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101-610: The volcano is the most visible landmark in Lake County other than the lake. The mountain is located between the towns of Lakeport and Clearlake , and lies just east of Kelseyville proper. It sits on the south shore of Clear Lake . Mount Konocti has five distinctive peaks: Wright Peak (4,299 feet or 1,310 meters), Howard Peak (4,286 ft or 1,306 m), South Peak (4,286 ft or 1,306 m), Buckingham Peak (3,967 ft or 1,209 m) and Clark Peak (2,880 ft or 880 m). Wright Peak, Howard Peak, and South Peak make up

202-452: A combination of these processes. Other mechanisms, such as melting from a meteorite impact , are less important today, but impacts during the accretion of the Earth led to extensive melting, and the outer several hundred kilometers of the early Earth was probably a magma ocean . Impacts of large meteorites in the last few hundred million years have been proposed as one mechanism responsible for

303-420: A depth of 2,488 m (8,163 ft). The temperature of this magma was estimated at 1,050 °C (1,920 °F). Temperatures of deeper magmas must be inferred from theoretical computations and the geothermal gradient. Most magmas contain some solid crystals suspended in the liquid phase. This indicates that the temperature of the magma lies between the solidus , which is defined as the temperature at which

404-427: A dissolved water content in excess of 10%. Water is somewhat less soluble in low-silica magma than high-silica magma, so that at 1,100 °C and 0.5 GPa , a basaltic magma can dissolve 8% H 2 O while a granite pegmatite magma can dissolve 11% H 2 O . However, magmas are not necessarily saturated under typical conditions. Carbon dioxide is much less soluble in magmas than water, and frequently separates into

505-406: A distinct fluid phase even at great depth. This explains the presence of carbon dioxide fluid inclusions in crystals formed in magmas at great depth. Viscosity is a key melt property in understanding the behaviour of magmas. Whereas temperatures in common silicate lavas range from about 800 °C (1,470 °F) for felsic lavas to 1,200 °C (2,190 °F) for mafic lavas, the viscosity of

606-605: A growth in housing units, adding a sum of 1,414 residential structures since 2001, a change of 4.3 percent. Lake County ranks 978 of 3,141, compared to change in residential structure growth in counties throughout the Unities States. Lake County had a median home value in the year 2005 of $ 255,300, according to the American Community Survey. This median is less than the overall California 2005 home median value of $ 477,700 and greater than median home value of $ 167,500 for

707-435: A high charge (the high-field-strength elements, or HSFEs), which include such elements as zirconium , niobium , hafnium , tantalum , the rare-earth elements , and the actinides . Potassium can become so enriched in melt produced by a very low degree of partial melting that, when the magma subsequently cools and solidifies, it forms unusual potassic rock such as lamprophyre , lamproite , or kimberlite . When enough rock

808-489: A household in the county was $ 49,627, and the median income for a family was $ 55,818. Males had a median income of $ 45,771 versus $ 44,026 for females. The per capita income for the county was $ 43,825. About 6.9% of families and 4.6% of the population were below the poverty line , including 22.8% of those under age 18 and 7.3% of those age 65 or over. (Source: U.S. Census Bureau) Within Lake County are two incorporated cities,

909-546: A hypothetical magma formed entirely from melted silica, NBO/T would be 0, while in a hypothetical magma so low in network formers that no polymerization takes place, NBO/T would be 4. Neither extreme is common in nature, but basalt magmas typically have NBO/T between 0.6 and 0.9, andesitic magmas have NBO/T of 0.3 to 0.5, and rhyolitic magmas have NBO/T of 0.02 to 0.2. Water acts as a network modifier, and dissolved water drastically reduces melt viscosity. Carbon dioxide neutralizes network modifiers, so dissolved carbon dioxide increases

1010-474: A layer that appears to contain silicate melt and that stretches for at least 1,000 kilometers within the middle crust along the southern margin of the Tibetan Plateau. Granite and rhyolite are types of igneous rock commonly interpreted as products of the melting of continental crust because of increases in temperature. Temperature increases also may contribute to the melting of lithosphere dragged down in

1111-420: A magma. In practice, it is difficult to unambiguously identify primary magmas, though it has been suggested that boninite is a variety of andesite crystallized from a primary magma. The Great Dyke of Zimbabwe has also been interpreted as rock crystallized from a primary magma. The interpretation of leucosomes of migmatites as primary magmas is contradicted by zircon data, which suggests leucosomes are

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1212-429: A population of 64,665. The racial makeup of Lake County was 52,033 (80.5%) White , 1,232 (1.9%) African American , 2,049 (3.2%) Native American , 724 (1.1%) Asian , 108 (0.2%) Pacific Islander , 5,455 (8.4%) from other races , and 3,064 (4.7%) from two or more races. Hispanic or Latino of any race were 11,088 persons (17.1%). There were a total of 34,031 homes in Lake County in 2005. This county has gone through

