When the continents and plates move it's called continental drift. Think of the molten rock in the asthenosphere, not as rock, but as a liquid. It has currents and it flows just like any other liquid. When the floating plates spread apart, it's called a spreading center. When they are moving together, it's called a subduction zone. When they are forced together, it is called a zone of convergence.
One of the plates usually moves under the other in a zone of convergence. As the plate moves down into the asthenosphere it begins to melt. The place where they meet has a crack or a trench. Some of the deepest parts of the oceans are these trenches. Scientific Evidence How do we back up these ideas? The team set up Coke can-sized seismometers strung like beads along 85 kilometres.
Then from multiple boreholes they detonated half a tonne of TNT in each. The New Zealand team suggests the jelly rock gains its consistency from a higher concentration of water or magma than is present in the lithosphere above it.
But it would not have to be too high. While the lithosphere contains 0. The finding of the jelly channel might also help resolve a year debate about whether the plates move as a result of being pushed or pulled. An early idea was that magma being extruded from the mid-oceanic ridges was pushing the plates apart. Another pushing force might come from slowly creeping convection currents beneath the plates that act like rollers beneath a conveyer belt.
On the other hand the major force might be a pulling one. As one edge of an oceanic plate dives back into the mantle beneath — as the Pacific one is doing — it pulls the rest of the slab after it. Today, these theories serve as the foundation upon which we understand the geologic processes that shape the Earth.
Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Image San Andreas Fault Tectonic plate boundaries, like the San Andreas Fault pictured here, can be the sites of mountain-building events, volcanoes, or valley or rift creation.
Photograph by Georg Gerster. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. Also called the geosphere. Media Credits The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. Media If a media asset is downloadable, a download button appears in the corner of the media viewer. Text Text on this page is printable and can be used according to our Terms of Service.
Interactives Any interactives on this page can only be played while you are visiting our website. Related Resources. Continental Drift versus Plate Tectonics.
Find about the potential geologic threats to your home in case of a major earthquake. The violent shaking from earthquakes can:. If your home was built before , you may have structural risks that could affect your safety. Follow the Seven Steps to Earthquake Safety. Decrease your risk of damage and injury from a major earthquake by identifying possible home hazards:. Do you know about the primary geologic hazards where you live? Other factors include:. If your home was built before , it may also be vulnerable to serious structural damage.
With safety planning, reinforcing the structure of your home, securing your personal property, and buying earthquake insurance , you stand a better chance of riding out the next California earthquake. Learn how to prepare your home. Phone:
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