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75-497: The system erupted violently over an eight-month period between June 1783 and February 1784 from the Laki fissure and the adjoining volcano Grímsvötn. It poured out an estimated 42 billion tonnes or 14 km (18 × 10 ^  cu yd) of basalt lava as well as clouds of poisonous hydrofluoric acid and sulfur dioxide compounds that contaminated the soil, leading to the death of over 50% of Iceland's livestock population, and

150-423: 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

225-531: A 25 km-long (15.5 mi) fissure of at least 130 vents opened with phreatomagmatic explosions because of the groundwater interacting with the rising basalt magma . Over a few days the eruptions became less explosive, Strombolian , and later Hawaiian in character, with high rates of lava effusion . This event is rated as 4 on the Volcanic Explosivity Index , but the eight-month emission of sulfuric aerosols resulted in one of

300-493: 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

375-432: A constant fog over all Europe, and a great part of North America. This fog was of a permanent nature; it was dry, and the rays of the sun seemed to have little effect towards dissipating it, as they easily do a moist fog, arising from water. They were indeed rendered so faint in passing through it, that when collected in the focus of a burning glass they would scarce kindle brown paper. Of course, their summer effect in heating

450-442: 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

525-464: A drought in eastern China. An estimated 120,000,000 tonnes of sulfur dioxide was emitted, about three times the total annual European industrial output in 2006 (but delivered to higher altitudes, hence its persistence), and equivalent to six times the total 1991 Mount Pinatubo eruption . This outpouring of sulfur dioxide during unusual weather conditions caused a thick haze to spread across western Europe, resulting in many thousands of deaths throughout

600-427: 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

675-465: 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

750-621: 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

825-623: 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

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900-507: 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

975-523: 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

1050-427: 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

1125-399: Is also a common rock on the surface of Mars , as determined by data sent back from the planet's surface, and by Martian meteorites . Pele%27s hair Pele's hair (closest modern Hawaiian translation: " lauoho o Pele " ) is a volcanic glass formation produced from cooled lava stretched into thin strands, usually from lava fountains , lava cascades, or vigorous lava flows. It

1200-401: 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

1275-417: Is an aphanitic (fine-grained) extrusive igneous rock formed from 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

1350-761: 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

1425-481: 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

1500-549: Is named after Pele , the Hawaiian goddess of volcanoes . Mentions of this type of lava can be found in 18th Century Hawaiian newspapers where it is called "Lauoho o Pele," "Lauoho Pele," and "Lauoho ehuehu a Pele." Wind often carries the light fibers high into the air and to places several kilometers away from the vent. It is common to find strands of Pele's hair on high places like treetops, radio antennas, and electric poles. Pele's hair has been produced by volcanoes around

1575-753: Is observed by geologists at about 20 volcanoes per year. Basalt 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

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1650-583: 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

1725-402: 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

1800-440: 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

1875-455: 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

1950-539: 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

2025-1228: 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

2100-760: The Sahel of Africa, resulting in, among other effects, low flow in the River Nile . The resulting famine that afflicted Egypt in 1784 cost it roughly one-sixth of its population. The eruption was also found to have affected South Arabia and the already ongoing Chalisa famine in India. The Great Tenmei famine of 1782–1788 in Japan may have been worsened by the Laki eruption. In the same year, Mount Asama erupted in Japan ( Tenmei eruption ). The eruption may have affected

2175-724: The Treaty of Paris , which formally ended the American Revolutionary War . A huge snowstorm hit the South ; the Mississippi River froze at New Orleans and there were reports of ice floes in the Gulf of Mexico . Gilbert White recorded his perceptions of the event at Selborne , Hampshire , England: The summer of the year 1783 was an amazing and portentous one, and full of horrible phaenomena; for besides

2250-491: The barley , which was coming into ear, became brown and withered at their extremities, as did the leaves of the oats; the rye had the appearance of being mildewed; so that the farmers were alarmed for those crops. The wheat was not much affected. The larch , Weymouth pine , and hardy Scotch fir , had the tips of their leaves withered. 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 / )

2325-524: 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"

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2400-524: 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

2475-456: The Earth was exceedingly diminished. Hence the surface was early frozen. Hence the first snows remained on it unmelted, and received continual additions. Hence the air was more chilled, and the winds more severely cold. Hence perhaps the winter of 1783–84 was more severe than any that had happened for many years. The cause of this universal fog is not yet ascertained ... or whether it was the vast quantity of smoke, long continuing, to issue during

