density - driven is the primarily driving force for deep currents.
density - driven is the primarily driving force for deep currents.
in one word what is the primarily driving force for deep currents?
density - driven
it has generally been accepted that tectonic plates are able to move because of the relative density of oceanic lithosphere and the relative weakness of the asthenosphere. dissipation of heat from the mantle is acknowledged to be the original source of the energy required to drive plate tectonics through convection or large scale upwelling and doming. the current view, though still a matter of some debate, asserts that as a consequence, a powerful source of plate motion is generated due to the excess density of the oceanic lithosphere sinking in subduction zones. when the new crust forms at mid-ocean ridges, this oceanic lithosphere is initially less dense than the underlying asthenosphere, but it becomes denser with age as it conductively cools and thickens. the greater density of old lithosphere relative to the underlying asthenosphere allows it to sink into the deep mantle at subduction zones, providing most of the driving force for plate movement. the weakness of the asthenosphere allows the tectonic plates to move easily towards a subduction zone. although subduction is thought to be the strongest force driving plate motions, it cannot be the only force since there are plates such as the north american plate which are moving, yet are nowhere being subducted. the same is true for the enormous eurasian plate. the sources of plate motion are a matter of intensive research and discussion among scientists. one of the main points is that the kinematic pattern of the movement itself should be separated clearly from the possible geodynamic mechanism that is invoked as the driving force of the observed movement, as some patterns may be explained by more than one mechanism. in short, the driving forces advocated at the moment can be divided into three categories based on the relationship to the movement: mantle dynamics related, gravity related (main driving force accepted nowadays), and earth rotation related.
plate tectonics
cook began racing in boston. he moved to the western united states in the early 1940s. he had a successful short track racing career in southern california, primarily driving for owner floyd johnson. cook made 39 starts in the nextel cup series from 1954 through 1970. most of cook's starts were in west coast races during the time the races counted for both nextel cup and pclm points, though he did compete in the inaugural world 600 at charlotte motor speedway and in the 1964 daytona 500 and richmond 250. after this foray, his nextel cup series starts were limited to an annual start in the motor trend 500, then held each january at riverside international raceway. he did compete regularly in the pclm series, primarily driving for owners floyd johnson or cos cancilla, finishing in the top ten in points eight times between 1956 and 1969, with a best points finish of 3rd on three occasions (1963, 1967 and 1968). he had five career victories in the pclm series, the last one coming at tri-cities speedway in west richland, washington in july 1969.
jim cook