Palagonite

Palagonite is an alteration product from the interaction of water with volcanic glass of chemical composition similar to basalt. Palagonite can also result from the interaction between water and basalt melt. The water flashes to steam on contact with the hot lava and the small fragments of lava react with the steam to form the light colored palagonite tuff cones common in areas of basaltic eruptions in contact with water. An example is found in the pyroclastic cones of the Galapagos Islands. Charles Darwin recognized the origin of these cones during his visit to the islands. Palagonite can also be formed by a slower weathering of lava into palagonite, resulting in a thin, yellow-orange rind on the surface of the rock. The process of conversion of lava to palagonite is called palagonitization.

Palagonite soil is a light yellow-orange dust, comprising a mixture of particles ranging down to sub-micrometer sizes, usually found mixed with larger fragments of lava. The color is indicative of the presence of iron in the +3 oxidation state, embedded in an amorphous matrix.

Palagonite tuff is a tuff composed of sideromelane fragments and coarser pieces of basaltic rock, embedded in a palagonite matrix. A composite of sideromelane aggregate in palagonite matrix is called hyaloclastite.

Palagonite layers at Moya beach (Mayotte)
Palagonite layers at Moya Beach, Mayotte.

Palagonite on Mars

Based on infrared spectroscopy, the fine-grained component of Mauna-Kea palagonite is the terrestrial material with the best match to the spectral properties of Martian dust, and is believed to be similar in composition and in origin to dusty component of the surface regolith of Mars.[1][2] The palagonitic tephra from a cinder cone in Hawaii has been used to create Martian regolith simulant for researchers.[3] The spectroscopic signature of palagonitic alteration on Mars is used as evidence for the existence of water on Mars.

References

  1. ^ R.B. Singer, "Mineralogy of High-Albedo Soils and Dust on Mars", AGU paper 2B1214, J. Geophys. Res. 10, 159-10,168, 1982; also R. B. Singer and T. L. Roush, "Spectral reflectance properties of particulate weathered coatings on rocks: Laboratory modeling and applicability to Mars", in Lunar Plan. Sci. Conf. XIV, 708-709, 1983.
  2. ^ E.A. Guinness,R. E. Arvidson, M. A. Dale-Bannister, R. B. Singer and E. A. Brukenthal, "On the Spectral Reflectance Properties of Materials Exposed at the Viking Landing Sites", Proc. 17th Lunar and Planetary Science Conf., Part 2, J. Geophys. Res. 92, E575-E587, 1987.
  3. ^ Allen, C. C.; Morris, R. V.; Lindstrom, D. J.; Lindstrom, M. M.; Lockwood, J. P. (March 1997). JSC Mars-1: Martian regolith simulant (PDF). Lunar and Planetary Exploration XXVIII. Archived from the original (PDF) on 10 September 2014. Retrieved 10 May 2014.
Bay of Angra

Bay of Angra (Portuguese: Baía de Angra) is a natural bay within the coastal extent of the municipality of Angra do Heroísmo, on the Portuguese island of Terceira in the archipelago of the Azores. Within an average depth of 40 metres (130 ft), the bay has been of historical importance to the island; since the 15th century, it was a port-of-call for returning merchant shipping from the East Indies and Brazil, laden with gold, silver, porcelain, spices, rare woods, and other goods. These ships would anchor in the Bay of Angra until supported by armed escorts, which would accompany the ships on the rest of their voyage to Portugal. The Bay at Angra provided shelter from northern and northwestern winds; only storms originating to the south or southeast, posed a threat. Nonetheless, the Bay is the final resting-place of several ships affected by the adverse winds: local archives and a rich oral tradition supports the foundering of many ships against the leeward shore.

Cockburn Island (Antarctica)

Cockburn Island is an oval island 2.7 kilometres (1.7 mi) long, consisting of a high plateau with steep slopes surmounted on the northwest side by a pyramidal peak 450 m (1,476 ft) high, lying in the north-east entrance to Admiralty Sound, south of the north-east end of the Antarctic Peninsula. It was discovered by a British expedition (1839-43) led by Captain James Clark Ross, who named it for Admiral Sir George Cockburn, then serving as First Naval Lord (commander-in-chief of the Royal Navy).