2550-463: 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

2625-522: The Rev. Jón and his parishioners were worshipping in the church. The spot at which the lava diverted away from the church became known thereafter as Eldmessutangi [ˈɛltˌmɛsːʏˌtʰauɲcɪ] ("Fire Mass Point"). This past week, and the two prior to it, more poison fell from the sky than words can describe: ash, volcanic hairs , rain full of sulfur and saltpeter , all of it mixed with sand. The snouts, nostrils, and feet of livestock grazing or walking on

2700-462: The alarming meteors and tremendous thunder-storms that affrighted and distressed the different counties of this kingdom, the peculiar haze, or smokey fog, that prevailed for many weeks in this island, and in every part of Europe, and even beyond its limits, was a most extraordinary appearance, unlike anything known within the memory of man. By my journal I find that I had noticed this strange occurrence from June 23 to July 20 inclusive, during which period

2775-480: 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

2850-478: 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

2925-413: The contaminated grass, while humans deaths were mostly from the subsequent famine. The parish minister and provost of Vestur-Skaftafellssýsla , Jón Steingrímsson (1728–1791), grew famous for the eldmessa [ˈɛltˌmɛsːa] ("fire mass ") that he delivered on 20 July 1783. The church farm of Kirkjubæjarklaustur was endangered by a branch of the lava flow that halted not far from the farm while

3000-432: The convective eruption column to altitudes of about 15 km (50,000 ft). The eruption continued until 7 February 1784, but most of the lava was ejected in the first five months. One study states that the event "occurred as ten pulses of activity, each starting with a short-lived explosive phase followed by a long-lived period of fire-fountaining". Grímsvötn volcano, from which the Laki fissure extends, also erupted at

3075-447: 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

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3150-638: The destruction of the vast majority of all crops. This led to a famine which then killed at least a fifth of the island's human population, although some have claimed a quarter. The Laki eruption and its aftermath caused a drop in global temperatures, as 120 million tonnes of sulfur dioxide was spewed into the Northern Hemisphere . This caused crop failures in Europe and may have caused droughts in North Africa and India . On 8 June 1783,

3225-445: The eruption, and the bubbles of gas and particles trapped within the tears can provide information about the composition of the magma chamber. The strands are created when molten lava is ejected into the air and form tiny droplets, which elongate perfectly straight. It usually forms in lava fountains, lava cascades, and vigorous lava flows. Pele's hair has a golden yellow color and looks like human hair or dry straw. In sunlight, it has

3300-545: 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

3375-444: The grass turned bright yellow and raw. All water went tepid and light blue in color and gravel slides turned grey. All the earth's plants burned, withered and turned grey, one after another, as the fire increased and neared the settlements. There is evidence that the Laki eruption weakened African and Indian monsoon circulations, leading to between 1 and 3 millimetres (0.04 and 0.12 in) less daily precipitation than normal over

3450-680: The haze dissipated in the autumn. The winter of 1783–1784 was very severe; the naturalist Gilbert White in Selborne , Hampshire , reported 28 days of continuous frost. The extreme winter is estimated to have caused 8,000 additional deaths in the UK. During the spring thaw, Germany and Central Europe reported severe flood damage. This is considered part of a volcanic winter . The meteorological impact of Laki continued, contributing significantly to several years of extreme weather in Europe. In France,

3525-740: 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 ,

3600-554: The lanes and hedges that they rendered the horses half frantic, and riding irksome. The country people began to look, with a superstitious awe, at the red, louring aspect of the sun; ... Benjamin Franklin recorded his observations in America in a 1784 lecture: During several of the summer months of the year 1783, when the effect of the sun's rays to heat the earth in these northern regions should have been greater, there existed

3675-604: 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

3750-416: 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

3825-710: 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

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3900-602: The most important climatic and socially significant natural events of the last millennium. The eruption, also known as the Skaftáreldar [ˈskaftˌauːrˌɛltar̥] (" Skaftá fires") or Síðueldur [ˈsiːðʏˌɛltʏr̥] produced an estimated 14 km (18 × 10 ^  cu yd) of basalt lava, and the total volume of tephra emitted was 0.91 km (1.2 × 10 ^  cu yd). Lava fountains were estimated to have reached heights of 800 to 1,400 m (2,600 to 4,600 ft). The gases were carried by

3975-406: 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;

4050-410: 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

4125-416: The population died in the famine after the fissure eruptions ensued. (Some sources specify a death toll of between 9,000 to 9,500 people.) Approximately 80% of sheep (190,500 head), 50% of cattle (11,500 head) and 50% of horses (28,000 head) died because of dental fluorosis and skeletal fluorosis from the 8 million tons of fluorine that were released. The livestock deaths were primarily caused by eating

