Mountain formation
Encyclopedia
Mountain formation refers to the geological processes that underlie the formation of mountain
s. These processes are associated with large-scale movements of the earth's crust (plate tectonics
).
The formation of mountain ranges occurs by means of lateral movements as opposed to vertical ones. Mountain formation is related to plate tectonics
. Folding
, faulting, volcanic activity
, igneous intrusion and metamorphism
are all parts of the orogenic process
of mountain building.
The understanding of specific landscape features in terms of the underlying tectonic processes is called tectonic geomorphology
, and the study of geologically young or ongoing processes is called neotectonics
.
Movements of tectonic plates
create volcano
es along the plate boundaries which erupt and form mountains. A volcanic arc system is a series of volcanoes that form near a subduction
zone where the crust of a sinking oceanic plate melts.
Most volcanoes occur in a band encircling the Pacific Ocean (the Pacific Ring of Fire
), and in another that extends from the Mediterranean across Asia to join the Pacific band in the Indonesian Archipelago. The most important types of volcanic mountain are composite cones or "stratovolcanoes" (Vesuvius, Kilimanjaro
and Mount Fuji
are examples) and shield volcanoes (such as Mauna Loa
on Hawaii, a hotspot
volcano).
A shield volcano has a gently sloping cone due to the low viscosity of the emitted material, primarily basalt
. Mauna Loa is the classic example, with a slope of 4°-6°. (The relation between slope and viscosity falls under the topic of angle of repose
.) The composite volcano or stratovolcano has a more steeply rising cone (33°-40°), due to the higher viscosity of the emitted material, and eruptions are more violent and less frequent than for shield volcanoes. Besides the examples already mentioned are Mount Shasta
, Mount Hood
and Mount Rainier
.
When plates collide
or undergo subduction
(that is ride one over another), the plates tend to buckle and fold, forming mountains. Most of the major continental mountain ranges are associated with thrusting and folding or orogenesis. Examples are the Jura
and the Zagros mountains.
s. A spreading apart of the surface causes tensional forces. When the tensional forces are strong enough to cause a plate to split apart, it will do so such that a center block will drop down relative to its flanking blocks.
An example is the Sierra Nevada Range, where delamination
created a block 650 km long and 80 km wide that consists of many individual portions tipped gently west, with east facing slips rising abruptly to produce the highest mountain front in the continental United States.
. Although originally attributed to a melting of subducted oceanic crust, recent evidence belies this connection. The mechanism for plume formation remains a research topic.
of the layers and the forces of isostasy
. Early bent plate models predicting fractures and fault movements have evolved into today's kinematic and flexural models.
Volcanoes>
Mountain
Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...
s. These processes are associated with large-scale movements of the earth's crust (plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
).
The formation of mountain ranges occurs by means of lateral movements as opposed to vertical ones. Mountain formation is related to plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
. Folding
Fold (geology)
The term fold is used in geology when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation. Synsedimentary folds are those due to slumping of sedimentary material before it is lithified. Folds in rocks vary in...
, faulting, volcanic activity
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
, igneous intrusion and metamorphism
Metamorphism
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...
are all parts of the orogenic process
Orogeny
Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...
of mountain building.
The understanding of specific landscape features in terms of the underlying tectonic processes is called tectonic geomorphology
Geomorphology
Geomorphology is the scientific study of landforms and the processes that shape them...
, and the study of geologically young or ongoing processes is called neotectonics
Neotectonics
Neotectonics is a subdiscipline of tectonics. It is the study of the motions and deformations of the Earth's crust which are current or recent in geologic time. The term may also refer to the motions/deformations in question themselves. The corresponding time frame is referred to as the...
.
