future — Volcano

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Super Volcanoes

About Super Volcanoes

The term "super volcano" implies an eruption of magnitude 8 on the Volcano Explosivity Index, meaning that more than 1,000 cubic kilometres (240 cubic miles) of magma (partially molten rock) are erupted. The most recent such event on Earth occurred 74,000 years ago at the Toba Caldera in Sumatra, Indonesia.

Several volcanoes around the world are capable of gigantic eruptions unlike anything witnessed in recorded history, based on geologic evidence of past events, the scientists said. Such eruptions would dwarf those of Mount St. Helens, Krakatoa, Pinatubo and anything else going back dozens of millennia.

"Super-eruptions are up to hundreds of times larger than these," said Stephen Self of the United Kingdom's (U.K.) Open University.

"An area the size of North America can be devastated, and pronounced deterioration of global climate would be expected for a few years following the eruption," Self said. "They could result in the devastation of world agriculture, severe disruption of food supplies, and mass starvation. These effects could be sufficiently severe to threaten the fabric of civilization."

The odds of a globally destructive volcano explosion in any given century are extremely low, and no scientist can say when the next one will occur. But the chances are five to 10 times greater than a globally destructive asteroid impact, according to the new British report.

New research is changing scientists' understanding of the timing of super volcanic eruptions, and prompting them to call for greater monitoring of sites to help save lives when the next big volcano explodes. Two recent papers highlight the shift. One looked at a Death Valley volcano thought to be 10,000 years old and found it last erupted just 800 years ago, and is still an eruption danger. The other found that large caldera volcanoes, such as the one under Crater Lake in Oregon, can recharge in a matter of decades, rather than the thousands of years previously thought.

The next super eruption, whenever it occurs, might not be the first one humans have dealt with. (Read more here.)

Impact of the Toba Supervolcano

Deforestation of Central India

A new study provides "incontrovertible evidence" that the volcanic super-eruption of Toba on the island of Sumatra about 73,000 years ago deforested much of central India, some 3,000 miles from the epicentre, researchers report.

Atmospheric Ash

The volcano ejected an estimated 800 cubic kilometres of ash into the atmosphere, leaving a crater (now the world's largest volcanic lake) that is 100 kilometres long and 35 kilometres wide. Ash from the event has been found in India, the Indian Ocean, the Bay of Bengal and the South China Sea.

An Instant Ice Age

The bright ash reflected sunlight off the landscape, and volcanic sulphur aerosols impeded solar radiation for six years, initiating an "Instant Ice Age" that – according to evidence in ice cores taken in Greenland – lasted about 1,800 years.

During this instant ice age, temperatures dropped by as much as 16 degrees centigrade (28 degrees Fahrenheit), said University of Illinois anthropology professor Stanley Ambrose, a principal investigator on the new study with professor Martin A.J. Williams, of the University of Adelaide. Williams, who discovered a layer of Toba ash in central India in 1980, led the research.

The climactic effects of Toba have been a source of controversy for years, and its impact on human populations is also hotly debated.

Near-Extinction of Humans

In 1998, Ambrose proposed in the Journal of Human Evolution that the effects of the Toba eruption and the Ice Age that followed could explain the apparent bottleneck in human populations that geneticists believe occurred between 50,000 and 100,000 years ago. The lack of genetic diversity among humans alive today suggests that during this time period humans came very close to becoming extinct.

To address the limited evidence of the terrestrial effects of Toba, Ambrose and his colleagues pursued two lines of inquiry: They analysed pollen from a marine core in the Bay of Bengal that included a layer of ash from the Toba eruption, and they looked at carbon isotope ratios in fossil soil carbonates taken from directly above and below the Toba ash in three locations in central India. Carbon isotopes reflect the type of vegetation that existed at a given locale and time. Heavily forested regions leave carbon isotope fingerprints that are distinct from those of grasses or grassy woodlands.

Vegetation Changes

Both lines of evidence revealed a distinct change in the type of vegetation in India immediately after the Toba eruption, the researchers report. The pollen analysis indicated a shift to a "more open vegetation cover and reduced representation of ferns, particularly in the first 5 to 7 centimetres above the Toba ash," they wrote in the journal Palaeogeography, Palaeoclimatology, Palaeoecology. The change in vegetation and the loss of ferns, which grow best in humid conditions, they wrote, "would suggest significantly drier conditions in this region for at least one thousand years after the Toba eruption."

Dry Conditions and Lower Temperatures

The dryness probably also indicates a drop in temperature, Ambrose said, "because when you turn down the temperature you also turn down the rainfall."

The carbon isotope analysis was even more explicit. It showed that forests covered central India when the eruption occurred, but wooded to open grassland predominated for at least 1,000 years after the eruption.

"This is unambiguous evidence that Toba caused deforestation in the tropics for a long time," Ambrose said. This disaster may have forced the ancestors of modern humans to adopt new cooperative strategies for survival that eventually permitted them to replace Neanderthals and other archaic human species, he said.

World Supervolcanoes

Long Valley
Valley Grande
Lake Taupo
Aira
Campi Flegri
Lake Toba
Siberian Traps
Yellowstone

Long Valley

The Caldera: Long Valley Caldera a 15- by 30-km oval-shaped depression located 20 km south of Mono Lake along the east side of the Sierra Nevada in east-central California. This area of eastern California has produced numerous volcanic eruptions over the past 3 million years, including the massive caldera-forming eruption 760,000 years ago. The most recent eruption occurred just 250 years ago in Mono Lake at the north end of Mono-Inyo Craters volcanic chain.

