The ancient Romans, watching black smoke and fire bursting into the sky from the top of the mountain, believed that before them was the entrance to hell or to the domain of Vulcan, the god of blacksmithing and fire. In honor of him, fire-breathing mountains are still called volcanoes.
In this article we will figure out what the structure of the volcano is and look into its crater.
Active and extinct volcanoes
There are many volcanoes on Earth, both dormant and active. The eruption of each of them can last days, months, or even years (for example, the Kilauea volcano, located in the Hawaiian archipelago, awoke back in 1983 and its activity still does not stop). After which the craters of volcanoes are able to freeze for several decades, only to then remind of themselves again with a new eruption.
Although, of course, there are also geological formations whose work was completed in the distant past. Many of them still retain the shape of a cone, but there is no information about exactly how their eruption occurred. Such volcanoes are considered extinct. As an example, Kazbek can be cited, since ancient times covered with shining glaciers. And in Crimea and Transbaikalia there are heavily eroded and destroyed volcanoes that have completely lost their original shape.
What types of volcanoes are there?
Depending on the structure, activity and location, in geomorphology (the so-called science that studies the described geological formations) separate types of volcanoes are distinguished.
In general, they are divided into two main groups: linear and central. Although, of course, this division is very approximate, since most of them are classified as linear tectonic faults in the earth’s crust.
In addition, there are also shield-shaped and dome structures of volcanoes, as well as so-called cinder cones and stratovolcanoes. By activity they are defined as active, dormant or extinct, and by location - as terrestrial, underwater and subglacial.
How do linear volcanoes differ from central ones?
Linear (fissure) volcanoes, as a rule, do not rise high above the surface of the earth - they have the appearance of cracks. The structure of volcanoes of this type includes long supply channels associated with deep splits in the earth's crust, from which liquid magma of basaltic composition flows. It spreads in all directions and, when solidified, forms lava covers that erase forests, fill depressions, and destroy rivers and villages.
In addition, during the explosion of a linear volcano, explosive ditches may appear on the earth's surface, extending several tens of kilometers. In addition, the structure of the volcanoes along the fissures is decorated with gentle shafts, lava fields, spatter and flat wide cones, radically changing the landscape. By the way, the main component of Iceland's relief is lava plateaus, which arose in this way.
If the composition of the magma turns out to be more acidic (increased content of silicon dioxide), then extrusive (i.e. squeezed out) shafts with a loose composition grow around the mouth of the volcano.
The structure of central type volcanoes
A central type volcano is a cone-shaped geological formation, which is crowned on top by a crater - a depression shaped like a funnel or bowl. It, by the way, gradually moves upward as the volcanic structure itself grows, and its size can be completely different and measured in both meters and kilometers.
A vent leads deep into the crater, through which magma rises up into the crater. Magma is a molten fiery mass that has a predominantly silicate composition. It is born in the earth's crust, where its hearth is located, and having risen to the top, it pours out onto the surface of the earth in the form of lava.
An eruption is usually accompanied by the release of small sprays of magma, which form ash and gases, which, interestingly, are 98% water. They are joined by various impurities in the form of flakes of volcanic ash and dust.
What determines the shape of volcanoes
The shape of a volcano largely depends on the composition and viscosity of the magma. Easily mobile basaltic magma forms shield (or shield-like) volcanoes. They tend to be flat in shape and have a large circumference. An example of these types of volcanoes is the geological formation located in the Hawaiian Islands and called Mauna Loa.
Cinder cones are the most common type of volcano. They are formed during the eruption of large fragments of porous slag, which, piling up, build a cone around the crater, and their small parts form sloping slopes. Such a volcano grows higher with each eruption. An example is the Plosky Tolbachik volcano that exploded in December 2012 in Kamchatka.
Structural features of dome and stratovolcanoes
And the famous Etna, Fuji and Vesuvius are examples of stratovolcanoes. They are also called layered, since they are formed by periodically erupting lava (viscous and quickly solidifying) and pyroclastic matter, which is a mixture of hot gas, hot stones and ash.
As a result of such emissions, these types of volcanoes have sharp cones with concave slopes, in which these deposits alternate. And lava flows from them not only through the main crater, but also from cracks, solidifying on the slopes and forming ribbed corridors that serve as support for this geological formation.
Dome volcanoes are formed with the help of viscous granite magma, which does not flow down the slopes, but solidifies at the top, forming a dome, which, like a cork, plugs the vent and is expelled by gases accumulated under it over time. An example of such a phenomenon is the dome that forms over Mount St. Helens in the northwestern United States (it formed in 1980).
What is a caldera
The central volcanoes described above are usually cone-shaped. But sometimes, during an eruption, the walls of such a volcanic structure collapse, and calderas are formed - huge depressions that can reach a depth of thousands of meters and a diameter of up to 16 km.
From what was said earlier, you remember that the structure of volcanoes includes a huge vent through which molten magma rises during an eruption. When all the magma is on top, a huge void appears inside the volcano. It is precisely into this that the top and walls of a volcanic mountain can fall, forming on the earth’s surface vast cauldron-shaped depressions with a relatively flat bottom, bordered by the remains of the crash.
The largest caldera today is the Toba caldera, located in (Indonesia) and completely covered with water. The lake formed in this way has very impressive dimensions: 100/30 km and a depth of 500 m.
What are fumaroles?
Volcanic craters, their slopes, foothills, and the crust of cooled lava flows are often covered with cracks or holes from which hot gases dissolved in the magma escape. They are called fumaroles.
As a rule, thick white steam billows over large holes because magma, as already mentioned, contains a lot of water. But besides this, fumaroles also serve as a source of release of carbon dioxide, all kinds of sulfur oxides, hydrogen sulfide, hydrogen halides and other chemical compounds that can be very dangerous for humans.
By the way, volcanologists believe that the fumaroles included in the structure of the volcano make it safer, since gases find a way out and do not accumulate in the depths of the mountain to form a bubble that will eventually push the lava to the surface.
Such a volcano includes the famous one, which is located near Petropavlovsk-Kamchatsky. The smoke billowing above it can be seen tens of kilometers away in clear weather.
Volcanic bombs are also part of the structure of Earth's volcanoes
If a long-dormant volcano explodes, then during the eruption the so-called volcanoes fly out of its crater. They consist of fused rocks or fragments of lava frozen in the air and can weigh several tons. Their shape depends on the composition of the lava.