Types of mountains
There are three main types of mountains: volcanic, fold, and block. A more detailed classification useful on a local scale predates plate tectonics and adds to the above categories.Volcanic mountains
Tectonic Plates
Tectonic Plates is a 1992 independent Canadian film directed by Peter Mettler. Mettler also wrote the screenplay based on the play by Robert Lepage. The film stars Marie Gignac, Céline Bonnier and Robert Lepage.-Plot summary:...
create volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
es along the plate boundaries which erupt and form mountains. A volcanic arc system is a series of volcanoes that form near a subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
zone where the crust of a sinking oceanic plate melts.
Most volcanoes occur in a band encircling the Pacific Ocean (the Pacific Ring of Fire
Pacific Ring of Fire
The Pacific Ring of Fire is an area where large numbers of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. In a horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements...
), and in another that extends from the Mediterranean across Asia to join the Pacific band in the Indonesian Archipelago. The most important types of volcanic mountain are composite cones or "stratovolcanoes" (Vesuvius, Kilimanjaro
Mount Kilimanjaro
Kilimanjaro, with its three volcanic cones, Kibo, Mawenzi, and Shira, is a dormant volcano in Kilimanjaro National Park, Tanzania and the highest mountain in Africa at above sea level .-Geology:...
and Mount Fuji
Mount Fuji
is the highest mountain in Japan at . An active stratovolcano that last erupted in 1707–08, Mount Fuji lies about south-west of Tokyo, and can be seen from there on a clear day. Mount Fuji's exceptionally symmetrical cone is a well-known symbol of Japan and it is frequently depicted in art and...
are examples) and shield volcanoes (such as Mauna Loa
Mauna Loa
Mauna Loa is one of five volcanoes that form the Island of Hawaii in the U.S. state of Hawaii in the Pacific Ocean, and the largest on Earth in terms of volume and area covered. It is an active shield volcano, with a volume estimated at approximately , although its peak is about lower than that...
on Hawaii, a hotspot
Hotspot (geology)
The places known as hotspots or hot spots in geology are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere. They may be on, near to, or far from tectonic plate boundaries. There are two hypotheses to explain them...
volcano).
A shield volcano has a gently sloping cone due to the low viscosity of the emitted material, primarily basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
. Mauna Loa is the classic example, with a slope of 4°-6°. (The relation between slope and viscosity falls under the topic of angle of repose
Angle of repose
The angle of repose or, more precisely, the critical angle of repose, of a granular material is the steepest angle of descent or dip of the slope relative to the horizontal plane when material on the slope face is on the verge of sliding. This angle is in the range 0°–90°.When bulk granular...
.) The composite volcano or stratovolcano has a more steeply rising cone (33°-40°), due to the higher viscosity of the emitted material, and eruptions are more violent and less frequent than for shield volcanoes. Besides the examples already mentioned are Mount Shasta
Mount Shasta
Mount Shasta is located at the southern end of the Cascade Range in Siskiyou County, California and at is the second highest peak in the Cascades and the fifth highest in California...
, Mount Hood
Mount Hood
Mount Hood, called Wy'east by the Multnomah tribe, is a stratovolcano in the Cascade Volcanic Arc of northern Oregon. It was formed by a subduction zone and rests in the Pacific Northwest region of the United States...
and Mount Rainier
Mount Rainier
Mount Rainier is a massive stratovolcano located southeast of Seattle in the state of Washington, United States. It is the most topographically prominent mountain in the contiguous United States and the Cascade Volcanic Arc, with a summit elevation of . Mt. Rainier is considered one of the most...
.
Fold mountains
Continental collision
Continental collision is a phenomenon of the plate tectonics of Earth that occurs at convergent boundaries. Continental collision is a variation on the fundamental process of subduction, whereby the subduction zone is destroyed, mountains produced, and two continents sutured together...
or undergo subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
(that is ride one over another), the plates tend to buckle and fold, forming mountains. Most of the major continental mountain ranges are associated with thrusting and folding or orogenesis. Examples are the Jura
Jura mountains
The Jura Mountains are a small mountain range located north of the Alps, separating the Rhine and Rhone rivers and forming part of the watershed of each...
and the Zagros mountains.