1313-425: A rock type commonly enriched in incompatible elements. Bowen's reaction series is important for understanding the idealised sequence of fractional crystallisation of a magma. Magma composition can be determined by processes other than partial melting and fractional crystallization. For instance, magmas commonly interact with rocks they intrude, both by melting those rocks and by reacting with them. Assimilation near

1414-567: A solidified crust. Most basalt 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 magmas, such as picritic basalt, komatiite , and highly magnesian magmas that form boninite , take the composition and temperatures to the extreme. All have 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

1515-407: A subduction zone. When rocks melt, they do so over a range of temperature, because most rocks are made of several minerals , which all have different melting points. The temperature at which the first melt appears (the solidus) is lower than the melting temperature of any one of the pure minerals. This is similar to the lowering of the melting point of ice when it is mixed with salt. The first melt

1616-439: A tetrahedral arrangement around the much smaller silicon ion. This is called a silica tetrahedron . In a magma that is low in silicon, these silica tetrahedra are isolated, but as the silicon content increases, silica tetrahedra begin to partially polymerize, forming chains, sheets, and clumps of silica tetrahedra linked by bridging oxygen ions. These greatly increase the viscosity of the magma. The tendency towards polymerization

1717-638: 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 magmas show a greater tendency to form phenocrysts . Higher iron and magnesium tends to manifest as a darker groundmass , including amphibole or pyroxene phenocrysts. Mafic or basaltic magmas have a silica content of 52% to 45%. They are typified by their high ferromagnesian content, and generally erupt at temperatures of 1,100 to 1,200 °C (2,010 to 2,190 °F). Viscosities can be relatively low, around 10 to 10 cP (10 to 100 Pa⋅s), although this

1818-613: A variety of species of concern including the uncommon herb , Legenere limosa , the rare Eryngium constancei , and the tule elk . Waterfowl, bear, and other wildlife abound in the Clear Lake basin. Due to its surrounding hilly terrain, Lake is the only one of California's 58 counties never to have been served by a railroad line. In 2015 President Barack Obama created the Berryessa Snow Mountain National Monument , incorporating these and other areas. In

1919-633: 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 lavas 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

2020-405: Is a steep, heavily forested area known locally as the "Black Forest", because it never gets direct sunshine. The Black Forest contains heavy stands of Douglas fir . Its northern and eastern slopes are host to several subdivisions developed in the 1960s and 1970s: Riviera Heights , Riviera West , and Kelseyville Riviera . The Konocti Harbor resort and the community of Soda Bay sit directly at

2121-409: Is added to the rock, the temperature remains at 1274 °C until either the anorthite or diopside is fully melted. The temperature then rises as the remaining mineral continues to melt, which shifts the melt composition away from the eutectic. For example, if the content of anorthite is greater than 43%, the entire supply of diopside will melt at 1274 °C., along with enough of the anorthite to keep

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2222-444: Is called the eutectic and has a composition that depends on the combination of minerals present. For example, a mixture of anorthite and diopside , which are two of the predominant minerals in basalt , begins to melt at about 1274 °C. This is well below the melting temperatures of 1392 °C for pure diopside and 1553 °C for pure anorthite. The resulting melt is composed of about 43 wt% anorthite. As additional heat

2323-410: Is concentrated in a thin layer in the toothpaste next to the tube, and only here does the toothpaste behave as a fluid. Thixotropic behavior also hinders crystals from settling out of the magma. Once the crystal content reaches about 60%, the magma 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 . Magma

2424-513: Is directly south of Howard Peak and southwest of Wright Peak. Wright Peak lies east and a little north of Howard Peak. The mountain is covered with heavy concentrations of chaparral similar to the European maquis shrubland . Oak , Pacific madrone , manzanita , western white pine and other plant species of the California coastal mountains dominate the area. On the northeast slope of Mount Konocti

2525-456: Is driven out of the oceanic lithosphere in subduction zones , and it causes melting in the overlying mantle. Hydrous magmas with the composition of basalt or andesite are produced directly and indirectly as results of dehydration during the subduction process. Such magmas, and those derived from them, build up island arcs such as those in the Pacific Ring of Fire . These magmas form rocks of

2626-417: Is expressed as NBO/T, where NBO is the number of non-bridging oxygen ions and T is the number of network-forming ions. Silicon is the main network-forming ion, but in magmas high in sodium, aluminium also acts as a network former, and ferric iron can act as a network former when other network formers are lacking. Most other metallic ions reduce the tendency to polymerize and are described as network modifiers. In