Volcanic Unrest: In May of 1980, a strong earthquake swarm that included four magnitude 6 earthquakes struck the southern margin of Long Valley Caldera associated with a 25-cm, dome-shaped uplift of the caldera floor. These events marked the onset of the latest period of caldera unrest that continues to this day. This ongoing unrest includes recurring earthquake swarms and continued dome-shaped uplift of the central section of the caldera (the resurgent dome) accompanied by changes in thermal springs and gas emissions.

Valley Grande

The 22-km-wide Valles caldera was formed as a result of two large volume eruptions that created the widespread Bandelier Tuff ignimbrite plateaus on all sides of the caldera. The lower member of the Bandelier Tuff, the Otawi, was emplaced about 1.7 million years ago (Ma) and resulted in the formation of most of the present-day Valles caldera, including the Toledo embayment at the NE side. The upper member, the Tshirege, is dated about 1.2 Ma, and also deposited voluminous welded pyroclastic flows over about the same area as the Otawi member. Post-caldera volcanism has included the emplacement of multiple ring-fracture lava domes and uplift of the caldera floor, forming the Redondo Peak resurgent dome. The El Cajete Pumice, Battleship Rock Ignimbrite, Banco Bonito Rhyolite, and the VC-1 Rhyolite were emplaced during the youngest eruption of Valles caldera, about 50,000-60,000 years ago. Seismic investigations show that a low-velocity zone lies beneath the caldera, and an active geothermal system with hot springs and fumaroles exists today.

Lake Taupo

Pre 65,000 years ago: All deposits at Taupo including a number of early lava domes clearly post-date the exceptionally large Whakamaru ignimbrite eruption dated at 330,000 years ago. About 150,000 years ago new activity formed a pumice-rich ignimbrite found along the northern shores of the lake, several basalt scoria cones and tuff rings about Acacia Bay and Mt. Tauhara. Our knowledge of this time intervals is very incomplete as few deposits of this age are exposed.

65,000 to 27,000 years ago: Between 65,000 years and 27,000 years ago there was a series of at least five explosive eruptions, from vents now under Lake Taupo. The older four eruptions produced layers of coarse pumice. The youngest produced fine gray ash suggesting the mixing of lake water with erupting magma.

The Oruanui eruption 26,500 years ago: The largest eruption from Taupo occurred 26,500 years ago producing 300 km3 of ignimbrite, 500 km3 of pumice and ash fall and a unknown volume of material inside the caldera. The Oruanui eruption is thought to have formed the caldera now filled by Lake Taupo, but this large eruption also shows the influence of lake water in its fine grain size and abundant evidence for heavy rain during the eruption. This implies the existence of a large lake prior to the eruption. The Oruanui ignimbrite is seen in many road cuttings about Taupo, draped by the layers of younger tephra. Fine ash from this eruption has been found throughout New Zealand and in many offshore core samples.

Aira

About 22,000 years ago a series of large-scale pyroclastic eruptions produced the Aira caldera (20 km wide at the northern end of Kagoshima Bay in southern Kyushu. It started with a Plinian pumice erution (Osumi pumice fall, 98 km3) followed by oxidized, fine-grained Tsumaya pyroclastic flow (13 km3), both erupted from a vent located at the present site of Sakuraijima volcano, 8 km south of the caldera centre. After a very short pause, violent explosive ejection of the basement rock fragments and pumiceous materials occurred at the central vent, gradually changing itself to a huge eruption column rapidly collapsing to form the Ito pyroclastic flow about 300 km3 in volume. The earliest phase produced up to 30-m-thick Kamewarizaka breccia developed along the caldera rim and charged with basement (lithic) fragments up to 2m across. The breccia is a near-vent variety of the bottom concentration zone of lithics in the Ito deposit. Various textural features and monotonous petrologic character indicate that the main part of the Ito pyroclastic flow was emplaced by a simple, short-lived eruptive mechanism. The Aira-Tn ash, a fine-grained counterpart of the Ito pyroclastic flow, covered a wide area more than 1000 km from the vent. Evacuation of more than 110 km3 of rhyolitic magma produced a funnel-shaped collapse structure with the centre of the magma chamber about 10 km deep. Like many other Japanese Quaternary calderas, the Aira caldera is considered to have formed not by a piston cylinder-type subsidence utilizing a ring fracture but by coring and high-angle slumping of the wall rocks into a funnel-shaped central vent. The outline of the caldera was strongly controlled by the faults bounding the volcano-tectonic graben forming Kagoshima Bay.

Campi Flegri

The Campi Flegrei caldera is a supervolcano. Although there’s no picture-postcard volcanic cone, hidden beneath the seemingly placid landscape lies a volcano of immense power. While a new eruption here would be more likely to result in the creation of another Vesuvius-like cone, the worst-case scenario could see it obliterating much of life in Europe.

Campi Flegrei is a large 13-km-wide caldera on the outskirts of Naples that contains numerous phreatic tuff rings and pyroclastic cones. The caldera margins are poorly defined and on the south lie beneath the Gulf of Pozzuoli. Episodes of dramatic uplift and subsidence within the dominantly trachytic caldera have occurred since Roman times. The earliest known eruptive products are dated 47,000 years before present (BP). The Campi Flegrei caldera formed following two large explosive eruptions, the massive Campanian ignimbrite about 36,000 years BP, and the >40 cu km Neapolitan Yellow Tuff (NYT) about 15,000 years BP. Following eruption of the NYT a large number of eruptions have taken place from widely scattered subaerial and submarine vents. Most activity occurred during three intervals: 15,000-9500, 8600-8200, and 4800-3800 years BP. Two eruptions have occurred in historical time, one in 1158 at Solfatara and the other in 1538 that formed the Monte Nuovo cinder cone.

