anomalies arise from topography of the boundary between the metallic nickel–iron core and the silicate mantle that dominate the Earth's spherical harmonic degree 2 and 3 potential field coefficients, and overwhelm all other internal mass anomalies. The mass anomalies due to phase changes in olivine and pyroxene in subducted lithosphere are hidden within the spherical harmonic degree 4–10 packet, and are an order of magnitude smaller than those from the core–mantle boundary. Then we explore the geometry of the Emperor and Hawaiian seamount chains and the 60° bend between them that aids in documenting the slow acceleration during both the Pacific Plate's northward motion that formed the Emperor seamount chain and its westward motion that formed the Hawaiian seamount chain, but it decelerated at the time of the bend (46 Myr). Although the 60° change in direction of the Pacific Plate at of the bend, there appears to have been nary a pause in a passive spreading history for the North Atlantic Plate, for example. This, too, supports phase change being the single driver for plate tectonics and conservation of angular momentum. Since mountain building we now know results from changes in momentum, we have calculated an experimental deformation index value (1–1000) based on a world topographic grid at 5 arcmin spacing and displayed those results for viewing.

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The Dellwood knolls and their role in triple junction tectonics off northern Vancouver Island

Canadian Journal of Earth Sciences ◽

10.1139/e80-057 ◽

1980 ◽

Vol 17 (5) ◽

pp. 577-593 ◽

Cited By ~ 25

Author(s):

R. P. Riddihough ◽

R. G. Currie ◽

R. D. Hyndman

Keyword(s):

Triple Junction ◽

Plate Tectonics ◽

Vancouver Island ◽

Ocean Bottom ◽

Ocean Bottom Seismometer ◽

Geological Evidence ◽

Topographic Features ◽

Narrow Valley ◽

The Pacific ◽

Geophysical Surveys

The Dellwood knolls are two small topographic features on the ocean floor off northern Vancouver Island. They have been proposed as a spreading centre connecting the Explorer ridge to the Queen Charlotte fault and the location of a triple junction between the Pacific, American, and Juan de Fuca plate systems.Detailed geophysical surveys and ocean-bottom seismometer deployments confirm that they are the site of active seismicity and recent volcanism. Modelling of the magnetic anomaly field shows that it is almost entirely produced by normally magnetized material, supporting geological evidence that the knolls are probably less than 1 Ma old. Although the two knolls are separated by a narrow valley with some downfaulting, they do not form a clearly linear spreading rift.Assessment of their role in the plate tectonics of the region suggests that spreading at the knolls was initiated around 1 Ma ago in crust now 4.5 Ma old as part of a complex, northwesterly ridge migration process at the northern end of the Explorer ridge. Reconstruction of this process, which involves asymmetric spreading and ridge jumping, provides an explanation for the creation of the associated Paul Revere and Winona ridges.

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Aeolian delivery to Ulleung Basin, Korea (Japan Sea), during development of the East Asian Monsoon through the last 12 Ma

Geological Magazine ◽

10.1017/s001675681900013x ◽

2019 ◽

Vol 157 (5) ◽

pp. 806-817 ◽

Cited By ~ 4

Author(s):

CH Anderson ◽

RW Murray ◽

AG Dunlea ◽

L Giosan ◽

CW Kinsley ◽

...

Keyword(s):

Asian Monsoon ◽

East Asian Monsoon ◽

East Asian ◽

Japan Sea ◽

Gobi Desert ◽

Taklimakan Desert ◽

The Tibetan Plateau ◽

Chinese Loess ◽

Source Regions ◽

The Pacific

AbstractWe reconstruct the provenance of aluminosilicate sediment deposited in Ulleung Basin, Japan Sea, over the last 12 Ma at Site U1430 drilled during Integrated Ocean Drilling Program Expedition 346. Using multivariate partitioning techniques (Q-mode factor analysis, multiple linear regressions) applied to the major, trace and rare earth element composition of the bulk sediment, we identify and quantify four aluminosilicate components (Taklimakan, Gobi, Chinese Loess and Korean Peninsula), and model their mass accumulation rates. Each of these end-members, or materials from these regions, were present in the top-performing models in all tests. Material from the Taklimakan Desert (50–60 % of aluminosilicate contribution) is the most abundant end-member through time, while Chinese Loess and Gobi Desert components increase in contribution and flux in the Plio-Pleistocene. A Korean Peninsula component is lowest in abundance when present, and its occurrence reflects the opening of the Tsushima Strait at c. 3 Ma. Variation in dust source regions appears to track step-wise Asian aridification influenced by Cenozoic global cooling and periods of uplift of the Tibetan Plateau. During early stages of the evolution of the East Asian Monsoon, the Taklimakan Desert was the major source of dust to the Pacific. Continued uplift of the Tibetan Plateau may have influenced the increase in aeolian supply from the Gobi Desert and Chinese Loess Plateau into the Pleistocene. Consistent with existing records from the Pacific Ocean, these observations of aeolian fluxes provide more detail and specificity regarding the evolution of different Asian source regions through the latest Cenozoic.

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Plate tectonics and planetary convection

Canadian Journal of Earth Sciences ◽

10.1139/e76-035 ◽

1976 ◽

Vol 13 (2) ◽

pp. 331-340 ◽

Cited By ~ 11

Author(s):

E. R. Kanasewich

Keyword(s):

Plate Tectonics ◽

Circular Plates ◽

Third Order ◽

African Plate ◽

Map Projections ◽

The North ◽

The Pacific ◽

Convective Pattern ◽

High Degree ◽

Great Circle Path

A series of azimuthal–equidistant map projections, centered on each of the plates of lithosphere, is used to demonstrate the high degree of ordering and symmetry in the major plates. The Pacific and African plates are approximately circular with a radius of 60°. The entire pattern is dominated by these two major plates, exactly antipodal to one another in the form of a dipole. Between the two 'circular' plates is a ring of elliptical plates with irregular boundaries but a organized geometric interrelationship. The average major and minor axes of the 'elliptical' plates, measured at the center of the earth, are 62° ± 6 °and 30° ± 5°, and the major axes are oriented at angles of 56° ± 3 °to lines joining the center of the African plate. The centers of the 'elliptical' plates are arranged within 6° ± 3 °of a great circle path through the North pole. This organized distribution of the major plates is most likely the result of convection currents involving the entire mantle, from the lithosphere to the core. To a first approximation, the convective pattern may be modelled by a superposition of third order spherical harmonics, P03, P13, and P23 in a pattern that regressed from a first spherical harmonic, −P01.

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