Tephra

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Volcanic tephra at Brown Bluff, Antarctica (2016) Brown Bluff-2016-Tabarin Peninsula-Volcanic tephra.jpg
Volcanic tephra at Brown Bluff, Antarctica (2016)

Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism. [1]

Contents

Tephra horizons in south-central Iceland: The thick and light-coloured layer at the centre of the photo is rhyolitic tephra from Hekla. Icelandic tephra.JPG
Tephra horizons in south-central Iceland: The thick and light-coloured layer at the centre of the photo is rhyolitic tephra from Hekla.

Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, they remain as tephra unless hot enough to fuse into pyroclastic rock or tuff. When a volcano explodes, it releases a variety of tephra including ash, cinders, and blocks. These layers settle on the land and, over time, sedimentation occurs incorporating these tephra layers into the geologic record.

Tephrochronology is a geochronological technique that uses discrete layers of tephra—volcanic ash from a single eruption—to create a chronological framework in which paleoenvironmental or archaeological records can be placed. Often, when a volcano explodes, biological organisms are killed and their remains are buried within the tephra layer. These fossils are later dated by scientists to determine the age of the fossil and its place within the geologic record.

A 2007 eruptive plume at Mount Etna produced volcanic ash, pumice, and lava bombs. 04Sep2007 Etna from SE Crater.jpg
A 2007 eruptive plume at Mount Etna produced volcanic ash, pumice, and lava bombs.

Overview

Rocks from the Bishop tuff, uncompressed with pumice on left; compressed with fiamme on right BishopTuff.jpg
Rocks from the Bishop tuff, uncompressed with pumice on left; compressed with fiamme on right

Tephra is any sized or composition pyroclastic material produced by an explosive volcanic eruption and precise geological definitions exist. [2] It consists of a variety of materials, typically glassy particles formed by the cooling of droplets of magma, which may be vesicular, solid or flake-like, and a varying proportions of crystalline and mineral components originating from the mountain and the walls of the vent. As the particles fall to the ground, they are sorted to a certain extent by the wind and gravitational forces and form layers of unconsolidated material. The particles are further moved by ground surface or submarine water flow. [3]

The distribution of tephra following an eruption usually involves the largest boulders falling to the ground quickest, therefore closest to the vent, while smaller fragments travel further – ash can often travel for thousands of miles, even circumglobal, as it can stay in the stratosphere for days to weeks following an eruption. When large amounts of tephra accumulate in the atmosphere from massive volcanic eruptions (or from a multitude of smaller eruptions occurring simultaneously), they can reflect light and heat from the sun back through the atmosphere, in some cases causing the temperature to drop, resulting in a temporary "volcanic winter". The effects of acidic rain and snow, the precipitation caused by tephra discharges into the atmosphere, can be seen for years after the eruptions have stopped. Tephra eruptions can affect ecosystems across millions of square kilometres or even entire continents depending on the size of the eruption. [4]

Classification

Volcanic breccia in Jackson Hole Volcanic breccia in Jackson Hole.JPG
Volcanic breccia in Jackson Hole

Tephra fragments are classified by size:

The use of tephra layers, which bear their own unique chemistry and character, as temporal marker horizons in archaeological and geological sites, is known as tephrochronology. [3]

Etymology

The word "tephra" and "pyroclast" both derive from Greek: The word τέφρα (téphra) means "ash", [5] while pyroclast is derived from the Greek πῦρ (pyr), meaning "fire", [6] and κλαστός (klastós), meaning "broken in pieces". [7] The word τέφραv (means "ashes") is used in broad context within an account by Aristotle of an eruption on Vulcano (Hiera) in Meteorologica. [8]

Environmental effects

The release of tephra into the troposphere affects the environment physically and chemically. Physically, volcanic blocks damage local flora and human settlements. Ash damages communication and electrical systems, coats forests and plant life, reducing photosynthesis, and pollutes groundwater. [9] Tephra changes below- and above-ground air and water movement. Chemically, tephra release can affect the water cycle. Tephra particles can cause ice crystals to grow in clouds, which increases precipitation. Nearby watersheds and the ocean can experience elevated mineral levels, especially iron, which can cause explosive population growth in plankton communities. [4] This, in turn, can result in eutrophication.