2727-619: Is host to nine American Viticultural Areas , notably Guenoc Valley , High Valley and the Red Hills , and about 20 winery operations. There are also several numbered county routes in Lake County. Lake Transit serves all areas around Clear Lake. Local routes serve Lakeport, Clearlake and Lower Lake. Connections are also provided to St. Helena (in Napa County) and Ukiah (in Mendocino County). Some routes operate on weekdays only; no service

2828-541: Is land and 73 square miles (190 km ) (5.5%) is water. Two main watercourses drain the county: Cache Creek , which is the outlet of Clear Lake ; and Putah Creek . Both of these flow to the Sacramento River . The main streams which flow into Clear Lake are Forbes Creek , Scotts Creek , Middle Creek , and Kelsey Creek . At the extreme north of the county Lake Pillsbury and the Van Arsdale Reservoir dam

2929-466: Is magma extruded onto the surface, are almost all in the range 700 to 1,400 °C (1,300 to 2,600 °F), but very rare carbonatite magmas may be as cool as 490 °C (910 °F), and komatiite magmas may have been as hot as 1,600 °C (2,900 °F). Magma has occasionally been encountered during drilling in geothermal fields, including drilling in Hawaii that penetrated a dacitic magma body at

3030-647: Is melted before the heat supply is exhausted. Pegmatite may be produced by low degrees of partial melting of the crust. Some granite -composition magmas are eutectic (or cotectic) melts, and they may be produced by low to high degrees of partial melting of the crust, as well as by fractional crystallization . Most magmas are fully melted only for small parts of their histories. More typically, they are mixes of melt and crystals, and sometimes also of gas bubbles. Melt, crystals, and bubbles usually have different densities, and so they can separate as magmas evolve. As magma cools, minerals typically crystallize from

3131-416: Is melted, the small globules of melt (generally occurring between mineral grains) link up and soften the rock. Under pressure within the earth, as little as a fraction of a percent of partial melting may be sufficient to cause melt to be squeezed from its source. Melt rapidly separates from its source rock once the degree of partial melting exceeds 30%. However, usually much less than 30% of a magma source rock

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3232-524: Is part of California's Wine Country , which also includes Napa , Sonoma , and Mendocino counties. It includes nine American Viticultural Areas and around 20 bonded wineries. Lake County has been inhabited by Pomo Native Americans for over ten thousand years. Pomos had been fishermen and hunters, known especially for their intricate basketry made from lakeshore tules and other native plants and feathers. Pomo people continue to live in Lake County. The area had European American settlers since at least

3333-615: 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 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

3434-545: Is produced by melting of the mantle or the crust in various tectonic settings, which on Earth include subduction zones , continental rift zones , mid-ocean ridges and hotspots . Mantle and crustal melts migrate upwards through the crust where they are thought to be stored in magma chambers or trans-crustal crystal-rich mush zones. During magma's storage in the crust, its composition may be modified by fractional crystallization , contamination with crustal melts, magma mixing, and degassing. Following its ascent through

3535-571: Is provided on Sundays and observed public holidays. Lampson Field ( IATA : CKE , ICAO : LID , FAA LID : 1O2 ) is the county's public airport. A 4,000 foot (1,200 m) airstrip is located in Gravelly Valley, north of Lake Pillsbury . There are also several private airstrips located throughout the county. The county was once host to the Paul Hoberg Airport in the Cobb area, which by

3636-419: Is riddled with natural caves . Although most of the natural caves collapsed or were filled in for safety in the early 20th century, persistent local belief holds that Konocti's central magma chamber is a vast, empty vertical cavern, partly filled with Clear Lake water and connecting with the lake via an underground seep. This cavern might be the largest on Earth, though its existence is difficult to prove due to

3737-448: Is still many orders of magnitude higher than water. This viscosity is similar to that of ketchup . Basalt lavas tend to produce low-profile shield volcanoes or flood basalts , because the fluidal lava flows for long distances from the vent. The thickness of a basalt lava, particularly on a low slope, may be much greater than the thickness of the moving lava flow at any one time, because basalt lavas may "inflate" by supply of lava beneath

3838-459: Is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as lava ) is found beneath the surface of the Earth , and evidence of magmatism has also been discovered on other terrestrial planets and some natural satellites . Besides molten rock, magma may also contain suspended crystals and gas bubbles . Magma

3939-413: Is typically also viscoelastic , meaning it flows like a liquid under low stresses, but once the applied stress exceeds a critical value, the melt cannot dissipate the stress fast enough through relaxation alone, resulting in transient fracture propagation. Once stresses are reduced below the critical threshold, the melt viscously relaxes once more and heals the fracture. Temperatures of molten lava, which

