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Outcrop 4:
Plate Tectonics
EARTH’S LANDSCAPE is determined by tectonic plates, pieces of the Earth’s crust and upper mantle that move according to continental drift. There are two types of plates: oceanic and continental. Oceanic plates are thinner and denser, and are primarily composed of mafic rocks like basalt. Continental plates are thicker and less dense, and are composed of more felsic rocks like granite.
Divergent Plate Boundary
Image source: domdomegg, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons https://commons.wikimedia.org/wiki/File:Oceanic-oceanic_constructive_plate_boundary.svg.
Boundaries where the plates interact can cause all kinds of geological landforms. At divergent boundaries, two plates pull apart. Magma from the mantle rises and forms new rocks. In the middle of the Atlantic Ocean, the Mid-Atlantic Ridge is a giant divergent boundary, where many different plates are pulling apart from each other.
Convergent Plate Boundary
Image source: domdomegg, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons https://commons.wikimedia.org/wiki/File:Oceanic-continental_destructive_plate_boundary.svg.
When an oceanic plate collides with a continental plate or another oceanic plate, subduction occurs, and the denser plate gets pulled underneath the other. This forms volcanic chains, like the Andes or the Aleutian Islands. When two continental plates collide, they form mountain ranges without volcanic activity, like the Himalayas.
At this location, you can see bedrock that was formed under the sea east of here and pushed up to form the Rensselaer Plateau.
Source: National Geographic Society. “Plate Tectonics.” National Geographic Society, 5 Mar. 2013, www.nationalgeographic.org/media/plate-tectonics/.
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