76-724: Lady Julia Percy Island , known as Deen Maar or Dhinmar in the Gunditjmara language , lies 8.1 kilometres (5.0 mi) off the coast, in the Barwon South West region of Victoria, Australia in Bass Strait . The island is an unincorporated area under the direct administration of the Government of Victoria . Lady Julia Percy Island is 12 kilometres (7.5 mi) south-south-west of Yambuk , and 21 kilometres (13 mi) south-west of Port Fairy . The island
152-423: A mantle wedge above the descending slab. The slab releases water vapor and other volatiles as it descends, which further lowers the melting point, further increasing the amount of decompression melting. Each tectonic setting produces basalt with its own distinctive characteristics. The mineralogy of basalt is characterized by a preponderance of calcic plagioclase feldspar and pyroxene . Olivine can also be
228-493: A basalt is diagnostic of how and where it erupted—for example, whether into the sea, in an explosive cinder eruption or as creeping pāhoehoe lava flows, the classic image of Hawaiian basalt eruptions. Basalt that erupts under open air (that is, subaerially ) forms three distinct types of lava or volcanic deposits: scoria ; ash or cinder ( breccia ); and lava flows. Basalt in the tops of subaerial lava flows and cinder cones will often be highly vesiculated , imparting
304-595: A comprehensive ecological survey. In the waters on the western side of Lady Julia Percy Island lie pieces of an RAAF Avro Anson aircraft. On 15 February 1944, Avro Anson AW-878 of 2 Air Observer's School (2 A.O.S.) took off from Mount Gambier airfield in South Australia at 0800 hours to carry out a radius of action navigation exercise. They were to fly from Mount Gambier to Douglas Point, radius of action to Lady Julia Percy Island, radius of action to Douglas Point and then back to Mount Gambier. At 1230 hours, when
380-442: A distinctive pillow shape, through which the hot lava breaks to form another pillow. This "pillow" texture is very common in underwater basaltic flows and is diagnostic of an underwater eruption environment when found in ancient rocks. Pillows typically consist of a fine-grained core with a glassy crust and have radial jointing. The size of individual pillows varies from 10 cm up to several metres. When pāhoehoe lava enters
456-427: A flow can shrink in the vertical dimension without fracturing, it cannot easily accommodate shrinking in the horizontal direction unless cracks form; the extensive fracture network that develops results in the formation of columns . These structures, or basalt prisms , are predominantly hexagonal in cross-section, but polygons with three to twelve or more sides can be observed. The size of the columns depends loosely on
532-408: A form of avoidance speech called gnee wee banott (turn tongue) which required special terms and grammar in conversations when a man and mother-in-law were speaking in each other's company. Thus, if one asked: "Where are you going just now?", this would be phrased in normal speech as: In Gunditjmara avoidance speech the same sentiment would be articulated quite differently: The term ngamadjidj
608-465: A high content of plagioclase; these are sometimes described as leucobasalts . It can be difficult to distinguish between lighter-colored basalt and andesite , so field researchers commonly use a rule of thumb for this purpose, classifying it as basalt if it has a color index of 35 or greater. The physical properties of basalt result from its relatively low silica content and typically high iron and magnesium content. The average density of basalt
684-621: A lightweight "frothy" texture to the rock. Basaltic cinders are often red, coloured by oxidized iron from weathered iron-rich minerals such as pyroxene . ʻAʻā types of blocky cinder and breccia flows of thick, viscous basaltic lava are common in Hawaiʻi. Pāhoehoe is a highly fluid, hot form of basalt which tends to form thin aprons of molten lava which fill up hollows and sometimes forms lava lakes . Lava tubes are common features of pāhoehoe eruptions. Basaltic tuff or pyroclastic rocks are less common than basaltic lava flows. Usually basalt