4040-408: Is typically the most abundant magmatic gas, followed by carbon dioxide and sulfur dioxide . Other principal magmatic gases include hydrogen sulfide , hydrogen chloride , and hydrogen fluoride . The solubility of magmatic gases in magma depends on pressure, magma composition, and temperature. Magma that is extruded as lava is extremely dry, but magma at depth and under great pressure can contain

4141-569: The 2nd Senate District , represented by Democrat Mike McGuire . The table below includes the number of actual offenses (including attempts) as reported by the Lake County Sheriff's Office, and the rate per 1,000 persons for each type of offense (crime for the cities of Lakeport and Clearlake is not included and listed in separate table further below). CAL FIRE determined 8 wildfires in their jurisdiction in Lake County were caused by arson in 2023. The county's largest employers are

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4242-658: The Eel River , providing water and power to Ukiah in Mendocino County . Clear Lake is believed to be the oldest warmwater lake in North America , due to a geological fluke. The lake sits on a huge block of stone which slowly tilts in the northern direction at the same rate as the lake fills in with sediment , thus keeping the water at roughly the same depth. The geology of the county is chaotic, being based on Franciscan Assemblage hills. Numerous small faults are present in

4343-666: The Snake River Plain of the northwestern United States. Intermediate or andesitic magmas contain 52% to 63% silica, and are lower in aluminium and usually somewhat richer in magnesium and iron than felsic magmas. 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, in 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

4444-612: The aerospace industry. Lake County's economy is largely driven by agriculture. The main crops in 2022 were: The first vineyards in Lake County were planted in the late 19th century, but Prohibition and its remoteness dealt a blow to the area's viticulture . A reemergence of the wine industry began in the 1970s, although most of the region's grapes are still trucked to neighboring Napa , Sonoma and Mendocino counties for vinification . The county saw its vineyard acreage increase from fewer than 100 acres (40 ha) in 1965 to more than 11,000 acres (4,500 ha) in 2023 The region

4545-458: The calc-alkaline series, an important part of the continental crust . With low density and viscosity, hydrous magmas are highly buoyant and will move upwards in Earth's mantle. The addition of carbon dioxide is relatively a much less important cause of magma formation than the addition of water, but genesis of some silica-undersaturated magmas has been attributed to the dominance of carbon dioxide over water in their mantle source regions. In

4646-453: The convection of solid mantle, it will cool slightly as it expands in an adiabatic process , but the cooling is only about 0.3 °C per kilometer. Experimental studies of appropriate peridotite samples document that the solidus temperatures increase by 3 °C to 4 °C per kilometer. If the rock rises far enough, it will begin to melt. Melt droplets can coalesce into larger volumes and be intruded upwards. This process of melting from

4747-706: The healthcare industry , Native American casinos , grocery stores, school districts , and electricity company Calpine , which operates in the Geysers geothermal field in the Mayacamas Mountains . The only significant manufacturing operations in Lake County are Stokes Ladders in Kelseyville , which builds orchard and industrial ladders, and Reynolds Systems in Middletown , which specializes in detonators , igniters , precision initiating couplers, leads and boosters for

4848-442: The 1840s. Lake County was created in 1861 from parts of Napa and Mendocino counties. The eastern boundary of Lake County, which was not clearly specified in the 1861 act, was clarified by legislative acts passed in 1864 and 1868. A major effect of the 1868 act was to include in Lake County the entire watershed of North Fork Cache Creek , which had previously been claimed by Colusa County . The 1911 California Blue Book lists

4949-520: The 2000 Census, 30% of housing units in Lake County were manufactured housing units. This was the highest percentage of any California county. In its early history, Lake County leaned Democratic in Presidential and congressional elections. It supported every Democratic presidential candidate between 1864 and 1916 except Alton B. Parker in his 1904 landslide defeat . Nonetheless, between 1920 and 1984 Lake County tended towards being Republican and

5050-470: The American Lung Association as having the cleanest air in the nation, including in 2013, 2014 and 2015. Lake County has also been ranked 24 times as having the cleanest air in California. Currently, the American Lung Association's website gives Lake County air a "C" grade for high ozone days and an "A" grade for particle pollution. The 2010 United States Census reported that Lake County had

5151-472: The Earth's mantle has cooled too much to produce highly magnesian magmas. Some silicic magmas 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

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5252-465: The Earth's upper crust, but this varies widely by region, from a low of 5–10 °C/km within oceanic trenches and subduction zones to 30–80 °C/km along mid-ocean ridges or near mantle plumes . The gradient becomes less steep with depth, dropping to just 0.25 to 0.3 °C/km in the mantle, where slow convection efficiently transports heat. The average geothermal gradient is not normally steep enough to bring rocks to their melting point anywhere in

