Volcanoes

hazard

"A potentially damaging physical event, phenomenon or human activity that may cause the loss of life or injury, property damage, social and economic disruption or environmental degradation."

The amount of average global temperature change produced by the Mt. Pinatubo eruption was about ___ degrees celsius.

-0.5

the task of monitoring the gas output of a volcano is two-fold:

1) The ongoing activity needs to be monitored as it may be dangerous in itself AND 2) Changes in the output of volcanic gases are a good predictive tool for an imminent eruption.

the task of monitoring the gas output of a volcano is two-fold:

1) The ongoing activity needs to be monitored as it may be dangerous in itself; AND 2) Changes in the output of volcanic gases are a good predictive tool for an imminent eruption.

A number of methods exist to estimate the shape of the volcano:

1. Estimating distances between different parts of a volcano. Motion of magma may cause the crater to widen or shrink or cause the top of the volcano to rise or fall. While changes involved may be small, on the order of a few millimeter per day, noticing them early and following their evolution may be of great value for the task of forecasting a volcano's behavior. an instrument that can evaluate a distance to a specially designed marker is used. One such device relies on lasers that are aimed at pre-positioned mirrors so that their reflected beam can be captured and used to evaluate the distance. Obviously, this method will work well in clear air, and in relatively forgiving terrain that would allow installation of markers. Positions of points on the edifice of a volcano may also be monitored with the help of the Global Positioning System (GPS). will determine the position to within a few meters.

The two basic goals of monitoring quiescent (i.e. not erupting) volcanoes are:

1. To know what the volcano is doing at present; (In order to have some idea of the interior processes within a volcano, numerous observations over many cycles of volcanic activity are needed.) 2. To guess what the volcano will do, and when. (requires both general knowledge of what volcanoes can do, and a good understanding of a specific volcanoes past behavior in hopes of understanding its patterns or eruption cycles.)

During the eruption, dual goals are pursued as well:

1. monitoring the eruption process for the needs of hazard mitigation (e.g., which way the ash will be carried by the wind) 2. determining when the eruption has stopped. (this decision is more important)

how many potentially active volcanoes are there in the US?

161

Then click Volcano Updates and note how many notifications (blocks of text with colored backgrounds) are displayed on Thursday, February 23. "Alert Level System" describes the levels, read it.

2 are on watch level(orange), 5 are on advisory (yellow) ADVISORY- Volcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level,volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase. WATCH- Volcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain,OReruption is underway but poses limited hazards.

A number of methods exist to estimate the shape of the volcano:

2. Measurements of the tilt of the volcano flank. Motions of magma that change the shape of the volcano will inevitably alter the tilt of its slopes. If a volcano edifice is filing with magma, it will likely inflate, making the slopes steeper. After an eruption the slopes may drop, becoming more horizontal. tool to measure such changes uses a container of liquid and a bubble of gas that moves in response to tilting the container. A number of such devices placed on the edifice of a volcano at different locations will provide a picture of the slope changes.

Now use the "filter" menu to open the "REGIONS" tab and choose Alaska. A map will zoom into the Alaska region. Which volcanoes have the ADVISORY level alert there?

3 - Takawangha, Trident, and Semispochoni

A number of methods exist to estimate the shape of the volcano:

3. Satellite Altimetry - change in shape captured all at once. The most recent tool in ground deformation studies, including volcano monitoring, uses data from satellites that measure topography (the height of the Earth's surface). When such a satellite passes over the patch of land surface it has previously surveyed, a time-lapsed measurement is obtained. Analysis of the differences in two surveys of the same area offers a "snapshot" of changes, provided these changes are large enough. Motions associated with volcanic activity are well within the range of detectable changes. As the satellites stay in orbit for long periods of time, a history of volcanic edifice motion may be constructed.

How many notifications for volcano alert status were posted on Thursday, February 23, 2023?

8

Eruption of the Pinatubo volcano in the Philippines in 1991

A few months after the eruption, average temperatures on Earth decreased by as much as 0.5 degrees and stayed at this level for over a year.

Gabbro

A mafic, coarse-grained igneous rock composed predominantly of ferromagnesian minerals and with lesser amounts of calcium-rich plagioclase feldspar.

On Thursday, February 23, 2023 volcano Takawangha in the Andreanof islands had ____ level of alert assigned to it

ADVISORY

The May 8th, 1902 eruption of Mt. Pelée, Martinique(Or, why we need volcanologists) continued

After the eruption, a lava dome (spire/plug) grew out of the volcanic vent. The residents of St. Pierre were ill prepared for a massive volcanic eruption. The memory and records of other minor eruptions that did not result in complete devastation (1792 and 1851-52) contributed to this false sense of security. Modern volcanological monitoring techniques allow for much better prediction and evacuation- Affected towns on the Caribbean island of Montserrat were evacuated well before the eruption of nearby Soufriere Hills in the late 1990sVolcano prediction and evacuation are not perfect. A predicted eruption of Guadeloupe (French West Indies) in 1976 failed to materialize, angering the residents who had been evacuated and prompted lawsuits.

coulee

An elongate lava dome that typically forms as a high-silica lava erupts on the steep flank of a volcano. The dome axis perpendicular to the volcano's slope is shorter than the axis parallel to the slope, creating an elliptical shape. The leading edge of the coulee is often blocky and steep

Andesite

An intermediate colored rock, generally gray greenish-gray, also classed as an aphanite because of the small crystal or grain size.

Single-cell organisms that exist through chemosynthesis are called

Archaea, These form the base of the food chain around the vents, and can in turn be eaten by organisms a little more familiar to us

Ash threating air traffic

Ash clouds from major explosive eruptions often linger at airplane heights (11 km) and can "sandblast" the turbines and scour the windows and fuselage. Ash can heat up and re-melt once inside the engine, coating the turbine, limiting oxygen flow, and shutting down the engine. 1982 British Airways 747 over Java. Unbeknownst to the pilot and passengers, the Javanese volcano Galunggung was erupting beneath them. As the plane passed through the ash cloud, the windows were rendered opaque by the corrosion, and all four engines failed because of the ingested ash. For over 13 minutes the pilot tried futilely to restart the engines, as the plane slowly descended from its cruising altitude of 37,000 feet down to 12,000 feet. engines restarted as they entered more oxygen-rich lower elevations. However, the danger was not over - the windshield was still opaque, and the instruments were not functioning. The pilot did manage to make an emergency landing in Jakarta

Trench

At the junction of two convergent plate, marks the actual plate boundary of the overriding plate. These trenches are the deepest parts of Earth's oceans.

Threat of earthquakes

Both the movement of magma near the surface and the eruption of a volcano can generate earthquakes. These are generally not as large as the ones associated with faults and plate boundaries (rarely more than magnitude 5), but they can still cause damage to structures nearby. In the case of Mount St. Helens, an earthquake triggered the landslide that released pressure on the magma, leading to the lateral blast eruption.

Ground deformation

Changes in the shape of the volcano edifice may give clues to the motions of magma within it. Volcano flanks can rise when magma moves towards the surface, fall after an eruption, and change their shape when magma moves internally from one section of volcanic plumbing to the other.

Ground deformation monitoring

Changes in the shape of the volcano edifice may give clues to the motions of magma within it. Volcano flanks can rise when magma moves towards the surface, fall after an eruption, and change their shape when magma moves internally from one section of volcanic plumbing to the other. Some changes in volcano shape are obvious to the eye, for example the notorious pre-eruption bulge on the flank of Mt. St. Helens that formed shortly before its dramatic eruption.

Volcanoes on Venus

Earth's sister planet. The two planets are roughly the same size and density, and both have atmospheres. It is therefore no surprise that both planets are volcanically active. Venus is second only to Earth in the number of volcanoes, with over 22,000 volcanic edifices, 1738 of which are larger than 20 km. Venus' thick atmosphere makes it very hard to study since we can't see through it normally. The U.S. Magellan mission (1990s) has mapped the surface using radar. It's also very hard to land there- the pressure at the surface is over 100 times greater than Earth, and the surface temperature of 420° C, hot enough to melt lead! Venus' largest volcano, the 8-km-tall Maat Mons. The pattern of volcanic activity on Venus differs from that on Earth. On Earth, most volcanoes line the boundaries between plates, while only a few pops up in the middle of plates at hot spots. Venus may not have active plate tectonics, and the random smattering of volcanoes on its surface may indicate that hot spot volcanism dominates.

methods that estimate the shape of a volcano

Estimating distances between different parts of a volcano, Measurements of the tilt of the volcano flank, Satellite Altimetry - change in shape captured all at once

what is the highest level of notification on the map?

Great Sitikin and Kilaeu (both have watch levels)

intrusive rock

Igneous rock that forms when magma hardens beneath Earth's surface.

Where does cryovolcanism occur?

