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Fault blocks are very large blocks of rock, sometimes hundreds of kilometres in extent, created by
tectonic Tectonics ( via Latin ) are the processes that result in the structure and properties of the Earth's crust and its evolution through time. The field of ''planetary tectonics'' extends the concept to other planets and moons. These processes ...
and localized stresses in
Earth's crust Earth's crust is its thick outer shell of rock, referring to less than one percent of the planet's radius and volume. It is the top component of the lithosphere, a solidified division of Earth's layers that includes the crust and the upper ...
. Large areas of bedrock are broken up into blocks by faults. Blocks are characterized by relatively uniform
lithology The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lit ...
. The largest of these fault blocks are called crustal blocks. Large crustal blocks broken off from tectonic plates are called
terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its d ...
s. Those terranes which are the full thickness of the
lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time ...
are called microplates. Continent-sized blocks are called variously ''microcontinents, continental ribbons, H-blocks, extensional allochthons and outer highs.'' Because most stresses relate to the tectonic activity of moving plates, most motion between blocks is horizontal, that is parallel to the Earth's crust by
strike-slip faults In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
. However vertical movement of blocks produces much more dramatic results. Landforms (
mountain A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. Although definitions vary, a mountain may differ from a plateau in having a limited summit area, and is usually higher t ...
s, hills, ridges, lakes, valleys, etc.) are sometimes formed when the faults have a large vertical displacement. Adjacent raised blocks ( horsts) and down-dropped blocks (
graben In geology, a graben () is a depression (geology), depressed block of the Crust (geology), crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German language, German, meaning 'ditch' or 't ...
s) can form high
escarpment An escarpment is a steep slope or long cliff that forms as a result of faulting or erosion and separates two relatively level areas having different elevations. Due to the similarity, the term '' scarp'' may mistakenly be incorrectly used inte ...
s. Often the movement of these blocks is accompanied by tilting, due to compaction or stretching of the crust at that point.


Fault-block mountains

Fault-block mountains often result from
rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben ...
ing, an indicator of
extensional tectonics Extensional tectonics is concerned with the structures formed by, and the Tectonics, tectonic processes associated with, the stretching of a planetary body's Crust (geology), crust or lithosphere. Deformation styles The types of structure and the ...
. These can be small or form extensive
rift valley A rift valley is a linear shaped lowland between several highlands or mountain ranges produced by the action of a geologic rift. Rifts are formed as a result of the pulling apart of the lithosphere due to extensional tectonics. The linear ...
systems, such as the
East African Rift The East African Rift (EAR) or East African Rift System (EARS) is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago. It was formerly considered to be part of a l ...
zone.
Death Valley Death Valley is a desert valley in Eastern California, in the northern Mojave Desert, bordering the Great Basin Desert. It is thought to be the Highest temperature recorded on Earth, hottest place on Earth during summer. Death Valley's Badwat ...
in
California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
is a smaller example. There are two main types of block mountains; uplifted blocks between two faults and tilted blocks mainly controlled by one fault. Lifted type block mountains have two steep sides exposing both sides scarps, leading to the horst and
graben In geology, a graben () is a depression (geology), depressed block of the Crust (geology), crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German language, German, meaning 'ditch' or 't ...
terrain seen in various parts of
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
including the
Upper Rhine Upper Rhine ( ; ; kilometres 167 to 529 of the Rhine) is the section of the Rhine between the Middle Bridge, Basel, Middle Bridge in Basel, Switzerland, and the Rhine knee in Bingen am Rhein, Bingen, Germany. It is surrounded by the Upper Rhine P ...
valley, a graben between two horsts – the
Vosges mountains The Vosges ( , ; ; Franconian (linguistics), Franconian and ) is a range of medium mountains in Eastern France, near its France–Germany border, border with Germany. Together with the Palatine Forest to the north on the German side of the bor ...
(in
France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
) and the
Black Forest The Black Forest ( ) is a large forested mountain range in the States of Germany, state of Baden-Württemberg in southwest Germany, bounded by the Rhine Valley to the west and south and close to the borders with France and Switzerland. It is th ...
(in
Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...
), and also the
Rila Rila (, ) is the highest mountain range of Bulgaria, the Balkans, Balkan Peninsula, and Southeast Europe. It is situated in southwestern Bulgaria and forms part of the Rila–Rhodope Mountains, Rhodope Massif. The highest summit is Musala at an e ...
Rhodope
Massif A massif () is a principal mountain mass, such as a compact portion of a mountain range, containing one or more summits (e.g. France's Massif Central). In mountaineering literature, ''massif'' is frequently used to denote the main mass of an ...
in
Bulgaria Bulgaria, officially the Republic of Bulgaria, is a country in Southeast Europe. It is situated on the eastern portion of the Balkans directly south of the Danube river and west of the Black Sea. Bulgaria is bordered by Greece and Turkey t ...
,
Southeast Europe Southeast Europe or Southeastern Europe is a geographical sub-region of Europe, consisting primarily of the region of the Balkans, as well as adjacent regions and Archipelago, archipelagos. There are overlapping and conflicting definitions of t ...
, including the well defined horsts of Belasitsa (linear horst), Rila mountain (vaulted domed shaped horst) and Pirin mountain – a horst forming a massive
anticline In structural geology, an anticline is a type of Fold (geology), fold that is an arch-like shape and has its oldest Bed (geology), beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex curve, c ...
situated between the complex
graben In geology, a graben () is a depression (geology), depressed block of the Crust (geology), crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German language, German, meaning 'ditch' or 't ...
valleys of Struma and that of Mesta. Tilted type block mountains have one gently sloping side and one steep side with an exposed scarp, and are common in the Basin and Range region of the western United States. An example of a
graben In geology, a graben () is a depression (geology), depressed block of the Crust (geology), crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German language, German, meaning 'ditch' or 't ...
is the basin of the
Narmada River The Narmada River, previously also known as ''Narbada'' or anglicised as ''Nerbudda'', is the 5th longest river in India and overall the longest west-flowing river in the country. It is also the largest flowing river in the state of Madhya Prade ...
in
India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
, between the Vindhya and Satpura horsts.


See also

*


Notes


References

* Plummer, Charles, David McGeary, and Diane Carlson. ''Physical Geology'' 8th ed. McGraw-Hill, Boston, 1999. * Monroe, James S., and Reed Wicander. The Changing Earth: Exploring Geology and Evolution. 2nd educational Belmont: Wadsworth Publishing Company, 1997. (pp. 234,-8)


External links


Fault-Block Mountains
Universe Today Universe Today (U.T.) is a North American-based non-commercial space and astronomy news website founded by Fraser Cain. The domain was registered on December 30, 1998, and the website went live in March 1999. ''Universe Today'' assumed its curre ...
{{DEFAULTSORT:Fault-Block Mountain Mountain geomorphology Structural geology