760-623: A lower total content of alkali oxides than trachybasalt and most basanites and tephrites. Basalt generally has a composition of 45–52 wt% SiO 2 , 2–5 wt% total alkalis, 0.5–2.0 wt% TiO 2 , 5–14 wt% FeO and 14 wt% or more Al 2 O 3 . Contents of CaO are commonly near 10 wt%, those of MgO commonly in the range 5 to 12 wt%. High-alumina basalts have aluminium contents of 17–19 wt% Al 2 O 3 ; boninites have magnesium (MgO) contents of up to 15 percent. Rare feldspathoid -rich mafic rocks, akin to alkali basalts, may have Na 2 O + K 2 O contents of 12% or more. The abundances of
836-507: A phenocryst, and when present, may have rims of pigeonite. The groundmass contains interstitial quartz or tridymite or cristobalite . Olivine tholeiitic basalt has augite and orthopyroxene or pigeonite with abundant olivine, but olivine may have rims of pyroxene and is unlikely to be present in the groundmass . Alkali basalts typically have mineral assemblages that lack orthopyroxene but contain olivine. Feldspar phenocrysts typically are labradorite to andesine in composition. Augite
SECTION 10
#1732766179170912-523: A significant constituent. Accessory minerals present in relatively minor amounts include iron oxides and iron-titanium oxides, such as magnetite , ulvöspinel , and ilmenite . Because of the presence of such oxide minerals, basalt can acquire strong magnetic signatures as it cools, and paleomagnetic studies have made extensive use of basalt. In tholeiitic basalt , pyroxene ( augite and orthopyroxene or pigeonite ) and calcium -rich plagioclase are common phenocryst minerals. Olivine may also be
988-496: A volcanic vent. Six successive lava flows can be seen in the coastal cliffs. It is Australia’s only off-shore volcano and the only large basalt island off the coast of western Victoria. Lady Julia Percy Island is considered part of the Newer Volcanics Province — this polycyclic volcano erupted in two phases, at 7.80 ± 0.08 Ma and 6.22 ± 0.06 Ma With regard to the flora, Frederic Wood Jones said in 1936 of
1064-425: A windswept area, clothed only by vegetation knee-high at the best, and at the worst, by loose volcanic soil or bare rock. This denudation of forest cover is due to human interference, for pigs were at one time turned down on the island, rabbits were liberated and are still living in their thousands, and sealers, fishermen and guano workers have cut down and burned the stunted and wind-blown trees that formerly covered
1140-427: Is 2.9 g/cm , compared, for example, to granite ’s typical density of 2.7 g/cm . The viscosity of basaltic magma is relatively low—around 10 to 10 cP —similar to the viscosity of ketchup , but that is still several orders of magnitude higher than the viscosity of water, which is about 1 cP). Basalt is often porphyritic , containing larger crystals ( phenocrysts ) that formed before the extrusion event that brought
1216-440: Is about 2 kilometres (1.2 mi) in length by 1 kilometre (0.62 mi) in width, with an area of 1.33 square kilometres (0.51 sq mi), comprising a plateau, varying in height from 32–46 metres (105–151 ft) asl , surrounded by cliffs, rock platforms and reefs. It contains an important seal breeding colony. It has a long history of human exploitation, which has drastically affected its vegetation communities, though it
1292-688: Is also an important rock type on other planetary bodies in the Solar System . For example, the bulk of the plains of Venus , which cover ~80% of the surface, are basaltic; the lunar maria are plains of flood-basaltic lava flows ; and basalt is a common rock on the surface of Mars . Molten basalt lava has a low viscosity due to its relatively low silica content (between 45% and 52%), resulting in rapidly moving lava flows that can spread over great areas before cooling and solidifying. Flood basalts are thick sequences of many such flows that can cover hundreds of thousands of square kilometres and constitute
1368-401: Is also produced by some subglacial volcanic eruptions. Basalt is the most common volcanic rock type on Earth, making up over 90% of all volcanic rock on the planet. The crustal portions of oceanic tectonic plates are composed predominantly of basalt, produced from upwelling mantle below the ocean ridges . Basalt is also the principal volcanic rock in many oceanic islands , including
1444-588: Is also referred to as Gunditjmara language and the Warrnambool language . Efforts to revive the language(s) are ongoing. The language in its several varieties, was spoken from Glenelg to the Gellibrand and through to roughly 100 kilometres (60 mi) inland. The effects of the colonisation of Victoria , which included the Eumeralla Wars , along with later government policies leading to