In the outer solar system, where moons are cold and rich in ice, there are ice volcanoes (termed cryovolcanoes) that spew water and other liquid or liquid-gas volatiles instead. Triton, Neptune's largest moon, has even been caught in the act. other moons show signs of past of recent cryovolcanism, including Saturn's Titan and Enceladus, and Jupiter's Europa.

Krakatau is formed by convergence of _____ tectonic plates

Indo-Australian and Eurasian

The most volcanically active body in our solar system is

Io

Why is Io so hot?

It is much smaller than the Earth (about the size of our moon) and should have cooled down by now. However, it is close enough to Jupiter that it is greatly affected by its gravity, and this gravitational attraction produces strong "tides" which contribute energy to the moon (in the form of heat). tidal heating

Volcanism on the moon

It turns out that the maria are composed of ancient (4.3-3.1 billion years old) basalt! The rocks making up the maria are basalt, a common rock on Earth. However, the exact composition is unique. First, no water-bearing minerals were found, though these minerals are common in Earth basalts. Second, there are a few minerals found in lunar basalts that are not found on Earth. The great age of the moon rocks suggest that the moon's interior was hot enough to form melts and erupt magma early in its history, but that it cooled down quickly and has remained volcanically inactive since

II. Duration of volcanic tremor

Length of time volcanic tremor was seen during a given time before an eruption of Mt. Spurr, Alaska, in 1992. Eruption time is marked by an arrow. At some of volcanoes (e.g. Galeras), a particular type of seismic signal, called a tornillo (screw in Spanish) was recognized as the "last warning" a volcano gives before an eruption.The lower axis, partially obscured by the color scale, is time in seconds. The upper panel is a time-history of shaking, while the panel below shows intensity of shaking at different frequencies of oscillation. A 1 cycle per second (cps) shaking seems to dominate.

Krakatau (Krakatoa), 1883 eruption aftermath

Most of those who died in the 1883 eruption of Krakatau died because of the associated tsunami. The collapse of the island, forming a below sea level caldera, displaced a massive amount of seawater, sending devastating tsunami towards the coasts of Java and Sumatra. 36,000 people are estimated to have died as coastal villages were wiped out by the waves, which reached 40 m in height. Before the 1883 eruption, the island of Krakatau consisted of three individual volcanoes. During the eruption, two of the volcanoes (and the north side of the third) collapsed into the vacating magma chamber, leaving only a remnant of the original island. A new island, Anak Krakatau (son of Krakatau) emerged at the center of the new caldera in 1927, and continues to grow as small eruptions continue. Ash in the atmosphere made for spectacular red sunsets in northern Europe. The 1883 eruption was not the only time Krakatau erupted violently. The islands of Verlaten and Lang are remnants of the volcano that was destroyed during the 416 AD eruption. The growth and occasional eruptions of Anak Krakatau show that this volcano is still active, and could erupt again.

Estimating distances between different parts of a volcano

Motion of magma may cause the crater to widen or shrink or cause the top of the volcano to rise or fall. While changes involved may be small, on the order of a few millimeter per day, noticing them early and following their evolution may be of great value for the task of forecasting a volcano's behavior.In a technique similar to one used by commercial surveyors, an instrument that can evaluate a distance to a specially designed marker is used. One such device relies on lasers that are aimed at pre-positioned mirrors so that their reflected beam can be captured and used to evaluate the distance.Obviously, this method will work well in clear air, and in relatively forgiving terrain that would allow installation of markers. Hawaii volcanoes are often monitored with this method. Global Positioning System (GPS) is used to find Positions of points on the edifice of a volcano

Measurements of the tilt of the volcano flank

Motions of magma that change the shape of the volcano will inevitably alter the tilt of its slopes. If a volcano edifice is filing with magma, it will likely inflate, making the slopes steeper. After an eruption the slopes may drop, becoming more horizontal.A tool to measure such changes is similar to the carpenter's level - it uses a container of liquid and a bubble of gas that moves in response to tilting the container. A number of such devices placed on the edifice of a volcano at different locations will provide a picture of the slope changes

Which one of the following volcanoes is associated with the least risk? Select only one answer.

Mt. Erebus

Of the historic eruptions discussed in class, the smallest (in terms of VEI) was

Mt. Peele

How do we know a lot about deep sea volcanoes?

Much of this work is done with submersibles, including Alvin. A hypothesis some researches make is that hydrothermal vents may have been ideal locations for the origins of life. The land surface of the Earth was likely inhospitable to life before photosynthesis yielded a more oxygen-rich atmosphere (with an ozone layer to block out harmful UV radiation). Deep sea vents, separated from the tumultuous surface, may have been able to sustain life during the Earth's early days.

Two types of pyroclastic flows

Nuee Ardente and a pumice flow

The largest volcano in our solar system is called ___.

Olympus Mons

The May 8th, 1902 eruption of Mt. Pelée, Martinique(Or, why we need volcanologists)

One of the more infamous volcanic eruptions of the 20th century occurred on the Caribbean island of Martinique in 1902. The Dutch colonial city of St. Pierre stood at the base of a volcano that was becoming increasingly active. Volcanoes had not yet been extensively studied, and the residents failed to heed what we might think of as "common sense" today. On May 8th, 1902, St. Pierre was entirely destroyed by pyroclastic flows, leaving only two survivors in a town of more than 20,000.Like many of the world's most dangerous volcanoes, Mt. Pelée is located over a subduction zone. In this case, the Atlantic Plate subducts under the Caribbean Plate, forming a chain of volcanoes and volcanic islands (the Lesser Antilles island arc). A nuée ardente (pyroclastic flow) covered the town of Saint-Pierre shortly after 8 am. All members of the "Volcano Commission" who participated in the meeting on May 7th perished.The pyroclastic flow swept down the mountain at a temperature of 200°-450° C, and may have reached a velocity of over 300 km/hr before slamming into St. Pierre 2 minutes later. Only two people in Saint-Pierre survived, one a prisoner who was protected from the heat by the walls of his underground cell.

Which of the Earth's layer is liquid?

Outer core

The outer shell of our planet is called the crust. Most common chemical elements composing it are:

Oxygen and Silicon

Where was the largest volcanic eruption in the last 50 years

Pacific ocean

Why doesn't Venus have active plate tectonics?

Perhaps because it is too hot at the surface. With a warmer, less stiff lithosphere, plates do not form or, if they do, there is not enough density contrast for subduction to begin.

Convergent Margins

Places where two tectonic plates move towards each other.

Which of the following cities were buried as a result of the eruption of Mt. Vesuvius in 79 AD? More than one choice may be possible. Select all that apply.

Pompeii, Herculaneum

Threat of lava flows

Rivers of runny, glowing lava, cause more property damage than injury. People usually have time to get out of the way by moving to higher ground or outrunning the flow, but their houses and belongings may be less fortunate. The temperature of an approaching lava flow (over 1000° C) is enough to cause wooden structures such as houses to combust even before the lava touches them. Basaltic lava flow during the 1984 eruption of Mauna Loa, Hawaii.

Volcanism on Io, only body outside the earth to exhibit active volcanism on a massive scale

Rocks: Types of volcanoes: ACTIVE VOLCANIC PLUMES, large calderas. PYROCLASTIC DEPOSITS, LAVA FLOWS AND FLOW FIELDS Biggest Volcano: Loki Patera Reason for volcanism: Based on the amount of heat released annually through volcanic eruptions, Io is the most volcanically active body in the solar system. it is close enough to Jupiter that it is greatly affected by its gravity, and this gravitational attraction produces strong "tides" which contribute energy to the moon (in the form of heat).

Volcanoes on Venus

Rocks: The crust of Venus appears to be almost entirely volcanic and basaltic. There is nothing there like Earth's continents—no granitic rocks at all, high in silicon and oxygen. Venus instead has large, bizarre fractured structures called coronae ("crowns") and tesserae ("mosaic chips"). Type of volcanoes: over 22,000 volcanic edifices, 1738 of which are larger than 20 km. Biggest Volcano: Theia Mons/Devana Chasma Reason for volcanoes: plumes of magma rise up from the mantle and push their way to the surface via cracks in the crust

Volcanoes on Moon

Rocks: ancient (4.3-3.1 billion years old) basalt, The rocks making up the maria are basalt, a common rock on Earth. However, the exact composition is unique. First, no water-bearing minerals were found, though these minerals are common in Earth basalts. Second, there are a few minerals found in lunar basalts that are not found on Earth. The heavily cratered highlands are covered with a layer of regolith, a mixture of fine dust and fragmented debris generated by meteorite impacts. Beneath the regolith, two crustal rocks types dominate the highlands: (1) breccia -- a coherent rock of broken and welded fragments, and(2) anorthosite -- the most abundant highlands rock; it is a feldspar-rich variety of gabbro (which, in turn, is the coarse-grained, equivalent of basalt) Volcano types: The mare lava flows are associated with a number of volcanic vents, in the form of domes and scoria cones. The domes are typically found in clusters. They are circular to elliptical, typically a few kilometers across and several hundred meters high. The basaltic domes on the moon appear to be the lunar equivalents of shield volcanoes found on earth. Construction of the relatively steep slopes of the lunar "shields" is poorly understood. Their steep slopes are probably not related to the extrusion of relatively viscous basalt, but rather to the style of extrusion, which may involve eruptions of short duration mixed with minor episodes of ash eruption. The lunar scoria cones are similar in size to terrestrial scoria cones, and they appear to be associated with older fissure systems. A common and intriguing volcanic landform found in the lunar maria are narrow, winding valleys called sinuous rilles. majority of the sinuous rilles are thought to the product of thermal erosion of the mare surface by exceptionally hot, fluid lava Biggest Volcano: Marius Hills reason for volcanism: meteoric impact, or impact by asteroids for larger craters, was the origin of almost all lunar craters, and by implication, most craters on other bodies as well. anorthosite crystallized early in the moon's formation from a global magma ocean. Under this scenario, the lighter plagioclase floated upward to form an anorthosite crust, and the heavier minerals olivine and pyroxene sank toward the bottom of the magma ocean to form the moon's upper mantle.

