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52-529: Broumovsko has been a protected landscape area since 1991. It is well known for its aesthetically and ecologically valuable landscape: extensive complexes of sandstone rock formation as well as cultural heritage, which comprises especially religious and folk architecture. The Broumovsko Protected Landscape Area is composed of two different geologic formations, the Police highlands and the Broumov basin, separated by

104-502: A protected area in Europe is a stub . You can help Misplaced Pages by expanding it . Table (landform) A tableland is an area containing elevated landforms characterized by a distinct, flat, nearly level, or gently undulating surface. They often exhibit steep, cliff-like edges, known as escarpments , that separate them from surrounding lowlands. Depending on either their size, other physical characteristics, or geographic location,

156-419: A continued supply of lava and its pressure on a solidified crust. Most basaltic lavas are of ʻaʻā or pāhoehoe types, rather than block lavas. Underwater, they can form pillow lavas , which are rather similar to entrail-type pahoehoe lavas on land. Ultramafic lavas, such as komatiite and highly magnesian magmas that form boninite , take the composition and temperatures of eruptions to the extreme. All have

208-455: A darker groundmass , including amphibole or pyroxene phenocrysts. Mafic or basaltic lavas are typified by relatively high magnesium oxide and iron oxide content (whose molecular formulas provide the consonants in mafic) and have a silica content limited to a range of 52% to 45%. They generally erupt at temperatures of 1,100 to 1,200 °C (2,010 to 2,190 °F) and at relatively low viscosities, around 10 to 10 cP (10 to 100 Pa⋅s). This

260-420: A dome forms on an inclined surface it can flow in short thick flows called coulées (dome flows). These flows often travel only a few kilometres from the vent. Lava tubes are formed when a flow of relatively fluid lava cools on the upper surface sufficiently to form a crust. Beneath this crust, which being made of rock is an excellent insulator, the lava can continue to flow as a liquid. When this flow occurs over

312-465: A massive dense core, which is the most active part of the flow. As pasty lava in the core travels downslope, the clinkers are carried along at the surface. At the leading edge of an ʻaʻā flow, however, these cooled fragments tumble down the steep front and are buried by the advancing flow. This produces a layer of lava fragments both at the bottom and top of an ʻaʻā flow. Accretionary lava balls as large as 3 metres (10 feet) are common on ʻaʻā flows. ʻAʻā

364-960: A silica content greater than 63%. They include rhyolite and dacite lavas. With such a high silica content, these lavas are extremely viscous, ranging from 10 cP (10 Pa⋅s) for hot rhyolite lava at 1,200 °C (2,190 °F) to 10 cP (10 Pa⋅s) for cool rhyolite lava at 800 °C (1,470 °F). For comparison, water has a viscosity of about 1 cP (0.001 Pa⋅s). Because of this very high viscosity, felsic lavas usually erupt explosively to produce pyroclastic (fragmental) deposits. However, rhyolite lavas occasionally erupt effusively to form lava spines , lava domes or "coulees" (which are thick, short lava flows). The lavas typically fragment as they extrude, producing block lava flows. These often contain obsidian . Felsic magmas can erupt at temperatures as low as 800 °C (1,470 °F). Unusually hot (>950 °C; >1,740 °F) rhyolite lavas, however, may flow for distances of many tens of kilometres, such as in

416-450: A silica content under 45%. Komatiites contain over 18% magnesium oxide and are thought to have erupted at temperatures of 1,600 °C (2,910 °F). At this temperature there is practically no polymerization of the mineral compounds, creating a highly mobile liquid. Viscosities of komatiite magmas are thought to have been as low as 100 to 1000 cP (0.1 to 1 Pa⋅s), similar to that of light motor oil. Most ultramafic lavas are no younger than

468-441: A similar manner to ʻaʻā flows but their more viscous nature causes the surface to be covered in smooth-sided angular fragments (blocks) of solidified lava instead of clinkers. As with ʻaʻā flows, the molten interior of the flow, which is kept insulated by the solidified blocky surface, advances over the rubble that falls off the flow front. They also move much more slowly downhill and are thicker in depth than ʻaʻā flows. Pillow lava

520-530: A solid crust that insulates the remaining liquid lava, helping to keep it hot and inviscid enough to continue flowing. The word lava comes from Italian and is probably derived from the Latin word labes , which means a fall or slide. An early use of the word in connection with extrusion of magma from below the surface is found in a short account of the 1737 eruption of Vesuvius , written by Francesco Serao , who described "a flow of fiery lava" as an analogy to

