Presentation on theme: "1.4 OUtline Plates converge or scrape past each other."— Presentation transcript:
1.4 OUtline Plates converge or scrape past each other
I. Tectonic plates push together at convergent boundaries Subduction: when one oceanic plate sinks beneath another Continental-continental collision Continental-continental collision: occurs when 2 plates carrying continental crust push together Both crusts are the same density, neither plate can sink beneath the other European Alps are found where the African & European plates are colliding Himalayas first formed when the Indian plate began colliding with the European Plate
B. Oceanic-Oceanic Subduction Oceanic-oceanic subduction: occurs when 1 plate with oceanic crust sinks under another plate with oceanic crust Two main features form at oceanic-oceanic subductions: Deep-Ocean Trenches – most are found in the Pacific Ocean; for example at the Mariana Trench the Pacific Plate is sinking under the Philippine Plate Island Arcs – there are chains of volcanic islands that form on the top plate, parallel to a deep ocean trench; as oceanic crust of the sinking plate melts, magma rises through the top plate Examples: Philippine Islands, Aleutian Islands
C. Oceanic-continental subduction Oceanic-continental subduction: occurs when ocean crust sinks under continental crust Deep-ocean trenches and coastal mountains form at these boundaries Deep-Ocean Trenches – some of the world’s youngest trenches are in the eastern Pacific Ocean; for example, the Pacific Plate is sinking under the North American Plate causing underwater earthquakes Coastal Mountains – continental crust buckles to form mountain ranges; parallel to a deep-ocean trench; some are active volcanoes
II. Tectonic plates scrape past each other at transform boundaries At a transform boundary, crust is neither formed nor destroyed As the plates move, their edges scrape & grind against each other Transform boundaries occur mostly on the sea floor near mid-ocean ridges They also occur on land; example: San Andreas Fault
III. The theory of plate tectonics helps geologists today Theory has helped to explain Earth’s past and to predict what might happen along plate boundaries in the future Theory of plate tectonics gives scientists a way to study & predict geologic events
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