1520-761: Is considered a key to understanding plate tectonics , its compositions have been much studied. Although MORB compositions are distinctive relative to average compositions of basalts erupted in other environments, they are not uniform. For instance, compositions change with position along the Mid-Atlantic Ridge , and the compositions also define different ranges in different ocean basins. Mid-ocean ridge basalts have been subdivided into varieties such as normal (NMORB) and those slightly more enriched in incompatible elements (EMORB). Isotope ratios of elements such as strontium , neodymium , lead , hafnium , and osmium in basalts have been much studied to learn about
1596-481: Is defined as volcanic rock with a content of between 45% and 52% silica and no more than 5% alkali metal oxides. This places basalt in the B field of the TAS diagram. Such a composition is described as mafic . Basalt is usually dark grey to black in colour, due to a high content of augite or other dark-coloured pyroxene minerals, but can exhibit a wide range of shading. Some basalts are quite light-coloured due to
SECTION 20
#17327661791701672-886: Is looking at ways to improve the environment for the birds, including a project to eradicate the rabbits. After consultation, the Eastern Maar Aboriginal Corporation and Gunditj Mirring Traditional Owners Aboriginal Corporation are supporting the project. There are several phases to the project, which is aimed to completely eradicate the pest by destroying every last rabbit. Baiting is done by hand using chopped carrots that have been had calicivirus or rabbit haemorrhagic disease virus (RHDV) in them, and by helicopter, dropping baited cereal pellets onto less accessible spots such as cliff ledges. Remaining rabbits are counted after each baiting drop. Some time after baiting, dogs specially trained to detect rabbits, along with eradication experts, spend around 10 days on
1748-518: Is now protected as a State Faunal Reserve. It is listed on Australia's Register of the National Estate . It is best viewed from The Crags or Yambuk Lake, both of which are in the Yambuk area. Deen Maar was well known to the Gunditjmara people ; they believed that the spirits of the dead were conveyed across the sea to the island from a cave called Tarnwirring ("the flowing of the wind") at
1824-729: Is of the Girai wurrung people Gadubanud ( Tindale Katubanut), also Yarro waetch, "Cape Otway tribe", was spoken by a group known as the Gadubanud , of the Cape Otway area. Barry Blake regards this as a dialect of the Warrnambool language, but Krishna-Pillay does not. Djargurd Wurrong (Warn tallin, Warn thalayn, Tjarcote, Dhautgart/Keerray (wurru)) was the language of the Djargurd Wurrong people. Other dialects or alternative names include: Speakers of these languages had
1900-589: Is one of four Australian fur seal breeding colonies in Victoria and, with an estimated 10-12,000 individuals, is the largest such colony in Australia. It is occasionally visited by Australian sea lions and southern elephant seals . Several seabird species use the island for breeding. These include some that inhabit the island permanently, such as the short-tailed shearwater , fairy prion , and common diving petrel , and also birds that visit from afar, such as
1976-402: Is regarded by some as a separate language, by others as a dialect. The dialect continuum consisted of various lects such as Kuurn Kopan Noot , Big Wurrung , Gai Wurrung , and others (each with variant spellings). There was no traditional name for the entire dialect continuum and it has been classified and labelled differently by different linguists and researchers. The group of languages
2052-583: Is rich in titanium compared to augite in tholeiitic basalt. Minerals such as alkali feldspar , leucite , nepheline , sodalite , phlogopite mica, and apatite may be present in the groundmass. Basalt has high liquidus and solidus temperatures—values at the Earth's surface are near or above 1200 °C (liquidus) and near or below 1000 °C (solidus); these values are higher than those of other common igneous rocks. The majority of tholeiitic basalts are formed at approximately 50–100 km depth within
2128-726: Is sung entirely in the Gunditjmara language. The first performance of the requiem, "Eumeralla, a war requiem for peace" on 15 June 2019 in Melbourne featured Cheetham with the Melbourne Symphony Orchestra , the MSO Chorus and the Dhungala Children's Choir. A likely phonemic inventory for the Warrnambool language is shown below. Rhotic consonants were not distinguished in older sources. It