Drangey

Drangey or Drang Isle is an island in the Skagafjörður fjord in northern Iceland. It is the remnant of a 700,000‑year‑old volcano, mostly made of volcanic palagonite tuff, forming a massive rock fortress.The island was first mentioned in the Icelandic classic Grettis saga as being the refuge of the outlaw Grettir, who spent his last years there with his brother Illugi and his slave Glaumur. He fled there with his two companions when enemies were seeking his life because of its high, impervious cliffs. It is described as having a flock of 80 sheep, and many birds nesting on the cliffs. In late autumn of 1031, Grettir was assassinated where he lay virtually dying in his shed on the island. Þorbjörn Öngull and his men were the perpetrators.

An old legend says that two night-prowling giants, a man and a woman, were traversing the fjord with their cow when they were surprised by the bright rays of daybreak. As a result of exposure to daylight, all three were turned into stone. Drangey represents the cow and Kerling (supposedly the female giant, the name means "Old Hag") is to the south of it. Karl (the male giant) was to the north of the island, but he disappeared long ago.

The bird life in Drangey is varied and lively, but the most common are diving birds: the guillemot, auk and puffin. The guillemot nests in the cliffs, while the auk mostly prefers deep cracks underneath the cliffs. The puffin, on the other hand, digs holes in the edge of the cliffs. In addition to these species, the black-legged kittiwake and fulmar nest in the cliffs and the raven and falcon also have their sanctuaries there.

Drangey has for ages been a harbinger of spring for the local residents. Every spring, they visited the island to collect both eggs and birds. They used ropes to climb down the fowling cliffs for the eggs, but the birds were caught using rafts placed on the sea underneath the cliffs. These rafts were covered with bird snares made of horsehair. The bird catchers mostly found shelter in sheds on the beach on the southernmost tip of the island. From this point, they also used to go fishing in their boats. At peak seasonal periods, there were as many as 200 men engaged in fowling and the catch was in excess of 200,000 birds when the yield was best. The use of snares was discontinued in 1966.

Fjaðrárgljúfur

Fjaðrárgljúfur (pronounced [ˈfjaːðraurˌkljuːvʏr̥]) is a canyon in south east Iceland. The Fjaðrá river flows through it.

The canyon has steep walls and winding water. It is up to 100 m (330 ft) deep and about 2 kilometres (1.2 miles) long. It is located near the Ring Road, not far from the village of Kirkjubæjarklaustur.Its origins dates back to the cold periods of the Ice Age, about two million years ago. The canyon was created by progressive erosion by flowing water from glaciers through the rocks and palagonite over millennia. A waterfall flows down the western side of the canyon, visible from an observation platform at the end of a one-mile hike up the eastern edge.In May 2019, authorities closed the canyon to visitors after it appeared in a music video by Justin Bieber. The resulting stream of visitors threatened to damage the canyon's environment.

Geology of São Tomé and Príncipe

São Tomé and Príncipe both formed within the past 30 million years due to volcanic activity in deep water along the Cameroon line. Long-running interactions with seawater and different eruption periods have generated a wide variety of different igneous and volcanic rocks on the islands with complex mineral assemblages.

Gluggafoss

Gluggafoss is a waterfall in southern Iceland, specifically in the Fljótshlíð area. As the most prominent member of a series of waterfalls running from the river Merkjá, it is also known as Merkjárfoss; both names are acknowledged on an on-site signpost. The waterfall is accessible off Route 261, some 17.3 km from the closest major town, Hvolsvöllur (which in turn is 106 km east of Reykjavík).

