outer, solid portion of the Earth. He proposed that volcanic island chains, like the Hawaiian Islands, are created by fixed “hot spots” in the mantle. Incorporating the much older idea of continental drift, as well as the concept of seafloor spreading, the theory of plate tectonics has provided an overarching framework in which to describe the past geography of continents and oceans, the processes controlling creation and destruction of landforms, and the evolution of Earth’s crust, atmosphere, biosphere, hydrosphere, and climates. Any interactives on this page can only be played while you are visiting our website. Fold mountain chains are also found along the edge of the continental plate, as the subduction of the oceanic plate crumples up the continental plate. The structure of the Earth Cross section of the earth. She or he will best know the preferred format. Tectonic activity accounts for some of the most dramatic and large-scale landforms on Planet Earth. Developed from the 1950s through the 1970s, plate tectonics is the modern version of continental drift, a theory first proposed by scientist Alfred Wegener in 1912. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Copyright 2020 Leaf Group Ltd. / Leaf Group Media, All Rights Reserved. At As they move past each other, friction builds up and energy is released as an earthquake. The Earth is made up of four distinct layers: The inner core is in the centre and is the hottest part of the Earth. A curved chain of these volcanoes, known as an island arc, usually occurs in these cases. Such landforms are formed due to the ejection of sand from a central point onto a surface. Where a constructive margin occurs on land it creates a rift valley. The crust is pushed/pulled down at various angles. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They are usually of low magnitude. The subduction process that occurs when an oceanic plate converges with another oceanic plate can lead to volcanoes being formed paralleling the trench. This margin is associated with plates that slide alongside each other. Gina Borgia, National Geographic Society This margin can be found on land as well as in the centre of oceans. Earthquakes at this margin can be of high magnitude due to the pressure that is built up between the two plates. Wegener didn't have an explanation for how continents could move around the planet, but researchers do now. When two continental plates converge, neither plate can be subducted due to the plates having a similar density. The volcanoes are very explosive, because the resulting magma from subduction is silica-rich andesitic magma with high levels of gas present and therefore very explosive. Fold mountains usually form along the edges of continents, because these margins tend to accumulate the greatest sedimentary deposits. Old fold mountains, which typically formed 250 million years ago or more, mark formerly active plate boundaries and tend to be significantly lower and more eroded; examples include the Appalachians and Urals. Today, the theory is almost universally accepted. three types of plate margin: constructive, destructive and conservative. West Yorkshire, All rights reserved. All students preparing for mock exams, other assessments and the summer exams for Edexcel A-Level Geography. The processes occurring here are that the plates are being pulled apart in a pattern of divergence. Washington, DC 20036, National Geographic Society is a 501 (c)(3) organization. At divergent boundaries, plates move away from each other, creating a new crust as magma is pushed up from the mantle. U.S Geological Survey: Understanding Plate Motions. massive slab of solid rock made up of Earth's lithosphere (crust and upper mantle). Today, these theories serve as the foundation upon which we understand the geologic processes that shape the Earth. Ocean trenches form at two kinds of convergent plate boundaries: where a continental and oceanic plate converge, or where two oceanic plates converge. They can either slide in the same direction but at different speeds or in opposite directions. Much cheaper & more effective than TES or the Guardian. Tectonic Landforms There are two basic forms of tectonic activity: compression and extension. Due to the lack of subduction there is no volcanic activity, but earthquakes are violent due to the constant friction that builds up between the two plates trying to override each other. The theory, which solidified in the 1960s, transformed the earth sciences by explaining many phenomena, including mountain building events, volcanoes, and earthquakes.In plate tectonics, Earth’s outermost layer, or lithosphere—made up of the crust and upper mantle—is broken into large rocky plates. This molten material will then force its way back up to the surface where it will emerge through the crust as an explosive composite cone volcano. To support his theory, Wegener pointed to matching rock formations and similar fossils in Brazil and West Africa. Fold mountains 100 million years old or less, such as the Himalayas, are known as young fold mountains and account for the planet’s highest, most impressive ranges. If no button appears, you cannot download or save the media.