Volcanoes on Mars

Rocks: composition of Martian rocks. Most large rocks appear to be basalts. These basalts are considered "primitive" because of their high magnesium compositions compared to more "evolved" Earth basalts. Types of volcanoes: shield volcanoes likely made from basalt, with slopes of no more than 5 degrees. Layered rocks found by the Opportunity rover at Meridiani Planum may be layers of ancient, weathered volcanic ash. Some small volcanoes on the surface of Mars (not in Tharsis) have steeper slopes (12°), more similar to Earth's stratovolcanoes. Mars may have had a dynamic and varied volcanic past, producing lavas and ashes of varied compositions. giant central volcanoes, peterae, tholi, and rootless cones Biggest Volcano: Olympus Mons Reason for Volcanism: The crust of Mars is not broken up into moving plates as on Earth. So rising plumes of heated rock from deep below built gigantic volcanoes over many millions of years.

Of the historic eruptions discussed in class, the largest was

Santorini

Haleakala

Shield Pyroclastic cone(s) The massive Haleakala shield volcano forms the eastern portion of the dumbbell-shaped island of Maui. The summit contains a dramatic 3.5 x 9.5 km summit crater that is widely breached on the N and SE sides. The "crater" is not of volcanic origin, but formed as a result of the coalescence of headward erosion of the Koolau and Kaupo valleys. Subsequently the crater has been partially filled by a chain of young cinder cones and lava flows erupted along a major rift zone that extends across the basaltic volcano from the SW to the E flanks. Another less prominent rift zone trends north from the summit. The most recent eruption was thought to have occurred between the exploring voyages of La Perouse in 1786 and Vancouver in 1793, but uncertainty surrounds the date of this event, which could have occurred in about 1750 CE (anthropological evidence) or several centuries earlier (radiocarbon dates).This volcano is located within the Hawaiian Islands, a UNESCO World Heritage property.

Mitigation

Since vulnerability is factored in to any calculation of risk, any steps that a community can take to decrease that vulnerability will also help reduce the risk. Examples include not living close to a volcano

Threat of Tsunamis

Some volcanoes (such as Krakatau) are at or near sea level. When these erupt explosively, they can displace ocean water (either due to the blast itself or the collapse of the caldera at the end). This displacement of water can generate tsunamis that can devastate coastlines around the region. Over 36,000 people died in Indonesia because of the tsunamis generated by the 1883 eruption of Krakatau.

Brava Volcano

Stratovolcano, Brava Island, 20 km W of Fogo, is the westernmost of the southern Cape Verde islands. The 10-km-wide island contains 15 morphologically youthful craters located along two or three lineaments intersecting along the crest of the island. The youthfulness of the craters and numerous minor earthquakes in recent years indicate that a significant volcanic hazard still exists (Wolff and Turbeville, 1985). Most of the younger eruptions originated from the interaction of phonolitic magmas with a large groundwater reservoir contained within an older volcanic series characterized by thick welded ignimbrites and block-and-ash flow deposits. Carbonatitic lavas are also found.

Hekla

Stratovolcano, Fissure vent(s) One of Iceland's most prominent and active volcanoes, Hekla lies near the southern end of the eastern rift zone. Hekla occupies a rift-transform junction, and has produced basaltic andesites, in contrast to the tholeiitic basalts typical of Icelandic rift zone volcanoes. Vatnafjöll, a 40-km-long, 9-km-wide group of basaltic fissures and crater rows immediately SE of Hekla forms a part of the Hekla-Vatnafjöll volcanic system. A 5.5-km-long fissure, Heklugjá, cuts across the 1491-m-high Hekla volcano and is often active along its full length during major eruptions. Repeated eruptions along this rift, which is oblique to most rifting structures in the eastern volcanic zone, are responsible for Hekla's elongated ENE-WSW profile. Frequent large silicic explosive eruptions during historical time have deposited tephra throughout Iceland, providing valuable time markers used to date eruptions from other Icelandic volcanoes. Hekla tephras are generally rich in fluorine and are consequently very hazardous to grazing animals. Extensive lava flows from historical eruptions, which date back to 1104 CE, cover much of the volcano's flanks

Ice glacier affected by volcanoes

Sulfur goes into atmosphere, increases the fraction of sulfuric acid in the rain and snow that fall after an eruption. In long-lasting glaciers, like the one in Greenland, layers of snow that fell after volcanic eruptions are rich in acid. numerous abrupt increases in the amount of acid are seen, many at the time of known eruptions.

Effusive eruption characteristics

Temp: High Viscosity: Low Gas: Very little

Explosive eruption characteristics

Temp: Low Viscosity: High Gas: A lot

Krakatau (Krakatoa), 1883 eruption

The 1883 eruption of Krakatau was a caldera-forming event followed by an explosive (VEI 6) eruption. Over 20 km3 of rock was expelled and deposited up to 500 km away. That's 20 times as big as Mount St. Helens! One of the most interesting features of the Krakatau eruption was the pyroclastic flows. Not only were these large and destructive (like Mount St. Helens), they also traveled a long distance. In fact, they traveled 40 km ACROSS WATER to slam into the nearby coast of Sumatra, where many people died from burns. Pyroclastic flows can be so full of air and hot gases that they can literally float on water. Ships 65 and 80 km from the eruption reported hurricane-force winds carrying pumice, likely the tail end of these pyroclastic flows (now cold enough not to sink ships). As a result, a lot of pumice ended up in the ocean. Since water + pumice is less dense than water alone, ships encountering concentrated pumice floats can sink (though none did for this particular eruption).

Examples of successful evacuation plans

The 1991 eruption of Mt. Pinatubo, Philippines: Over 56,000 people were evacuated from the area 30 km from the volcano, with the final evacuations called only a day before the cataclysmic eruption. 500 people died as a result of this eruption. The 1997 eruption of Soufriere Hills, Montserrat, Caribbean. Over 12,000 were evacuated from harm's way.

Krakatau (Krakatoa), 1883

The August 27, 1883 eruption of Krakatau in Indonesia was one of the largest eruptions in recorded history. In fact, the blast was perhaps one of the loudest sounds ever heard. The blast was heard 4,800 km away from its source, and subaudible sound waves from the blast traveled around the planet seven times! Indonesia is a very seismically and volcanically active area, as demonstrated by the recent major earthquakes and tsunami. The volcanic eruptions of Krakatau (1883), Tambora (1815), and Toba (~74,000 yrs ago) and many others are related to these tectonic processes. The subduction of the Indo-Australian Plate under the Eurasian Plate just to the south of the Indonesian archipelago is the cause of all of this violent activity, producing some of the largest volcanic eruptions in the world in both historic and prehistoric times.

threat of the blast

The actual blast is rarely dangerous, since it is usually focused straight up. In odd cases, such as Mount St. Helens, the blast can be focused sideways, flattening everything in its path.

Ararat volcano of 1840

The double-peaked stratovolcano Mount Ararat, also known as Agri Dagi, is Turkey's highest, largest volume, and easternmost volcano. It is glacier-clad along with its twin volcano, Kucuk Ararat (or Lesser Ararat), and covers an area of 1000 km2 at the eastern end of a SSW-ESE line of volcanoes extending from Nemrut Dagi. Construction of the Greater and Lesser Ararat volcanoes was followed by a period of extensive flank eruptions, many erupted along N-S fissures. The initial stage of flank eruptions produced a cluster of cinder cones and dacitic-rhyolitic lava domes surrounding Greater Ararat and a series of pyroclastic cones and domes on the W flank of Lesser Ararat. Late-stage activity formed large pyroclastic cones lower on the flanks of the two volcanoes. Ararat appears to have been active during the 3rd millennium BCE; pyroclastic-flow deposits overlie early Bronze Age artifacts and human remains. Karakhanian et al. (2002) reported historical evidence for a phreatic eruption and pyroclastic flow at the time of a July 1840 earthquake and landslide.

sulfur (short term)

The emission of large quantities of SO2 into the atmosphere is the main reason volcanoes have a strong short-term impact on climate. After an eruption, SO2 interacts with water in the atmosphere to make tiny droplets of sulfuric acid, H2SO4. These droplets reflect back the sun's rays, causing global cooling. The droplets linger in the air because their tiny size allows them to persist in the stratosphere for months to years. In contrast, dust or silicate rock particles, which are larger and much denser, rapidly settle out of the stratosphere.