2204-402: Is suppressed. Above this depth, submarine eruptions are often explosive, tending to produce pyroclastic rock rather than basalt flows. These eruptions, described as Surtseyan, are characterised by large quantities of steam and gas and the creation of large amounts of pumice . When basalt erupts underwater or flows into the sea, contact with the water quenches the surface and the lava forms
2280-523: Is the only reptile present. The surrounding waters are visited by great white sharks . Feral rabbits still exist on the island. Rabbits have been competing with native and other species of seabird, by taking up valuable space that could be used for nesting sites for the birds. They can also make the soil unsuitable for future use as nesting sites. As of August 2023 the Victorian Department of Energy, Environment and Climate Action (DEECA)
2356-440: Is too hot and fluid to build up sufficient pressure to form explosive lava eruptions but occasionally this will happen by trapping of the lava within the volcanic throat and buildup of volcanic gases . Hawaiʻi's Mauna Loa volcano erupted in this way in the 19th century, as did Mount Tarawera , New Zealand in its violent 1886 eruption. Maar volcanoes are typical of small basalt tuffs, formed by explosive eruption of basalt through
Lady Julia Percy Island - Misplaced Pages Continue
2432-455: Is ultimately derived from Late Latin basaltes , a misspelling of Latin basanites "very hard stone", which was imported from Ancient Greek βασανίτης ( basanites ), from βάσανος ( basanos , " touchstone "). The modern petrological term basalt , describing a particular composition of lava -derived rock, became standard because of its use by Georgius Agricola in 1546, in his work De Natura Fossilium . Agricola applied
2508-447: Is unclear to determine whether the retroflex consonant was a glide [ɻ] or a flap [ɽ]. Both were written as r . Although most Australian Aboriginal languages use three vowels /a/, /i/, and /u/, the amount of vowels are not clearly distinguished within the other sources for the Warrnambool language, although it may be likely that it had a five-vowel system as /a, e, i, o, u/. There is some fluctuation between /i/ and /e/, and /u/ and /o/. In
2584-694: The 2016 Australian census . There are several ongoing efforts to revive the Gunditjmara language. These include the Gunditj Wurrung online lesson series on YouTube and the Laka Gunditj Language Program. Proponents of the revival of the language include Vicki Couzens and Corey Theatre, who uses music as a medium for language revival. Gunditjmara composer, singer and guitarist, Corey Theatre in collaboration with Australian composer and music director Iain Grandage created
2660-539: The Clementine mission demonstrate that the lunar maria possess a continuum of titanium concentrations, and that the highest concentrations are the least abundant. Lunar basalts show exotic textures and mineralogy, particularly shock metamorphism , lack of the oxidation typical of terrestrial basalts, and a complete lack of hydration . Most of the Moon 's basalts erupted between about 3 and 3.5 billion years ago, but
2736-1228: The Paraná Traps in Brazil, the Siberian Traps in Russia , the Karoo flood basalt province in South Africa, and the Columbia River Plateau of Washington and Oregon . Basalt is also prevalent across extensive regions of the Eastern Galilee , Golan , and Bashan in Israel and Syria . Basalt also is common around volcanic arcs, specially those on thin crust . Ancient Precambrian basalts are usually only found in fold and thrust belts, and are often heavily metamorphosed. These are known as greenstone belts , because low-grade metamorphism of basalt produces chlorite , actinolite , epidote and other green minerals. As well as forming large parts of
2812-445: The albatross , sooty oystercatcher , and crested tern . The island is home to breeding little penguins (2000 pairs), common diving-petrels (1000 pairs), fairy prions (1000 pairs), and short-tailed shearwaters (15,000 pairs). Ground-dwelling birds include the stubble quail , swamp harrier , peregrine falcon , nankeen kestrel , white-fronted chat , Richard's pipit , welcome swallow , and little grassbird . White's skink