Block mountains
When a fault block is raised or tilted, block mountains can result. Higher blocks are called horsts and troughs are called grabenGraben
In geology, a graben is a depressed block of land bordered by parallel faults. Graben is German for ditch. Graben is used for both the singular and plural....
s. A spreading apart of the surface causes tensional forces. When the tensional forces are strong enough to cause a plate to split apart, it will do so such that a center block will drop down relative to its flanking blocks.
An example is the Sierra Nevada Range, where delamination
Delamination (geology)
In geophysics, delamination refers to the loss and sinking of the portion of the lowermost lithosphere from the tectonic plate to which it was attached.This can occur when the lower portion of the lithosphere becomes more dense than the surrounding mantle...
created a block 650 km long and 80 km wide that consists of many individual portions tipped gently west, with east facing slips rising abruptly to produce the highest mountain front in the continental United States.
Models
Hotspot volcanoes
Hotspots are supplied by a magma source in the Earth's mantle called a mantle plumeMantle plume
A mantle plume is a hypothetical thermal diapir of abnormally hot rock that nucleates at the core-mantle boundary and rises through the Earth's mantle. Such plumes were invoked in 1971 to explain volcanic regions that were not thought to be explicable by the then-new theory of plate tectonics. Some...
. Although originally attributed to a melting of subducted oceanic crust, recent evidence belies this connection. The mechanism for plume formation remains a research topic.
Fault blocks
Several movements of the earth's crust that lead to mountains are associated with faults. These movements actually are amenable to analysis that can predict, for example, the height of a raised block and the width of an intervening rift between blocks using the rheologyRheology
Rheology is the study of the flow of matter, primarily in the liquid state, but also as 'soft solids' or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an applied force....
of the layers and the forces of isostasy
Isostasy
Isostasy is a term used in geology to refer to the state of gravitational equilibrium between the earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density. This concept is invoked to explain how different topographic...
. Early bent plate models predicting fractures and fault movements have evolved into today's kinematic and flexural models.
See also
- SeamountSeamountA seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...
- BatholithBatholithA batholith is a large emplacement of igneous intrusive rock that forms from cooled magma deep in the Earth's crust...
- Thrust faultThrust faultA thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
- Transform faultTransform faultA transform fault or transform boundary, also known as conservative plate boundary since these faults neither create nor destroy lithosphere, is a type of fault whose relative motion is predominantly horizontal in either sinistral or dextral direction. Furthermore, transform faults end abruptly...
- Continental collisionContinental collisionContinental collision is a phenomenon of the plate tectonics of Earth that occurs at convergent boundaries. Continental collision is a variation on the fundamental process of subduction, whereby the subduction zone is destroyed, mountains produced, and two continents sutured together...
- TectonicsTectonicsTectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...
- OrogenyOrogenyOrogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...
- Mantle plumeMantle plumeA mantle plume is a hypothetical thermal diapir of abnormally hot rock that nucleates at the core-mantle boundary and rises through the Earth's mantle. Such plumes were invoked in 1971 to explain volcanic regions that were not thought to be explicable by the then-new theory of plate tectonics. Some...
- Mantle convectionMantle convectionMantle convection is the slow creeping motion of Earth's rocky mantle caused by convection currents carrying heat from the interior of the Earth to the surface. The Earth's surface lithosphere, which rides atop the asthenosphere , is divided into a number of plates that are continuously being...
- Geology of the Yosemite areaGeology of the Yosemite areaThe exposed geology of the Yosemite area includes primarily granitic rocks with some older metamorphic rock. The first rocks were laid down in Precambrian times, when the area around Yosemite National Park was on the edge of a very young North American continent...
External links
- NASA Goddard Planetary Geodynamics Laboratory: home page
- NASA Goddard Planetary Geodynamics Laboratory: Volcanology Research
- Plate tectonics pictures from UNR
- Rotating globe showing areas of earthquake activity