5353-568: The acquisition by non-profit Lake County Land Trust of the 255-acre Black Forest, which would eventually be transferred to the Bureau of Land Management . The majority of Konocti had been owned by private parties, most notably the Fowler family, which had discouraged exploration and study of the mountain. In 2009, the County of Lake purchased 1,520 acres on top of the mountain, and Mt. Konocti County Park opened to

5454-476: The anorthite is melted. If the anorthite content of the mixture is less than 43%, then all the anorthite will melt at the eutectic temperature, along with part of the diopside, and the remaining diopside will then gradually melt as the temperature continues to rise. Because of eutectic melting, the composition of the melt can be quite different from the source rock. For example, a mixture of 10% anorthite with diopside could experience about 23% partial melting before

5555-638: The area around Konocti for as much as 11,000 years. The name "Konocti" is derived from the Pomo "kno", mountain, and "htai", woman. In 1987, a group of investors formed the Mt. Konocti Gondola Company, in order to raise capital for a $ 4.5 million project to build a gondola lift that would take passengers from the Buckingham peninsula to Buckingham Peak, where a restaurant and an amphitheater could be built. The project prompted conservationist opposition, and eventually led in 2004 to

5656-687: The base of the mountain, on the south shore of the lake. Mount Konocti probably first erupted some 350,000 years ago and last erupted 11,000 years ago. Mount Konocti has an explosive, eruptive history with devastating lava flows ending about 13,000 years ago that formed the mountains from Clearlake Oaks to Ukiah . Clear Lake is much older and is possibly the oldest securely dated lake in North America. Core samples taken by U.S. Geological Survey geologists in 1973 and 1980 have been dated to 480,000 years. Archaeologists have found evidence that native people, principally Pomo and Wappo people, have inhabited

5757-548: The county seat of Lakeport and Clearlake , the largest city, and the communities of Kelseyville , Blue Lakes, Clearlake Oaks , Clearlake Park, Cobb , Finley, Glenhaven, Hidden Valley Lake , Clearlake Riviera , Loch Lomond, Lower Lake , Lucerne , Middletown , Nice , Spring Valley, Upper Lake , Whispering Pines, and Witter Springs. Lake County is mostly agricultural, with tourist facilities and some light industry. Major crops include pears , walnuts and, increasingly, wine grapes . According to official estimates based on

5858-458: The crust or upper mantle, so magma is produced only where the geothermal gradient is unusually steep or the melting point of the rock is unusually low. However, the ascent of magma towards the surface in such settings is the most important process for transporting heat through the crust of the Earth. Rocks may melt in response to a decrease in pressure, to a change in composition (such as an addition of water), to an increase in temperature, or to

5959-603: The crust, magma may feed a volcano and be extruded as lava, or it may solidify underground to form an intrusion , such as a dike , a sill , a laccolith , a pluton , or a batholith . While the study of magma has relied on observing magma after its transition into a lava flow , magma has been encountered in situ three times during geothermal drilling projects , twice in Iceland (see Use in energy production ) and once in Hawaii. Magma consists of liquid rock that usually contains suspended solid crystals. As magma approaches

6060-455: The crystallization process would not change the overall composition of the melt plus solid minerals. This situation is described as equillibrium crystallization . However, in a series of experiments culminating in his 1915 paper, Crystallization-differentiation in silicate liquids , Norman L. Bowen demonstrated that crystals of olivine and diopside that crystallized out of a cooling melt of forsterite , diopside, and silica would sink through

6161-618: The dominant geographic feature in the county and the largest non-extinct natural lake wholly within California. ( Lake Tahoe is partially in Nevada ; the Salton Sea was formed by flooding; Tulare Lake was drained by the agricultural industry.) Lake County forms the Clearlake, California micropolitan statistical area . It is directly north of the San Francisco Bay Area . Lake County

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6262-588: The early 1980s was considered abandoned. In 1888 the Vaca Valley and Clear Lake Railroad reached Rumsey , but the planned line to Clear Lake was never built. The Clear Lake Railroad started work on a line from Hopland to Lakeport: "In November 1911 first ground was broken for the Hopland-Clear Lake railroad to Hopland. Mrs Harriet Lee Hammond, wife of the president of the road started construction. ... There were six miles of track out of Hopland ...", but this

6363-399: The eutectic temperature of 1274 °C. This shifts the remaining melt towards its eutectic composition of 43% diopside. The eutectic is reached at 1274 °C, the temperature at which diopside and anorthite begin crystallizing together. If the melt was 90% diopside, the diopside would begin crystallizing first until the eutectic was reached. If the crystals remained suspended in the melt,