2888-524: The hypabyssal and plutonic equivalents of basalt. During the Hadean , Archean , and early Proterozoic eons of Earth's history, the chemistry of erupted magmas was significantly different from what it is today, due to immature crustal and asthenosphere differentiation. The resulting ultramafic volcanic rocks, with silica (SiO 2 ) contents below 45% and high magnesium oxide (MgO) content, are usually classified as komatiites . The word "basalt"
2964-524: The lanthanide or rare-earth elements (REE) can be a useful diagnostic tool to help explain the history of mineral crystallisation as the melt cooled. In particular, the relative abundance of europium compared to the other REE is often markedly higher or lower, and called the europium anomaly . It arises because Eu can substitute for Ca in plagioclase feldspar, unlike any of the other lanthanides, which tend to only form cations . Mid-ocean ridge basalts (MORB) and their intrusive equivalents, gabbros, are
3040-787: The stolen generation , had a drastic and ongoing negative effect on the languages. Today the descendants of the speakers of these lects commonly refer to themselves as Gunditjmara, a term derived from an affix used to denote membership with a specific group of locality. AIATSIS ( AUSTLANG ) uses the name and spelling "Dhauwurd Wurrung" for the main grouping, following the Victorian Aboriginal Corporation for Languages and Ian Clark , and gives also detail on alternative groupings and names suggested by various other linguists. Alternative spellings include Djargurd Wurrung, Thaguwurung, Tyaupurt wurung, Dauwert woorong, Dhauhwurru, Dhau-urt-wuru, Tourahonong, and many others, and
3116-463: The Earth's crust, basalt also occurs in other parts of the Solar System. Basalt commonly erupts on Io (the third largest moon of Jupiter ), and has also formed on the Moon , Mars , Venus , and the asteroid Vesta . The dark areas visible on Earth's moon , the lunar maria , are plains of flood basaltic lava flows. These rocks were sampled both by the crewed American Apollo program and
Lady Julia Percy Island - Misplaced Pages Continue
3192-602: The Gunditjmara Six Seasons. The piece is sung entirely in the Gunditjmara language and was performed in collaboration with Aboriginal (Gunditjmara and Bundjalung) Australian musician Archie Roach at the 2016 Port Fairy Spring Music Festival . Australian composer and soprano, Deborah Cheetham , wrote Australia's first requiem based on the frontier wars between Aboriginal Australian people in South Western Victoria and settlers which
3268-401: The aircraft had not returned to base, overdue signals were sent out. At 1300 hours a search was carried out over the route of the exercise and at 1430 hours part of the aircraft was sighted on Lady Julia Percy Island. A fishing boat searched in the vicinity of the island that evening and passed through small pieces of wreckage strewn over about three miles. A further search by boat was carried out
3344-480: The basalt/andesite field of the QAPF diagram. Basalt is further distinguished from andesite by its silica content of under 52%. It is often not practical to determine the mineral composition of volcanic rocks, due to their very small grain size, in which case geologists instead classify the rocks chemically, with particular emphasis on the total content of alkali metal oxides and silica ( TAS ); in that context, basalt
3420-478: The characteristic igneous rocks formed at mid-ocean ridges. They are tholeiitic basalts particularly low in total alkalis and in incompatible trace elements, and they have relatively flat REE patterns normalized to mantle or chondrite values. In contrast, alkali basalts have normalized patterns highly enriched in the light REE, and with greater abundances of the REE and of other incompatible elements. Because MORB basalt
3496-447: The crust, forming an apron of mixed basalt and wall rock breccia and a fan of basalt tuff further out from the volcano. Amygdaloidal structure is common in relict vesicles and beautifully crystallized species of zeolites , quartz or calcite are frequently found. During the cooling of a thick lava flow, contractional joints or fractures form. If a flow cools relatively rapidly, significant contraction forces build up. While