For example, if lava is liquid and does not have time to cool sufficiently in the air, a volcanic bomb that falls to the ground turns into a cake. And low-viscosity basaltic lavas rotate in the air, thereby taking on a twisted shape or becoming like a spindle or pear. Viscous - andesitic - pieces of lava after falling become like a bread crust (they are round or multifaceted and covered with a network of cracks).
The diameter of a volcanic bomb can reach seven meters, and these formations are found on the slopes of almost all volcanoes.
Types of volcanic eruptions
As N.V. Koronovsky pointed out in the book “Fundamentals of Geology,” which examines the structure of volcanoes and types of eruptions, all types of volcanic structures are formed as a result of various eruptions. Among them, 6 types stand out in particular.
When did the most famous volcanic eruptions occur?
The years of volcanic eruptions can, perhaps, be considered serious milestones in the history of mankind, because at this time the weather changed, a huge number of people died, and even entire civilizations were erased from the Earth (for example, as a result of the eruption of a giant volcano, the Minoan civilization died in 15 or 16 century BC).
In 79 AD e. Vesuvius erupted near Naples, burying the cities of Pompeii, Herculaneum, Stabia and Oplontium under a seven-meter layer of ash, leading to the death of thousands of inhabitants.
In 1669, several eruptions of Mount Etna, as well as in 1766, of Mayon Volcano (Philippines) led to terrible destruction and the death of many thousands of people under lava flows.
In 1783, the Laki volcano exploded in Iceland, causing a drop in temperature that led to crop failure and famine in Europe in 1784.
And on the island of Sumbawa, who woke up in 1815, the next year left the entire Earth without a summer, lowering the world temperature by 2.5 °C.
In 1991, a volcano in the Philippines also temporarily lowered it with its explosion, albeit by 0.5 °C.
The content of the article
VOLCANOES, separate elevations above channels and cracks in the earth's crust, through which eruption products are brought to the surface from deep magma chambers. Volcanoes usually have the shape of a cone with a summit crater (from several to hundreds of meters deep and up to 1.5 km in diameter). During eruptions, a volcanic structure sometimes collapses with the formation of a caldera - a large depression with a diameter of up to 16 km and a depth of up to 1000 m. As the magma rises, the external pressure weakens, associated gases and liquid products escape to the surface and a volcanic eruption occurs. If ancient rocks, and not magma, are brought to the surface, and the gases are dominated by water vapor formed when groundwater is heated, then such an eruption is called phreatic.
Active volcanoes include those that erupted in historical times or showed other signs of activity (emission of gases and steam, etc.). Some scientists consider active volcanoes that are reliably known to have erupted within the last 10 thousand years. For example, the Arenal volcano in Costa Rica should be considered active, since volcanic ash was discovered during archaeological excavations of a prehistoric site in this area, although for the first time in human memory its eruption occurred in 1968, and before that no signs of activity appeared.
Volcanoes are known not only on Earth. Images taken from spacecraft reveal huge ancient craters on Mars and many active volcanoes on Io, a moon of Jupiter.
VOLCANIC PRODUCTS
Lava
- This is magma that pours onto the earth's surface during eruptions and then solidifies. Lava may erupt from the main summit crater, a side crater on the side of the volcano, or from fissures associated with a volcanic chamber. It flows down the slope as a lava flow. In some cases, lava outpourings occur in rift zones of enormous extent. For example, in Iceland in 1783, within the chain of Laki craters, stretching along a tectonic fault for a distance of approx. 20 km, there was an outpouring of ~12.5 km 3 of lava, distributed over an area of ~570 km 2 .
Composition of lava.
The hard rocks formed when lava cools contain mainly silicon dioxide, oxides of aluminum, iron, magnesium, calcium, sodium, potassium, titanium and water. Typically, lavas contain more than one percent of each of these components, and many other elements are present in smaller quantities.
| AVERAGE CHEMICAL COMPOSITION OF SOME LAVAS (in weight percent) |
|||||||
| Oxides | Nepheline basalt | Basalt | Andesite | Dacite | Phonolite | Trachyte | Rhyolite |
| SiO2 | 37,6 | 48,5 | 54,1 | 63,6 | 56,9 | 60,2 | 73,1 |
| Al2O3 | 10,8 | 14,3 | 17,2 | 16,7 | 20,2 | 17,8 | 12,0 |
| Fe2O3 | 5,7 | 3,1 | 3,5 | 2,2 | 2,3 | 2,6 | 2,1 |
| FeO | 8,3 | 8,5 | 5,5 | 3,0 | 1,8 | 1,8 | 1,6 |
| MgO | 13,1 | 8,8 | 4,4 | 2,1 | 0,6 | 1,3 | 0,2 |
| CaO | 13,4 | 10,4 | 7,9 | 5,5 | 1,9 | 2,9 | 0,8 |
| Na2O | 3,8 | 2,3 | 3,7 | 4,0 | 8,7 | 5,4 | 4,3 |
| K2O | 1,0 | 0,8 | 1,1 | 1,4 | 5,4 | 6,5 | 4,8 |
| H2O | 1,5 | 0,7 | 0,9 | 0,6 | 1,0 | 0,5 | 0,6 |
| TiO2 | 2,8 | 2,1 | 1,3 | 0,6 | 0,6 | 0,6 | 0,3 |
| P2O5 | 1,0 | 0,3 | 0,3 | 0,2 | 0,2 | 0,2 | 0,1 |
| MnO | 0,1 | 0,2 | 0,1 | 0,1 | 0,2 | 0,2 | 0,1 |
There are many types of volcanic rocks, varying in chemical composition. Most often there are four types, the membership of which is determined by the content of silicon dioxide in the rock: basalt - 48-53%, andesite - 54-62%, dacite - 63-70%, rhyolite - 70-76% ( see table). Rocks that contain less silicon dioxide contain large amounts of magnesium and iron. When lava cools, a significant part of the melt forms volcanic glass, in the mass of which individual microscopic crystals are found. The exception is the so-called phenocrystals are large crystals formed in magma in the depths of the Earth and brought to the surface by a flow of liquid lava. Most often, phenocrysts are represented by feldspars, olivine, pyroxene and quartz. Rocks containing phenocrysts are usually called porphyrites. The color of volcanic glass depends on the amount of iron present in it: the more iron, the darker it is. Thus, even without chemical analysis, one can guess that a light-colored rock is rhyolite or dacite, a dark-colored rock is basalt, and a gray rock is andesite. The type of rock is determined by the minerals visible in the rock. For example, olivine, a mineral containing iron and magnesium, is characteristic of basalts, quartz - of rhyolites.