6464-512: The extensive basalt magmatism of several large igneous provinces. Decompression melting occurs because of a decrease in pressure. It is the most important mechanism for producing magma from the upper mantle. The solidus temperatures of most rocks (the temperatures below which they are completely solid) increase with increasing pressure in the absence of water. Peridotite at depth in the Earth's mantle may be hotter than its solidus temperature at some shallower level. If such rock rises during

6565-420: The importance of each mechanism being a topic of continuing research. The change of rock composition most responsible for the creation of magma is the addition of water. Water lowers the solidus temperature of rocks at a given pressure. For example, at a depth of about 100 kilometers, peridotite begins to melt near 800 °C in the presence of excess water, but near 1,500 °C in the absence of water. Water

6666-432: The late 19th century, the worldwide popularity of mineral water for the relief of myriad physical ailments resulted in the development of mineral resorts around Clear Lake. Lake County has a mediterranean climate with hot summer daytime temperatures in its lower elevations. Nighttime temperatures remain cool year-round, somewhat moderating average temperatures and relieving the summer heat. Lake County has been ranked by

6767-476: The magma completely solidifies, and the liquidus , defined as the temperature at which the magma is completely liquid. Calculations of solidus temperatures at likely depths suggests that magma generated beneath areas of rifting starts at a temperature of about 1,300 to 1,500 °C (2,400 to 2,700 °F). Magma generated from mantle plumes may be as hot as 1,600 °C (2,900 °F). The temperature of magma generated in subduction zones, where water vapor lowers

6868-408: The magma. Gabbro may have a liquidus temperature near 1,200 °C, and the derivative granite-composition melt may have a liquidus temperature as low as about 700 °C. Incompatible elements are concentrated in the last residues of magma during fractional crystallization and in the first melts produced during partial melting: either process can form the magma that crystallizes to pegmatite ,

6969-600: The main part of the mountain, while Buckingham Peak and Clark Peak are located off to the side. Konocti Road runs about 4 miles (6.4 km) east from the Taylor Planetarium & Observatory in the town of Kelseyville, snaking between Howard and South Peaks and ending at the mountain's summit, Wright Peak. Snow Mountain and Lassen Peak can be seen from Wright Peak. Benson Ridge lies to the south of Clark Peak and west of South Peak. Buckingham Peak lies north of Howard and Wright Peaks and northeast of Clark Peak. South Peak

7070-428: The major crops as Bartlett pears and beans. Other crops include grain, alfalfa, hay, prunes, peaches, apples, grapes and walnuts. Stockraising included goats, hogs, turkeys and dairying. Some vineyards were planted in the 1870s by European Americans, but the first in the state were established in the 18th century by Spanish missionaries. By the early 20th century, the area was earning a reputation for producing some of

7171-419: The mantle than subalkaline magmas. Olivine nephelinite magmas are both ultramafic and highly alkaline, and are thought to have come from much deeper in the mantle of the Earth than other magmas. Tholeiitic basalt magma Rhyolite magma Some lavas of unusual composition have erupted onto the surface of the Earth. These include: The concentrations of different gases can vary considerably. Water vapor

7272-424: The melt at different temperatures. This resembles the original melting process in reverse. However, because the melt has usually separated from its original source rock and moved to a shallower depth, the reverse process of crystallization is not precisely identical. For example, if a melt was 50% each of diopside and anorthite, then anorthite would begin crystallizing from the melt at a temperature somewhat higher than

7373-438: The melt at the eutectic composition. Further heating causes the temperature to slowly rise as the remaining anorthite gradually melts and the melt becomes increasingly rich in anorthite liquid. If the mixture has only a slight excess of anorthite, this will melt before the temperature rises much above 1274 °C. If the mixture is almost all anorthite, the temperature will reach nearly the melting point of pure anorthite before all

7474-449: The melt deviated from the eutectic, which has the composition of about 43% anorthite. This effect of partial melting is reflected in the compositions of different magmas. A low degree of partial melting of the upper mantle (2% to 4%) can produce highly alkaline magmas such as melilitites , while a greater degree of partial melting (8% to 11%) can produce alkali olivine basalt. Oceanic magmas likely result from partial melting of 3% to 15% of

7575-402: The melt on geologically relevant time scales. Geologists subsequently found considerable field evidence of such fractional crystallization . When crystals separate from a magma, then the residual magma will differ in composition from the parent magma. For instance, a magma of gabbroic composition can produce a residual melt of granitic composition if early formed crystals are separated from

7676-429: The melting temperature, may be as low as 1,060 °C (1,940 °F). Magma densities depend mostly on composition, iron content being the most important parameter. Magma expands slightly at lower pressure or higher temperature. When magma approaches the surface, its dissolved gases begin to bubble out of the liquid. These bubbles had significantly reduced the density of the magma at depth and helped drive it toward