Gluggafoss has a total height of approximately 52 m and features two main drops: one for 44 m into a narrow recess, then another for a further 8.5 m (in three main channels). The cliff supporting Gluggafoss has an upper palagonite (or tuff rock) portion and a lower basalt portion. Distinctive of Gluggafoss' geology are the holes and tunnels formed by the river through the soft palagonite. Known in Icelandic as gluggar, or 'windows', these holes allow observers at the base of the waterfall to see partly obscured water flow. According to the on-site signpost, the upper half of the waterfall could be seen only through three such vertically arranged holes prior to 1947. Hekla, due roughly 30 km north-northeast, erupted in that year, filling the river Merkjá and the tunnels of Gluggafoss with volcanic ash; this severely diminished the waterfall's exterior visibility for decades. By the present day, however, erosion has undone the blockages.Small trails on the adjacent hills allow visitors to see both drops of the waterfall up close, and also to obtain a view from above. Seljalandsfoss is another waterfall nearby and of similar (or larger) size.

Hjörleifshöfði

Hjörleifshöfði (Icelandic: ['hjœːrˌlifs'hœːfˌði]) is a 221 m (725 ft)-high inselberg in southern Iceland. It consists of palagonite. The mountain is located on the Mýrdalssandur outwash plain about 15 km (9.3 mi) east of Vík í Mýrdal, and was an island in the Atlantic Ocean.

Hyaloclastite

Hyaloclastite is a volcaniclastic accumulation or breccia consisting of glass (from the Greek hyalus) fragments (clasts) formed by quench fragmentation of lava flow surfaces during submarine or subglacial extrusion. It occurs as thin margins on the lava flow surfaces and between pillow lavas as well as in thicker deposits, more commonly associated with explosive, volatile-rich eruptions as well as steeper topography. Hyaloclastites form during volcanic eruptions under water, under ice or where subaerial flows reach the sea or other bodies of water. It commonly has the appearance of angular flat fragments sized between a millimeter to few centimeters. The fragmentation occurs by the force of the volcanic explosion, or by thermal shock and spallation during rapid cooling.

Several minerals are found in hyaloclastite masses. Sideromelane is a basalt glass rapidly quenched in water. It is transparent and pure, lacking the iron oxide crystals dispersed in the more commonly occurring tachylite. Fragments of these glasses are usually surrounded by a yellow waxy layer of palagonite, formed by reaction of sideromelane with water.

Hyaloclastite ridges, formed by subglacial eruptions during the last glacial period, are a prominent landscape feature of Iceland and the Canadian province of British Columbia. Hyaloclastite is usually found at subglacial volcanoes, such as tuyas, which is a type of distinctive, flat-topped, steep-sided volcano formed when lava erupts through a thick glacier or ice sheet.

In lava deltas, hyaloclastites form the main constituent of foresets formed ahead of the expanding delta. The foresets fill in the seabed topography, eventually building up to sea level, allowing the subaerial flow to move forwards until it reaches the sea again.

Lómagnúpur

Lómagnúpur (764 m (2,507 ft)) is a subglacial mound in southern Iceland.

Mafic

Mafic is an adjective describing a silicate mineral or igneous rock that is rich in magnesium and iron, and is thus a portmanteau of magnesium and ferric. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include basalt, diabase and gabbro. Mafic rocks often also contain calcium-rich varieties of plagioclase feldspar.

Chemically, mafic rocks are enriched in iron, magnesium and calcium and typically dark in color. In contrast the felsic rocks are typically light in color and enriched in aluminium and silicon along with potassium and sodium. The mafic rocks also typically have a higher density than felsic rocks. The term roughly corresponds to the older basic rock class.

Mafic lava, before cooling, has a low viscosity, in comparison with felsic lava, due to the lower silica content in mafic magma. Water and other volatiles can more easily and gradually escape from mafic lava. As a result, eruptions of volcanoes made of mafic lavas are less explosively violent than felsic-lava eruptions. Most mafic-lava volcanoes are shield volcanoes, like those in Hawaii.

Mineraloid

A mineraloid is a naturally-occurring mineral-like substance that does not demonstrate crystallinity. Mineraloids possess chemical compositions that vary beyond the generally accepted ranges for specific minerals. For example, obsidian is an amorphous glass and not a crystal. Jet is derived from decaying wood under extreme pressure. Opal is another mineraloid because of its non-crystalline nature. Pearl, considered by some to be a mineral because of the presence of calcium carbonate crystals within its structure, would be better considered a mineraloid because the crystals are bonded by an organic material, and there is no definite proportion of the components.