As the magma rises to the surface, the released gases form tiny bubbles with a diameter often up to 1.5 mm, less often up to 2.5 cm. They are stored in the solidified rock. This is how bubbly lavas are formed. Depending on the chemical composition of lavas, they vary in viscosity, or fluidity. With a high content of silicon dioxide (silica), lava is characterized by high viscosity. The viscosity of magma and lava largely determines the nature of the eruption and the type of volcanic products. Liquid basaltic lavas with low silica content form extensive lava flows more than 100 km long (for example, one lava flow in Iceland is known to stretch for 145 km). The thickness of lava flows is usually from 3 to 15 m. More liquid lavas form thinner flows. Flows 3-5 m thick are common in Hawaii. When the surface of a basalt flow begins to solidify, its interior may remain liquid, continuing to flow and leaving behind an elongated cavity, or lava tunnel. For example, on the island of Lanzarote (Canary Islands) a large lava tunnel can be traced for 5 km. The surface of a lava flow can be smooth and wavy (in Hawaii, this lava is called pahoehoe) or uneven (aa-lava). Hot lava, which is highly fluid, can move at speeds of more than 35 km/h, but more often its speed does not exceed several meters per hour. In a slow-moving flow, pieces of the solidified upper crust may fall off and be covered by lava; As a result, a zone enriched with debris is formed in the near-bottom part. When lava hardens, columnar units (multifaceted vertical columns with a diameter of several centimeters to 3 m) or fracturing perpendicular to the cooling surface are sometimes formed. When lava flows into a crater or caldera, a lava lake forms and cools over time. For example, such a lake was formed in one of the craters of the Kilauea volcano on the island of Hawaii during the eruptions of 1967-1968, when lava entered this crater at a speed of 1.1·10 6 m 3 / h (part of the lava subsequently returned to the crater of the volcano). In neighboring craters, within 6 months the thickness of the crust of solidified lava on lava lakes reached 6.4 m.
Domes, maars and tuff rings.
Very viscous lava (most often of dacite composition) during eruptions through the main crater or side cracks does not form flows, but a dome with a diameter of up to 1.5 km and a height of up to 600 m. For example, such a dome was formed in the crater of Mount St. Helens (USA) after an exceptionally strong eruption in May 1980. The pressure under the dome can build up, and weeks, months or years later it can be destroyed by the next eruption. In some parts of the dome, magma rises higher than in others, and as a result, volcanic obelisks protrude above its surface - blocks or spiers of solidified lava, often tens and hundreds of meters high. After the catastrophic eruption of the Montagne Pelee volcano on the island of Martinique in 1902, a lava spire formed in the crater, which grew by 9 m per day and as a result reached a height of 250 m, and collapsed a year later. On the Usu volcano on Hokkaido (Japan) in 1942, during the first three months after the eruption, the Showa-Shinzan lava dome grew by 200 m. The viscous lava that composed it made its way through the thickness of the previously formed sediments.
Maar is a volcanic crater formed during an explosive eruption (most often with high humidity of the rocks) without the outpouring of lava. A ring shaft of debris ejected by the explosion is not formed, unlike tuff rings - also explosion craters, which are usually surrounded by rings of debris products.
Clastic material,
released into the air during an eruption is called tephra, or pyroclastic debris. The deposits they form are also called. Pyroclastic rock fragments come in different sizes. The largest of them are volcanic blocks. If the products are so liquid at the time of release that they solidify and take shape while still in the air, then the so-called. volcanic bombs. Material smaller than 0.4 cm in size is classified as ashes, and fragments ranging in size from a pea to a walnut are classified as lapilli. Hardened deposits composed of lapilli are called lapilli tuff. There are several types of tephra, differing in color and porosity. Light-colored, porous, non-sinking tephra is called pumice. Dark vesicular tephra consisting of lapilli-sized units is called volcanic slag. Pieces of liquid lava that remain in the air for a short time and do not have time to completely harden form splashes, often forming small spatter cones near the outlets of lava flows. If this spatter sinteres, the resulting pyroclastic deposits are called agglutinates.
An airborne mixture of very fine pyroclastic material and heated gas, ejected from a crater or fissures during an eruption and moving above the ground surface at a speed of ~100 km/h, forms ash flows. They spread over many kilometers, sometimes crossing waters and hills. These formations are also known as scorching clouds; they are so hot that they glow at night. Ash flows may also contain large debris, incl. and pieces of rock torn out from the walls of a volcano. Most often, scorching clouds are formed when a column of ash and gases ejected vertically from a vent collapses. Under the influence of gravity, counteracting the pressure of the erupting gases, the edges of the column begin to settle and descend down the slope of the volcano in the form of a hot avalanche. In some cases, scorching clouds appear along the periphery of a volcanic dome or at the base of a volcanic obelisk. It is also possible for them to be released from the ring cracks around the caldera. Ash flow deposits form the ignimbrite volcanic rock. These flows transport both small and large fragments of pumice. If ignimbrites are deposited thick enough, the internal horizons can be so hot that the pumice fragments melt to form sintered ignimbrite, or sintered tuff. As the rock cools, columnar formations may form in its interior, which are less clear-cut and larger than similar structures in lava flows.
Small hills consisting of ash and blocks of various sizes are formed as a result of a directed volcanic explosion (as, for example, during the eruptions of Mount St. Helens in 1980 and Bezymyanny in Kamchatka in 1965).
Directed volcanic explosions are a fairly rare phenomenon. The deposits they create are easily confused with the clastic deposits with which they are often adjacent. For example, during the eruption of Mount St. Helens, an avalanche of rubble occurred immediately before the directed explosion.
Underwater volcanic eruptions.
If there is a body of water above the volcanic source, during the eruption the pyroclastic material is saturated with water and spreads around the source. Deposits of this type, first described in the Philippines, were formed as a result of the 1968 eruption of Taal Volcano, located at the bottom of the lake; they are often represented by thin wavy layers of pumice.
We sat down.