3572-545: The evolution of the Earth's mantle . Isotopic ratios of noble gases , such as He / He, are also of great value: for instance, ratios for basalts range from 6 to 10 for mid-ocean ridge tholeiitic basalt (normalized to atmospheric values), but to 15–24 and more for ocean-island basalts thought to be derived from mantle plumes . Source rocks for the partial melts that produce basaltic magma probably include both peridotite and pyroxenite . The shape, structure and texture of
3648-538: The fact that they could speak the local language. Ngamadjidj is also the name given to a rock art site in a shelter in the Grampians National Park , sometimes translated as the "Cave of Ghosts". Only three speakers were known to speak the language still by 1880, with another four still fluent in the Bi:gwurrung (Peek-Whurrung) dialect. No fluent speakers have been recorded between 1975 and
3724-529: The four crew members were never located. Those presumed to have lost their lives in this accident were: Flight Sergeant James Henry MacLellan (410684) Pilot; Flight Sergeant Dennis Leslie Baulderstone (416712); LAC Norman Thomas Kruck (433368); and LAC Brian Carter Ladyman (436921). Formed some seven million years ago, the island is much older than other volcanoes in the region, and is also unusual in being built by both submarine and terrestrial eruptions. It provides exposures of internal volcanic structure, including
3800-531: The island often for months at a time. There are two graves on the island – one of a sealer buried in 1822, and one of a man named Hardman buried in 1828 by Captain Wishart of the Fairy . Guano was mined on the island for fertiliser until 1861, being transported to Port Fairy in barges. In January 1936 a scientific expedition from Melbourne University 's McCoy Society visited the island for six weeks and carried out
3876-434: The island to find the last few rabbits. The project team will monitor Deen Maar for a further three years before declaring eradication of the pest. Access to Lady Julia Percy Island is restricted by law, and landing is by permit only. Access is only possible in a tiny boat, and entails climbing up a small cliff upon landing. Boat cruises from Port Fairy to the waters around the island are available; they allow people to see
SECTION 50
#17327661791703952-481: The island, following his leadership of the 1936 McCoy Society expedition: A century ago it was covered with a dense, almost impenetrable, growth of the mixed bushy scrub that characterizes certain parts of the coast of the adjacent mainland. Some sixty years ago this dense scrub was still standing over the major portion of the island; but to-day the whole of the plateau is devoid of any growth more majestic than bracken fern and thistles. The whole plateau is, at present,
4028-413: The island. The landscape of the island's plateau is now bleak and windswept. It lacks trees and is still largely covered with grasses and bracken on thin black soil. In some areas, the soil has collapsed into the underlying rabbit warrens . The dominant vegetation communities are grassland and closed fernland. The vulnerable Shore Spleenwort ( Asplenium obtusatum ) still survives there. The island
4104-740: The islands of Hawaiʻi , the Faroe Islands , and Réunion . The eruption of basalt lava is observed by geologists at about 20 volcanoes per year. Basalt is the rock most typical of large igneous provinces . These include continental flood basalts , the most voluminous basalts found on land. Examples of continental flood basalts included the Deccan Traps in India , the Chilcotin Group in British Columbia , Canada ,
4180-502: The language group is also referred to as the Warrnambool language or the Gunditjmara language. Gunditj Wurrung, meaning "Gunditj language" is used by a contemporary teacher of the language, Gunditjmara musician Corey Theatre . Keerray Woorroong (Girai Wurrung, Kirrae wuurong, Kiriwurrung, etc.) is regarded by the Victorian Aboriginal Corporation for Languages (following Clark) as a separate language; it
4256-604: The magma as it decompresses during its approach to the surface; the erupted lava then solidifies before the gases can escape. When vesicles make up a substantial fraction of the volume of the rock, the rock is described as scoria . The term basalt is at times applied to shallow intrusive rocks with a composition typical of basalt, but rocks of this composition with a phaneritic (coarser) groundmass are more properly referred to either as diabase (also called dolerite) or—when they are more coarse-grained (having crystals over 2 mm across)—as gabbro . Diabase and gabbro are thus