Out of interest the prevailing wind direction for Naples, Italy is south-south-westerly (with the exception of ENE for Dec and Jan). Should this erupt, the largest fallout would move north…

Lake Toba

The 35 x 100 km Toba caldera, the Earth's largest Quaternary caldera, was formed during four major Pleistocene ignimbrite-producing eruptions beginning at 1.2 million years ago. The latest of these produced the Young Toba Tuff (YTT) about 74,000 years ago. The YTT represents the world's largest known Quaternary eruption, ejecting about 2500-3000 km3 (dense rock equivalent) of ignimbrite and air fall ash from vents at the NW and SE ends of present-day Lake Toba. Resurgent doming forming the massive Samosir Island and Uluan Peninsula structural blocks postdated eruption of the YTT. Additional post-YTT eruptions include emplacement of a series of lava domes, growth of the solfatarically active Pusukbukit volcano on the south margin of the caldera, and formation of Tandukbenua volcano at the NW-most rim of the caldera. Lack of vegetation suggests that this volcano may be only a few hundred years old (Chesner and Rose, 1991).

One of the largest known volcanic eruptions took place only 74,000 yrs ago, when over 2500 km3 of magma was ejected from Toba — a volcano-tectonic depression that is often referred to as Earth's largest Quaternary caldera. The caldera is 18 x 60 miles (30 by 100 km) and has a total relief of 5,100 feet (1700m).Over what was probably a two-week span, thousands of cubic kilometres of debris spewed from Toba Caldera on northern Sumatra. Pyroclastic flows (fast-moving clouds of hot gas, rock fragments, and ash) buried at least 20,000 square kilometres around the caldera. As far away as India, ash from the Toba eruption lies in layers up to 6 meters (about 20 feet) thick; on Samosir Island, the ash layer is more than 600 meters (more than a quarter mile) thick.

Following the eruption, the ground collapsed, leaving the modern caldera, which filled with water to make Lake Toba. Samosir Island is a resurgent volcanic dome, a mound of rock uplifted by pressure from un-erupted magma in the chamber beneath the volcano. The Pusukbukit Volcano on the western shore of the lake also formed after the catastrophic eruption.

The caldera probably formed in stages. Large eruptions occurred 840,000, about 700,000, and 75,000 years ago. The eruption 75,000 years ago produced the Young Toba Tuff. The Young Toba Tuff was erupted from ring fractures that surround most or all of the present-day lake.

Siberian Traps

The Siberian Traps were the largest volcanic eruption in Earth history and they occurred right at the same time as the largest extinction event in Earth history.

The Siberian Traps form a large igneous province in Siberia. The massive eruptive event spans the Permian-Triassic boundary, about 251 to 250 million years ago, and was essentially coincident with the Permian-Triassic extinction event in what was one of the largest known volcanic events of the last 500 million years of Earth's geological history. The term 'traps' is derived from the Swedish word for stairs (trappa, or sometimes trapp), referring to the step-like hills forming the landscape of the region. Vast volumes of basaltic lava paved over a large expanse of primeval Siberia in a flood basalt event.

Today the area covered is about 2 million km3 and estimates of the original coverage are as high as 7 million km3. The original volume of lava is estimated to range from 1 to 4 million km3. The area covered lies between 50 and 75 degrees north latitude and 60 to 120 degrees east longitude. The volcanism continued for a million years and spanned the Permian-Triassic boundary.

Yellowstone

The Yellowstone hotspot, also referred to as the Snake River Plain-Yellowstone hotspot, is a volcanic hotspot responsible for large scale volcanism in Oregon, Nevada, Idaho, and Wyoming, United States. It created the eastern Snake River Plain through a succession of caldera forming eruptions. The resulting calderas include the Island Park Caldera, the Henry's Fork Caldera, and the Bruneau-Jarbidge caldera. The hotspot currently lies under the Yellowstone Caldera. The hotspot's most recent supereruption, known as the Lava Creek eruption, took place 640,000 years ago and created the Lava Creek Tuff and the Yellowstone Caldera. Credit: Wikipedia

The first of these caldera-forming eruptions 2.1 million years ago created a widespread volcanic deposit known as the Huckleberry Ridge Tuff, an outcrop of which can be viewed at Golden Gate, south of Mammoth Hot Springs. This titanic event, one of the five largest individual volcanic eruptions known anywhere on the Earth, formed a caldera more than 60 miles (100 km) across.

A similar, smaller but still huge eruption occurred 1.3 million years ago. This eruption formed the Henrys Fork Caldera, located in the area of Island Park, west of Yellowstone National Park, and produced another widespread volcanic deposit called the Mesa Falls Tuff.

The region's most recent caldera-forming eruption 640,000 years ago created the 35-mile-wide, 50-mile-long (55 by 80 km) Yellowstone Caldera. Pyroclastic flows from this eruption left thick volcanic deposits known as the Lava Creek Tuff, which can be seen in the south-facing cliffs east of Madison, where they form the north wall of the caldera. Huge volumes of volcanic ash were blasted high into the atmosphere, and deposits of this ash can still be found in places as distant from Yellowstone as Iowa, Louisiana, and California.