Disciplines and fossil record

In addition to tephrochronology, tephra is used by a variety of scientific disciplines including geology, paleoecology, anthropology, and paleontology, to date fossils, identify dates within the fossils record, and learn about prehistoric cultures and ecosystems. For example, carbonatite tephra found at Oldoinyo Lengai (a volcano in the East African Rift Valley) has buried and preserved fossilized footprints of humans near the site of the eruption. [10] Under certain conditions, volcanic blocks can be preserved for billions of years[ citation needed ] and can travel up to 400 km away from the eruption.[ citation needed ] Volcanic eruptions around the world have provided valuable scientific information on local ecosystems and ancient cultures.[ citation needed ]

Volcanoes

Africa

The Waw an Namus volcano is surrounded by an apron of dark tephra, which has a notable color contrast to the surrounding Sahara Desert.

Africa's volcanoes have had an impact on the fossil record. Geographically a part of Africa, El Hierro is a shield volcano and the youngest and smallest of the Canary Islands. The most recent El Hierro eruption occurred underwater, in 2011, and caused earthquakes and landslides throughout the Canary Islands. Instead of ash, floating rocks, 'restingolites' were released after every eruption. [11] After the 2011 eruption, fossils of single-celled marine organisms were found in the restingolites verifying the origin theory that Canary Island growth comes from a single buoyant jet of magma from the Earth's core instead of cracks in the ocean floor. This is reflected in the decreasing age of the islands east to west from Fuerteventura to El Hierro. [12]

There are about 60 volcanoes in Ethiopia, located in east Africa. In Southern Ethiopia, the Omo Kibish Rock Formation is composed of layers of tephra and sediment. Within these layers, several fossils have been discovered. In 1967, 2 Homo sapiens fossils were discovered in the Omo Kibish Formation by Richard Leaky, a paleoanthropologist. After radiocarbon dating, they were determined to be 195 thousand years old. [13] Other mammals discovered in the formation include Hylochoerus meinertzhageni (forest hog) and Cephalophus (antelope). [14]

Asia

In Asia, several volcanic eruptions are still influencing local cultures today. In North Korea, Paektu Mountain, a stratovolcano, first erupted in 946 AD and is a religious site for locals. It last erupted in 1903. In 2017, new fossil evidence was discovered that determined the date of Paektu Mountain's first eruption, which had been a mystery. A team of scientists directed by Dr. Clive Oppenheimer, British volcanologist, discovered a larch trunk embedded within Paektu Mountain. After radiocarbon dating, the larch was determined to be 264 years old which coincides with the 946 AD eruption. Its tree rings are being studied and many new discoveries are being made about North Korea during that time. [15]

In northeastern China, a large volcanic eruption in the early Cretaceous caused the fossilization of an entire ecosystem known as the Jehol Biota when powerful pyroclastic flows inundated the area. The deposits include many perfectly preserved fossils of dinosaurs, birds, mammals, reptiles, fish, frogs, plants, and insects. [16]

Europe

Europe's volcanoes provide unique information about the history of Italy. One example is Mount Vesuvius, a stratovolcano located in southern Italy, [17] which last erupted in March 1944. Earlier, in 79 AD, in an eruption which lasted 12 to 18 hours, Vesuvius had covered the city of Pompeii in molten lava, ash, pumice, volcanic blocks, and toxic gases. Much of the town was preserved and organic materials fossilized by the volcanic ash, and that has provided valuable information about the Roman culture. [18] Also, in Italy, Stromboli volcano, a stratovolcano, last erupted in July 2019.