4332-416: The magma to the surface, embedded in a finer-grained matrix . These phenocrysts are usually made of augite, olivine , or a calcium-rich plagioclase, which have the highest melting temperatures of any of the minerals that can typically crystallize from the melt, and which are therefore the first to form solid crystals. Basalt often contains vesicles ; they are formed when dissolved gases bubble out of
4408-710: The mantle. Many alkali basalts may be formed at greater depths, perhaps as deep as 150–200 km. The origin of high-alumina basalt continues to be controversial, with disagreement over whether it is a primary melt or derived from other basalt types by fractionation. Relative to most common igneous rocks, basalt compositions are rich in MgO and CaO and low in SiO 2 and the alkali oxides, i.e., Na 2 O + K 2 O , consistent with their TAS classification . Basalt contains more silica than picrobasalt and most basanites and tephrites but less than basaltic andesite . Basalt has
4484-406: The most voluminous of all volcanic formations. Basaltic magmas within Earth are thought to originate from the upper mantle . The chemistry of basalts thus provides clues to processes deep in Earth's interior . Basalt is composed mostly of oxides of silicon, iron, magnesium, potassium, aluminum, titanium, and calcium. Geologists classify igneous rock by its mineral content whenever possible;
4560-533: The next morning in the same area which resulted in the recovery from the sea and the island of the port and starboard wingtips, the port aileron, the door to the gunner's cockpit, portion of a main spar, the top cover of a fuel tank bay and a Mae West . The top cover of the fuel tank bay had the number AW-878 in pencil on the underneath side and the Mae West was identified as having been drawn and signed for by Flight Sergeant MacLellan on 15 February 1944. The bodies of
4636-410: The oldest samples are 4.2 billion years old, and the youngest flows, based on the age dating method of crater counting , are estimated to have erupted only 1.2 billion years ago. From 1972 to 1985, five Venera and two VEGA landers successfully reached the surface of Venus and carried out geochemical measurements using X-ray fluorescence and gamma-ray analysis. These returned results consistent with
SECTION 60
#17327661791704712-438: The orthography adopted by Blake, 'where there was a back vowel occurring before a syllable-final palatal, /o/ was used instead of /u/, to give a better idea of the more likely pronunciation (i.e. puroyn "night")'. Basalt Basalt ( UK : / ˈ b æ s ɔː l t , - əl t / ; US : / b ə ˈ s ɔː l t , ˈ b eɪ s ɔː l t / ) is an aphanitic (fine-grained) extrusive igneous rock formed from
4788-410: The rapid cooling of low- viscosity lava rich in magnesium and iron ( mafic lava) exposed at or very near the surface of a rocky planet or moon . More than 90% of all volcanic rock on Earth is basalt. Rapid-cooling, fine-grained basalt is chemically equivalent to slow-cooling, coarse-grained gabbro . The eruption of basalt lava is observed by geologists at about 20 volcanoes per year. Basalt
4864-475: The rate of cooling; very rapid cooling may result in very small (<1 cm diameter) columns, while slow cooling is more likely to produce large columns. The character of submarine basalt eruptions is largely determined by depth of water, since increased pressure restricts the release of volatile gases and results in effusive eruptions. It has been estimated that at depths greater than 500 metres (1,600 ft), explosive activity associated with basaltic magma
4940-411: The relative volume percentages of quartz (crystalline silica (SiO 2 )), alkali feldspar , plagioclase , and feldspathoid ( QAPF ) are particularly important. An aphanitic (fine-grained) igneous rock is classified as basalt when its QAPF fraction is composed of less than 10% feldspathoid and less than 20% quartz, and plagioclase makes up at least 65% of its feldspar content. This places basalt in
5016-595: The robotic Russian Luna program , and are represented among the lunar meteorites . Lunar basalts differ from their Earth counterparts principally in their high iron contents, which typically range from about 17 to 22 wt% FeO. They also possess a wide range of titanium concentrations (present in the mineral ilmenite ), ranging from less than 1 wt% TiO 2 , to about 13 wt.%. Traditionally, lunar basalts have been classified according to their titanium content, with classes being named high-Ti, low-Ti, and very-low-Ti. Nevertheless, global geochemical maps of titanium obtained from
