What is plate tectonics? The Theory of Plate Tectonics explains how and why crustal plates drift around on the surface of the Earth. Tectonic plates have three major boundaries. Divergent boundaries are areas on the Earth’s surface where two plates are moving apart. Convergent boundaries are areas where tectonics plates collide. Transform boundaries are places where two tectonic plates move horizontally past each other without increasing or decreasing in size.
San Juan Batista Mission
What is a divergent boundary? Divergent boundaries usually form deep in the ocean where two ocean plates are moving apart. In the upper mantle molten rock collects in magma chambers at the edges of ocean plates.
Pressure from expanding gases in the molten rock (magma) force it upward toward a crack on the seafloor. The molten lava flows onto the seafloor forming pillow basalt. When the pillow basalt cools it forms new seafloor between the divergent plates. This explains what is plate tectonics theory of divergent boundaries.
The continents on each side of the Atlantic Ocean have been drifting apart forming new seafloor in the Atlantic Ocean basin for millions of years. The rate the African Plate and the South American Plate are moving apart is 2.3 cm each year.
Our Earthquakes textbook contains sixteen
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Chapters include information about P waves, S waves, three major earthquake scales, and different types of faults. Myrna
Ascension Island has been a nesting area for green turtles for thousands of years. Green turtles lay their eggs on the same beach where they were born. Every 4 or 5 years the female turtles return to the island to lay their eggs.
When the turtles started laying their eggs on Ascension Island the trip to the island was much shorter. Each year the trip increases 2.3 cm. Recently a female turtle that laid her eggs on Ascension Island was tracked returning to her feeding grounds on the coast of Brazil. Her return trip was 2983 km long. It takes between five and six weeks for the turtles to swim that distance. This supports the question, what is plate tectonics theory of divergent boundaries.
Subduction zones form a horseshoe shaped ring around the Pacific Ocean. Each subduction zone is a convergent boundary. When a continental plate converges with an ocean plate the ocean plate always subducts beneath the continental plate.
Basalt rocks contain iron-rich minerals that are denser and heavier than continent rocks. The difference in weight causes the ocean plate to subduct beneath the continental plate. The ocean plate melts in the upper mantle and it is recycled into new rocks. This clarifies what is plate tectonics theory of convergent boundaries.
What is a transform fault? Transform faults are areas where two plates slip past each other. Because we live on a round planet you will see on maps where the lines of divergent boundaries zig-zag on the ocean floor. The short distance between the spreading ridges are transform faults.
The San Andreas Fault runs through California. It is more than 1200 km long. The fault separates the North American Plate and the Pacific Plate. My husband is standing on the Pacific Plate and looking across the San Andreas Fault to the North American Plate. The picture was taken at San Juan Batista Mission. The Mission has been damaged several times by earthquakes. Recent research indicates the epicenter of the 1906 San Francisco earthquake was near the town of San Juan Batista.
The Pacific Plate moves in a north easterly direction relative to the North American Plate. The San Andreas fault is also called a right-lateral strike slip fault. If you look across the fault it looks like the land has moved to the right.This describes what is plate tectonics theory of right lateral strike-slip faults.
Plate Movements Moving plates on our planet converge, separate and slide past each other.
Nazca Plate This plate converges with the Pacific Plate producing very large earthquakes off the coast of Chile.
Thrust Faults These faults occur where large blocks of land can be forced over the top of another block of land at a low angle.
Divergent Boundary These boundaries form the global mid-ocean ridge system which is the largest mountain chain on Earth.
Crustal Plates There are large and small plates that cover the Earth. Subduction zones form where these plates are recycled.
Mid Ocean Ridge The global mid-ocean-ridge system is the longest chain of mountains on Earth and was not discovered until the 20th Century.
Earthquake Epicenter The epicenter of an earthquake is a point on the Earth's surface, not where the earthquake originates.
Caribbean Plate This plate is small but very complex. It has a subduction zone, transform fault, and triple junction.
What is an Earthquake Find out what causes the Earth to shake, rattle and roll during an earthquake.
Convergent Boundary There are two types of boundaries where plates converge. They produce great mountain ranges and large earthquakes.
Transform Boundary These boundaries are found all around our ocean floors where oceanic plates are separating.
Pacific Plate The Pacific Plate is the largest plate on Earth. Great earthquakes and towering volcanoes surround the plate along the Pacific Ring of Fire.
Ocean Trenches Find out how plates diving beneath other crustal plates create trenches on the ocean floor that are deepest points on Earth.
S Waves Find out about S waves and how they are produced and travel through the Earth.
The Theory of Plate Tectonics Find out lots of fascinating facts and interesting trivia on plate tectonics.
Kids Fun Science The links on our home page include information about volcanoes, science activities, plate tectonics, the rock cycle and much more
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