572-575: A temperature of 1,100 to 1,200 °C (2,010 to 2,190 °F). On the Earth, most lava flows are less than 10 km (6.2 mi) long, but some pāhoehoe flows are more than 50 km (31 mi) long. Some flood basalt flows in the geologic record extend for hundreds of kilometres. The rounded texture makes pāhoehoe a poor radar reflector, and is difficult to see from an orbiting satellite (dark on Magellan picture). Block lava flows are typical of andesitic lavas from stratovolcanoes. They behave in

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624-501: A volcano extrudes silicic lava, it can form an inflation dome or endogenous dome , gradually building up a large, pillow-like structure which cracks, fissures, and may release cooled chunks of rock and rubble. The top and side margins of an inflating lava dome tend to be covered in fragments of rock, breccia and ash. Examples of lava dome eruptions include the Novarupta dome, and successive lava domes of Mount St Helens . When

676-467: Is a stub . You can help Misplaced Pages by expanding it . Lava Lava is molten or partially molten rock ( magma ) that has been expelled from the interior of a terrestrial planet (such as Earth ) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust , on land or underwater, usually at temperatures from 800 to 1,200 °C (1,470 to 2,190 °F). The volcanic rock resulting from subsequent cooling

728-402: Is a large subsidence crater, can form in a stratovolcano, if the magma chamber is partially or wholly emptied by large explosive eruptions; the summit cone no longer supports itself and thus collapses in on itself afterwards. Such features may include volcanic crater lakes and lava domes after the event. However, calderas can also form by non-explosive means such as gradual magma subsidence. This

780-456: Is also often called lava . A lava flow is an outpouring of lava during an effusive eruption . (An explosive eruption , by contrast, produces a mixture of volcanic ash and other fragments called tephra , not lava flows.) The viscosity of most lava is about that of ketchup , roughly 10,000 to 100,000 times that of water. Even so, lava can flow great distances before cooling causes it to solidify, because lava exposed to air quickly develops

832-415: Is basaltic lava that has a smooth, billowy, undulating, or ropy surface. These surface features are due to the movement of very fluid lava under a congealing surface crust. The Hawaiian word was introduced as a technical term in geology by Clarence Dutton . A pāhoehoe flow typically advances as a series of small lobes and toes that continually break out from a cooled crust. It also forms lava tubes where

884-719: Is concentrated in a thin layer in the toothpaste next to the tube and only there does the toothpaste behave as a fluid. Thixotropic behavior also hinders crystals from settling out of the lava. Once the crystal content reaches about 60%, the lava ceases to behave like a fluid and begins to behave like a solid. Such a mixture of crystals with melted rock is sometimes described as crystal mush . Lava flow speeds vary based primarily on viscosity and slope. In general, lava flows slowly, with typical speeds for Hawaiian basaltic flows of 0.40 km/h (0.25 mph) and maximum speeds of 10 to 48 km/h (6 to 30 mph) on steep slopes. An exceptional speed of 32 to 97 km/h (20 to 60 mph)

936-546: Is mostly determined by composition but also depends on temperature and shear rate. Lava viscosity determines the kind of volcanic activity that takes place when the lava is erupted. The greater the viscosity, the greater the tendency for eruptions to be explosive rather than effusive. As a result, most lava flows on Earth, Mars, and Venus are composed of basalt lava. On Earth, 90% of lava flows are mafic or ultramafic, with intermediate lava making up 8% of flows and felsic lava making up just 2% of flows. Viscosity also determines

988-444: Is one of three basic types of flow lava. ʻAʻā is basaltic lava characterized by a rough or rubbly surface composed of broken lava blocks called clinker. The word is Hawaiian meaning "stony rough lava", but also to "burn" or "blaze"; it was introduced as a technical term in geology by Clarence Dutton . The loose, broken, and sharp, spiny surface of an ʻaʻā flow makes hiking difficult and slow. The clinkery surface actually covers

1040-474: Is similar to the viscosity of ketchup , although it is still many orders of magnitude higher than that of water. Mafic lavas tend to produce low-profile shield volcanoes or flood basalts , because the less viscous lava can flow for long distances from the vent. The thickness of a solidified basaltic lava flow, particularly on a low slope, may be much greater than the thickness of the moving molten lava flow at any one time, because basaltic lavas may "inflate" by

1092-454: Is the lava structure typically formed when lava emerges from an underwater volcanic vent or subglacial volcano or a lava flow enters the ocean. The viscous lava gains a solid crust on contact with the water, and this crust cracks and oozes additional large blobs or "pillows" as more lava emerges from the advancing flow. Since water covers the majority of Earth 's surface and most volcanoes are situated near or under bodies of water, pillow lava