5092-403: The rock at the landing sites being basalts, including both tholeiitic and highly alkaline basalts. The landers are thought to have landed on plains whose radar signature is that of basaltic lava flows. These constitute about 80% of the surface of Venus. Some locations show high reflectivity consistent with unweathered basalt, indicating basaltic volcanism within the last 2.5 million years. Basalt
5168-462: The sea it usually forms pillow basalts. However, when ʻaʻā enters the ocean it forms a littoral cone , a small cone-shaped accumulation of tuffaceous debris formed when the blocky ʻaʻā lava enters the water and explodes from built-up steam. The island of Surtsey in the Atlantic Ocean is a basalt volcano which breached the ocean surface in 1963. The initial phase of Surtsey's eruption
5244-468: The seal colony and watch whales and seabirds on the way. [REDACTED] Media related to Lady Julia Percy Island at Wikimedia Commons Gunditjmara language Dhauwurd Wurrung is a term used for a group of languages spoken by various groups of the Gunditjmara people of the Western District of Victoria , Australia. Keerray Woorroong (also spelt Girai Wurrung and variants)
5320-670: The term "basalt" to the volcanic black rock beneath the Bishop of Meissen's Stolpen castle , believing it to be the same as the "basaniten" described by Pliny the Elder in AD ;77 in Naturalis Historiae . On Earth, most basalt is formed by decompression melting of the mantle . The high pressure in the upper mantle (due to the weight of the overlying rock ) raises the melting point of mantle rock, so that almost all of
5396-400: The top of a rocky sea cliff, It is also the place where ancestral creator being Bunjil was said to have left this world, and other spirits continue to fly over to Deen Maar before ascending to the stars. The island was also known as Tirngoona , meaning "where the sun go away longa night". The island was given the name "Lady Julia's Island" in 1800 by Lieutenant James Grant after either
5472-580: The upper mantle is solid. However, mantle rock is ductile (the solid rock slowly deforms under high stress). When tectonic forces cause hot mantle rock to creep upwards, pressure on the ascending rock decreases, and this can lower its melting point enough for the rock to partially melt , producing basaltic magma. Decompression melting can occur in a variety of tectonic settings, including in continental rift zones, at mid-ocean ridges , above geological hotspots , and in back-arc basins . Basalt also forms in subduction zones , where mantle rock rises into
5548-543: The wife or daughter of Hugh Percy, 2nd Duke of Northumberland . In 1802 Matthew Flinders expanded the name to Lady Julia Percy's Island as he sailed past on his ship the Investigator . Also in 1802, Nicolas Baudin sailed past in his ship the Géographe , and recorded the island as Ile aux Alouettes , a name that has not persisted. During the early 19th century, sealing took place with sealing gangs living on
5624-474: Was also applied to John Green, manager at Coranderrk , an Aboriginal reserve north-east of Melbourne between 1863 and 1924. It was also recorded as being used to describe other missionaries such as William Watson in Wellington, New South Wales , by the local Wiradjuri people. The term was a compliment, as it meant that the local people thought that they had been an Aboriginal person once - based largely on
5700-400: Was highly explosive, as the magma was quite fluid, causing the rock to be blown apart by the boiling steam to form a tuff and cinder cone. This has subsequently moved to a typical pāhoehoe-type behaviour. Volcanic glass may be present, particularly as rinds on rapidly chilled surfaces of lava flows, and is commonly (but not exclusively) associated with underwater eruptions. Pillow basalt
5776-582: Was used to denote white people by the Gunditjmara, with the same word used in the Wergaia dialect of the Wemba Wemba language . The word is also used to refer to ghosts , as people with pale skins were thought to be the spirits of ancestors. The first known use is to refer to William Buckley , an escaped convict who lived with the Wathaurong people near Geelong from 1803 until 1856. The term
#169830