North Arch volcanic field

North Arch volcanic field is an underwater volcanic field north of Oahu, Hawaii. It covers an area of about 25,000 square kilometres (9,700 sq mi) and consists of large expanses of alkali basalt, basanite and nephelinite that form extensive lava flows and volcanic cones. Some lava flows are longer than 100 kilometres (62 mi).

This volcanic field appears to be somehow related to the Hawaii hotspot, although the exact mechanisms are debated. Similar volcanic units are also found on the adjacent islands, such as the Honolulu Volcanics on Oahu. The volcanic field was formed through effusive and explosive eruptions between 1.5 and 0.5 million years ago, although eruptions before and after these dates also took place.

Río Murta (volcano)

Río Murta is a volcano in Chile.

The volcano consists of a complex of lava flows along the valleys at the Río Murta. These flows display columnar joints, lava tubes and pillow lavas, and have volumes of less than 1 cubic kilometre (0.24 cu mi). These landforms along with the presence of palagonite indicate that the eruptions happened beneath glaciers.Volcanic activity in the region is in part influenced by the Chile Triple Junction, the point where the Chile Rise is subducted into the Peru-Chile Trench. This point forms a gap in the Andean Volcanic Belt, with Southern Volcanic Zone volcanism north of the gap generated by the fast subduction of the older and colder Nazca Plate beneath the South America Plate and Austral Volcanic Zone volcanism south of the gap formed by the slow subduction of the younger and warmer Antarctic Plate. In between these two subduction processes, a slab window opened up and allowed the rise of alkali basalt magmas.Río Murta rocks are basalts with a low content of potassium. They contain phenocrysts of clinopyroxene, olivine and plagioclase. The chemical composition is unlike that of other regional basaltic volcanoes, and reflects the influence of oceanic asthenosphere.The basement in the region is formed by various Paleozoic to Mesozoic sediments and volcanic rocks. The plutons of the Northern Patagonian Batholith were intruded into this basement and may have an origin in the subduction of the Nazca Plate-Farallon Plate.The age of these flows is controversial. Potassium-argon dating has yielded ages of 900,000 - 850,000 years before present, some flows are too young to date and the relatively well conserved appearance suggest a Holocene age. 40 kilometres (25 mi) northwest of Río Murta lies Cerro Hudson, an active arc volcano.

Sideromelane

Sideromelane is a vitreous basaltic volcanic glass, usually occurring in palagonite tuff, for which it is characteristic. It is a less common form of tachylite, with which it usually occurs together; however it lacks the iron oxide crystals dispersed in the glass, and therefore appearing transparent and pure, with yellow-brown color, instead of tachylite opaque black. It forms at higher temperatures and with more rapid chilling. Presence of sideromelane indicates higher temperature of the lava, and solidifying of the flow closer to the vent, probably by rapid quenching in a wet environment.

Sideromelane often forms during explosions of submarine volcanoes and subglacial volcanoes, and often occurs as fragments embedded in a palagonite matrix, forming hyaloclastite deposits. Sideromelane is a mafic rock.

South Arch volcanic field

South Arch volcanic field is an underwater volcanic field south of Hawaiʻi Island. It was active during the last 10,000 years, and covers an area of 35 by 50 kilometres (22 mi × 31 mi) at a depth of 4,950 metres (16,240 ft).

Although the field is related to the Hawaiian hotspot, it does not appear to be a precursory volcano, but seems to have formed when the weight of the growing Hawaiian volcanoes caused the oceanic crust to buckle, opening up pathways for magma to ascend in front of the hotspot.

Tachylite

Tachylite (also spelled tachylyte) is a form of basaltic volcanic glass. This glass is formed naturally by the rapid cooling of molten basalt. It is a type of mafic igneous rock that is decomposable by acids and readily fusible. The color is a black or dark-brown, and it has a greasy-looking, resinous luster. It is very brittle and occurs in dikes, veins and intrusive masses. The word originates from the Ancient Greek takhus meaning swift.