North America

The Mount St. Helens National Volcanic Monument after the 1980 eruption 606 Mt St Helens NVM, ash covered landscape (35404396313).jpg
The Mount St. Helens National Volcanic Monument after the 1980 eruption

Several volcanic eruptions have been studied in North America. On 18 May 1980, Mount St. Helens, a stratovolcano in Washington state, erupted, spreading five hundred million tons of tephra ash across Washington, Oregon, Montana and Idaho causing earthquakes, rockslides, and megatsunami which severely altered the topography of nearby areas. [19] In Yellowstone National Park, eruption-related flooding caused trees to collapse and wash into lake beds where they fossilized. Nearby forests were flooded, removing bark, leaves, and tree limbs. [20] In 2006, the Augustine Volcano in Alaska erupted generating earthquakes, avalanches, and projected tephra ash approximately two hundred and ninety kilometers away. This dome volcano is over forty thousand years old and has erupted 11 times since 1800. [21]

South America

Satellite image of Chaiten volcano lava dome, Chile: The circular dome is brown and is surrounded by an ash covered landscape. Chaiten Volcano Lava Dome, Chile.jpg
Satellite image of Chaitén volcano lava dome, Chile: The circular dome is brown and is surrounded by an ash covered landscape.

In South America, there are several historic active volcanoes. In southern Chile, the Chaitén volcano erupted in 2011 adding 160 meters to its rim. Prehistoric weapons and tools, formed from obsidian tephra blocks, were dated at 5,610 years ago and were discovered 400 km away. [22] Due to the location of the subduction zone of the eastern Pacific's Nazca Plate, there are twenty one active volcanoes in southern Peru. [23] In 2006, fossils, found under a layer of volcanic ash in Peru, were excavated by a team of paleontologists led by Mark D. Uhen, professor at George Mason University. The fossils were identified as 3 different types of archaeocetes, prehistoric whales, and are older than 36.61 million years which, as of 2011, makes them the oldest whale fossils discovered. [24]

Related Research Articles

<span class="mw-page-title-main">Volcano</span> Rupture in a planets crust where material escapes

A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. The process that forms volcanoes is called volcanism.

<span class="mw-page-title-main">Hekla</span> Stratovolcano in South of Iceland

Hekla, or Hecla, is an active stratovolcano in the south of Iceland with a height of 1,491 m (4,892 ft). Hekla is one of Iceland's most active volcanoes; over 20 eruptions have occurred in and around the volcano since the year 1210. During the Middle Ages, the Icelandic Norse called the volcano the "Gateway to Hell" and the idea spread over much of Europe.

<span class="mw-page-title-main">Stratovolcano</span> Type of conical volcano composed of layers of lava and tephra

A stratovolcano, also known as a composite volcano, is a conical volcano built up by many alternating layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and explosive eruptions. Some have collapsed summit craters called calderas. The lava flowing from stratovolcanoes typically cools and solidifies before spreading far, due to high viscosity. The magma forming this lava is often felsic, having high to intermediate levels of silica, with lesser amounts of less viscous mafic magma. Extensive felsic lava flows are uncommon, but can travel as far as 8 km (5 mi).

<span class="mw-page-title-main">Volcanologist</span> Scientist who studies volcanoes

A volcanologist, or volcano scientist, is a geologist who focuses on understanding the formation and eruptive activity of volcanoes. Volcanologists frequently visit volcanoes, sometimes active ones, to observe and monitor volcanic eruptions, collect eruptive products including tephra, rock and lava samples. One major focus of inquiry in recent times is the prediction of eruptions to alleviate the impact on surrounding populations and monitor natural hazards associated with volcanic activity. Geologists who research volcanic materials that make up the solid Earth are referred to as igneous petrologists.

<span class="mw-page-title-main">Pyroclastic rock</span> Clastic rocks composed solely or primarily of volcanic materials

Pyroclastic rocks are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroclasts. Pyroclastic rocks are a type of volcaniclastic deposit, which are deposits made predominantly of volcanic particles. 'Phreatic' pyroclastic deposits are a variety of pyroclastic rock that forms from volcanic steam explosions and they are entirely made of accidental clasts. 'Phreatomagmatic' pyroclastic deposits are formed from explosive interaction of magma with groundwater. The word pyroclastic is derived from the Greek πῦρ, meaning fire; and κλαστός, meaning broken.