4200-475: 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

4275-411: 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

4350-601: The remainder of 1783 and the winter of 1784. The summer of 1783 was the hottest on record and a rare high-pressure zone over Iceland caused the winds to blow to the south-east. The poisonous cloud drifted to Bergen in Denmark–Norway , then spread to Prague in the Kingdom of Bohemia (now the Czech Republic) by 17 June, Berlin by 18 June, Paris by 20 June, Le Havre by 22 June, and Great Britain by 23 June. The fog

4425-595: 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

4500-403: 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

4575-462: 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

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4650-568: The sequence of extreme weather events included a failed harvest in 1785 that caused poverty for rural workers, as well as droughts, bad winters and summers. These events contributed significantly to an increase in poverty and famine that may have contributed to the French Revolution in 1789. Laki was only one factor in a decade of climatic disruption, as Grímsvötn was erupting from 1783 to 1785, and there may have been an unusually strong El Niño effect from 1789 to 1793. In North America,

4725-410: The skin. Gloves should be worn while examining it. Pele's hair may occur along with Pele's tears . They indicate to volcanologists information about the eruption, such as the temperatures and the magma's path to the surface. Plagioclase starts to crystallize from the magma of Pele's hair at around 1,160 °C (about 2120 °F). Also, the shape of the tears can provide an indication of the velocity of

4800-605: The summer from Hekla in Iceland, and that other volcano which arose out of the sea near that island, which smoke might be spread by various winds, over the northern part of the world, is yet uncertain. According to contemporary records, Hekla did not erupt in 1783; its previous eruption was in 1766. The Laki fissure eruption was 70 km (45 mi) east and the Grímsvötn volcano was erupting about 120 km (75 mi) northeast. Katla , only 50 km (31 mi) southeast,

4875-670: 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

4950-468: The time, from 1783 until 1785. The outpouring of gases, including an estimated 8 million tonnes of fluorine and an estimated 120 million tonnes of sulfur dioxide , gave rise to what has since become known as the "Laki haze" across Europe. The consequences for Iceland, known as the Móðuharðindin [ˈmouːðʏˌharðɪntɪn] ( mist hardships), were disastrous. An estimated 20–25% of

5025-580: 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

5100-414: The wind varied to every quarter without making any alteration in the air. The sun, at noon, looked as blank as a clouded moon, and shed a rust-coloured ferruginous light on the ground, and floors of rooms; but was particularly lurid and blood-coloured at rising and setting. All the time the heat was so intense that butchers' meat could hardly be eaten on the day after it was killed; and the flies swarmed so in

5175-656: The winter of 1784 was the longest and one of the coldest on record. It was the longest period of below-zero temperatures in New England , with the largest accumulation of snow in New Jersey , and the longest freezing over of Chesapeake Bay . At the time, the capital of the United States was situated on the Chesapeake at Annapolis, Maryland ; the weather delayed Congressmen who were traveling there to vote for

5250-500: The world, for example in Nicaragua ( Masaya ), Italy ( Etna ), Ethiopia ( Erta’ Ale ), and Iceland, where it is known as nornahár [ˈnɔ(r)tnaˌhauːr̥] ('witches' hair'). It is usually found in gaps in the ground, mostly near vents, skylights, ocean entry, or in corners where Pele's hair can accumulate. It is not recommended to touch Pele's hair, because it is very brittle and very sharp, and small broken pieces can enter

5325-400: 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

5400-438: Was informed by a tenant that finding himself cold in bed, about three o'clock in the morning, he looked out at his window, and to his great surprise saw the ground covered with a white frost: and I was assured that two men at Barton, about three miles (five kilometres) off, saw in some shallow tubs, ice of the thickness of a crown-piece . Sir John goes on to describe the effect of this "frost" on trees and crops: The aristae of

5475-477: Was most affected. The records show that the additional deaths were among outdoor workers; the death rate in Bedfordshire , Lincolnshire , and the east coast was perhaps two or three times the normal rate. It has been estimated that 23,000 British people died from the poisoning. The weather became very hot, causing severe thunderstorms with large hailstones that were reported to have killed cattle , until

5550-471: Was so thick that ships stayed in port, unable to navigate, and the sun was described as "blood coloured". Inhaling sulfur dioxide gas causes victims to choke as their internal soft tissues swell – the gas reacts with the moisture in the lungs and produces sulfurous acid . The local death rate in Chartres was up by 5% during August and September, with more than 40 dead. In Great Britain, the east of England

5625-530: Was still renowned after its spectacular eruption 28 years earlier in 1755. Sir John Cullum of Bury St Edmunds , Suffolk , England, recorded his observations on 23 June 1783 (the same date on which Gilbert White noted the onset of the unusual atmospheric phenomena), in a letter to Sir Joseph Banks , then President of the Royal Society : ... about six o'clock, that morning, I observed the air very much condensed in my chamber-window; and, upon getting up,

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