7777-481: The more abundant elements in the source rock. The ions of these elements fit rather poorly in the structure of the minerals making up the source rock, and readily leave the solid minerals to become highly concentrated in melts produced by a low degree of partial melting. Incompatible elements commonly include potassium , barium , caesium , and rubidium , which are large and weakly charged (the large-ion lithophile elements, or LILEs), as well as elements whose ions carry

7878-415: The most abundant chemical elements in 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 magma in terms of the weight or molar mass fraction of the oxides of the major elements (other than oxygen) present in the magma. Because many of

7979-439: The presence of carbon dioxide, experiments document that the peridotite solidus temperature decreases by about 200 °C in a narrow pressure interval at pressures corresponding to a depth of about 70 km. At greater depths, carbon dioxide can have more effect: at depths to about 200 km, the temperatures of initial melting of a carbonated peridotite composition were determined to be 450 °C to 600 °C lower than for

8080-630: The properties of a magma (such as its viscosity and temperature) are observed to correlate with silica content, silicate magmas are divided into four chemical types based on silica content: felsic , intermediate , mafic , and ultramafic . Felsic or silicic magmas have a silica content greater than 63%. They include rhyolite and dacite magmas. With such a high silica content, these magmas are extremely viscous, ranging from 10 cP (10 Pa⋅s) for hot rhyolite magma at 1,200 °C (2,190 °F) to 10 cP (10 Pa⋅s) for cool rhyolite magma at 800 °C (1,470 °F). For comparison, water has

8181-437: The public on September 24, 2011. Pomo legend has it that around the year 1818, after a long drought, the level of Clear Lake dropped so low that a previously unknown cave on the eastern flank of Konocti was exposed. A group of Pomo men entered the cave, and discovered a vast underground lake, containing "blind fish". Repeated attempts by divers to locate this cave have been unsuccessful. Local people have long known that Konocti

8282-411: The rate of flow is proportional to the shear stress . Instead, a typical magma 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 magma. A familiar example of plug flow is toothpaste squeezed out of a toothpaste tube. The toothpaste comes out as a semisolid plug, because shear

8383-526: The rest of the nation in that year. In 2005, the American Community Survey reported that 14.4% of Lake County's owner-occupied dwellings are valued over a half a million dollars. In the county, the population was spread out, with 24.1% under the age of 18, 6.0% from 18 to 24, 23.6% from 25 to 44, 26.8% from 45 to 64, and 19.5% who were 65 years of age or older. The median age was 43 years. For every 100 females there were 97.6 males. For every 100 females age 18 and over, there were 94.7 males. The median income for

8484-405: The roof of a magma chamber and fractional crystallization near its base can even take place simultaneously. Magmas of different compositions can mix with one another. In rare cases, melts can separate into two immiscible melts of contrasting compositions. When rock melts, the liquid is a primary magma . Primary magmas have not undergone any differentiation and represent the starting composition of

8585-405: The same composition with no carbon dioxide. Magmas of rock types such as nephelinite , carbonatite , and kimberlite are among those that may be generated following an influx of carbon dioxide into mantle at depths greater than about 70 km. Increase in temperature is the most typical mechanism for formation of magma within continental crust. Such temperature increases can occur because of

8686-442: The same lavas ranges over seven orders of magnitude, from 10 cP (10 Pa⋅s) for mafic lava to 10 cP (10 Pa⋅s) for felsic magmas. The viscosity is mostly determined by composition but is also dependent on temperature. The tendency of felsic lava to be cooler than mafic lava increases the viscosity difference. The silicon ion is small and highly charged, and so it has a strong tendency to coordinate with four oxygen ions, which form

8787-404: The source rock. Some calk-alkaline granitoids may be produced by a high degree of partial melting, as much as 15% to 30%. High-magnesium magmas, such as komatiite and picrite , may also be the products of a high degree of partial melting of mantle rock. Certain chemical elements, called incompatible elements , have a combination of ionic radius and ionic charge that is unlike that of

8888-456: The south end of the lake as well as many old volcanoes , the largest being Cobb Mountain . The geologic history of the county shows events of great violence, such as the eruption of Mount Konocti and Mount St. Helena and the collapse of Cow Mountain , which created the hills around the county seat of Lakeport . Blue Lakes , Lake Pillsbury, and Indian Valley Reservoir are the county's other major bodies of water. Lake County has habitats for

8989-425: The southwestern side of the mountain, was built by boy scouts as an aviation marker. The wreckage of a 1946 Navion A aircraft, which crashed on Wright Peak in 1970, claiming two lives, is commemorated with an interpretive panel. A fire lookout tower was erected in 1977 atop Wright Peak. The structure is a historical landmark, and after 12 years of closure, it was staffed again with volunteers in 2016, until it