Satellite Altimetry - change in shape captured all at once

The most recent tool in ground deformation studies, including volcano monitoring, uses data from satellites that measure topography (the height of the Earth's surface). When such a satellite passes over the patch of land surface it has previously surveyed, a time-lapsed measurement is obtained. Analysis of the differences in two surveys of the same area offers a "snapshot" of changes, provided these changes are large enough. Motions associated with volcanic activity are well within the range of detectable changes. As the satellites stay in orbit for long periods of time, a history of volcanic edifice motion may be constructed.

Volcanism on Europa

The new work shows how internal heat produced by tides—warping of Europa's shape as it changes distance from Jupiter during its orbit—could partially melt its rocky layer, a process that could feed volcanoes on the ocean floor

Why are there volcanoes on other planets?

The planets and major moons of the solar system were very hot when they first formed, and they have gradually been losing that heat as they cool over time. Volcanism is a very efficient way of moving "heat" from the interior of a planet to the surface. Planets and moons that still have hot interiors may still have active volcanoes today, and others likely had volcanoes in their past before they cooled down.

I. Number, size and depth of local earthquakes

The plot below shows earthquakes before, during and after the eruption of Mt. Spurr, Alaska. Each triangle on the diagram shows one earthquake, plotted according to the depth (left axis) at which it took place. Size of triangles is proportional to the size of earthquakes. Arrows show times of Mt. Spurr eruptions. Lower axis shows a time line, in months. Note a marked change in the size (bigger) and location (deeper) of earthquakes once the eruptions start.

greenhouse gases (long term)

The presence of certain volcanic gases in the atmosphere, most significantly water vapor and carbon dioxide, leads to the heating of the lower atmosphere through a "greenhouse" effect. In this way, volcanic eruptions contribute to the warming of the atmosphere. This effect appears to be minor, however, even for very large eruptions.

risk

The probability of harmful consequences, or expected losses (deaths, injuries, property, livelihoods, economic activity disrupted or environment damaged) resulting from interactions between natural or human-induced hazards and vulnerable conditions. Risk = Hazards x Vulnerability.

Volcanoes on Mars

The solar system's biggest volcanoes are found on Mars, though none are thought to be active today. The mighty Olympus Mons stands 25 km above its base, and it is but one of four large volcanoes found in the Tharsis region of Mars.Based on the shapes, volcanoes on Mars show great similarity to volcanoes on Earth. The big Tharsis volcanoes are shield volcanoes likely made from basalt, with slopes of no more than 5°. While similar in shape to Mauna Loa (Earth's biggest volcano), they are much bigger. We cannot date the volcanism on Mars. The big Tharsis volcanoes aren't heavily cratered and may have formed in the last third of Martian history. They are not active today- Mars is much smaller than Earth (only the size of the Earth's core) and has thus cooled down enough that it doesn't melt, even at depth. Most large rocks appear to be basalts. These basalts are considered "primitive" because of their high magnesium compositions compared to more "evolved" Earth basalts. Some small volcanoes on the surface of Mars (not in Tharsis) have steeper slopes (12°), more similar to Earth's stratovolcanoes. Mars may have had a dynamic and varied volcanic past, producing lavas and ashes of varied compositions.

Why do deep-sea organisms cluster around hydrothermal vents?

These vents provide energy (in the form of heat) and nutrients (all of those dissolved minerals). Organisms at deep-sea vents form communities very different from those at the surface.

Monitoring volcanoes through noise (earthquakes and tremors)

Volcanic activity is accompanied by a variety of ground vibrations (called seismic waves - scroll the page down when link opens!)) that may be felt if one is close enough to the source, but most commonly are monitored with the help of devices called seismometers. These devices are either placed on the ground or else buried, and they typically record the history of ground motion, called a seismogram. (We will be going over this in more detail during the Earthquakes portion of the class.)A broad range of pulses (small earthquakes) and sequences of pulses accompany magma movement inside a volcano. Other types of seismic activity associated with volcanoes have mechanisms that are not as well-defined. Some events appear to be related to the process of gas exsolution (formation and popping of gas bubbles), to the motion of water through various cavities. Seismic activity of volcanoes at present is the best predictor of impending eruptions. As the table below illustrates, seismic activity at a volcano preparing to erupt follows a sequence. First, multiple earthquakes, called a "swarm", appear around the volcano. The swarm of earthquakes evolves in terms of where earthquakes occur, what types of earthquakes are seen etc.As the eruption draws closer, other types of ground shaking are observed, specifically a volcanic tremor. A tremor, unlike an earthquake, is a near-continuous shaking that can last many minutes or even hours.

Volcanic Noise: earthquakes and tremors

Volcanic activity is accompanied by a variety of ground vibrations (called seismic waves) that may be felt if one is close enough to the source, but most commonly are monitored with the help of devices called seismometers. Some events appear to be related to the process of gas exsolution (formation and popping of gas bubbles), to the motion of water through various cavities within the plumbing system of a volcano, to the interaction of hot magma with groundwater close to the surface, or to other processes.Seismic activity of volcanoes at present is the best predictor of impending eruptions. As the eruption draws closer, other types of ground shaking are observed, specifically a volcanic tremor. A tremor, unlike an earthquake, is a near-continuous shaking that can last many minutes or even hours.

convergent plate boundary explosion

Volcanic eruptions are more violent at converging boundaries than at divergent boundaries

threat of landslides

Volcanic eruptions can trigger massive landslides on the volcanoes' slopes.A landslide, triggered by an earthquake, started the big 1980 eruption of Mount St. Helens.

Ash in the air (short term effect)

Volcanic eruptions emit large quantities of dust. Dust particles block and diffuse sunlight, and as a consequence the lower part of the atmosphere becomes cooler. The presence of dust in the atmosphere leads to exceptionally colorful sunsets. The effect of dust is not very long lived, as dust particles fall back to the surface. In cases of an exceptionally large eruption, like for example the Krakatau eruption of 1883, the effect may last a few months. CAN LAST A FEW MONTHS

Earth's volcanoes gas for rocks and water

Volcanic magma contains 1- 5% dissolved gas, with water (H2O), carbon dioxide (CO2) and sulfur dioxide (SO2) being the most abundant. In essence, volcanoes are a part of the global air and water recycling system. Rocks carried into the interior of the planet by the process of subduction take water and gases with them. Some of the gases and water return to the surface through volcanoes at subduction zones. However, some fraction of the former surface cover may take a longer journey through the rocky mantle of the Earth, possibly even all the way to the boundary with the iron core, before coming back to the surface through upwelling beneath mid-ocean ridges, and in mantle plumes. Thus, volcanoes in all tectonic settings serve as conduits for elements of the hydrosphere and atmosphere that were incorporated into the mantle by subduction.

What traits of volcanic activity are used as clues to predict their future behavior?

Volcanic tremors: Unstable movement of magma and volcanic gases can create tremors and earthquakes around the volcano. An increase in tremors can be a sign of increased volcanic activity. Gas emissions: The amount and composition of gas emissions, such as sulfur dioxide, carbon dioxide, and water vapor, can provide clues about the state of the magma chamber and how close the volcano may be to erupting. Ground deformation: The surface of the volcano can deform as magma and gases move underneath it. Monitoring ground deformation can help scientists understand how the magma is moving and accumulating, and whether an eruption may be imminent. Historical activity: The past behavior of a volcano, including its eruption history and the types of eruptions it has produced, can be used to predict future behavior. Some volcanoes are more likely to produce explosive eruptions, while others may have more frequent but less intense eruptions. Thermal anomalies: Changes in the temperature of the volcano, such as an increase in surface temperature or the appearance of new hotspots, can indicate increased volcanic activity. Seismicity: Monitoring the frequency and intensity of earthquakes around a volcano can also provide information about the movement of magma and potential for eruption.

threat of gas

Volcanoes emit large volumes of volcanic gas in addition to solid material. Many of these are harmless (water, CO2) but under specific conditions they can be harmful. The classic example of this was Lake Nyos, a volcano in Cameroon, West Africa. Lake Nyos is a very deep volcanic crater lake. Gases rising from the volcano below enter the lake. These gases tend to remain dissolved in the cooler bottom part of the lake, rarely mixing with the atmosphere above. In 1986 something perturbed this balance and the dissolved CO2 all bubbled up at once. While CO2 is not toxic by itself (we breathe it every day), it is denser than air and thus hugs the landscape if released all at once. The CO2 gas cloud crept down the mountainside, suffocating 1742 people. very toxic gasses that flux out of volcanoes, such as sulfur dioxide (SO2) and hydrofluoric vapor (HF).

divergent plate boundary explosion

Volcanoes with high silica and gas content are effusive.

threat of lahars

Water + fresh volcanic ash = bad news. Whether the water comes from lakes and streams, melting ice, or heavy rain, when it mixes with volcanic ash on steep volcanic slopes, it can form a raging torrent that can carry away houses, cars, bridges, and anything else in its path. Lahars can also remain a threat well after the initial eruption. Lahars can flow at velocities of 60 km/hr or more. They are more dangerous than simple floods because they are denser and usually carry large and heavy materials. tend to flow down river valleys, which happen to also be places where people want to live and farm. The 1985 eruption of Nevado de Ruiz in Colombia produced a lahar that completely buried the sleeping town of Armero, killing 25,000 people.