Recent weather forecasting software indicates that ash from an eruption will enter the jetstream and flow to europe within a few days. With significant ash being supplied to the jetstream, ash will encompass most of the northern hemisphere within a week.


Yellowstone caldra (large)

Dec 2013. Credit: BBC. The supervolcano that lies beneath Yellowstone National Park in the US is far larger than was previously thought, scientists report. A study shows that the magma chamber is about 2.5 times bigger than earlier estimates suggested. A team found the cavern stretches for more than 90km (55 miles) and contains 200-600 cubic km of molten rock. The team found that the magma chamber was colossal. Reaching depths of between 2km and 15km (1 to 9 miles), the cavern was about 90km (55 miles) long and 30km (20 miles) wide. It pushed further into the north east of the park than other studies had previously shown, holding a mixture of solid and molten rock.

Volcanoes

How volcanoes destroy

Lava Flows

Although instantly associated with volcanoes, lava flows only account for a fraction of a percent of the total number of deaths due to volcanoes in the last few years. Lava is slow and can be outrun, but it does damage property and infrastructure in places such as Hawaii where the Kilauea volcano regularly spews forth a basaltic magma that becomes lava as it leaves the ground.

Gases

These kill slightly more people than lava. Denser than air carbon dioxide and hydrogen sulfide are the most dangerous as they flow into and fill low lying areas. Carbon dioxide is colourless and odourless and can asphyxiate people who breath it unawares. Hydrogen sulphide has a "rotten egg" smell, but a single breath can kill in high enough concentrations. Fortunately, such concentrations are relatively rare. Other gases can also be problematic for humans, albeit indirectly. In 1783, the laki fissure eruption killed an estimated 10,000 Icelanders, but due to starvation and famine after the loss of crops and livestock due to long-term exposure to hydrogen fluoride.

Tephra, Ash, and pyroclastic flows

Tephra includes the fragmented rocks and blocks ejected in the air by the eruption itself. Fortunately, tephra and ash typically affect the regions closest to the volcano, having increasing less effect the further from the eruption you go. Ash, however, can be ejected high into the atmosphere, allowing it to be deposited many miles away. But its that ash and rock that lands near the volcano that is the most problematic. Much of the tephra and ash comes back down into the volcano's crater, but this often results in pyroclastic flow which can leave a wake of destruction in its path as hot ash and rock are forced down and out away from the volcano's cone due to the force of the eruption.

Relatively few people have actually lost their lives due to tephra and ash falls, however, the danger ash poses most is the accumulation on the roofs of homes and buildings, particularly if the ash becomes wet. Wet ash soaks up water, and creates a very heavy mud, about 10 inches of which are sufficient to collapse a roof, injuring or killing the building's occupants.

Pyroclastic flows have claimed far more victims, however, making this one of the more dangerous features of a volcanic eruption. 27 percent of the lives lost in recorded volcanic eruptions were due to pyroclastic flows, the effects of which are most notable in Pompeii and Herculaneum, where pyroclastic flows of ash, rock, gases, and bits of lava quickly rushed in along the ground, burying both cities. Residents had seconds to realize what had occurred, and probably each killed instantly as the heat from the flows cooked their bodies and boiled their brains -the ash burying them along with the buildings, homes, and artifacts of their cities. Alun Salt discusses a recent find of a throne at Herculaneum at Clio Audio, describing the effects of pyroclastic flows and preservation of material remains.

Lahars and Tsunamis

Another immediate killer from volcanic eruptions are the occasional lahars as well as the tsunamis some volcanoes create due to earth quakes caused by the eruption or pyroclastic flows that dump into the sea, displacing water. Lahar is an Indonesian word that refers to the mud flows created by large amounts of ash and water. The heat from a volcanic event can melt snow and ice and, as the resulting water mixes with ash, a mud is formed which then flows down the mountain, obliterating towns and settlements. Lahars and tsunamis are together responsible for a whopping 34% of the deaths that have been recorded due to volcanoes.

Post Eruption

The most significant killer is, by itself, responsible for a full 30% of the deaths related to volcanoes. That killer is post-eruption famine and disease that takes place months later. Gases and ash ejected into the atmosphere can affect crops and livestock and even global temperatures! 1816 was called the "year without summer" due to the eruption of Tambora in Indonesia the year before. Global temperatures dropped to between 0.4 and 1.0 Celsius and crops were affected around the globe. In Europe, particularly in Great Britain, a typhus epidemic that broke out that year was blamed on the unseasonably cold weather. Volcanic eruptions can have regional and global effects due to the dramatic and huge changes they make on the environment.

Textbook theory behind volcanoes may be wrong

In the typical textbook picture, volcanoes, such as those that are forming the Hawaiian islands, erupt when magma gushes out as narrow jets from deep inside Earth. But that picture is wrong, according to a new study from researchers at Caltech and the University of Miami in Florida.

New seismology data are now confirming that such narrow jets don't actually exist, says Don Anderson, the Eleanor and John R. McMillian Professor of Geophysics, Emeritus, at Caltech. In fact, he adds, basic physics doesn't support the presence of these jets, called mantle plumes, and the new results corroborate those fundamental ideas.

"Mantle plumes have never had a sound physical or logical basis," Anderson says. "They are akin to Rudyard Kipling's 'Just So Stories' about how giraffes got their long necks."

Anderson and James Natland, a professor emeritus of marine geology and geophysics at the University of Miami, describe their analysis online in the September 8 issue of the Proceedings of the National Academy of Sciences.

