![]() The Appalachians stretch from the province of Newfoundland, in southeastern Canada, through the southern state of Alabama in the United States. The Appalachians are just one remnant of the Central Pangean Mountains. As tectonic activity ripped apart the ancient supercontinent Pangea, the African, Eurasian, and North American plates drifted apart. Plate tectonics created this ancient mountain range, then called the Central Pangean Mountains. The crust that is now the Appalachians began folding over 300 million years ago, when the North American and African continental plates collided. Today, some of the highest peaks of the Appalachians are less than a third of the height of Everest. ![]() Millions of years ago, the Appalachians were taller than the Himalayas! Millions of years of erosion, however, have taken their toll. The Appalachians, stretching along North America’s east coast, are generally low-lying, gentle slopes. Not all fold mountains are soaring peaks. ![]() Alpine geology includes sedimentary and metamorphic rock, as well as igneous rocks that once were part of the ocean floor and were later uplifted in the process of folding. The J-shaped Adriatic microplate is a remnant of the African plate to the south, and today it carries the eastern Italian Peninsula as well as the entire Adriatic Sea. Here, the tiny Adriatic microplate is colliding with the much larger Eurasian plate to the north. The Alps stretch across Italy, Slovenia, Austria, Germany, Switzerland, Lichtenstein, Monaco, and France. The Alps roughly mark the top of the “boot” of the Italian Peninsula. The sedimentary and metamorphic rocks of the Andes are dotted by active and dormant volcanoes. The Andes are mostly being folded and uplifted from the thicker, less-dense rocks of the South American plate. Here, the dense oceanic crust of the Nazca plate is subducting beneath the less-dense continental crust of the South American plate. They stretch along the entire west coast of South America, from Colombia in the north and through Ecuador, Peru, Bolivia, Chile, and Argentina to the south. The Andes are the world’s longest mountain chain. Dikes of igneous rock also intrude throughout the rock formations of the Himalayas. Metamorphic rocks of the region include schist and gneiss. The sedimentary rocks of the Himalayas include shale and limestone. Here, the Indian plate is colliding northward with the Eurasian plate. The crust beneath the Himalaya, the most towering mountain range on Earth, is still the process of being compressed. The Himalayas stretch through the borders of China, Bhutan, Nepal, India, and Pakistan. The rugged, soaring heights of the Himalayas, Andes, and Alps are all active fold mountains. Many fold mountains are also formed where an underlying layer of ductile minerals, such as salt, is present.įold mountains are the most common type of mountain in the world. Most fold mountains are composed primarily of sedimentary rock and metamorphic rock formed under high pressure and relatively low temperatures. This can make them more susceptible to folding and warping. Rocks on the edge of continental crust are often weaker and less stable than rocks found in the continental interior. For this reason, most fold mountains are found on the edge or former edge of continental plate boundaries. Convergent plate boundaries are sites of collisions, where tectonic plates crash into each other. Compression describes a set of stresses directed at one point in a rock or rock formation.Īt a compression zone, tectonic activity forces crustal compression at the leading edge of the crust formation. They are created at convergent plate boundaries, sometimes called continental collision zones or compression zones. In the creation of fold mountains, Earth’s crust itself is warped into folded forms.įold mountains are often associated with continental crust. The huge difference between the rock folds and cloth folds is that in the tabletop experiment, the table itself does not fold. “Nappe” is French for “tablecloth” and it is believed the formations were named after the tabletop experiment. Some of the key structures in fold mountains are nappes. Nappes are common, dramatic folded rocks or rock formations. The vocabulary of fold mountains owes something to this simple tablecloth experiment. Now push the edge of the tablecloth or rug-wrinkles will develop and fold on top of each other. ![]() Cover a table with a tablecloth, or place a rug flat on the floor. An orogenic event takes millions of years to create a fold mountain, but you can mimic it in seconds. At these colliding, compressing boundaries, rocks and debris are warped and folded into rocky outcrops, hills, mountains, and entire mountain ranges.įold mountains are created through a process called orogeny. Fold mountains are created where two or more of Earth’s tectonic plates are pushed together. ![]()
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