A mountain range is a series or chain of mountains that are close together. The world's tallest mountain ranges form when pieces of Earth's crust—called plates—smash against each other in a process called plate tectonics , and buckle up like the hood of a car in a head-on collision. The Himalaya in Asia formed from one such massive wreck that started about 55 million years ago. The summit of Mount Everest, at 29, feet 8, meters , is the highest point on Earth.
The tallest mountain measured from top to bottom is Mauna Kea, an inactive volcano on the island of Hawaii in the Pacific Ocean. Measured from the base, Mauna Kea stands 33, feet 10, meters tall, though it only rises 13, feet 4, meters above the sea. Volcanic mountains form when molten rock from deep inside the Earth erupts through the crust and piles up on itself.
The islands of Hawaii were formed by undersea volcanoes, and the islands seen above water today are the remaining volcano tops. Well-known volcanoes on land include Mount St. Sometimes volcanic eruptions break down mountains instead of building them up, like the eruption that blew the top off Mount St. When magma pushes the crust up but hardens before erupting onto the surface, it forms so-called dome mountains. Wind and rain pummel the domes, sculpting peaks and valleys.
Plateau mountains are similar to dome mountains, but form as colliding tectonic plates push up the land without folding or faulting. They are then shaped by weathering and erosion. Other types of mountains form when stresses within and between the tectonic plates lead to cracking and faulting of the Earth's surface, which forces blocks of rock up and down.
Mountains often serve as geographic features that define natural borders of countries. Their height can influence weather patterns, stalling storms that roll off the oceans and squeezing water from the clouds. The other side is often much drier. The rugged landscapes even provide refuge—and protection—for fleeing and invading armies.
All rights reserved. Both types of crust float on the denser mantle. It was also found that oceanic crust is youngest near the axes of mid-ocean ridges, and becomes progressively older away from the axes. In none of the oceans is there oceanic crust older than million years. On the other hand, continental crust over three billion years old has been found. As this information became available, the theories of sea-floor spreading and plate tectonics were developed.
These theories answer most of the objections raised to earlier proposed mechanisms which attempted to account for continental drift. Continental drift, and its supporting theories of sea-floor spreading and plate tectonics, are now accepted as valid by most geologists throughout the world.
These theories help explain the origin and location of mountains. According to the theory of sea-floor spreading, new ocean crust is formed by the injection of liquid and solid rocks from the underlying mantle into fractures along mid-ocean ridges Figure 7. For example, Iceland is on top of the Mid-Atlantic Ridge. It was formed, and is still growing, in this way. As new crust moves away from the axis of the mid-ocean ridge, it fuses with the part of the mantle that overlies the athenosphere and becomes part of the lithosphere Figures 1 and 7.
While new ocean crust forms along mid-ocean ridges, old ocean crust sinks into the mantle along deep-sea trenches Figure 9. Since there is no evidence that the earth is expanding or shrinking, it follows that along any great circle on the earth's surface, as much crust is consumed back into the mantle along deep-sea trenches as is formed along mid-ocean ridges.
The lithosphere is divided into plates that move horizontally on top of the asthenosphere. These plates interact along three types of boundaries: spreading boundaries, where new ocean crust is formed along mid-ocean ridges Figure 7 ; converging boundaries, where continents collide Figure 8 or where, in ocean basins, old ocean crust sinks into the mantle along deep-sea trenches Figure 9 ; and conservative boundaries, where plates slide past each other along fractures faults Figure Crust is neither formed nor destroyed along conservative boundaries.
Many of earth's mountain ranges are located along plate boundaries, or former plate boundaries. Spreading boundaries produce mountains along rifts like the East African Rift Figure 6 , and along mid-ocean ridges. Volcanoes and fault-block mountains are common along boundaries.
Most of the mountains along mid-ocean ridges are underwater, but a few volcanoes along these ridges rise above sea level. Converging boundaries in ocean basins produce volcanoes and complex mountains associated with deep-sea trenches island arcs like those of Japan, the Philippines, and Indonesia; see Figure 6. Continents are less dense than oceanic crust and the underlying mantle, so when continents collide along converging boundaries, they do not sink into the mantle.
Instead, the edges of the continents crumple and thicken as they are fused together Figure 8. In the process, complexly folded and faulted mountains such as the Alps, Himalayas, and Applachians are formed Figure 6.
Fault-block mountains and complex mountains occur along conservative boundaries where plates slide past each other. This fault actually a series of faults is part of the complex system of folds and faults that occur along the boundary between the Pacific Ocean Plate and the North American Plate. Volcanoes can occur along any type of plate boundary.
They can also occur in the middle of a plate over hot spots, plumes of very hot rock rising through the mantle.
The Hawaiian Islands have formed over such a hot spot. The islands are spread out in a line because the Pacific Ocean Plate moves over a hot spot. At present it is not known for sure whether just the plate moves, or both the plate and the hot spot move. The island of Hawaii, today directly over the hot spot, is still growing at the southeast end of the chain.
The oldest island formed over this hot spot, Midway, now at the northwest end of the chain, consists of a coral reef on top of an extinct volcano. Midway is now slowing sinking into the ocean because the lithosphere is not strong enough to support its weight. Mountains in West Virginia Both complex mountains and erosional mountains are present in West Virginia. The Allegheny Front and the St. Clair Fault form a dividing line between the two types Figure The complex mountains are located along and east of the Allegheny Front and the St.
Clair Fault. The Allegheny Front is a high, east-facing escarpment cliff or steep slope. Like a syncline, a basin has its youngest rocks in its center. Also called a thrust sheet. Also called lithospheric plate. 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.
The Rights Holder for media is the person or group credited. Jeannie Evers, Emdash Editing. Caryl-Sue, National Geographic Society. For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.
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For example, sedimentary rock shale becomes slate when heat and pressure are added. The more heat and pressure you add, the further the rock metamorphoses until it becomes gneiss. If it is heated further, the rock will melt completely and reform as an igneous rock. Empower your students to learn about the rock cycle with this collection of resources. These tectonic plates rest upon the convecting mantle, which causes them to move. The movements of these plates can account for noticeable geologic events such as earthquakes, volcanic eruptions, and more subtle yet sublime events, like the building of mountains.
Teach your students about plate tectonics using these classroom resources. Weathering is the process of the weakening and breakdown of rocks, metals, and manmade objects. There are two main types of weathering: chemical and physical.
An example of chemical weathering is acid rain. Caused mostly by the burning of fossil fuels, acid rain is a form of precipitation with high levels of sulfuric acid, which can cause erosion in the materials in which it comes in contact.
An example of physical weathering is wind blowing across the desert playas. This process causes rocks to form a specific pyramid-like shape and they are called ventifacts. Select from these resources to teach about the process of weathering in your classroom.
Metamorphic rocks start as one type of rock and—with pressure, heat, and time—gradually change into a new type of rock. In , after decades of tediously collecting and mapping ocean sonar data, scientists began to see a fairly accurate picture of the seafloor emerge. The Tharp-Heezen map illustrated the geological features that characterize the seafloor and became a crucial factor in the acceptance of the theories of plate tectonics and continental drift.
Today, these theories serve as the foundation upon which we understand the geologic processes that shape the Earth. The theory of plate tectonics revolutionized the earth sciences by explaining how the movement of geologic plates causes mountain building, volcanoes, and earthquakes.
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