According to current mantle-plume theory, Anderson explains, heat from Earth's core somehow generates narrow jets of hot magma that gush through the mantle and to the surface. The jets act as pipes that transfer heat from the core, and how exactly they're created isn't clear, he says. But they have been assumed to exist, originating near where Earth's core meets the mantle, almost 3,000 kilometers underground — nearly halfway to the planet's center. The jets are theorized to be no more than about 300 kilometers wide, and when they reach the surface, they produce hot spots.

While the top of the mantle is a sort of fluid sludge, the uppermost layer is rigid rock, broken up into plates that float on the magma-bearing layers. Magma from the mantle beneath the plates bursts through the plate to create volcanoes. As the plates drift across the hot spots, a chain of volcanoes forms — such as the island chains of Hawaii and Samoa.

"Much of solid-Earth science for the past 20 years — and large amounts of money — have been spent looking for elusive narrow mantle plumes that wind their way upward through the mantle," Anderson says.

To look for the hypothetical plumes, researchers analyze global seismic activity. Everything from big quakes to tiny tremors sends seismic waves echoing through Earth's interior. The type of material that the waves pass through influences the properties of those waves, such as their speeds. By measuring those waves using hundreds of seismic stations installed on the surface, near places such as Hawaii, Iceland, and Yellowstone National Park, researchers can deduce whether there are narrow mantle plumes or whether volcanoes are simply created from magma that's absorbed in the sponge-like shallower mantle.

No one has been able to detect the predicted narrow plumes, although the evidence has not been conclusive. The jets could have simply been too thin to be seen, Anderson says. Very broad features beneath the surface have been interpreted as plumes or super-plumes, but, still, they're far too wide to be considered narrow jets.

But now, thanks in part to more seismic stations spaced closer together and improved theory, analysis of the planet's seismology is good enough to confirm that there are no narrow mantle plumes, Anderson and Natland say. Instead, data reveal that there are large, slow, upward-moving chunks of mantle a thousand kilometers wide.

In the mantle-plume theory, Anderson explains, the heat that is transferred upward via jets is balanced by the slower downward motion of cooled, broad, uniform chunks of mantle. The behavior is similar to that of a lava lamp, in which blobs of wax are heated from below and then rise before cooling and falling. But a fundamental problem with this picture is that lava lamps require electricity, he says, and that is an outside energy source that an isolated planet like Earth does not have.

The new measurements suggest that what is really happening is just the opposite: Instead of narrow jets, there are broad upwellings, which are balanced by narrow channels of sinking material called slabs. What is driving this motion is not heat from the core, but cooling at Earth's surface. In fact, Anderson says, the behavior is the regular mantle convection first proposed more than a century ago by Lord Kelvin. When material in the planet's crust cools, it sinks, displacing material deeper in the mantle and forcing it upward.

"What's new is incredibly simple: upwellings in the mantle are thousands of kilometers across," Anderson says. The formation of volcanoes then follows from plate tectonics — the theory of how Earth's plates move and behave. Magma, which is less dense than the surrounding mantle, rises until it reaches the bottom of the plates or fissures that run through them. Stresses in the plates, cracks, and other tectonic forces can squeeze the magma out, like how water is squeezed out of a sponge. That magma then erupts out of the surface as volcanoes. The magma comes from within the upper 200 kilometers of the mantle and not thousands of kilometers deep, as the mantle-plume theory suggests.

"This is a simple demonstration that volcanoes are the result of normal broad-scale convection and plate tectonics," Anderson says. He calls this theory "top-down tectonics," based on Kelvin's initial principles of mantle convection. In this picture, the engine behind Earth's interior processes is not heat from the core but cooling at the planet's surface. This cooling and plate tectonics drives mantle convection, the cooling of the core, and Earth's magnetic field. Volcanoes and cracks in the plate are simply side effects.

The results also have an important consequence for rock compositions — notably the ratios of certain isotopes, Natland says. According to the mantle-plume idea, the measured compositions derive from the mixing of material from reservoirs separated by thousands of kilometers in the upper and lower mantle. But if there are no mantle plumes, then all of that mixing must have happened within the upwellings and nearby mantle in Earth's top 1,000 kilometers.

The paper is titled "Mantle updrafts and mechanisms of oceanic volcanism." http://www.sciencedaily.com/releases/2014/09/140908152924.htm

Story Source:

The above story is based on materials provided by California Institute of Technology. The original article was written by Marcus Woo. Note: Materials may be edited for content and length.

Journal Reference:

Don L. Anderson and James H. Natland. Mantle updrafts and mechanisms of oceanic volcanism. PNAS, September 8, 2014 DOI: 10.1073/pnas.1410229111

Volcanoes in Europe

This map indicates volcanic areas in Europe. European listed volcanoes are:

  • Chaine des Puys, France — Location: 45.5N, 2.8E. Elevation: 4,800 feet (1,464 m). Chaine des Puys is a volcanic province in south-central France. Eruptions began about 150,000 years ago. The most recent eruption was about 4,040 B.C. Puy de Dome is the one of the youngest volcanic feature in the province. The most recent eruption at Puy de Dome was about 5,760 B.C. Deposits at Puy de Dome indicate that the volcano had Strombolian and Pelean type eruptions. Volcanism began in the Massif Central of France about 20 million years ago. Compositions include basalt, andesite trachyte, and rhyolite. Volcanism far from the edges of tectonic plates, such as Chaine des Puys, is rare. Changes in the mantle may have led to volcanism at Chaine des Puys. Several lines of evidence indicate thinning of the crust and upwelling of the asthenosphere. The rising mantle "diapir" was probably a total of 30-60 miles (50-100 km) in diameter. The question has been raised if a hot spot is involved but no definitive evidence has been found.
  • Stromboli , Italy — Location: 38.8 N, 15.2 E. Elevation:2,900 ft (900 m). Stromboli is one of the Aeolian Islands of Italy. It is one of the most active volcanoes on Earth. It has been in nearly continuous eruption for about 2,000 years. Latest: July 2003 — The effusive eruption that began at Stromboli on February 15, on the upper eastern corner of the Sciara del Fuoco (a horseshoe-shaped scarp), continued until at least June 16, with a general decrease in lava-effusion rate. In the first week of June, there was Strombolian activity at the NE crater; most ejecta fell within the crater and pulsating dark ash was emitted. On June 11 lava flows were occasionally emitted from hornitos. On June 15 a Strombolian explosion occurred, with abundant ash emissions.
  • Etna , Italy — Location: 37.7N, 15.0E. Elevation: 10,990 feet (3,350 m). Etna has the longest history of documented eruptions of any volcano. The first reported eruption was in 1,500 BC. Latest: July 2003 — An ash plume below ~4 km above sea level drifted SE on June 7. At Bocca Nuova crater strong gas emissions and occasional strong explosions occurred. Gas was also emitted from two pits in Voragine crater. On February 12, a series of 10 earthquakes were recorded on Etna's NE flank in the same area that was affected by the eruption that ended on Jan. 28. The largest, one with a magnitude of 3.8, occurred on the 13th (0632).
  • St Helens , Italy — Location: 46.20 N, 122.18 W. Elevation: 2549 m. The eruptive history of Mount St. Helens began about 40,000 years ago with dacitic volcanism, which continued intermittently until about 2,500 years ago. This activity included numerous explosive eruptions over periods of hundreds to thousands of years, which were separated by apparent dormant intervals ranging in length from a few hundred to about 15,000 years. The range of rock types erupted by the volcano changed about 2,500 years ago, and since then, Mount St. Helens repeatedly has produced lava flows of andesite, and on at least two occasions, basalt. Other eruptions during the last 2,500 years produced dacite and andesite pyroclastic flows and lahars, and dacite, andesite, and basalt air fall tephra. Lithologic successions of the last 2,500 years include two sequences of andesite-dacite-basalt during the Castle Creek period, and dacite-andesite-dacite during both the Kalama and Goat Rocks periods. Major dormant intervals of the last 2,500 year range in length from about 2 to 7 centuries.
  • Vesuvius, Italy — the volcano most famous for blanketing the towns of Pompeii and Herculaneum with lava and debris in A.D. 79, may be sitting atop a magma reservoir buried eight kilometres deep in the earth's crust that is at least 400 square kilometres wide; this puts Mt. Vesuvius into the Super Volcano category for size if not power.
  • Kos, Greece — Location: 36.8N, 27.3E. Elevation: 430 m. Kos has solfatara fields and hot springs. Most of the rocks are Pleistocene in age. There have not been any eruptions in the last 10,000 years.
  • Methana , Greece — Location: 37.6N, 23.3E. Elevation: 760 m. The peninsula of Methana is made of lava domes and lava flows. Volcanism began in the late Tertiary or early Quaternary. The most recent activity has been at Kameno Vouno, on the Northwest part of the peninsula. There was an explosive eruption at this vent in 258 BC. The eruption also produced a dome and lava flows. The dome has a crater about 100 m in diameter and 25 m deep. Radial fissures intruded the dome. The flow is about 1,250 m long and about 150 m thick near the vent and 70-80 m thick near its terminus. The flow reached the coast and extended the shoreline by 500 m. Strabo in his "Geographica" recorded this eruption. An eruption was suspected in August of 1922, but not confirmed.
  • Milos , Greece — Location: 36.7N, 24.4E. Elevation: 751 m. Milos is a Pliocene to Holocene stratovolcano with no historic eruptions. Effusive rocks (domes and lava flows) make up most of the island.
  • Nisyros , Greece — Location: 36.4 N, 27.1 E. Height: 2,290 feet (698 m). The island of Nisyros is a stratovolcano at the eastern end of the Hellenic island arc. This arc of volcanoes is related to the northward subduction of the African plate beneath the Aegean microplate.
  • Santorini, Crete/Greece — Location: 36.4N, 25.4E. Elevation: 1,850 feet (564 m) — Its explosion in about 1628 is believed to have been the main cause of the disappearance of the Minoan civilisation and disruptions to all the human cultures around the Mediterranean. The eruption of Santorini in Greece in 1,650 B.C. was one of the largest (VEI=6) in the last 10,000 years. About 7 cubic miles (30 cubic km) of rhyodacite magma was erupted. The plinian column during the initial phase of the eruption was about 23 miles (36 km) high. The removal of such a large volume of magma caused the volcano to collapse, producing a caldera. Ash fell over a large area in the eastern Mediterranean and Turkey. The eruption probably caused the end of the Minoan civilization on the island of Crete. Santorini is complex of overlapping shield volcanoes. Basalt and andesite lava flows that make the shield are exposed in the cliff below the town of Phira. Some of t he cliff is thought to be a caldera wall associated with an eruption 21,000 year ago. Druitt and Francaviglia (1992) found evidence of at least 12 large explosive eruptions in the last 200,000 years at Santorini. The white layer at the top is the Minoan tephra from the 1,650 B.C. eruption. Akroteri, a Minoan city on the south part of Thera, is being excavated. About 3-6 feet (1-2 m) of ash fell on the city that had a population of about 30,000. The residents appear to have been successfully evacuated prior to the eruption. No bodies have been found in the ash like those at Vesuvius. The Kameni Islands formed after the caldera. Eleven eruptions since 197 B.C. have made the two islands. The most recent eruption at Santorini was in 1950 on Nea Kameni, the northern island. The eruption was phreatic and lasted less than a month. It constructed a dome and produced lava flows.