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1144-422: Is typical of many shield volcanoes. Cinder cones and spatter cones are small-scale features formed by lava accumulation around a small vent on a volcanic edifice. Cinder cones are formed from tephra or ash and tuff which is thrown from an explosive vent. Spatter cones are formed by accumulation of molten volcanic slag and cinders ejected in a more liquid form. Another Hawaiian English term derived from

1196-516: Is usually of higher viscosity than pāhoehoe. Pāhoehoe can turn into ʻaʻā if it becomes turbulent from meeting impediments or steep slopes. The sharp, angled texture makes ʻaʻā a strong radar reflector, and can easily be seen from an orbiting satellite (bright on Magellan pictures). ʻAʻā lavas typically erupt at temperatures of 1,050 to 1,150 °C (1,920 to 2,100 °F) or greater. Pāhoehoe (also spelled pahoehoe , from Hawaiian [paːˈhoweˈhowe] meaning "smooth, unbroken lava")

1248-646: Is very common. Because it is formed from viscous molten rock, lava flows and eruptions create distinctive formations, landforms and topographical features from the macroscopic to the microscopic. Volcanoes are the primary landforms built by repeated eruptions of lava and ash over time. They range in shape from shield volcanoes with broad, shallow slopes formed from predominantly effusive eruptions of relatively fluid basaltic lava flows, to steeply-sided stratovolcanoes (also known as composite volcanoes) made of alternating layers of ash and more viscous lava flows typical of intermediate and felsic lavas. A caldera , which

1300-494: The Hawaiian language , a kīpuka denotes an elevated area such as a hill, ridge or old lava dome inside or downslope from an area of active volcanism. New lava flows will cover the surrounding land, isolating the kīpuka so that it appears as a (usually) forested island in a barren lava flow. Lava domes are formed by the extrusion of viscous felsic magma. They can form prominent rounded protuberances, such as at Valles Caldera . As

1352-889: The Proterozoic , with a few ultramafic magmas known from the Phanerozoic in Central America that are attributed to a hot mantle plume . No modern komatiite lavas are known, as the Earth's mantle has cooled too much to produce highly magnesian magmas. Some silicate lavas have an elevated content of alkali metal oxides (sodium and potassium), particularly in regions of continental rifting , areas overlying deeply subducted plates , or at intraplate hotspots . Their silica content can range from ultramafic ( nephelinites , basanites and tephrites ) to felsic ( trachytes ). They are more likely to be generated at greater depths in

1404-520: The Snake River Plain of the northwestern United States. Intermediate or andesitic lavas contain 52% to 63% silica, and are lower in aluminium and usually somewhat richer in magnesium and iron than felsic lavas. Intermediate lavas form andesite domes and block lavas and may occur on steep composite volcanoes , such as in the Andes . They are also commonly hotter than felsic lavas, in

1456-418: The most abundant elements of the Earth's crust , with smaller quantities of aluminium , calcium , magnesium , iron , sodium , and potassium and minor amounts of many other elements. Petrologists routinely express the composition of a silicate lava in terms of the weight or molar mass fraction of the oxides of the major elements (other than oxygen) present in the lava. The silica component dominates

1508-989: The aspect (thickness relative to lateral extent) of flows, the speed with which flows move, and the surface character of the flows. When highly viscous lavas erupt effusively rather than in their more common explosive form, they almost always erupt as high-aspect flows or domes. These flows take the form of block lava rather than ʻaʻā or pāhoehoe. Obsidian flows are common. Intermediate lavas tend to form steep stratovolcanoes, with alternating beds of lava from effusive eruptions and tephra from explosive eruptions. Mafic lavas form relatively thin flows that can move great distances, forming shield volcanoes with gentle slopes. In addition to melted rock, most lavas contain solid crystals of various minerals, fragments of exotic rocks known as xenoliths , and fragments of previously solidified lava. The crystal content of most lavas gives them thixotropic and shear thinning properties. In other words, most lavas do not behave like Newtonian fluids, in which

1560-637: The cultural landscape of Broumovsko region was particularly influenced by the Baroque era. There is a unique set of ten Baroque churches built in the 18th century in villages around Broumov, on the territory of the Broumov monastic estate, by famous architects, father and son Christoph Dientzenhofer and Kilian Ignaz Dientzenhofer . Walled manors and country estates of the Broumov type are also highly remarkable. There are several smaller protected areas within Broumovsko: This article related to

