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65-470: About half a million years ago, the Clearwater Valley was filled by a lake backed up by a lava dam near Hemp Creek. White Horse Bluff is a complex volcanic formation that erupted underneath this lake. The outer lava cooled rapidly as it encountered the lake, then water percolated into the still-molten interior of the lava, initiating violent explosions. As the pile of debris grew, dykes fed more lava to

130-583: A balance between its slowly consolidating hardness and toughness, and the amount and velocity of flowing water's erosive capacity to remove it from its outset. Unconsolidated tephra is quickly moved by precipitation and flowing water in drainages, at times creating a lahar . Upstream of the dam this material would rapidly accumulate to fill the lake, and downstream it would tend to erode its slopes and base. The often rapid accumulation of unconsolidated pyroclastic material on steep sideslopes tends to be inherently unstable over time; pyroclastic dams may be emplaced by

195-419: 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

260-455: 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

325-420: 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

390-674: 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 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

455-871: 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

520-462: A magma into immiscible silicate and nonsilicate liquid phases . Silicate lavas are molten mixtures dominated by oxygen and silicon , 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

585-465: 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

650-416: A river valley in sufficient quantity and height to temporarily overcome the explosive nature (steam) of its contact with water, and the erosive force of flowing water to remove it. The latter depends on the quantity of water flow and stream gradient. The lava may flow during numerous successive or repetitive eruptions and may emanate from single or numerous vents or fissures. Lava of this nature, like basalt ,

715-450: 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

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780-441: 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

845-523: 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

910-496: 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

975-402: 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

1040-559: Is a type of natural dam produced directly or indirectly by volcanism , which holds or temporarily restricts the flow of surface water in existing streams, like a man-made dam . There are two main types of volcanic dams, those created by the flow of molten lava , and those created by the primary or secondary deposition of pyroclastic material and debris . This classification generally excludes other, often larger and longer lived dam-type geologic features, separately termed crater lakes , although these volcanic centers may be associated with

1105-470: 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 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

1170-415: 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

1235-719: 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)

1300-412: Is described as partially polymerized. Aluminium in combination with alkali metal oxides (sodium and potassium) also tends to polymerize 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

1365-524: Is established, for water and sediment elsewhere in the drainage. Large examples of lava dams from the geologic record include those repeatedly developed from the western side of the Grand Canyon , with the largest remnant now termed Prospect Dam , and in several locations within the Snake River drainage. The former 'Lake Idaho', which existed for more than 6.5 million years, filled the western portion of

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1430-546: 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

1495-444: 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

1560-474: 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

1625-427: Is similarly recorded. The longevity, and extent varies widely, having periods ranging from a few days, weeks or years to several hundred thousand years or more, and dimensions ranging from a few meters to hundreds, to several thousand. The emplacement, internal structure, distribution and longevity of such dams can be related variously to the amount, rapidity and duration of ( primary ) geothermal energy released, and

1690-454: 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

1755-422: 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

1820-431: Is usually associated with less explosive eruptions; more viscous lavas with lower mafic content, like dacites and rhyolites , can also flow, but tend to be more closely associated with eruptions of greater explosiveness and the formation of pyroclastics. Once initially established, continued lava flow creates a steeper upstream face as it battles the rising water, but with most lava flowing unimpeded downstream covering

1885-516: 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")

1950-646: 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

2015-489: 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

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2080-626: The Karymsky Volcano in Russia. The caldera lake associated with Taal Volcano , which was previously open to the South China Sea, was permanently closed by a pyroclastic dam during the 1749 eruption, and remains in equilibrium at a higher level to this day, while the pyroclastic dam comprising the low rim of crater Lake Nyos in Cameroon is considered less stable. Like all forms of natural dams,

2145-819: 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

2210-508: 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

2275-425: 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 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

2340-424: The accumulation of widely variable pyroclastic particles, broadly termed tephra . Unlike lava dams, which are formed by coherent, molten liquid gravity surface flow, filling the valley bottom directly and solidifying rapidly from the outside inward, pyroclastic dams are produced by less coherent airborne gravity currents or falls of tephra particles from the atmosphere, which solidify on the surface more slowly from

2405-989: 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

2470-512: The base of the White Horse Bluff. The McDiarmids excavated a cavity about a meter deep and almost high enough for a standing person. This natural refrigerator kept ice solid even on the hottest of summer days and was a luxury in this remote place. It is still there today and, in September 2014, the temperature at the entrance was measured at 5 degrees Celsius. Lava dam A volcanic dam

2535-813: The behind such a structure and created the western section of the Snake River Plain , and accumulated 4,000 ft (1,200 m) of lake sediments. Other locations include near American Falls, Idaho , and numerous others. Many of these were overtopped, washed out, or skirted by the outburst flood originating from ancestral Lake Bonneville . Many other examples exist globally including, Caburgua Lake in Chile and Mývatn in Iceland. Examples in western Canada and others in northwestern United States include, Lava Lake and The Barrier , which still impounds Garibaldi Lake , and Lava Butte . Pyroclastic dams are created in an existing drainage either by their direct emplacement or by