  • Yali , Greece — Location: 36.6N, 27.1E. Elevation: 176 m. Yali is made of Holocene lava domes with no historic eruptions.
  • Grimsvötn , Iceland — Location: 64.50N, 17.36W. Grímsvötn is a central volcano in the Grímsvötn volcanic system of Iceland. This system is about 62 miles (100 km) long and ~9 miles (15 km) wide. It is mostly covered with ice named Vatnajokull. The total volume of lava erupted from the Grimsvotn system is about 50-55 cubic km. The ice does not cover only about 19 cubic km of this lava. The system rises to the northeast from about 1000 ft (300 m) above sea level in the southwest. It reaches its tallest point at Grímsvötn volcano. This volcano has a 35 sq km caldera. A high temperature hydrothermal area is located in this caldera. Grímsvötn has erupted 45 times. The last eruption of the volcano was in 1996. Latest: July 2003 — An eruption began at Grímsvötn in the Vatnajokull glacier in southeast Iceland on December 18, 1998 and appears to have ended on December 28. The most vigorous eruption occurred during the first two days and the activity became intermittent in the last few days. The Grimsfjall seismograph (located 3 km from the eruption site) recorded that the continuous tremor stopped at 10:50 a.m. on December 28.
  • Askja , Iceland — Location: 65.03 N, 16.75W. Elevation: 4,954 feet (1,510 m). Askja, a huge caldera in a mountain area called Dyngjufjoll. There are different levels of the small crater and the lake, which is collapsed ground filled with ground water. The lake has been formed after a big eruption of the crater in front in 1875. The name of the lake is Oeskjuvatn; the crater itself is called viti (hell). A spring can be found on the left side.
  • Krafla , Iceland — Location: 65.73N, 16.78W. Elevation: 2,133 feet (650 m). Krafla is a caldera which is ~6 miles (10 km) across. This caldera was mostly filled with eruptive material over the last glacial period. The fissure swarm connected to Krafla is 62 miles (100 km) long and ~3-6 miles (5-10 km) wide. About 35 eruptive fissures have opened along this swarm since the last glacial period. A high temperature geothermal field is located in Krafla's caldera. This field reaches temperatures of 644 degrees F (340 degrees C) at 1.25 miles (2 km) depth. This energy is now used in a geothermal power plant. Krafla has been quite active throughout history. It has erupted 29 times. Its last eruption was in 1984. In 1724, Krafla began an eruption that lasted for five years. This eruption was called "The Myvatn Fires." It was named for the nearby area of Myvatn, which is a rich farming district and very well populated. During this eruption, lava flowed from a ~7 mile (11 km) long fissure until it reached ~12.5 miles (20 km) in length after one year.
  • Hekla , Iceland — Location: 63.98 N, 19.70 W. Elevation: 4,890 ft. (1,491 m). Hekla is the most active volcano in Iceland with eruption events numbering from as low as 15 major eruptions to the huge number of 167 since 1104, the most recent being in 1991. Latest Jul03 — On 26 February 2000, Iceland's most famous volcano, Mt. Hekla, began erupting at 1819 GMT. The seismic networks of the Science Institute, University of Iceland and the Iceland Meteorological Office recorded a short-term precursory earthquake activity. A seismograph near the summit of Hekla beginning at 1700 detected small earthquakes. The National Civil Defence of Iceland issued a warning, and the public was alerted. Thunder, lightening, and earth tremors accompanied the eruption. A 6-7 km long fissure appeared and a steam column rose nearly 15 km (45,000 feet) into the sky. A discontinuous curtain of fire emanated from the entire fissure. The lava flows down the slopes of Hekla and covers a large part of the Hekla ridge.
  • Katla , Iceland — Location: 63.6N, 19.1 W. Elevation: ~800m. The eruption at Eldgja (a fissure system of Katla volcano) in ~935 AD lasted 3-8 years and produced 19.6 cubic km of lava, making it the largest basaltic flood lava eruption in historic time. The fissure was about 30 km long. An estimated 219 Mt of SO2 was released to the atmosphere during the eruption which may have produced as much as ~450 Mt of H2SO4 aerosol. The amount of volcanic Eldgja eruption was over several years in duration the environmental impacts probably did not exceed those produced by Laki and Tambora.
  • Herdubreid , Iceland — Location: 65N, 16W. Herdubried is a flat-topped volcanic mountain in northern Iceland. The elevation at the summit is 5,000 feet (1,500 m) and relief is 3,300 feet (1,000 m). Herdubried erupted through glacial ice. The cap at the top of the mountain is formed by lava erupted subaerially after the ice had been penetrated.
  • Eldfell, Heimaey, Iceland — Location: 63.4N, 20.3W. Elevation: 915 feet (279 m). Eldfell ("fire mountain" in Icelandic) is a volcano on the island of Heimaey in the Vestmannaeyjar archipelago 15 miles (25 km) south of Iceland. In January of 1973, an eruption began along a 1.5-mile (2 km) long fissure not far from the center of the town of Vestmannaeyjar. The fissure extended across the entire island, producing a spectacular curtain of fire. Nearly all of the island's 5,300 residents were evacuated to the mainland. This eruption is famous because the Icelanders sprayed seawater on the lava to slow and stop its movement. It was the largest effort ever exerted to control volcanic activity. More than 19 miles (30 km) of pipe and 43 pumps were used to deliver seawater at rate up to 1.3 cubic yards (1 cubic meters) per second. Eight million cubic yards (6 million cubic meters) of water had been pumped onto the flows by the end of the eruption. About 70 homes and farms were buried under tephra and 300 buildings were burned by fires or buried under lava flows.
  • Oraefajokull , Iceland — Location: 64.00N, 16.65 W. Elevation: 6,950 ft. (2,119 m). Oraefajokull is the largest active post-glacial volcano in Iceland; its height and volume exceed that of any other. Its north-western rim is Hvannadalshnukur,the highest peak in Iceland. Its crater is 3 miles (5 km) wide and it has a rim averaging 6,068 ft. (1,850 m) high. This volcano has been also known as Knappafell and Knappafellsjokull. Oraefajokull is also renown for its magnificent glaciers that sweep down into the surrounding lowland plains from the volcano's lofty heights. North and northwest of Oraefajokull is the largest glacier in Iceland, Vatnajokull. Oraefajokull has erupted only twice in historical times, once in 1362 and then again in 1727.