Warning systems

When communities near active volcanoes have access to technology, warning systems are not a problem. Japan has many active volcanoes, and some communities in their shadows have volcano-warning sirens.When lower-tech communities are faced with volcanic hazards, they have a few options. One is to rely on high-tech solutions from other communities. These monitoring and warning systems need to be maintained, so unless there is continued support for the effort, the best systems can go into disuse. The other possibility is to try a low-tech solution that can be maintained locally.

Monitoring volcanoes through gases

When the volume of gas emitted by a volcano is large, it becomes a hazard in its own right whether tied to an eruption or not. When magma within a volcano gets closer to the surface, dissolved gases have an easier time exsolving and escaping. It follows that as an eruption becomes imminent, volcanic gas output grows and the chemical composition of the gas changes. In particular, the amount of the more volatile S (sulfur) gases increases faster than that of the less volatile Cl (chlorine) gases. This means that the S/Cl ratio of fumarole gases increases prior to eruptions, and therefor may be used as an eruption predictor.

Which of the volcanoes in the US that have a level of activity assigned to them is closest to the North Pole?

Wrangell

what is the northernmost volcano on land with an assigned level of activity?

Wrangell (Alaska) Mount Baker (washington)

what is the easternmost volcano on land with an assigned level of activity?

Yellowstone

hydrothermal vent

a consequence of volcanism on the sea floor. Most are associated with mid-ocean ridges, the extensive system of fissure volcanoes that mark many oceanic plate boundaries. Often called "black smokers" because of the dark clouds of ash and water that come out, these deep-sea hydrothermal vents occur when cool ocean water seeps into the sea floor along cracks (left). The water comes into contact with hotter rock or magma below, heats up, dissolves some material from the surrounding rocks, and rises toward the surface. This superheated water erupts, bringing with it dissolved material and heat. The heated water, as hot as 400 degrees C, emerges back at the surface. As it cools again it releases its dissolved components, creating a black "smoke" as these minerals precipitate and fall out.

Igneous

a type of rock that forms from the cooling of molten rock at or below the surface

Cryovolcanism

a type of volcanism that results from the eruption of magmas derived from the partial melting of ice In the outer solar system, where moons are cold and rich in ice, there are ice volcanoes (termed cryovolcanoes) that spew water and other liquid or liquid-gas volatiles instead. Triton, Neptune's largest moon, has even been caught in the act. other moons show signs of past of recent cryovolcanism, including Saturn's Titan and Enceladus, and Jupiter's Europa.

Fumarole

a vent in a volcanic area from which fumes or gases escape

Santorini is ___.

a volcano that erupted near the end of Minoan civilization; likely origin of Atlantis myth

Which volcanic hazard lead to casualties among people and livestock near Lake Nyos?

abrupt release of carbon dioxide

Ash falls

all of ash, pumice, and lapilli is of much greater concern than lava flows. Larger lapilli and blocks fall near the source, smashing through roofs and cars. Finer ash accumulates farther from the source, blanketing the landscape and collapsing roofs. The ancient roman city of Pompeii was buried by over 6 meters of ash and lapilli, entombing many of the residents. . Breathing in ash can cause serious damage to the lungs and when it blankets the landscape it ruins crops. Rabaul Caldera, Mt. Pinatubo, Mt St Helens

Vulcano is _

an island in the Mediterranean Sea

Mid ocean ridges

are called so because they are in essence long mountains, rising by 1.5-2 km over the floor of the ocean. They are fissure volcanoes producing basaltic lava. Also known as a spreading center, divergent or constructive boundary between two tectonic plates. Form lava flows that freeze into shapes called pillows or pillow lavas Explosive eruption

Volcanism on these terrestrial bodies (Earth, moon, and Mars) produces a similar rock called

basalt

The big problem with warning systems, monitoring, and evacuation

biggest concern is knowing when and when NOT to call for an evacuation. If you evacuate too early or too often, people might not listen to you next time. Sometimes magma rising into a volcano can cool and solidify before it erupts, causing all of the "signs" of an eruption without ever causing one. Evacuations are costly, and tourists are likely to stay away from areas that are being investigated for volcanic activity. Even the possibility of an evacuation can be costly in terms of lost revenue from tourism, and a full-scale evacuation can cost millions. Policymakers have to make tough decisions- make the call too late and people die.

Which of the following types of volcanoes have the steepest slopes?

cinder cones

felsic lava

common in continental volcanos, light colored, thick and pastey, and high in silica

Addition of S (sulfur) to the atmosphere leads to the formation of sulfuric acid droplets that absorb solar radiation and promote formation of reflective clouds.

cooling

Ash in the atmosphere blocks and diffuses solar radiation.

cooling

mafic rocks

dark-colored rocks that have low silica content and are rich in iron and magensium.

key organisms sustained by underwater volcanic processes

deep-sea clams, deep-sea crabs, deep-sea fish, and deep-sea shrimp

Black smokers are located predominantly at ___ plate boundaries.

divergent

Compared to the Earth, Venus lacks plate tectonics because it is smaller than the Earth and is therefore colder

false

The eruption of Mt. Pelee in 1902 killed people in the city of St. Pierre but not on ships in St. Pierre's harbor.

false

The island of Santorini was formed as a result of a single eruption event that happened ~1630 BCE

false

flood basalts are associated with?

fissures

pillow basalt

glass-encrusted basalt blobs that form when magma extrudes on the sea floor and cools very quickly

Silicic rocks

granite and rhyolite

Threat of pyroclastic flows

hazardous largely because of their speed. They travel down the slopes of a volcano at speeds reaching 100-300 km/hr, leaving no time for escape. They can also travel great distances from their source- 10s to even 100s of kilometers for the largest eruptions. They are often hot and full of toxic gases, causing death by burning and asphyxiation. Because of their great speeds, pyroclastic flows often flatten forests and towns in the way. The 1902 eruption of Mt. Pelée on Martinique left only a layer of dust but killed everything in its path Pyroclastic flow rushes down the slopes of a Mayon Volcano, the Philippines, 1984.

Plinian eruption components

he magma column within the edifice contains two pressure surfaces: - the exsolution surface separates a zone of magma containing dissolved gases from an overlying zone containing exsolved gas bubbles - the fragmentation surface at the top of the magma column separates the zone of magma containing exsolved gas from the overlying eruption column. • The eruption column is a region of hot gas and broken pyroclastic particles above the fragmentation surface. It has three vertical regions: - the gas thrust region driven by gas expansion, - the convective thrust region driven by release of thermal energy from internal ash;- the umbrella region at the top of the eruption column.

Addition of greenhouse gases, CO2 and water vapor, traps heat close to Earth's surface.

heating

What is the tectonic setting of Haleakala volcano?

hot spot (intraplate) on a continent

A "black smoker" is a descriptive term for what?

hydrothermal vents

Where do underwater creatures get their energy from?

hydrothermal vents

extrusive rock

igneous rock that forms when volcanic material erupts, cools, and crystallizes on Earth's surface

Oceanic crust generally ___ continental crust.

is less complex than

What does an underwater volcano produce?

it does not put an eruptive column that shoots into the atmosphere (unless the volcano was close to the surface anyway). Second, magma cools much, much faster in water than in air, producing pillow basalts rather than lava flows. These eruptions contribute a lot of heat to the surrounding water. These "hydrothermal plumes" (hot water columns) provide energy that help to fuel some of the most exotic life on Earth.