Tachylites have the appearance of pitch and are often more or less vesicular and sometimes spherulitic. They are very brittle and break down readily under a hammer. Small crystals of feldspar or olivine are sometimes visible in them with the unaided eye. All tachylites weather rather easily and by oxidation of their iron become dark brown or red. Three modes of occurrence characterize this rock. In all cases they are found under conditions which imply rapid cooling, but they are much less common than acid volcanic glasses (or obsidians), the reason being apparently that the basic rocks have a stronger tendency to crystallize, partly because they are more liquid and the molecules have more freedom to arrange themselves in crystalline order.

Tunkin Depression

Tunkin Depression is a volcanic field in Russia.

The Tunkin Depression itself is a 200 kilometres (120 mi) tectonic depression, part of the Baikal Rift Zone, between Lake Baikal and Khövsgöl Nuur. The depression consists of a number of basins and is covered by alluvial sediments of the Irkut River. The basin is bordered by the Tunka ridge to the north and by the Chamar-Daban mountains to the south. The history of the Baikal Rift begins in the Mesozoic, when intracontinental extension took place at the rift. In the Cenozoic, rifting proper commenced generating basins that were filled by sediments and basaltic volcanism. The causes of the rifting are unclear and may involve either tectonic effects of the India-Asia collision, mantle plumes and asthenospheric processes.The volcanic field consists of numerous cinder cones and lava flows west of the western tip of Lake Baikal. The largest number of individual volcanoes is found close to the town of Tunka and is named the Khobok group. The highest of these volcanoes is Khara-Boldok or Ulyborskiy, which is 125–120 metres (410–394 ft) high. This cone further features a 90–85 metres (295–279 ft) wide crater. Four other groups of volcanoes are found in the Tunkin Depression.The Tunkin volcanic field has filled the Tunkin Depression with about 500 metres (1,600 ft) of volcanic products, which range from Miocene to Quaternary and include basaltic lava flows and tuffs. Subsidence is still occurring, and the volcanic cones are consequently lowering; one of the cones now rises only about 6 metres (20 ft) above terrain.The field has produced basalt, which in this field contains carbonatite, olivine or palagonite. The basalts range from alkali basalts to tholeiites. Volcanism may have protracted through the Pleistocene and Holocene; potassium-argon dating of some cones has yielded several ages, including 1.58 ± 0.14 million years ago and 700,000 ± 400,000 years before present.

Vega Island

Vega Island is a small island to the northwest of James Ross Island, on the Antarctic Peninsula. It is separated from James Ross Island by Herbert Sound. The island was named by Otto Nordenskjold, leader of the Swedish Antarctic Expedition (1901-04) in honor of the ship making the first voyage through the Northeast Passage, 1878-79.

Vega Island is an important site for paleontology. The region is extremely rich in terrestrial and marine fossils which span the boundary of the Cretaceous and Tertiary periods, covering the point in time when dinosaurs became extinct. Fossils found on the island include hadrosaurs, plesiosaurs, and mosasaurs.

Volcanic glass

Volcanic glass is the amorphous (uncrystallized) product of rapidly cooling magma. Like all types of glass, it is a state of matter intermediate between the close-packed, highly ordered array of a crystal and the highly disordered array of gas. Volcanic glass can refer to the interstitial, or matrix, material in an aphanitic (fine grained) volcanic rock or can refer to any of several types of vitreous igneous rocks. Most commonly, it refers to obsidian, a rhyolitic glass with high silica (SiO2) content.

Other types of volcanic glass include:

Pumice, which is considered a glass because it has no crystal structure.

Apache tears, a kind of nodular obsidian.

Tachylite (also spelled tachylyte), a basaltic glass with relatively low silica content.

Sideromelane, a less common form tachylyte.

Palagonite, a basaltic glass with relatively low silica content.

Hyaloclastite, a hydrated tuff-like breccia of sideromelane and palagonite.

Pele's hair, threads or fibers of volcanic glass, usually basaltic.

Pele's tears, tear-like drops of volcanic glass, usually basaltic.

Limu o Pele (Pele's seaweed), thin sheets and flakes of brownish-green to near-clear volcanic glass, usually basaltic.

Types of basalts
Basalts by tectonic setting
Basalts by form and flow
Basalts by chemistry
Important minerals

Languages

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