Large Volcanos outside Europe

  • Tambora, Sumbawa, Indonesia – Location: 8.3S, 118.0E. Elevation: 9,348 feet (2,850 m). Tambora is a stratovolcano, forming the Sanggar Peninsula of Sumbawa Island. The diameter of the volcano at sea level is about 38 miles (60 km). Prior to the 1815 eruption, the volcano may have been as tall as 13,000 feet (4,000 m). The 1815 eruption formed a caldera about 4 miles (6 km) in diameter. The caldera is 3,640 feet (1,110 m) deep. The 1815 eruption of Tambora was the largest eruption in historic time. About 150 cubic kilometres of ash were erupted (about 150 times more than the 1980 eruption of Mount St. Helens). Ash fell as far as 800 miles (1,300 km) from the volcano. In central Java and Kalimantan, 550 miles (900 km) from the eruption, one centimetre of ash fell. The Volcanic Explosivity of the eruption was VEI7. The eruption column reached a height of about 28 miles (44 km). The collapse of the eruption column produced numerous pyroclastic flows. As these hot pyroclastic flows reached the ocean where they caused additional explosions. During these explosions, most of the fine-fraction of the ash was removed. The eruption formed a caldera. An estimated 92,000 people were killed by the eruption. About 10,000 direct deaths were caused by bomb impacts, tephra fall, and pyroclastic flows. An estimated 82,000 were killed indirectly by the eruption by starvation, disease, and hunger. The 1815 eruption of Tambora caused the "Year without a summer." Daily minimum temperatures were abnormally low in the northern hemisphere from late spring to early autumn. Famine was widespread because of crop failures. The final death toll was probably in the hundreds of thousands.
  • Krakatau , Indonesia — Krakatau volcano lies in the Sunda strait between the islands of Java and Sumatra. In about 416 A.D., caldera collapse destroyed the volcano and formed a 4-mile (7-km) wide caldera. The islands of Krakatau, Verlaten, and Lang are remnants of this volcano. The eruption and collapse of the caldera in 1883 produced one of the largest explosions on Earth in recorded time (VEI=6) and destroyed much of Krakatau Island, leaving only a remnant. Since 1927, small eruptions have been frequent and have constructed a new island, Anak Krakatau (Child of Krakatau). Explosive, Vulcanian-type eruptions occurred at 1/2- to 10-minute intervals. The largest explosions produced turbulent clouds of ash and lapilli that rose 4,000 feet (1,200 m) above the vent. This episode of activity, which began in December of 1959, ended in 1963. Anak Krakatau has had at least nine episodes of activity since 1963, most lasting less than one year. The most recent episode began in March of 1994 and has continued to at least March of 1995 (last reported observation). Activity is similar to the 1959-1963 eruption.
  • Rabaul , New Guinea — Location: 4.3S, 152.2E. Elevation: 2,257 feet (688 m). Eruptions in 1937, 1941 (VEI2), 1994, 1997 and 2000.
  • Taupo , New Zealand — Location: 39.1S, 175.7E. Elevation: 6,487 feet (1,978 m). Tongariro is compound volcano, made of several coalescing volcanic cones. Most of the volcanic centre is made of four andesite massifs: Kakaramea, Pihanga, Tongariro, and Ruapehu. Maungkatote and Hauhungatahi are two smaller eroded eruptive centres. Pukeonake is made of a satellite cone and associated flows. Ohakune consists of four craters. An extensive ring plain made of stream, debris flow, lahar, lava, and ashflow deposits surrounds the volcanic centre. Cronin and Neall (1997) summarized the eruptive history of Tongariro for the last 75,000 years: 22,500 to 10,000 years ago: 1 large volume and large magnitude eruption 10,000 to 9,700 years ago: very frequent (1 eruption at least every 50 years) large volume and large magnitude eruptions 9,700 to present: years ago: frequent, low volume and low magnitude eruptions
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