Volcanic eruptions may be associated with mudflows or mud-stone flows. They are sometimes called lahars (originally described in Indonesia). The formation of lahars is not part of the volcanic process, but one of its consequences. On the slopes of active volcanoes, loose material (ash, lapilli, volcanic debris) accumulates in abundance, ejected from volcanoes or falling from scorching clouds. This material is easily involved in the movement of water after rains, when ice and snow melt on the slopes of volcanoes or when the sides of crater lakes break through. Mud streams rush down the riverbeds at great speed. During the eruption of the Ruiz volcano in Colombia in November 1985, mudflows moving at speeds above 40 km/h carried more than 40 million m 3 of debris onto the foothill plain. At the same time, the city of Armero was destroyed and approx. 20 thousand people. Most often, such mudflows occur during an eruption or immediately after it. This is explained by the fact that during eruptions, accompanied by the release of thermal energy, snow and ice melt, crater lakes break through and drain, and slope stability is disrupted.
Gases,
released from the magma before and after the eruption, they look like white streams of water vapor. When tephra is mixed with them during an eruption, the emissions become gray or black. Low gas emissions in volcanic areas can continue for years. Such outlets of hot gases and vapors through openings at the bottom of the crater or the slopes of the volcano, as well as on the surface of lava or ash flows, are called fumaroles. Special types of fumaroles include solfataras, containing sulfur compounds, and mofets, in which carbon dioxide predominates. The temperature of fumarole gases is close to the temperature of magma and can reach 800° C, but can also drop to the boiling point of water (~100° C), the vapors of which serve as the main component of fumaroles. Fumarole gases originate both in shallow near-surface horizons and at great depths in hot rocks. In 1912, as a result of the eruption of the Novarupta volcano in Alaska, the famous Valley of Ten Thousand Smokes was formed, where on the surface of volcanic emissions an area of approx. 120 km 2, many high-temperature fumaroles arose. Currently, only a few fumaroles with fairly low temperatures are active in the Valley. Sometimes white streams of steam rise from the surface of a lava flow that has not yet cooled; most often it is rainwater heated by contact with a hot lava flow.
Chemical composition of volcanic gases.
The gas released from volcanoes consists of 50-85% water vapor. Over 10% is carbon dioxide, approx. 5% is sulfur dioxide, 2-5% is hydrogen chloride and 0.02-0.05% is hydrogen fluoride. Hydrogen sulfide and sulfur gas are usually found in small quantities. Sometimes hydrogen, methane and carbon monoxide are present, as well as small amounts of various metals. Ammonia was found in gas emissions from the surface of a lava flow covered with vegetation.
Tsunami
Huge sea waves, associated mainly with underwater earthquakes, but sometimes caused by volcanic eruptions on the ocean floor, which can cause the formation of several waves, occurring at intervals of several minutes to several hours. The eruption of the Krakatoa volcano on August 26, 1883 and the subsequent collapse of its caldera was accompanied by a tsunami over 30 m high, causing numerous casualties on the coasts of Java and Sumatra.
TYPES OF ERUPTIONS
Products arriving at the surface during volcanic eruptions vary significantly in composition and volume. The eruptions themselves vary in intensity and duration. The most commonly used classification of eruption types is based on these characteristics. But it happens that the nature of eruptions changes from one event to another, and sometimes during the same eruption.
Plinian type
named after the Roman scientist Pliny the Elder, who died in the eruption of Vesuvius in 79 AD. Eruptions of this type are characterized by the greatest intensity (a large amount of ash is thrown into the atmosphere to a height of 20-50 km) and occur continuously for several hours and even days. Pumice of dacite or rhyolite composition is formed from viscous lava. Products of volcanic emissions cover a large area, and their volume ranges from 0.1 to 50 km 3 or more. An eruption may result in the collapse of a volcanic structure and the formation of a caldera. Sometimes an eruption produces scorching clouds, but lava flows are not always formed. Fine ash is carried over long distances by strong winds at speeds of up to 100 km/h. Ash emitted in 1932 by the Cerro Azul volcano in Chile was discovered 3,000 km away. The Plinian type also includes the strong eruption of Mount St. Helens (Washington, USA) on May 18, 1980, when the height of the eruptive column reached 6000 m. During 10 hours of continuous eruption, approx. 0.1 km 3 tephra and more than 2.35 tons of sulfur dioxide. During the eruption of Krakatoa (Indonesia) in 1883, the volume of tephra was 18 km 3, and the ash cloud rose to a height of 80 km. The main phase of this eruption lasted approximately 18 hours.
An analysis of the 25 most violent historical eruptions shows that the quiet periods preceding Plinian eruptions averaged 865 years.
Peleian type.
Eruptions of this type are characterized by very viscous lava, which hardens before leaving the vent with the formation of one or several extrusive domes, the squeezing of the obelisk above it, and the emission of scorching clouds. The 1902 eruption of the Montagne-Pelée volcano on the island of Martinique belonged to this type.
Vulcan type.
Eruptions of this type (the name comes from the island of Vulcano in the Mediterranean Sea) are short-lived - from several minutes to several hours, but recur every few days or weeks for several months. The height of the eruptive column reaches 20 km. The magma is fluid, basaltic or andesitic in composition. The formation of lava flows is typical, and ash emissions and extrusive domes do not always occur. Volcanic structures are built from lava and pyroclastic material (stratovolcanoes). The volume of such volcanic structures is quite large - from 10 to 100 km 3. The age of stratovolcanoes ranges from 10,000 to 100,000 years. The frequency of eruptions of individual volcanoes has not been established. This type includes the Fuego volcano in Guatemala, which erupts every few years; basaltic ash emissions sometimes reach the stratosphere, and their volume during one of the eruptions was 0.1 km 3.
Strombolian type.
This type is named after the volcanic island of Stromboli in the Mediterranean Sea. The Strombolian eruption is characterized by continuous eruptive activity over several months or even years and a not very high height of the eruptive column (rarely above 10 km). There are known cases when lava was splashed within a radius of ~300 m, but almost all of it returned to the crater. Lava flows are typical. Ash covers have a smaller area than during Vulcan-type eruptions. The composition of eruption products is usually basaltic, less often – andesitic. The Stromboli volcano has been active for more than 400 years, the Yasur volcano on Tanna Island (Vanuatu) in the Pacific Ocean has been active for more than 200 years. The structure of the vents and the nature of the eruptions of these volcanoes are very similar. Some Strombolian-type eruptions produce cinder cones composed of basaltic or, less commonly, andesitic scoria. The diameter of the cinder cone at the base ranges from 0.25 to 2.5 km, the average height is 170 m. Cinder cones are usually formed during a single eruption, and volcanoes are called monogenic. For example, during the eruption of the Paricutin volcano (Mexico), during the period from the beginning of its activity on February 20, 1943 to the end of March 9, 1952, a cone of volcanic slag 300 m high was formed, the surrounding area was covered with ash, and the lava spread over an area of 18 km 2 and destroyed several populated areas. points.