2600-449: The bluff. Subsequent erosion by glaciers and meltwater has exposed these dykes which give the impression that a giant hand has plastered gobs of lava onto the face. The Rock Roses are a unique collection of small columns. Unlike most formations of columnar basalt which are vertical like organ pipes, these are horizontal and the ends of the columns point out, rather like the tiles on a shower wall. About 50 m (164 ft) further west,

2665-614: The columns suddenly change direction and resemble the wall of a log house. The Rock Roses were formed by the molten lava in the dyke contacting the cooler and older adjoining rocks. A trail starts from the Green Mountain Road off the Clearwater Valley Road (also called Wells Gray Park Road). It takes 1.5 hours to hike to the top of White Horse Bluff. White Horse Bluff can be viewed from the Clearwater River Road on

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2730-413: The erosion or failure of volcanic dams can produce catastrophic floods , debris flows and associated landslides , depending on the size of the impounded lake . 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

2795-418: 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

2860-654: 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 / )

2925-427: The former may tend to emplace a dam directly while the latter tends to enhance placement or provide additional material. Unless violently expelled and generally speaking, larger sized tephra falls closest to the crater and smaller tephra landing farther away, with its distribution more highly influenced by prevailing wind velocity and direction. Once initially established, a pyroclastic dam's continued longevity remains

2990-491: 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

3055-499: The inner portion outward; pyroclastics are also deposited both in the valley bottom and widely distributed on the adjacent slopes. Their airborne nature is less restricted to the immediate drainage and they may roil over drainage boundaries; their particulate components allow for continued redistribution after initial placement by gravity and water. The explosiveness of pyroclastic eruptions, both laterally and vertically, range from fiery surges , to hot flows , to warm falls of tephra;

3120-714: The landsliding of such material into rivers and streams. Pyroclastic material, given sufficient time to consolidate or 'weld' into hard rock, produce assemblages variously classified as ignimbrites, variously brecciated or agglomerated , along with various types of tuffs and volcanic ash , and are mostly of felsic composition. While evidence of pyroclastic dams occur within the geologic record, such as Lake Reporoa in New Zealand, they are best known and studied in relation to recent and current volcanic eruptions. Examples worldwide include associations with El Chichon in Mexico, and

3185-404: 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

3250-464: 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

3315-467: 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

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3380-422: 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

3445-521: 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

3510-451: The now-dried river bed and its alluvial sediments, sometimes for miles. Thus emplaced, the shape of a lava dam resembles an elongated blob, wedged in the valley bottom. At the same time, the water continues to flow, the lake continues to rise and accumulate sediment, which previously had migrated unimpeded downstream. Sediment filling, over-topping, downward erosion, waterfalls and under-cutting inevitably follow, unless an alternative outlet

3575-528: The opposite or west bank of the Clearwater River . The origin of the name, White Horse Bluff, is still debated by Clearwater Valley pioneers, but a First Nations legend about a white horse seems to be the most popular theory. Apparently several horses, including a striking white one, were once pastured beside the Clearwater River near the base of the bluff. In the fall, when the animals were to be moved,

3640-440: 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

3705-409: 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

3770-446: The rock material made available; other considerations include the rock types produced, their physical and toughness characteristics, and their various modes of deposition. Depositional modes include gravity flow of molten lava at the surface, gravity flow or fall of pyroclastics through the air, as well as the redistribution and transportation of those materials by gravity and water. Lava dams are formed by lava flowing or spilling into

3835-606: 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

3900-423: 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 a silica content greater than 63%. They include rhyolite and dacite lavas. With such

3965-512: The ruins are left today. Eventually, the McDiarmids operated four cabins or fishing camps along the river and their home base on the Clearwater Valley Road was called Trophies Lodge. Hundreds of guests enjoyed wilderness vacations and the Clearwater's fabulous fishing over a 25-year period starting in 1945. About 1950, a guest at The Longhouse detected a cold draft blowing outward from some cracks near

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4030-414: The source of material for volcanic dams, and the lowest portion of its confining rim may be considered as such a dam, especially if the lake level within the crater is relatively high. Volcanic dams generally occur worldwide, in association with former and active volcanic provinces, and are known to have existed in the geologic record, in historic times and occur in the present day. Their removal or failure

4095-456: The weight or molar mass fraction of the oxides of the major elements (other than oxygen) present in the lava. The silica component dominates 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

4160-415: The white horse could not be found. In the spring, however, it was found grazing at the top, having somehow climbed up from the river and survived the winter on its own. Mac and Cecile McDiarmid built one of their Clearwater River fishing camps at the foot of the White Horse Bluff in the late 1940s. It was nicknamed "The Longhouse" because it was 12 m (39 ft) long and 5 m (16 ft) wide. Only

4225-480: 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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