<span class="mw-page-title-main">Volcanism of Iceland</span>

Iceland experiences frequent volcanic activity, due to its location both on the Mid-Atlantic Ridge, a divergent tectonic plate boundary, and being over a hotspot. Nearly thirty volcanoes are known to have erupted in the Holocene epoch; these include Eldgjá, source of the largest lava eruption in human history. Some of the various eruptions of lava, gas and ash have been both destructive of property and deadly to life over the years, as well as disruptive to local and European air travel.

<span class="mw-page-title-main">Mount Tongariro</span> Compound volcano in New Zealand

Mount Tongariro is a compound volcano in the Taupō Volcanic Zone of the North Island of New Zealand. It is located 20 km (12 mi) to the southwest of Lake Taupō, and is the northernmost of the three active volcanoes that dominate the landscape of the central North Island.

<span class="mw-page-title-main">Kikai Caldera</span> Mostly-submerged caldera in the Ōsumi Islands of Kagoshima Prefecture, Japan

Kikai Caldera is a massive, mostly submerged caldera up to 19 kilometres (12 mi) in diameter in the Ōsumi Islands of Kagoshima Prefecture, Japan.

<span class="mw-page-title-main">Tephrochronology</span> Geochronological technique

Tephrochronology is a geochronological technique that uses discrete layers of tephra—volcanic ash from a single eruption—to create a chronological framework in which paleoenvironmental or archaeological records can be placed. Such an established event provides a "tephra horizon". The premise of the technique is that each volcanic event produces ash with a unique chemical "fingerprint" that allows the deposit to be identified across the area affected by fallout. Thus, once the volcanic event has been independently dated, the tephra horizon will act as time marker. It is a variant of the basic geological technique of stratigraphy.

<span class="mw-page-title-main">Nemo Peak</span> Mountain in Russia

Nemo Peak is a stratovolcano located at the northern end of Onekotan Island, Kuril Islands, Russia. It is truncated by two nested calderas, with the cone of Nemo Peak itself rising in the southwest end of the youngest caldera and a crater lake partially filling the northeast part, named Ozero Chernoye.

<span class="mw-page-title-main">Corcovado Volcano</span> Mountain in Chile

Corcovado Volcano is a stratovolcano located about 25 kilometres (16 mi) south of the mouth of the Yelcho River, in the Palena Province, Los Lagos Region, Chile. The glacially eroded volcano is flanked by Holocene cinder cones. The volcano's base has likely prehistoric lava flows that are densely vegetated. The most distinctive feature of this volcano is its stepped top, similar to that of Puntiagudo Volcano. At its foot lies a series of lakes. Corcovado dominates the landscape of the Gulf of Corcovado area and is visible from Chiloé Island, weather permitting.

<span class="mw-page-title-main">Melimoyu</span> Mountain in Chile

Melimoyu is a stratovolcano in Chile. It is an elongated volcanic complex that contains two nested calderas of 1 kilometre (0.62 mi) and 8 kilometres (5.0 mi) width. An ice cap has developed on the volcano with a couple of outlet glaciers. Melimoyu has not erupted in recent times, but during the Holocene two large eruptions took place and ejected ash at large distances from the volcano.

Mentolat is an ice-filled, 6 km (4 mi) wide caldera in the central portion of Magdalena Island, Aisén Province, Chilean Patagonia. This caldera sits on top of a stratovolcano which has generated lava flows and pyroclastic flows. The caldera is filled with a glacier.

<span class="mw-page-title-main">Torfajökull</span> Volcano in Iceland

Torfajökull is a rhyolitic stratovolcano, with a large caldera capped by a glacier of the same name and associated with a complex of subglacial volcanoes. Torfajökull last erupted in 1477 and consists of the largest area of silicic extrusive rocks in Iceland. This is now known to be due to a VEI 5 eruption 55,000 years ago.

