PTNR - Earth's Dynamic Surface (Lesson)
Earth's Dynamic Surface
Minerals, like every natural resource, are not evenly distributed on the Earth's surface. Many reasons account for this disparity, but a significant reason is the constant movement of the tectonic plates that make up the surface of the planet.
How Plates Move
Convection within the Earth's mantle causes the plates to move. Mantle material is heated above the core. The hot mantle rises up toward the surface (see image below). As the mantle rises, it cools. At the surface, the material moves horizontally away from a mid-ocean ridge crest. The material continues to cool. It sinks back down into the mantle at a deep-sea trench. The material sinks back down to the core. It moves horizontally again, completing a convection cell.
Plates move for two reasons. The upwelling mantle at the mid-ocean ridge pushes plates outward. Cold lithosphere sinking into the mantle at a subduction zone pulls the rest of the plate down with it.
Seafloor spreading takes place as plates move apart from each other at a mid-ocean ridge. Mantle convection drives seafloor spreading.
Click here to watch this PBS Science Odyssey video to learn more.
Links to an external site.
Volcanoes
A volcano is a vent from which the material from a magma chamber escapes. This may include lava, rock fragments, ash, and gases. Volcanic eruptions can come from many types of structures. Most people think of volcanoes as large, peaky cones. But volcanoes can be large and broad, or tiny little cones. Volcanic eruptions can come from fractured domes, a vent in the ground, or a giant hole in the ground.
Where They Are
Volcanoes are a vibrant manifestation of plate tectonics processes. Volcanoes are common along convergent and divergent plate boundaries. They are also found within lithospheric plates at hotspots. Wherever mantle is able to melt, volcanoes are likely to be the result.
Earthquake!
An earthquake is sudden ground movement. This movement is caused by the sudden release of the energy stored in rocks. An earthquake happens when so much stress builds up in the rocks that the rocks break. An earthquake's energy is transmitted by seismic waves.
Causes of Earthquakes
Almost all earthquakes occur at plate boundaries. All types of plate boundaries have earthquakes. Convection within the Earth causes the plates to move. As the plates move, stresses build. When the stresses build too much, the rocks break. The break releases the energy that was stored in the rocks. The sudden release of energy is an earthquake. During an earthquake, the rocks usually move several centimeters. Rarely, they may move as much as a few meters.
Convergent Plate Boundaries
Earthquakes at convergent plate boundaries mark the location of the subducting lithosphere. The motion of the lithosphere as it plunges through the mantle causes the quakes. At greater depths, the plate heats up enough to deform plastically.
A cross-section of earthquake epicenters. The depth outlines the subducting plate. There are shallow, intermediate, and deep earthquakes.
Ocean-Ocean: Japan
Earthquakes in Japan are caused by ocean-ocean convergence. The Philippine Plate and the Pacific Plate are subducting beneath oceanic crust on the North American or Eurasian plates. This complex plate tectonics situation creates a chain of volcanoes, the Japanese islands, and as many as 1,500 earthquakes annually.
Self Assessment: Plate Tectonics Lab Activity
Click here to look over this map showing Earth's tectonic plates. Links to an external site.
RESOURCES IN THIS MODULE ARE OPEN EDUCATIONAL RESOURCES (OER) OR CREATED BY GAVS UNLESS OTHERWISE NOTED. SOME IMAGES USED UNDER SUBSCRIPTION.