Hawaiian type
eruptions are characterized by outpourings of liquid basaltic lava. Fountains of lava ejected from cracks or faults can reach a height of 1000 and sometimes 2000 m. Few pyroclastic products are ejected; most of them are splashes falling near the source of the eruption. Lavas flow from fissures, holes (vents) located along a fissure, or craters, sometimes containing lava lakes. When there is only one vent, the lava spreads radially, forming a shield volcano with very gentle slopes – up to 10° (stratovolcanoes have cinder cones and slope steepness of about 30°). Shield volcanoes are composed of layers of relatively thin lava flows and do not contain ash (for example, the famous volcanoes on the island of Hawaii - Mauna Loa and Kilauea). The first descriptions of volcanoes of this type relate to volcanoes in Iceland (for example, the Krabla volcano in northern Iceland, located in the rift zone). The eruption of the Fournaise volcano on Reunion Island in the Indian Ocean is very close to the Hawaiian type.
Other types of eruptions.
Other types of eruptions are known, but they are much less common. An example is the underwater eruption of the Surtsey volcano in Iceland in 1965, which resulted in the formation of an island.
SPREAD OF VOLCANOES
The distribution of volcanoes across the surface of the globe is best explained by the theory of plate tectonics, according to which the Earth's surface consists of a mosaic of moving lithospheric plates. When they move in the opposite direction, a collision occurs, and one of the plates sinks (moves) under the other in the so-called. subduction zone, where earthquake epicenters are located. If the plates move apart, a rift zone forms between them. Manifestations of volcanism are associated with these two situations.
Subduction zone volcanoes are located along the boundaries of subducting plates. The oceanic plates that form the floor of the Pacific Ocean are known to subduct beneath continents and island arcs. Subduction areas are marked in the topography of the ocean floor by deep-sea trenches parallel to the coast. It is believed that in zones of plate subduction at depths of 100-150 km, magma is formed, and when it rises to the surface, volcanic eruptions occur. Since the plunging angle of the plate is often close to 45°, volcanoes are located between the land and the deep-sea trench at a distance of approximately 100-150 km from the axis of the latter and in plan form a volcanic arc that follows the contours of the trench and coastline. There is sometimes talk of a “ring of fire” of volcanoes around the Pacific Ocean. However, this ring is intermittent (as, for example, in the region of central and southern California), because subduction does not occur everywhere.
Rift zone volcanoes exist in the axial part of the Mid-Atlantic Ridge and along the East African Rift System.
There are volcanoes associated with “hot spots” located inside plates in places where mantle plumes (hot magma rich in gases) rise to the surface, for example, the volcanoes of the Hawaiian Islands. It is believed that the chain of these islands, extending in a westerly direction, was formed during the westward drift of the Pacific Plate while moving over a “hot spot.” Now this “hot spot” is located under the active volcanoes of the island of Hawaii. Towards the west of this island, the age of the volcanoes gradually increases.
Plate tectonics determines not only the location of volcanoes, but also the type of volcanic activity. The Hawaiian type of eruptions predominates in areas of “hot spots” (Fournaise volcano on Reunion Island) and in rift zones. Plinian, Peleian and Vulcanian types are characteristic of subduction zones. There are also known exceptions, for example, the Strombolian type is observed in various geodynamic conditions.
Volcanic activity: recurrence and spatial patterns.
Approximately 60 volcanoes erupt annually, and about a third of them erupted in the previous year. There is information about 627 volcanoes that have erupted over the past 10 thousand years, and about 530 in historical time, and 80% of them are confined to subduction zones. The greatest volcanic activity is observed in the Kamchatka and Central American regions, with quieter zones in the Cascade Range, the South Sandwich Islands and southern Chile.
Volcanoes and climate.
It is believed that after volcanic eruptions, the average temperature of the Earth’s atmosphere drops by several degrees due to the release of tiny particles (less than 0.001 mm) in the form of aerosols and volcanic dust (while sulfate aerosols and fine dust enter the stratosphere during eruptions) and remains so for 1 –2 years. In all likelihood, such a decrease in temperature was observed after the eruption of Mount Agung on Bali (Indonesia) in 1962.
VOLCANIC HAZARD
Volcanic eruptions threaten human lives and cause material damage. After 1600, as a result of eruptions and associated mudflows and tsunamis, 168 thousand people died, and 95 thousand people became victims of disease and hunger that arose after the eruptions. As a result of the eruption of the Montagne Pelee volcano in 1902, 30 thousand people died. As a result of mudflows from the Ruiz volcano in Colombia in 1985, 20 thousand people died. The eruption of the Krakatoa volcano in 1883 led to the formation of a tsunami that killed 36 thousand people.
The nature of the danger depends on the action of various factors. Lava flows destroy buildings, block roads and agricultural lands, which are excluded from economic use for many centuries until new soil is formed as a result of weathering processes. The rate of weathering depends on the amount of precipitation, temperature, runoff conditions and the nature of the surface. For example, on the wetter slopes of Mount Etna in Italy, agriculture on lava flows resumed only 300 years after the eruption.
As a result of volcanic eruptions, thick layers of ash accumulate on the roofs of buildings, which threatens their collapse. The entry of tiny ash particles into the lungs leads to the death of livestock. Ash suspended in the air poses a danger to road and air transport. Airports are often closed during ashfalls.
Ash flows, which are a hot mixture of suspended dispersed material and volcanic gases, move at high speed. As a result, people, animals, plants die from burns and suffocation and houses are destroyed. The ancient Roman cities of Pompeii and Herculaneum were affected by such flows and were covered with ash during the eruption of Mount Vesuvius.
Volcanic gases released by volcanoes of any type rise into the atmosphere and usually cause no harm, but some of them may return to the earth's surface in the form of acid rain. Sometimes the terrain allows volcanic gases (sulfur dioxide, hydrogen chloride or carbon dioxide) to spread near the surface of the earth, destroying vegetation or polluting the air in concentrations exceeding permissible limits. Volcanic gases can also cause indirect harm. Thus, the fluorine compounds contained in them are captured by ash particles, and when the latter fall onto the earth's surface, they contaminate pastures and water bodies, causing severe diseases in livestock. In the same way, open sources of water supply to the population can be contaminated.