9090-468: The surface and the overburden pressure drops, dissolved gases bubble out of the liquid, so that magma near the surface consists of materials in solid, liquid, and gas phases . Most magma is rich in silica . Rare nonsilicate magma can form by local melting of nonsilicate mineral deposits or by separation of a magma into separate immiscible silicate and nonsilicate liquid phases. Silicate magmas are molten mixtures dominated by oxygen and silicon ,

9191-401: The surface in the first place. The temperature within the interior of the earth is described by the geothermal gradient , which is the rate of temperature change with depth. The geothermal gradient is established by the balance between heating through radioactive decay in the Earth's interior and heat loss from the surface of the earth. The geothermal gradient averages about 25 °C/km in

9292-409: The unstable and eroding structure of the volcano's cone. Heavy vegetation also conceals cave entrances. No accurate map or survey of the caves has been created due to the heavy underbrush and unstable hillsides. Arctostaphylos manzanita subsp. elegans , a manzanita subspecies, is commonly called "Konocti manzanita". A B-24 bomber attached to the 566th Bombardment Squadron during World War II

9393-613: The upward intrusion of magma from the mantle. Temperatures can also exceed the solidus of a crustal rock in continental crust thickened by compression at a plate boundary . The plate boundary between the Indian and Asian continental masses provides a well-studied example, as the Tibetan Plateau just north of the boundary has crust about 80 kilometers thick, roughly twice the thickness of normal continental crust. Studies of electrical resistivity deduced from magnetotelluric data have detected

9494-462: The upward movement of solid mantle is critical in the evolution of the Earth. Decompression melting creates the ocean crust at mid-ocean ridges , making it by far the most important source of magma on Earth. It also causes volcanism in intraplate regions, such as Europe, Africa and the Pacific sea floor. Intraplate volcanism is attributed to the rise of mantle plumes or to intraplate extension, with

9595-467: The viscosity. Higher-temperature melts are less viscous, since more thermal energy is available to break bonds between oxygen and network formers. Most magmas contain solid crystals of various minerals, fragments of exotic rocks known as xenoliths and fragments of previously solidified magma. The crystal content of most magmas gives them thixotropic and shear thinning properties. In other words, most magmas do not behave like Newtonian fluids, in which

9696-582: The vote. On November 4, 2008, Lake County voted 52.6% for Proposition 8, which amended the California Constitution to ban same-sex marriages. In 2022, the county was won by Republicans in several statewide races. Lake County is in California's 4th congressional district , represented by Mike Thompson ( D – St. Helena ). In the state legislature , Lake is in the 4th Assembly District , represented by Democrat Cecilia Aguiar-Curry , and

9797-417: The world's greatest wines. However, in 1920, national prohibition essentially ended Lake County's wine production. With authorized cultivation limited to sacramental purposes, most of the vineyards were ripped out and replanted with walnut and pear orchards. According to the U.S. Census Bureau , the county has a total area of 1,329 square miles (3,440 km ), of which 1,256 square miles (3,250 km )

9898-450: Was also abandoned. ★ As of 2022, the U.S. Census continues to use the community's former name of Clear Lake Riviera . The population ranking of the following table is based on the 2010 census of Lake County. † county seat 39°05′N 122°46′W  /  39.09°N 122.76°W  / 39.09; -122.76 Magma Magma (from Ancient Greek μάγμα ( mágma )  'thick unguent ')

9999-425: Was deemed unsafe in 2019. Cellular and communication tower facilities are located on top of Buckingham Peak, Wright Peak, Howard Peak and South Peak. Lake County, California Lake County is a county located in the north central portion of the U.S. state of California . As of the 2020 census , the population was 68,163. The county seat is Lakeport . The county takes its name from Clear Lake ,

10100-433: Was named Princess Konocti by Lakeport -born pilot William H. Wambold. The trail to Wright Peak in the Mt. Konocti County Park snakes by the remnants of Mary Downen's cabin, a homesteader who lived on the mountain from 1909 until her death in 1942. Starting in 1921, hikers were required to sign a ledger, which was maintained at her cabin. A giant "K", standing for Kelseyville and formed by painted rocks on Clark Peak, on

10201-547: Was won by just four Democratic nominees – Franklin D. Roosevelt in 1932 and 1936, Lyndon B. Johnson in 1964 and Jimmy Carter in 1976. Ronald Reagan in 1984 remains the last Republican to win a majority in the county, which has reverted to leaning Democratic. In 2016, Republicans broke 40% of the vote for the first time since 2004, and Democrats failed to win 50% of the vote for the first time since 1996. Democrats broke 50% again in 2020, increasing their margin of victory, although Republicans still increased their percentage of

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