Main reason for the high casualty count in Mt. Pelee eruption is

lack of understanding of volcanic processes

composite volcano (stratovolcano)

large volcano composed of alternating lava flows and pyroclastic material, generally of andesitic composition, with surface slopes of 30° at the summit and 6 ° -10 ° at the base high viscosity because it is felsic, which means it contains silicate rich minerals. convergent plate boundaries

specific types of volcanic hazards

lava and pyroclastic flows, blasts, bombs and blocks, ash falls, lahars, landslides, toxic / suffocating gases

mafic magma

magma that is silica poor, low viscosity, releases volatiles, high density, high temperature

felsic magma

magma with a high silica content and large volume of gas (explosive eruptions)

Lava Domes

most viscous lavas types that contain the highest content of silica i.e. rhyolites and dacites

Reason for volcanism

moving heat from the inside to the outside of the planet

what presents a systematic obstacle to successful continuous visual monitoring of an active volcano?

nightime darkness

Visual Monitoring

oldest method, provides a qualitative assessment of the state of a volcano (e.g. erupting or not, if erupting - what is coming out, etc.) In many parts of the world, continuously staffed observatories exist for the purpose of watching the state of a particular volcano. Recent technology enables anyone with an Internet connection to become a volcano watcher.

Visual monitoring

oldest monitoring method is direct observation of volcanoes by a human observer. This provides a qualitative assessment of the state of a volcano (e.g. erupting or not, if erupting - what is coming out, etc.) In many parts of the world, continuously staffed observatories exist for the purpose of watching the state of a particular volcano. Recent technology enables anyone with an Internet connection to become a volcano watcher. Another high-tech way of visual monitoring is by airplane or satellite.

1815 Tambora eruption on Sumbawa Island in Indonesia

one of the largest known eruptions in the past 10,000 years; the ash column extended 44km (28ft). It produced ash fallout over a 4x105 km2 area and caused darkness for about 2 days as far away as 600 km from the volcano. Studies, including tree ring observations, indicate that the 1816 summer was approximately 1.5 °C COOLER than the summer of 1815. The year following the eruption was one of hardship felt across the globe. The summer was cold and wet in western Europe, crops failed, people starved, disease spread, and social unrest grew

A volcanic hazard translates into volcanic risk when ___.

people and property are likely to be affected

white smokers

produced by Cooler vents, dominated by deposits of calcium-rich minerals, including anhydrite gypsum (CaSO4) and calcite (CaCO3). Minerals in ocean crustal rocks are rich in calcium, which dissolves easily on cold seawater. Where the warmed seawater rises back to the surface, the calcium-enriched water produces "white smokers" along with deposits of minerals that also host deep-sea bed communities.

what type of change is certain to increase the risk posed by a dormant volcano

rapid population growth nearby

The largest volcano in our solar system is a __

shield volcano

Which of the following types of volcanoes are largest in area?

shield volcanoes

Short term climate effects of volcanoes

short-term cooling of the atmosphere in the aftermath of major eruptions.

Two ways of mitigating volcano risk

short-term measures (know when to run) long term measures (think before building)

The timing of major eruptions in the past can be determined by identifying layers rich in ___ in ice sheets from Greenland.

sulfuric acid, H2SO4

volcanic gases

the amount of the more volatile S (sulfur) gases increases faster than that of the less volatile Cl (chlorine) gases. This means that the S/Cl ratio of fumarole gases increases prior to eruptions, and therefor may be used as an eruption predictor.

Volcanism on Io

the innermost of Jupiter's 4 big moons, is the only place in the solar system (besides Earth) where we have actually witnessed volcanic eruptions. Based on the amount of heat released annually through volcanic eruptions, Io is the most volcanically active body in the solar system. The 1979 Voyager I flyby showed volcanic plumes up to 300 km in height (see left), and a vividly colored surface dominated by flow-like features and large calderas. new volcanic field, roughly the size of Arizona, appeared between the March and September flybys.

Climate effects of volcanoes

the most noticeable effect volcanoes have on Earth's climate is that of short-term cooling of the atmosphere in the aftermath of major eruptions.

Which of the following is not used to predict impending volcanic eruptions?

the times of high tides

How does cryovolcanism occur?

there must be enough heat in the interior to melt ice, and the water or other volatiles must rise to the surface and escape. Heat sources include gravity and tides (Europa), solar heating (Triton), and leftover heat from when they were formed.

Main disadvantage of visual observations

they critically depend on the ability to see the monitored object.

Main disadvantage of visual observations (human visual monitoring)

they critically depend on the ability to see the monitored object.

Volcanism on Io is caused by what?

tidal heating caused by Jupiter

Cryovolcanism takes place on

trition

Chemosynthesis

ultimate source of energy, process of converting inorganic matter into organic matter using energy derived from various chemical compounds.

Lava Tubes

when lava flows at the surface the outside cools rapidly allowing the inside to remain very hot. This sometimes leads to the formation of lava tubes - channels within a lava flow that allow lava to travel, sometimes for very long distances, below a thin surface of solidified lava. When the eruption supplying the lava stops and all the liquid lava drains, a tube, or hollow tunnel, within the body of the lava flow is left behind.

On the right of the map, click the top icon (three horizontal bars), then choose "VOLCANOES", and pick the Takawangha volcano from the dropdown - what is its Alert level?

yellow - advisory

Long-term measures of mitigation

• Forecasting: Know what kind of volcano you have, and what kinds of hazards it has produced in the past and is likely to produce in the future. Each volcano is unique. • Land-use policy: If you know a particular area is in the "danger zone" and people aren't already living there, try to keep people from moving in.

Short-term measures of mitigation

• Monitoring: Keep tabs on the volcano and look for signs that could indicate increased activity. • Evacuation plans: Come up with an evacuation plan for the community and practice it! • Warning systems: How will people in your community know when to evacuate?

Why is this theory supported?

• Volcanoes, including those in the deep sea, are a product of interior planetary activity, and thus must have been present throughout much of the history of our planet. • Water covered some parts of the planet's surface for a significant fraction of its history. • Hydrothermal circulation driven by submarine volcanoes supplies nutrients and heat - two components necessary for the formation of primitive life forms. • Most primitive organisms residing around present-day hydrothermal vents (called Archaea) are among the oldest living creatures known. We belong to the branch Eukarya. The simple chemosynthetic organisms at deep-sea vents are Archaea, some of the oldest living entities known.

After magma escapes from a volcano,

, it solidifies as it cools becoming rock. Volcanic rocks have special names; a table below lists the main types of volcanic rocks. As you will see, there is considerable difference in the chemical composition of these rocks, primarily in the proportion of silica (SiO2)

What is the average rate of spreading along the Mid-Atlantic Ridge?

2.5 cm/year

Cinder (Scoria) Cones

: generally small, conical volcanoes built up of pyroclastic material, with slopes of 25° to 50° low viscosity, lot of gas convergent plate boundaries

Blocky

A mafic to intermediate lava that flows very slowly. Surface is broken into angular fragments

Santorini Volcano eruption explained

An eruption on Santorini was not entirely unexpected at the time. A "precursor" eruption most likely occurred, perhaps months ahead of the cataclysmic blast. Volcanologists recognize this precursor from a thin, yellow tephra layer that underlies the massive tephra left by the "main event." This smaller eruption, and perhaps the general growing volcanic activity, may have prompted residents to evacuate. Perhaps the eruption destroyed the cities of Santorini, but not the people.The eruption itself was massive, a VEI 6.9 eruption (nearly 10 times as big as Krakatau). 30-40 km3 of material was erupted, resulting in the formation of a caldera that is the present island group collectively called Santorini.

Monogenetic Volcano

Barren Island, North of Sumatra, is an example of a monogenetic volcano. Monogenetic means having a single origin, and such volcanoes are created by a single episode of eruption. The eruption may last a few hours or a few months, but, once the eruption ends, it is not repeated at the same place.

Astenosphere

Beneath the lithosphere is the asthenosphere. Tiny amounts of melted rock dispersed through the otherwise solid asthenosphere make the asthenosphere weak compared to the lithosphere. The D" (dee double prime) layer is a mysterious layer beginning approximately 200 km above the boundary between the core and mantle. (This boundary is referred to as the core-mantle boundary.)

Icelandic eruption

Characterized by effusions of molten basaltic lava that flow from long, parallel fissures. Such outpourings often build lava plateaus.

Which type of plate boundary involves two plates that move closer together?

Convergent

A'a

Cooler mafic lava that flows slowly with a spiky, cindery surface.

Strombolian

Episodic, short-lived, explosive outbursts of lava ejected a few tens or hundreds of meters into the air. The most common type of ejected material are bombs and lapilli, commonly made of basalt. The eruption does not create a sustained eruptive column.

Why do volcanoes form at subduction zones?

First, the plate that subducts (goes down under the other) does not disintegrate right away. On the contrary, material forming a tectonic plate remains relatively intact (as shown in previous cartoons), and descends into the interior of the Earth in the form of a dipping planar body, often called a "slab". Second, the plate that subducts take with it various chemical compounds that accumulated on top of it (or within it). Most significantly, it carries with it rocks that are rich in water (water is part of the chemical composition), which form when the basalt composing oceanic crust reacts with sea water. Once these rocks are taken into the Earth's interior by the descending plate, the increase in heat and pressure cause water-rich chemical compounds to break down, thereby releasing their water. Third, the temperature at which rocks melt depends on a number of conditions. Temperature and pressure combinations at which a particular rock melts form a "solidus curve" (see plot below). The shape of the solidus curve for the material forming Earth's upper mantle depends on the fraction of water dissolved in that material.