Mud-stone flows and tsunamis also cause enormous destruction.
Eruption forecast.
To forecast eruptions, volcanic hazard maps are compiled showing the nature and distribution areas of products of past eruptions, and eruption precursors are monitored. Such precursors include the frequency of weak volcanic earthquakes; If usually their number does not exceed 10 in one day, then immediately before the eruption it increases to several hundred. Instrumental observations of the most minor surface deformations are carried out. The accuracy of measuring vertical displacements, recorded, for example, by laser devices, is ~0.25 mm, horizontal - 6 mm, which makes it possible to detect a surface tilt of only 1 mm per half kilometer. Data on changes in height, distance and slope are used to identify the center of heave preceding an eruption or surface subsidence after an eruption. Before an eruption, the temperatures of the fumaroles increase, and sometimes the composition of volcanic gases and the intensity of their release change.
The precursor phenomena that preceded most of the fairly fully documented eruptions are similar to each other. However, it is very difficult to predict with certainty exactly when an eruption will occur.
Volcanological observatories.
To prevent a possible eruption, systematic instrumental observations are carried out in special observatories. The oldest volcanological observatory was founded in 1841-1845 on Vesuvius in Italy, then in 1912 the observatory began operating on the Kilauea volcano on the island. Hawaii and, around the same time, several observatories in Japan. Monitoring of volcanoes is also carried out in the USA (including at Mount St. Helens), Indonesia at the observatory at the Merapi volcano on the island of Java, in Iceland, Russia by the Institute of Volcanology of the Russian Academy of Sciences (Kamchatka), Rabaul (Papua New Guinea), on the islands of Guadeloupe and Martinique in the West Indies, and monitoring programs have been launched in Costa Rica and Colombia.
Notification methods.
Civil authorities, to whom volcanologists provide the necessary information, must warn about impending volcanic danger and take measures to reduce the consequences.
The public warning system can be sound (sirens) or light (for example, on the highway at the foot of the Sakurajima volcano in Japan, flashing warning lights warn motorists about ash fall). Warning devices are also installed that are triggered by elevated concentrations of dangerous volcanic gases, such as hydrogen sulfide. Roadblocks are placed on roads in hazardous areas where an eruption is taking place.
Reducing the dangers associated with volcanic eruptions.
To mitigate volcanic danger, both complex engineering structures and very simple methods are used. For example, during the eruption of the Miyakejima volcano in Japan in 1985, cooling of the lava flow front with sea water was successfully used. By creating artificial gaps in the hardened lava that limited the flows on the slopes of volcanoes, it was possible to change their direction. To protect against mud-stone flows - lahars - fencing embankments and dams are used to direct the flows into a certain channel. To avoid the occurrence of lahar, the crater lake is sometimes drained using a tunnel (Kelud volcano on Java in Indonesia). In some areas, special systems are being installed to monitor thunderclouds, which could bring downpours and activate lahars. In places where eruption products fall out, various shelters and safe shelters are built.
Since ancient times, people have seen black clouds, fire, and fiery stones sometimes bursting out of it.
The ancient Romans believed that this island was the gateway to hell, and that Vulcan, the god of fire and blacksmithing, lived here. By the name of this god, these began to be called volcanoes.
A volcanic eruption can last for several days or even months. After a strong eruption, the volcano returns to a state of rest for several years and even decades. Such volcanoes are called valid.
There are volcanoes that erupted in times long past. Some of them have retained the shape of a beautiful cone. People have no information about their activities. They are called extinct, as, for example, in the Caucasus, Elbrus and Kazbek, the peaks of which are covered with sparkling, dazzling white. In ancient volcanic areas, deeply destroyed and eroded volcanoes are found. In our country such regions are Crimea, Transbaikalia and other places.
Volcanoes are usually cone-shaped with slopes that are gentler at their bases and steeper at their summits.
If you climb to the top of an active volcano during its calm state, you can see a crater - a deep depression with steep walls, similar to a giant bowl. The bottom of the crater is covered with fragments of large and small stones, and jets of gas and steam rise from cracks in the bottom and walls of the crater. Sometimes they calmly emerge from under stones and from cracks, sometimes they burst out violently, with hissing and whistling. The crater is filled with suffocating; rising up, they form a cloud at the top of the volcano. The volcano can quietly smoke for months and years until an eruption occurs. This event is often preceded by ; An underground rumble is heard, the release of vapors and gases intensifies, clouds thicken over the top of the volcano.
Then, under the pressure of gases escaping from the bowels of the earth, the bottom of the crater explodes. Thick black clouds of gases and water vapor mixed with ash are thrown out thousands of meters, plunging the surrounding area into darkness. With an explosion and roar, pieces of red-hot stones fly from the crater, forming giant sheaves of sparks. Ash falls from black, thick clouds onto the ground, and sometimes torrential rains fall, forming streams of mud that roll down the slopes and flood the surrounding area. The flash of lightning continuously cuts through the darkness. The volcano rumbles and trembles, molten fiery liquid lava rises through its mouth. It seethes, overflows over the edge of the crater and rushes in a fiery stream along the slopes of the volcano, burning and destroying everything in its path.
During some volcanic eruptions, lava does not flow. Volcanic eruptions also occur at the bottom of seas and oceans. Sailors learn about this when they suddenly see a column of steam above the water or “stone foam” floating on the surface - pumice. Sometimes ships encounter unexpectedly appeared shoals formed by new volcanoes at the bottom. Over time, these shoals - igneous masses - are eroded by sea waves and disappear without a trace.
Some underwater volcanoes form cones that protrude above the surface of the water in the form of islands.
For a very long time people could not explain the causes of volcanic eruptions. This natural phenomenon terrified people. However, the ancient Greeks and Romans, and later the Arabs, concluded that in the bowels of the Earth there is a large sea of underground fire. The disturbances of this sea cause volcanic eruptions on the surface of the Earth.
At the end of the last century, a special science separated from geology - volcanology. Now volcanological stations are being organized near some active volcanoes - observatory, where scientists conduct constant observations of volcanoes. We have such a volcanological station set up in Kamchatka in the village of Klyuchi. When one of the volcanoes begins to act, volcanologists immediately go to the volcano and observe the eruption.
By studying volcanic lava, you can understand how molten material turned into solid rock.