1612-459: The erosion of duricrusts are also quite common in parts of Australia and South America. In addition, the eruption of either lava or pyroclastic flows can deposit a solid surface layer of volcanic rock that is relatively flat. As in case of the duricrusts, the resulting lava or pyroclastic flows are sufficiently tough to form the flat-lying caprock of tablelands when breached and incised by rivers and streams. This article related to topography

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1664-418: The eruption. A cooling lava flow shrinks, and this fractures the flow. Basalt flows show a characteristic pattern of fractures. The uppermost parts of the flow show irregular downward-splaying fractures, while the lower part of the flow shows a very regular pattern of fractures that break the flow into five- or six-sided columns. The irregular upper part of the solidified flow is called the entablature , while

1716-654: The flood basalts of South America formed in this manner. Flood basalts typically crystallize little before they cease flowing, and, as a result, flow textures are uncommon in less silicic flows. On the other hand, flow banding is common in felsic flows. The morphology of lava describes its surface form or texture. More fluid basaltic lava flows tend to form flat sheet-like bodies, whereas viscous rhyolite lava flows form knobbly, blocky masses of rock. Lava erupted underwater has its own distinctive characteristics. ʻAʻā (also spelled aa , aʻa , ʻaʻa , and a-aa , and pronounced [ʔəˈʔaː] or / ˈ ɑː ( ʔ ) ɑː / )

1768-517: The flow of water and mud down the flanks of the volcano (a lahar ) after heavy rain . Solidified lava on the Earth's crust is predominantly silicate minerals : mostly feldspars , feldspathoids , olivine , pyroxenes , amphiboles , micas and quartz . Rare nonsilicate lavas can be formed by local melting of nonsilicate mineral deposits or by separation of a magma into immiscible silicate and nonsilicate liquid phases . Silicate lavas are molten mixtures dominated by oxygen and silicon ,

1820-595: The form of relatively flat-lying sandstones and conglomerates that have not been strongly deformed by tectonics . The primary control on the geomorphology of sedimentary tablelands is the dip of the layers of the sandstones, conglomerates, and associated sedimentary strata . Sedimentary tablelands only form if the dip of the sedimentary layers is negligible. If the sedimentary layers are tilted, although otherwise little deformed, asymmetric ridges known as cuestas develop. A really extensive sedimentary tablelands are often known as plateaus . As plateaus are dissected by

1872-412: The formation of a thick indurated surface layer duricrust by deep weathering beneath a relatively flat surface. Second, the breaching and incision of the duricrust layer by rivers or streams. Finally, the inward migration of valley walls and escarpments by slope erosion and denudation of mesas and buttes. An example of such tablelands is the laterite-capped Panchgani Tableland of India. Tablelands formed by

1924-499: The headward erosion and incision of river and stream courses and the retreat of their bounding escarpments, plateaus are fragmented into tablelands of smaller and smaller extent known as mesas , buttes , or pinnacles . Further erosion eventually reduces these landforms to piles of bouderly rubble as known as rock labyrinths . The tepui of South America are a type of sedimentary tableland composed of erosional outliers of flat-lying Precambrian quartz arenite sandstone that tower over

1976-497: The icy satellites of the Solar System 's giant planets . The lava's viscosity mostly determines the behavior of lava flows. While the temperature of common silicate lava ranges from about 800 °C (1,470 °F) for felsic lavas to 1,200 °C (2,190 °F) for mafic lavas, its viscosity ranges over seven orders of magnitude, from 10 cP (10 Pa⋅s) for felsic lavas to 10 cP (10 Pa⋅s) for mafic lavas. Lava viscosity

2028-440: The landforms comprising a tableland are individually referred to by a number of names including either butte , mesa , plateau , potrero , tepui , or tuya . Table Mountains are also a type of tableland. A homologous landform under the sea is called either a tablemount or guyot . Sedimentary tablelands are tablelands that typically have developed from the erosion of coarse-grained, clastic, sedimentary rocks in

2080-404: The lava's chemical composition. This temperature range is similar to the hottest temperatures achievable with a forced air charcoal forge. Lava is most fluid when first erupted, becoming much more viscous as its temperature drops. Lava flows quickly develop an insulating crust of solid rock as a result of radiative loss of heat. Thereafter, the lava cools by a very slow conduction of heat through

2132-610: The lava. Other cations , such as ferrous iron, calcium, and magnesium, bond much more weakly to oxygen and reduce the tendency to polymerize. Partial polymerization makes the lava viscous, so lava high in silica is much more viscous than lava low in silica. Because of the role of silica in determining viscosity and because many other properties of a lava (such as its temperature) are observed to correlate with silica content, silicate lavas are divided into four chemical types based on silica content: felsic , intermediate , mafic , and ultramafic . Felsic or silicic lavas have

