Why does crustal plate movement happen

Then the magma injects into the crack. This process repeats thousands of times, bring the magma towards the surface. A volcano will form if the magma reaches the surface. When magma does reach the surface it is then called lava. You will learn more about volcanoes in the following lessons. As the volcano erupts it may build a mountain. The lava along with ash and other pyroclastic material will continue to build the mountain higher with each eruption. This is a cross section of the Earth in the Southern Hemisphere.

The map shows a subduction zone that has created the Peru-Chile Trench at the western edge of South America.

This subduction zone has produced the Andes Mountains which run along the entire west coast of South America. It also shows you the Mid-Atlantic Ridge which is spreading the Atlantic Ocean making it wider and wider. The cross section shows two processes at work;. The pink lines on this map of the Pacific Ocean represent deep ocean trenches. These trenches are some of the lowest points on the crust of the Earth.

Marianas Trench north of New Guinea is the deepest point on the Earth's surface at 36, feet below sea level. Marianas Trench is 7, feet deeper than Mount Everest is high!!!! Trenches surround almost all of the Pacific Ocean. There are trenches wherever continental plates and oceanic plates collide.

The Java Trench in the Indian Ocean is the deepest point of that ocean at 24, feet below sea level. Write the answers to the following questions in complete sentences on a piece of paper. Use the page titles located directly under the questions to move your way through the lesson to locate the answers. When you finish the questions click on the Earth icon to return the program to the beginning.

Earthquakes and Faults Why do tectonic plates move? Brief history of the plate tectonics theory Before colliding with Asia, where was India? What is an earthquake? What is the highest magnitude an earthquake can reach? What are the biggest historical earthquakes? Why do earthquakes happen in clusters? Where are earthquakes expected in the world, especially in Asia? What is a supercontinent? Are all the faults on Earth active? How can human activities cause climate change?

Why do urbanisation and deforestation make flooding more likely? Earthquake Hazards Is Singapore threatened by earthquakes? Can we predict earthquakes? Why does a building on solid bedrock resist better to an earthquake than a building on sediment or reclaimed land? Why does a building with base isolation resist better to an earthquake than a building without base isolation?

Why does a building with full bracing resist better to an earthquake than a building with no bracing? Impacts of Volcanic Hazards What are the principal signals of a volcanic unrest? How can we forecast volcanic eruptions? Tsunamis Where is a tsunami most likely to happen? Can Singapore be affected by a tsunami? Can animals sense an impending tsunami? What should we do during a tsunami? Why do trees seem to resist more to tsunamis than houses?

Tremendous heat and pressure within the earth cause the hot magma to flow in convection currents. Based on evidence that has been found at plate boundaries, make some hypotheses about the movement of those plates.

The earth has changed in many ways since it first formed 4. They have gradually moved over the course of hundreds of millions of years—alternately combining into supercontinents and pulling apart in a process known as continental drift. The supercontinent of Pangaea formed as the landmasses gradually combined roughly between and mya. It is widely accepted by scientists today.

Earthquakes and volcanoes are the short-term results of this tectonic movement. The long-term result of plate tectonics is the movement of entire continents over millions of years Fig. The presence of the same type of fossils on continents that are now widely separated is evidence that continents have moved over geological history.

Evaluate and interpret several lines of evidence for continental drift over geological time scales. The shapes of the continents provide clues about the past movement of the continents. The edges of the continents on the map seem to fit together like a jigsaw puzzle. For example, on the west coast of Africa, there is an indentation into which the bulge along the east coast of South America fits.

The shapes of the continental shelves—the submerged landmass around continents—shows that the fit between continents is even more striking Fig. Some fossils provide evidence that continents were once located nearer to one another than they are today. Fossils of a marine reptile called Mesosaurus Fig. Another example is the fossil plant called Glossopteris, which is found in India, Australia, and Antarctica Fig.

The presence of identical fossils in continents that are now widely separated is one of the main pieces of evidence that led to the initial idea that the continents had moved over geological history. Evidence for continental drift is also found in the types of rocks on continents. There are belts of rock in Africa and South America that match when the ends of the continents are joined. Mountains of comparable age and structure are found in the northeastern part of North America Appalachian Mountains and across the British Isles into Norway Caledonian Mountains.

These landmasses can be reassembled so that the mountains form a continuous chain. Evidence from glacial striations in rocks, the deep grooves in the land left by the movement of glaciers, shows that mya there were large sheets of ice covering parts of South America, Africa, India, and Australia.

These striations indicate that the direction of glacial movement in Africa was toward the Atlantic ocean basin and in South America was from the Atlantic ocean basin. This evidence suggests that South America and Africa were once connected, and that glaciers moved across Africa and South America. There is no glacial evidence for continental movement in North America, because there was no ice covering the continent million years ago.

North America may have been nearer the equator where warm temperatures prevented ice sheet formation. Mid-ocean ridges or spreading centers are fault lines where two tectonic plates are moving away from each other.

Mid-ocean ridges are the largest continuous geological features on Earth. They are tens of thousands of kilometers long, running through and connecting most of the ocean basins. Oceanographic data reveal that seafloor spreading is slowly widening the Atlantic ocean basin, the Red Sea, and the Gulf of California Fig.

The gradual process of seafloor spreading slowly pushes tectonic plates apart while generating new rock from cooled magma. Ocean floor rocks close to a mid-ocean ridge are not only younger than distant rocks, they also display consistent bands of magnetism based on their age Fig.

Geomagnetic reversal allows scientists to study the movement of ocean floors over time. Paleomagnetism is the study of magnetism in ancient rocks.

In other words, the particles will point in the direction of the magnetic field present as the rock was cooling. Seafloor spreading gradually pushes tectonic plates apart at mid-ocean ridges. When this happens, the opposite edge of these plates push against other tectonic plates.

Subduction occurs when two tectonic plates meet and one moves underneath the other Fig.