Volcanologists also study extinct and destroyed ancient volcanoes. The accumulation of such observations and knowledge is very important for geology.
Ancient destroyed volcanoes, active tens of millions of years ago and almost level with the surface of the Earth, help scientists recognize how molten masses located in the bowels of the Earth penetrate into the solid earth's crust and what results from their contact with rocks. Usually, at the points of contact, due to chemical processes, mineral ores are formed - deposits of iron, zinc and other metals.
Jets of steam in the craters of volcanoes, which are called fumaroles, carry with them some substances in a dissolved state. Sulfur, ammonia, and boric acid, which are used in industry, are deposited along the cracks of the crater and around such fumaroles.
Volcanic ash and lava contain many compounds of the element potassium and become very fertile soils. Gardens are planted on such soils or the land is used for field cultivation. Therefore, although it is unsafe to live in the vicinity of volcanoes, villages or cities almost always grow there.
Why do volcanic eruptions occur and where does such enormous energy come from within the globe?
The discovery of the phenomenon of radioactivity in some chemical elements, especially uranium and thorium, suggests that heat accumulates inside the Earth from the decay of radioactive elements. The study of atomic energy further supports this view.
The accumulation of heat in the Earth at great depths heats up the substance. Earth. The temperature rises so high that this substance should melt, but under the pressure of the upper layers of the earth's crust it is kept in a solid state. In those places where the pressure of the upper layers weakens due to the movement of the earth's crust and the cracks formed, the hot masses pass from a solid state to a liquid state.
A mass of molten rock, saturated with gases, formed deep in the bowels of the Earth is called. Under strong pressure from the released gases, melting the surrounding rocks, it makes its way and forms a vent, or channel, of the volcano.
The released gases explode by clearing a path along the vent, breaking apart solid rocks and throwing pieces of them to great heights. This phenomenon always precedes the outpouring of lava and is always accompanied by earthquakes in the vicinity of the volcano.
Just as something dissolved in a fizzy drink tends to come out when you uncork a bottle, forming foam, so in the crater of a volcano the foaming magma is rapidly ejected by the gases released from it, spraying and tearing the red-hot mass into pieces.
Having lost a significant amount of gas, magma pours out of the crater and flows like lava along the slopes of the volcano.
If magma in the earth's crust does not find its way to the surface, then it hardens in the form of veins in cracks in the earth's crust. It happens that molten magma solidifies underground over a large area and forms a huge homogeneous body that expands deeper. Its dimensions can reach hundreds of kilometers in diameter. Such frozen bodies embedded in the earth's crust are called batholiths.
Sometimes magma penetrates along a crack, lifts the layers of the earth like a dome and freezes in a shape similar to a loaf of bread. This kind of education is called laccolith.
Lava varies in content and can be liquid or thick. If lava is liquid, then it spreads quickly enough, forming on its way Lavaiads. The gases that escape from the crater throw out hot fountains of lava, the splashes of which freeze into stone drops - lava tears. Thick lava flows quite slowly, breaks into blocks that pile on top of each other. If clots of such lava rotate during takeoff, they take the form of a spindle or ball. Such frozen pieces of lava of different sizes are called volcanic bombs. If lava, overflowing with gases, hardens, then stone foam forms - pumice. Pumice is very light and floats on water, and during underwater eruptions it floats to the sea surface. The pea- or hazelnut-sized fragments of lava ejected during an eruption are called lapilli. There is even finer igneous material - volcanic ash. It falls on the volcanic slopes and travels over very long distances, gradually turning into tuff. Tuff is a very light, porous material, it saws easily. It comes in various colors.
Several dozen active volcanoes are currently known on the globe. Most of them are located along the shores of the Pacific Ocean, including our volcanoes in Kamchatka.
When most people hear the word “volcano,” they think of Vesuvius, Fuji, or the volcanoes of Kamchatka—elegant, cone-shaped mountains.
In fact, there are other types of volcanoes that are completely different from the ones we are used to. We've already talked about it.
Now let's look at another type of volcanism - fissure.
Eruption of the Plosky Tolbachik volcano (photo from your-kamchatka.com)
The role of volcanoes in the development of life on Earth is significant. According to some hypotheses, the first living organisms arose around underwater volcanoes; volcanoes were able to melt the icy Earth and cause the spring of life 700 million years ago; volcanoes in Siberia “helped” begin the era of dinosaurs, and volcanoes in India helped end it. A volcano in Indonesia almost destroyed the human race, and a volcano in Yellowstone covered half of the modern United States with ash several times.
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How does a typical volcano form? Many of them are located in areas where tectonic plates collide. Examples are volcanoes in the “ring of fire” around the Pacific Ocean: in Kamchatka, Japan, Indonesia, New Zealand, and on the Pacific coast of North and South America.
When an oceanic tectonic plate collides with a continental plate, the oceanic plate moves downward as it is denser and heavier due to its chemical composition. In this case, the impurities contained in the ocean plate (in particular, water) are heated and begin to seep upward through the mantle under the continental plate. Oddly enough, this causes the solid matter in the upper layer of the mantle to melt and turn into magma. This occurs for the same reason that snow melts when salt is sprinkled on it: contamination of the solid with impurities lowers the melting point. Due to the large amount of gases dissolved in the magma and under high pressure, the magma rises and causes a volcanic eruption.
Volcanoes also form where plates diverge, for example, along the Great Rift Valley at the border of the African and Arabian tectonic plates.
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Erta Ale volcano in Ethiopia. (photo - Mikhail Korostelev)
As a result of this divergence, after a few million years, the modern territory of Somalia, Tanzania and Mozambique in eastern Africa will separate from the continent and a new ocean will arise in the middle of Africa.
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Kilimanjaro is a volcano in northeastern Tanzania, the highest peak in Africa.
Moreover, most of the places where plates diverge are not on the continent, but underwater, along mid-ocean ridges. It was in these places that one of the main biological discoveries of the twentieth century was made - the ecological systems of hydrothermal vents.
In the 1990s, German scientist Günter Wachtershauser proposed a hypothesis for the origin of life around hydrothermal vents, which was called the “iron and sulfur world.” According to this hypothesis, life on Earth was generated not by the Sun, but by the energy of volcanoes, and at the initial stage, even before the appearance of proteins and DNA, it used hydrogen sulfide, hydrogen cyanide, iron, nickel and carbon monoxide.