Which statement below is not correct?

For a subduction zone, the volcanoes are located on the downgoing plate.

Vessicles

Gas bubbles in the magma, forces magma to expand

Pahoehoe

Hot mafic lava that moves in quick flowing streams. Looks ropey. The word pahoehoe comes from Hawai'i, and means "smooth unbroken lava flow". Such lava flows are always composed of basalt, a mafic volcanic rock with the lowest percentage of silica, SiO2. Pahoehoe lava flows easily and often solidifies into ropy, or rippled, textures

Magma Viscosity

How readily magma can escape through the opening in the solid surface of a volcano depends on its viscosity. Viscosity is a physical property of liquids, defined as an ability of liquids to resist flow. Thus a liquid with low viscosity (e.g., water) will have little resistance and flow readily, while a liquid with high viscosity (e.g. honey) will resist and flow in a sluggish manner.

the only known place where the mid ocean ridge is above sea level

Iceland

Dome flow, coulee flow, obsidian flow

Intermediate to felsic lava. Forms relatively compact, stubby flows with a broad variety of surface texture EFFUSIVE

Convergent

Material that melts beneath subduction zone volcanoes is rich in water and other compounds that were dragged down by the descending plate. The presence of water allows melting to occur at a lower temperature than it does at a divergent boundary. Magma ascending above a subducting plate run into the overriding plate. This causes it to pool at the boundary. As the magma stalls it reacts with the surrounding material and undergoes chemical changes (e.g. becoming more Si rich)The resulting magmas have a wide range of compositions, but tend to be rich in silica and relatively cool.

An order of events for the Mount St. Helens eruption:

Rising magma was stopped beneath the crater, probably by being cooled by melting glacial ice. The magma then intruded North making a cryptodome (hidden volcanic dome not exposed at the surface) and causing huge uplift on the North side of the volcano. Uplift over-steepened and weakened the cone, leading to a landslide.1. The collapse of the North sector of the volcano unleashed very gas-rich magma in a near horizontal direction, causing a deadly "directed blast."2. The directed blast was short-lived. Once the north slope had collapsed, most of the eruption came right out the top in the major and longer-lived Plinian phase. The lateral blast leveled forests for miles around, reaching speeds of over 300 km/hr. The eruption left the summit of Mount St. Helens more than 1000 feet lower. Over 1 cubic kilometer of tephra was launched into the air. This eruption is classified as a VEI (Volcanic Explosivity Index) 5, or paroxysmal, eruption.Mount St. Helens is still a very active volcano, with steam eruptions as recent as Fall 2004. It's just a matter of "when," not "if," it will erupt again. You can get of glimpse from the VolcanoCam (they are sadly offline now circa 2022) that changes every 5 minutes or so. Of course, sometimes there's too much cloud cover. And Mount St. Helens is just one of nine active volcanoes in the Cascades range. One, Mount Rainier, is unsettlingly close to Seattle/ Tacoma.

Santorini Volcano location significance

Santorini is located in the Aegean Sea, a region known for its earthquakes, volcanoes, and ancient Greek archaeological remains. The geological activity occurs because of the interaction of the Aegean and African Plates. The African Plate subducts under the Aegean Plate, forming the Ionian trench and the active volcanoes of the Cyclades, including Santorini.

Explosive eruptions are divided into three groups,

Strombolian, Vulcanian, Plinian

In the 1980 eruption of Mt. St. Helens part two:

Sunday May 18 1980, a 5.1 earthquake and a landslide unseal the pressurized magma body in two places.A "lateral blast" begins, as the bulging north slope of the volcano gives way and the magma finds its escape path out of the side (rather than the top) or the volcano The big May 18, 1980 eruption of Mount St. Helens began at 8:32 am. The landslide came first, releasing the pressure on the magma within the volcano. The initial blast came out the side of the volcano toward the north. This phase of the eruption lasted only minutes, but the big "Plinian" phase, which shot tephra to heights exceeding 24 km, lasted for hours. Scientists and policymakers were taken aback by the nature and magnitude of the eruption- of the 57 people killed in the eruption, only three died in the red "keep out" zone. 51 of the victims died in places designated as "safe. The Plinian eruptive column formed soon after the eruption began, topping out at ~24 km before settling down to 14-19 km, where it stayed for a couple of hours. The entire eruption lasted 16 hours. The ash cloud from the eruption grew large enough to rain ash over parts of Washington, Oregon, Idaho, Montana, and beyond.

Crust

The Earth's outermost layer, its crust, is rocky and rigid. There are two kinds of crust: continental crust, and ocean crust. Continental crust is thicker, and predominantly felsic in composition, meaning that it contains minerals that are richer in silica. The composition is important because it makes continental crust less dense than ocean crust. Ocean crust is thinner, and predominantly mafic in composition. Mafic rocks contain minerals with less silica, but more iron and magnesium. Mafic rocks (and therefore ocean crust) are denser than the felsic rocks of continental crust.

Which statement(s) below are true? More than one choice may be possible.

The composition of extrusive igneous rocks in oceanic crust is basaltic. The thickness of sediment on the ocean floor increases with increasing distance from a mid-ocean ridge. All oceanic crust at mid-ocean ridges has normal magnetic polarity. The depth of the seafloor decreases as one approaches the axis of a mid-ocean ridge.

Core

The core is primarily composed of iron, with lesser amounts of nickel. Lighter elements such as sulfur, oxygen, or silicon may also be present. The core is extremely hot (~3500° to more than 6000°C). But despite the fact that the boundary between the inner and outer core is approximately as hot as the surface of the sun, only the outer core is liquid. The inner core is solid because the pressure at that depth is so high that it keeps the core from melting.

Mantle

The crust floats on the mantle. The mantle is almost entirely solid rock, but it is in constant motion, flowing very slowly. It is ultramafic in composition, meaning it has even more iron and magnesium than mafic rocks, and even less silica. Although the mantle has a similar chemical composition throughout, it has layers with different mineral compositions and different physical properties. Rocks higher in the mantle are typically composed of peridotite, a rock dominated by the minerals olivine and pyroxene. The Tablelands rock in Figure 3.2 is a type of peridotite. Lower in the mantle, extreme pressures transform minerals and create rocks like eclogite (Figure 3.5), which contains garnets.

pyrcoclastic flow

The form of volcanic eruption that presents the most immediate danger to people in the vicinity of a volcano, can reach 100 km/hr.

Lithosphere

The lithosphere can't be classified neatly as either crust or mantle because it consists of both. It is formed from the crust as well as the uppermost layer of the mantle which is stuck to the underside of the crust. Tectonic plates are fragments of lithosphere.

divergent

The material melting at the mid-ocean ridge is dry. There is almost no water dissolved in rock that ascends and melts when the overlying plate breaks up. Rock fills in the gap left between the two separating plates coming very close to the surface. As the rock rises the pressure drops allowing it to melt.Magmas retain their high temperature, and their composition is typically relatively low in silica (SiO2)

Vulcanian

These are larger, more vigorous eruptions that do form an eruptive column. The name originates with another Italian volcano, called Vulcano. A vulcanian eruption initiates as a series of discrete, canon-like explosions lasting no more then a few hours, followed by a relatively quiet and sustained eruption of ash that will form a rising column. Eruptive columns may be 5 - 10 km high. Ejected material is most commonly andesite or dacite

Plinian eruption

This type of eruption is the most dramatic. It involves a massive outpouring of ash that forms a high column, and also a wind-driven umbrella. Unlike the previous two types, this one is named after a person, Pliny the Younger, a Roman statesman who wrote an account of the 79 AD eruption of volcano Vesuvius that destroyed the city of Pompeii. A long (over 12 hour) duration; Formation of a sustained eruptive column that can rise up to 45 km, and has an umbrella. Plinian eruptions produce mainly rhyolite and dacite, mostly in the form of ash.

Santorini Volcano today

Today, Santorini is still active. Fumaroles, hot springs, and sulfur deposits are all still being formed on Palea Kameni, the small volcanic island in the center of the caldera. Basaltic lavas were erupted as recently as 1950 on this island.It has erupted before, and will likely erupt again. Santorini is now a popular tourist destination and has a few modern towns of its own, located right on the Caldera wall. If this volcano erupts, hopefully the residents will have as much warning as the ancient Minoans, and be able to abandon their homes and retreat to safety.

Which statements below are true

Viscosity increases as the silica content increases. Viscosity increases as the complexity of silicate structures increases

island arcs

Volcanoes associated with subduction zones are arranged in elongated groups parallel to the plate boundary. On maps (i. e. of the Pacific Ocean below) island chains look curved, and thus are commonly referred to as

A depression in a volcano

Withdrawal of magma from the magma chamber causes overlying rocks to collapse, forming a depression

Fissure

a linear opening (a crack, a gap) in the Earth's surface through which lava (typically of basaltic composition) erupts.

