hello great and welcome to the seventh week of our discussion on plate tectonics now this week let's talk about the possible causes of blade movements and that includes the slab pool the rich push and the convection current at the end of the lesson you should be able to one describe convection current slab pull and reach push and number two explain what causes plate tectonics there are three forces that interact to create plate motion we have the convection current the slab pull theory and the ridge push now let's explain how each force cause plate movement let's start with lesson one convection current have you seen the apparatus where the luggage of the travelers are placed what do you call that device [Music] well that is a conveyor belt it is used to transfer heavy objects from one point to another one of the forces that drives plate movement works the same way the conveyor belt does and that is the conduction current now what is a convection current convection helps to move heat within the earth convection current refers to the continuous loop of sinking hot soft rocks caused by energy transfer in the asthenosphere convection creates loops of sinking and rising materials in the mantle this circular pattern is called convection cell this carries heat to the surface of the mantle much faster than hitting by conduction a convecting mantle is essential feature of plate tectonics convection in the mantle behaves the same way convection happens in a pot soap on a hot stove the material near the heat source becomes hot and expands making it less dense than the materials above buoyancy causes it to rise and cooler materials flow in from the sides then sinks at the bottom creating cycles of the sinking of cold and rising of warm water this convection circling within the mantle pushed the magma up forming new crusts and exerting a lateral force on the plate pushing it apart to create seafloor spreading when colder magma sinks during convection it pulls the surface together making the denser crust to subduct convection currents in the asthenosphere drive plate motion this theory of mental convection was proposed by arthur holmes according to him as the mantle became heated its density decreases and eventually rise and up when the material cooled it would sink exhibiting a circling behavior that would look like a conveyor belt the pressure heated magma broke the continents apart forcing the pieces to drift in opposite directions he also speculated that when the material sink continents will be brought back together again next is lesson 2 slab pool theory slab pool theory states that gravity and the plates themselves are the ones responsible for the plate tectonics through subduction process to clearly explain how slab pool works let's take a closer look at this simple demonstration in here the paper clip chain represents abducting tectonic plates now look closely as to what happens as the chain moves off the edge this simple demonstration explains that slab pull is a strong force that drives abducting tectonic plates the weight of the tectonic plate drives subduction in oceanic crust as the slob is pulled down into the mantle it drags the rest of the plate along with it causing tectonic plate movement a very dense slab will sink faster than a less dense slot because of the gravitational pull and it will exert greater force on the plate attached to it slab pool theory believes that mantle convection is not the cause of plate tectonics but rather it is a product of subduction now we have lesson 3 the ridge push ridge push or sliding plate force is a proposed driving force for blade motion in plate tectonics this occurs at mid ocean ridges as the result of the rigid lithosphere sliding down the hut raised asthenosphere below mid ocean ridges this gravity-driven mechanism results from the elevated position of the oceanic ridge which causes slabs of lithosphere to slide down the flux of the ridge this gravity sliding ridge push model was proposed by bot a geologist which states that the pushing on the plates is actually due to difference in gravitational potential energy between a plate at its spreading center and subduction zone the asthenosphere is a zone of soft plastic material which is less dense than the riding plate above it it acts as a massive shear zone for the overriding plate the plate will effectively slide down the slope of the asthenosphere due to the weight difference between the plate and its spreading center and the subduction zone since the plate gets thicker and denser the farther away from the spreading center the ridge push force will increase towards the subduction zone and that ends our lesson i hope you learned something today thank you for watching thank you