<span class="mw-page-title-main">Chaitén (volcano)</span> Active volcano in Palena Province, Los Lagos Region, Chile

Chaitén is a volcanic caldera 3 kilometres (2 mi) in diameter, 17 kilometres (11 mi) west of the elongated ice-capped Michinmahuida volcano and 10 kilometres (6 mi) northeast of the town of Chaitén, near the Gulf of Corcovado in southern Chile. The most recent eruptive phase of the volcano erupted on 2008. Originally, radiocarbon dating of older tephra from the volcano suggested that its last previous eruption was in 7420 BC ± 75 years. However, recent studies have found that the volcano is more active than thought. According to the Global Volcanism Program, its last eruption was in 2011.

<span class="mw-page-title-main">Surtseyan eruption</span> Style of reaction between magma and seawater

A Surtseyan eruption is an explosive style of volcanic eruption that takes place in shallow seas or lakes when rapidly rising and fragmenting hot magma interacts explosively with water and with water-steam-tephra slurries. The eruption style is named after an eruption off the southern coast of Iceland in 1963 that caused the emergence of a new volcanic island, Surtsey.

<span class="mw-page-title-main">2010 eruptions of Eyjafjallajökull</span> Volcanic events in Iceland

Between March and June 2010 a series of volcanic events at Eyjafjallajökull in Iceland caused enormous disruption to air travel across Western Europe.

<span class="mw-page-title-main">Volcanic ash</span> Natural material created during volcanic eruptions

Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, produced during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer to all explosive eruption products, including particles larger than 2 mm. Volcanic ash is formed during explosive volcanic eruptions when dissolved gases in magma expand and escape violently into the atmosphere. The force of the gases shatters the magma and propels it into the atmosphere where it solidifies into fragments of volcanic rock and glass. Ash is also produced when magma comes into contact with water during phreatomagmatic eruptions, causing the water to explosively flash to steam leading to shattering of magma. Once in the air, ash is transported by wind up to thousands of kilometres away.

<span class="mw-page-title-main">946 eruption of Paektu Mountain</span> Major volcanic eruption in Korea

The 946 eruption of Paektu Mountain, a stratovolcano on the border of North Korea and China also known as Changbaishan, occurred in late 946 CE. This event is known as the Millennium Eruption or Tianchi eruption. It is one of the most powerful volcanic eruptions in recorded history; classified at least a VEI 6.

References

  1. This is the broad definition of tephra (Greek tephra, "ash") proposed by the Icelandic volcanologist Sigurður Þórarinsson (Sigurdur Thorarinsson) in 1954, in connection with the eruption of Hekla (Thorarinsson, "The eruption of Hekla, 1947-48II, 3, The tephra-fall from Hekla, March 29th, 1947", Visindafélag Íslendinga (1954:1-3). The term had been used earlier in Sigurdur Thorarinsson's 1944 doctoral studies, but not in English. See Thorarinsson, S (1944). "Tefrokronologiska studier pA Island". Geografiska Annaler. 26 (1–2): 1–217. doi:10.1080/20014422.1944.11880727.
  2. Lowe, David J.; Abbott, Peter M.; Suzuki, Takehiko; Jensen, Britta J. L. (2022). "Global tephra studies: role and importance of the international tephra research group 'Commission on Tephrochronology' in its first 60 years". History of Geo-Space Sciences. 13 (2): 93–132. Bibcode:2022HGSS...13...93L. doi: 10.5194/hgss-13-93-2022 . hdl: 10289/15024 .
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  6. πῦρ  in Liddell and Scott.
  7. κλαστός  in Liddell and Scott.
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  14. Assefa, Zelalem; Yirga, Solomon; Reed, Kaye E. (September 2008). "The large-mammal fauna from the Kibish Formation" (PDF). Journal of Human Evolution. 55 (3): 501–512. Bibcode:2008JHumE..55..501A. doi:10.1016/j.jhevol.2008.05.015. PMID   18691734. S2CID   5923387.
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