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2184-464: The lower and upper boundaries. These are described as pipe-stem vesicles or pipe-stem amygdales . Liquids expelled from the cooling crystal mush rise upwards into the still-fluid center of the cooling flow and produce vertical vesicle cylinders . Where these merge towards the top of the flow, they form sheets of vesicular basalt and are sometimes capped with gas cavities that sometimes fill with secondary minerals. The beautiful amethyst geodes found in

2236-467: The lower part that shows columnar jointing is called the colonnade . (The terms are borrowed from Greek temple architecture.) Likewise, regular vertical patterns on the sides of columns, produced by cooling with periodic fracturing, are described as chisel marks . Despite their names, these are natural features produced by cooling, thermal contraction, and fracturing. As lava cools, crystallizing inwards from its edges, it expels gases to form vesicles at

2288-422: The mantle than subalkaline magmas. Olivine nephelinite lavas are both ultramafic and highly alkaline, and are thought to have come from much deeper in the mantle of the Earth than other lavas. Tholeiitic basalt lava Rhyolite lava Some lavas of unusual composition have erupted onto the surface of the Earth. These include: The term "lava" can also be used to refer to molten "ice mixtures" in eruptions on

2340-521: The minimal heat loss maintains a low viscosity. The surface texture of pāhoehoe flows varies widely, displaying all kinds of bizarre shapes often referred to as lava sculpture. With increasing distance from the source, pāhoehoe flows may change into ʻaʻā flows in response to heat loss and consequent increase in viscosity. Experiments suggest that the transition takes place at a temperature between 1,200 and 1,170 °C (2,190 and 2,140 °F), with some dependence on shear rate. Pahoehoe lavas typically have

2392-446: The physical behavior of silicate magmas. Silicon ions in lava strongly bind to four oxygen ions in a tetrahedral arrangement. If an oxygen ion is bound to two silicon ions in the melt, it is described as a bridging oxygen, and lava with many clumps or chains of silicon ions connected by bridging oxygen ions is described as partially polymerized. Aluminium in combination with alkali metal oxides (sodium and potassium) also tends to polymerize

2444-440: The range of 850 to 1,100 °C (1,560 to 2,010 °F). Because of their lower silica content and higher eruptive temperatures, they tend to be much less viscous, with a typical viscosity of 3.5 × 10 cP (3,500 Pa⋅s) at 1,200 °C (2,190 °F). This is slightly greater than the viscosity of smooth peanut butter . Intermediate lavas show a greater tendency to form phenocrysts . Higher iron and magnesium tends to manifest as

2496-409: The rate of flow is proportional to the shear stress . Instead, a typical lava is a Bingham fluid , which shows considerable resistance to flow until a stress threshold, called the yield stress, is crossed. This results in plug flow of partially crystalline lava. A familiar example of plug flow is toothpaste squeezed out of a toothpaste tube. The toothpaste comes out as a semisolid plug, because shear

2548-502: The ridge of the Broumov Walls. One of the main phenomena of this area is the cretaceous sandstone relief with vast rock towns, table mountains and cuestas . The deep cold gorges of the rock towns support rare floral life, rich alpine vegetation is found here in inverse positions, while on the rock plateaus warm and dry pine woods can be found. For many centuries, the area was managed by Benedictine monks from Broumov Monastery;

2600-625: The rocky crust. For instance, geologists of the United States Geological Survey regularly drilled into the Kilauea Iki lava lake, formed in an eruption in 1959. After three years, the solid surface crust, whose base was at a temperature of 1,065 °C (1,949 °F), was still only 14 m (46 ft) thick, even though the lake was about 100 m (330 ft) deep. Residual liquid was still present at depths of around 80 m (260 ft) nineteen years after

2652-426: The surrounding jungle underlain by crystalline basement rocks. Flat-lying, coarse-grained, clastic sedimentary rocks are not the only layered rocks that serve as the caprock that form the surface of tablelands. Flat-lying duricrusts and volcanic rocks also form the caprock of various tablelands. In case of duricrusts, e.g. laterite or silcrete , the formation of tablelands involves a three stage process. First,

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2704-480: Was recorded following the collapse of a lava lake at Mount Nyiragongo . The scaling relationship for lavas is that the average speed of a flow scales as the square of its thickness divided by its viscosity. This implies that a rhyolite flow would have to be about a thousand times thicker than a basalt flow to flow at a similar speed. The temperature of most types of molten lava ranges from about 800 °C (1,470 °F) to 1,200 °C (2,190 °F) depending on

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