Lahar

a mixture of tephra and water (and often surrounding soils turned into muds) that descends down the slope of a volcano.

Volcano

a place that allows hot material contained inside the earth to escape also refers to an elevated part of the ground (a hill, a mountain, a ridge) that is composed of the material previously ejected. The word originates from the name of the Roman god of fire, Vulcan. In turn, Vulcan is related to the Greek god Hephaestus, the smith of the Olympians.

Hypothesis

a tentative explanation for the observation(s). The hypothesis may not be correct, but it puts the scientist's understanding of the system being studied into a form that can be tested.

Parts of the trench may be filled in by material scraped off the subducting plate. This pile of scraped-off material is called an

accretionary prism

hot spot volcanoes

an area where material from deep in the mantle rises and then melts, forming magma effusive

Quantative observation

are measurements, which by definition consist of both a number and a unit. • Examples of quantitative observations include the following: the melting point of crystalline sulfur is 115.21 degrees Celsius, and 35.9 grams of table salt dissolve in 100 grams of water at 20 degrees Celsius.

Tephra can take many forms, including,

ash, lapilli, bombs (fly liquid, fall solid) blocks (large rocks that fly and fall solid) spatter (range from lapilli to bombs) Pele's hair (spun volcanic gas)

Which of the following statements associated with convergent plate boundaries is NOT correct?

at ocean-continent subduction zones, the continental plate subducts

Theory

attempts to explain why nature behaves as it does.

lava dome

bulbous mass of highly viscous, gas-poor lava extruded like toothpaste from a volcano high viscosity convergent plate boundary settings

Nuee ardente

contains dense lava fragments derived from the collapse of a growing lava dome or a dome flow. a lava dome that appears as a coherent rock structure may spontaneously disintegrate into very small fractions. The resulting mixture of very hot gas and very small rock pieces then goes down the slope of the mountain.

pumice flow

contains pumice derived from the collapse of an eruption column. In this case, the mixture of rock fragments and gas is initially lighter than air, forming an eruption column. If the thrust within the column drops lower than some critical value, it can no longer ascend, and instead flows down the slope of a volcano.

Which setting is associated with the highest viscosity magmas?

convergent plate boundaries in which over-riding plate is continental (subduction zones)

The thinnest of Earth's layers is the ___.

crust

subduction zone

defines a place where two tectonic plates converge, and one of them subducts (goes under) the other.

Summit crater

depression formed by explosive erosion of the summit vent; generally smaller than a caldera

qualitative observation

describe properties or occurrences in ways that do not rely on numbers. • Examples of qualitative observations include the following: the outside air temperature is cooler during the winter season, table salt is a crystalline solid, sulfur crystals are yellow, and dissolving a penny in dilute nitric acid forms a blue solution and a brown gas.

law of definite proportions

discovered by the French scientist Joseph Proust (1754-1826), states that a chemical substance always contains the same proportions of elements by mass. Thus sodium chloride (table salt) always contains the same proportion by mass of sodium to chlorine, in this case 39.34% sodium and 60.66% chlorine by mass, and sucrose (table sugar) is always 42.11% carbon, 6.48% hydrogen, and 51.41% oxygen by mass.

At which type of plate boundary is new lithosphere added?

divergent

Which setting is associated with the lowest viscosity magmas?

divergent plate boundaries

Pelean eruption

eruption is associated with explosive outbursts that generate pyroclastic flows, dense mixtures of hot volcanic fragments and gas described in the section Lava, gas, and other hazards Pelean eruptions are named for the destructive eruption of Mount Pelée on the Caribbean island of Martinique Links in 1902.

scientific theory

explanation of a part of the natural world that can be repeatedly tested and verified by the scientific method, using observation, measurement, and evaluation of results. Often, theories are tested under controlled conditions in an experiment. In circumstances not amenable to experimental testing, theories are evaluated through principles of abductive reasoning. Established scientific theories have withstood rigorous scrutiny and embody scientific knowledge.

Hawaiin eruption

fluid lava flows from a volcano's summit and radial fissures to form shield volcanoes, which are quite large and have gentle slopes.

What are the three parts of an eruption cloud?

gas thrust region, convective region, umbrella region

What is the term for molten rock once it reaches the surface?

lava

Which is not a product of volcanic eruptions?

magma

molten rock is called ___ when it is underground

magma

The black and white linear features off the coast of west coast U.S. on the picture below are called:

magnetic stripes

explosive eruption

material is flung from a volcano with such force that rock is pulverized into ash and drops of molten lava are flung far into the air. HIGH VISCOSITY

Which is not a volcanic gas?

methane

effusive eruption

molten rock expelled from the volcano flows relatively gently down the flanks. LOW VISCOSITY

Island arcs are associated with which type of convergent plate boundary?

ocean-ocean

the plate that does not subduct is called the

overriding plate because it rides over the subducting plate at a convergent margin.

In the 1980 eruption of Mt. St. Helens:

part of the Cascades Mountain Range of the Pacific Northwest, where the small oceanic Juan de Fuca plate is subducting under the North American Plate offshore. This tectonic movement causes rare great earthquakes and volcanic eruptions in the Cascade volcanoes. Mount St. Helens had not erupted since 1857, and was considered one of the "prettier" stratovolcanoes in the Cascades Range. A study of its past, using layers of ash and other deposits from prior eruptions, also revealed that it was probably the most active, and very capable of unleashing devastating eruptive forces as it had repeatedly over the past 40,000 years. The first sign of activity this time around was a magnitude 4 earthquake on March 20, 1980. The volcano continued to show signs of unrest. A week after the initial quake, the first of several phreatic (steam) explosions occurred. A crater 80 meters across opened up and produced a "steam blast" containing bits of broken up rock and gas. There was still no sign of the fresh magma and very little gas...

Scientific Laws

principles that are used to predict the behavior of the natural world. Laws usually resist change because they wouldn't have been adopted if they didn't fit the data, though we occasionally revise laws in the face of new unexpected information. Laws are often written in the form of an equation, as they refer to rules for how the natural world always behaves under certain conditions. Other examples of scientific laws:• Newton's Laws of Motion• Newton's Law of Universal Gravitation• Law of Conservation of Energy

Observations can be

qualitative or quantitative

Flood basalts

regionally extensive lava flows that come from fissures; thick accumulations build lava plateaus

Which two of the following igneous rocks have the highest silica content?

rhyolite and granite

Which type of volcano has the gentlest slope?

shield

Which type of volcano is the largest in area?

shield volcano

Destructive boundary

since material forming one of the converging plates is removed from the surface. Of course, material that used to form that plate does not disappear. It is moved into the interior of the planet.

law

states only what happens

Experiments

systematic observations or measurements, preferably made under controlled conditions—that is, under conditions in which a single variable changes.

All rocks produced by an explosive volcanic eruption are called

tephra

Which of the following is approximately a constant value at all subduction zones?

the depth below the volcanic arc at which melting initiates

Continental crust is thicker and less dense than oceanic crust

true

shield volcano

very broad volcano with surface slopes of <10°produced by eruption of basaltic lava low viscosity divergent plate boundaries

When an overriding plate has continental lithosphere, volcanoes do not form islands, but rather follow the shape of the convergent margin, forming a

volcanic arc or volcanic front.

Santorini Volcano (1645 BC) and the Legend of Atlantis. Many speculate that the destruction of this island may be the source of the legend of the Lost City of Atlantis

volcanic island in the Aegean Sea during Minoan (Bronze Age) times. It is now three separate islands with ruins. Geologists have pieced together the evidence and now conclude that the eruption that destroyed Santorini in 1645 BC was one of the largest in the past 10,000 years. Volcanologists have to turn to the geologic and archaeologic record to piece together the order of events for the eruption of Santorini.

What comes out of a volcano

• Hot rock (solid): • Ash (very small rock particles) and rocks of various sizes • Very hot rock (liquid): lava once molten rock reaches the surface • Volcanic gas • While inside the volcano, hot material that will be ejected is called MAGMA when molten rock is still underground

Chemical composition of volcano

•oxygen (O) •silicon (Si) •aluminum (Al) •iron (Fe) •magnesium (Mg) •titanium (Ti) •calcium (Ca) •sodium (Na) •potassium (K) phosphorous (P) While inside the volcano, magmas are subject to high pressure and contain dissolved gases making up between 1% and 5% of their volume. The most abundant gas in the magmas, between 70% and 90% of the total, is water vapor or steam, seen below in the form of rings that emerge from the volcano Etna in Italy. Other types of volcanic gases: - Carbon Dioxide (CO2) - Sulfur Dioxide (SO2) Also: N, H, CO, S, Ar, Cl, and F. Combined with H and/or H2O, these gases may produce HCl, HF, H 2SO 4, H 2S (all toxic!)