What type of plate movement is this weirdly ominous video describing? It is describing plates moving AWAY from each other. These are known as DIVERGENT or CONSTRUCTIVE boundaries Sketch meand label me!
Stuff to know about divergent plates:•As plates diverge, they can form Grabens if they are onContinental crust. This means that some of the land drops asthe crust of the earth stretches.
Or they can form HALF-GRABENSThese features build MOUNTAINS.
Which type of Graben is this? This type covers an area THIS big in the USA (known as Basin and Range)
If you think logically, these aren’t TOO tricky!There are two types of crust, so there are 3 types ofconvergent boundary:•Oceanic – Continental As we go through the next few slides, write•Continental – Continental down an example of each type/•Oceanic - Oceanic combination.
Ocean-Continent Collision:Underneath the oceanwater there are a numberof long, narrow, curvingtrenches thousands ofkilometers long and 8 to 10km deep cutting into theocean floor. Trenches arethe deepest parts of theocean floor and are createdby subduction.
Andes MountainsOcean-Continent Collision:Off the coast of South America, the oceanic Nazca Plate ispushing into and being subducted under the continental part ofthe South American Plate. At the same time, the SouthAmerican Plate is being lifted up, creating the Andes Mountains.Strong, destructive earthquakes and the rapid uplift ofmountain ranges are common in this region. Such earthquakeshave been known to jolt the land up several meters.
Ocean-Ocean Collision:When two oceanic plate collide, itcan result in the formation ofvolcanoes, too. One oceanic platesinks beneath the other, and overmillions of years, the erupted lavaand volcanic debris pile up on theocean floor. Finally, a volcano risesabove sea level to form an islandvolcano. Such volcanoes are typicallystrung out in chains called islandarcs.This is how theAleutian Islandshave formed andwhy theyexperiencenumerous strongearthquakes.
Continent-Continent Collision:The Himalayan Mountains werecreated when two continentalplates met head-on,and neitherwas subducted. Continentalrocks are relatively lightand, like two colliding icebergs,resist downwardmotion. Instead,the crust buckledand was pushedupward andsideways. Viola!Mountains!
Continent-Continent Collision:India collided into Asia 50 millionyears ago, causing the EurasianPlate to crumple up and overridethe Indian Plate.After the collision, the slowcontinuous convergence of the twoplates over millions of years pushedup the Himalayas and the TibetanPlateau to their present heights.The Himalayas, towering as high as8,854 m above sea level, are thehighest continental mountains inthe world.
Most transform boundariesare found on the oceanfloor. A few occur onland, an example is the SanAndreas fault in California.Transform boundaries arethe result of two platessliding past each other.
The San Andreas Fault• Stretches about 1,300 km long and in someplaces tens of kilometers wide.• Slices through two thirds of the length ofCalifornia.• The Pacific Plate has been grindinghorizontally past the North American Platefor 10 million years, at an average rate ofabout 5 cm/yr.• Land on the west side of thefault (on the Pacific Plate) ismoving in a northwesterlydirection RELATIVE to the landon the east side of the faultzone (on the North AmericanPlate).
Sometimes a plate boundary can contain more than one typeof movement. Sounds weird? These plates are divergent, but what is happening at this little bit here?
Shade the cards that are about the world pattern of earthquakes and volcanoes in red. Then shade those that are about tectonic plates and active zones in blue.Choose a red card. Find a blue card that can be linked with it. Keepgoing until you have matched all of the statements
Check your answersActive zones are found around the edges of many of the world’s tectonic plates.Earthquakes and volcanoes occur in linear patterns in some parts of the world.In places, the North American and Pacific Plates are moving past each other.Volcanoes and earthquakes occur along the west coast of North America.Many volcanoes and earthquakes are clustered together on islands and continents around the edge of thePacific Ocean.Around the edge of the Pacific plate is an active zone called the ‘ring of fire’.The North American and Eurasian plates are moving away from one another.Volcanoes can be found in a line running north to south down the middle of the Atlantic Ocean.Australia is found in the middle of the Indo-Australian plate.Volcanoes and earthquakes are not found in Australia.The east coasts of North and South America are not close to active zones.There are no volcanoes or earthquakes on the east coast of North or South America.There is an active zone where the Nazca and South American plates move together.A belt of volcanoes and earthquakes is located along the west coast of South America.The Eurasian and Indo-Australian plates are moving towards each other.Many earthquakes happen in the Himalayan mountains to the north of India.
Look at the map below. It shows recent volcanoes andearthquakes. Volcanoes are shown in blue, earthquakes inred. Are they scattered randomly, or is there some kind ofpattern? If so, can you explain why?
Copy the table below and use the information from the lessons to:
HOMEWORK By this time next week I’d like you ALL to have pictures of the three different types of convergentboundary to stick into your books, plus a sketch of a transform boundary. DRAWN. By your own fair hands.(Remember: oceanic-continental, oceanic-oceanic, and continental- continental)The library has books, or if you don’t have access to internet at home you are welcome to attend the Humanities Achievement session onThursday in H12 at 3pm. There are netbooks available. There are also textbooks in the cupboard in H12, or the electronic copy on Fronter.