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Underwater volcano eruption
A couple of billion years later, volcanoes helped life on Earth once again. In the 1950s and 1960s, geologists Sir Douglas Mawson and Brian Harland found fossil evidence of a glacier that covered tropical latitudes between 850 and 630 million years ago. The researchers suggested that the Earth went through a period when it was completely covered in ice. This hypothesis is called Snowball Earth. Mawson and Harland were objected to by the Russian climatologist Mikhail Budyko, who made calculations and showed that there would be no one to defrost the frozen Earth, since the ice would reflect the sun's rays into outer space and the Earth would remain a “snowball” forever. Only in 1992, the American Joseph Lynn Kirschvink substantiated the assumption that the Earth was thawed by the greenhouse effect from gases released into the atmosphere by volcanoes. After this, real spring came on Earth: large multicellular animals of the Ediacaran and Cambrian periods arose.
Magmatism(Magmatism) - geological processes associated with the formation of magma, its movement in the earth's crust and its outpouring to the surface, including the activity of volcanoes (volcanism).
Volcanism(Volcanism; Vulcanism; Vulcanicity) - a set of processes and phenomena caused by the movement of magma in the upper mantle, the earth’s crust and its penetration from the depths of the Earth to the earth’s surface. A typical manifestation of volcanism is the formation of igneous geological bodies during the introduction of magma and its solidification in sedimentary rocks, as well as the outpouring of magma (lava) onto the surface with the formation of specific landforms (volcanoes).
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Karymsky Volcano is one of the most active volcanoes in Kamchatka
“Volcanism is a phenomenon due to which, during geological history, the outer shells of the Earth were formed - the crust, hydrosphere and atmosphere, i.e., the habitat of living organisms - the biosphere” - this opinion is expressed by the majority of volcanologists, however, this is far from the only idea about the development of geographical shells.
According to modern concepts, volcanism is an external, so-called effusive form of magmatism - a process associated with the movement of magma from the interior of the Earth to its surface. At a depth of 50 to 350 km, pockets of molten matter - magma - form in the thickness of our planet. Along areas of crushing and fractures of the earth's crust, magma rises and pours out onto the surface in the form of lava (it differs from magma in that it contains almost no volatile components, which, when pressure drops, separate from the magma and go into the atmosphere. With these outpourings of magma on the surface, volcanoes.
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Fuji is the highest mountain peak (3776 m) in Japan. It is a volcano with a crater with a diameter of about 500 meters and a depth of up to 200 meters. The most destructive eruptions occurred in 800, 864 and 1707.
Currently, over 4 thousand have been identified around the globe. volcanoes.
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From here
TO current include volcanoes that have erupted and exhibited solfataric activity (the release of hot gases and water) over the last 3500 years of the historical period. In 1980 there were 947 of them.
TO potentially active These include Holocene volcanoes that erupted 3500-13500 years ago. There are approximately 1343 of them.
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Mount Ararat is a volcano that is considered extinct. In fact, it, like other volcanoes of the Caucasus that exhibited volcanic activity in the late Quaternary: Ararat, Aragats, Kazbek, Kabardzhin, Elbrus, etc., is potentially active. In the central sector of the North Caucasus, eruptions of the Elbrus volcano were repeatedly observed in the late Pleistocene and Holocene.
TO conditionally extinct volcanoes are considered to be inactive in the Holocene, but have retained their external forms (younger than 100 thousand years old).
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Shasta is an extinct volcano in the southern Cascade Mountains in the United States.
Extinct volcanoes significantly reworked by erosion, dilapidated, showing no activity during the last 100 thousand. years.
Fissure volcanoes manifest themselves in the outpouring of lava onto the earth's surface along large cracks or splits. At certain periods of time, mainly at the prehistoric stage, this type of volcanism reached quite a wide scale, as a result of which a huge amount of volcanic material - lava - was carried to the surface of the Earth. Powerful fields are known in India on the Deccan Plateau, where they covered an area of 5,105 km2 with an average thickness of 1 to 3 km. Also known in the northwestern United States and Siberia. At that time, basaltic rocks from fissure eruptions were depleted in silica (about 50%) and enriched in ferrous iron (8-12%). The lavas are mobile, liquid, and therefore could be traced tens of kilometers from the place of their outpouring. The thickness of individual streams was 5-15m. In the USA, as well as in India, many kilometers of strata accumulated, this happened gradually, layer by layer, over many years. Such flat lava formations with a characteristic stepped relief form are called plateau basalts or traps.
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Trap basalts in the upper Colorado River.
Siberian Traps - one of the largest trap provinces is located on the East Siberian Platform. Siberian traps poured out at the boundary of the Paleozoic and Mesozoic, Permian and Triassic periods. At the same time, the largest (Permian-Triassic) extinction of species in the history of the Earth occurred. They are developed over an area of about 4 million km², the volume of erupted melts amounted to about 2 million km³ of effusive and intrusive rocks.
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The Putorana plateau is composed of trap basalts. Waterfall on the Putorana plateau. (Author - Sergey Gorshkov)
250 million years ago, at the border of the Paleozoic and Mesozoic eras, massive lava eruptions occurred in the territory of a volcanic province called the Siberian Traps, centered in the area of modern Norilsk. Over the course of several hundred thousand years, 2 million cubic kilometers of lava spread over an area of about 4 million square kilometers. At the same time, the largest extinction event in Earth's history occurred, destroying 96% of marine and about 70% of terrestrial animal species. One theory is that the mass extinction was caused by a "volcanic winter." First, volcanic dust polluted the atmosphere, causing global cooling and a lack of light for plants. At the same time, sulfurous volcanic gases caused acid rain from sulfuric acid, which destroyed plants on land and shellfish in the sea. Then global warming occurred due to the emitted carbon dioxide and the greenhouse effect.
After every major extinction event, new species flourish. After the extinction of Paleozoic species, dinosaurs became the favorites. In turn, dinosaurs went extinct 65 million years ago. For a long time, the extinction of dinosaurs was explained by the collision of the Earth with an asteroid that fell in the Yucatan Peninsula in southern Mexico. But according to new research by Gerta Keller from Princeton and Thierry Adatte from Switzerland, the main cause of the death of dinosaurs was the Deccan Traps - volcanoes that flooded half of the territory of modern India with lava over 30 thousand years and also caused a “volcanic winter”.
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Deccan Plateau (Deccan Plateau or Southern Plateau), which covers the territory of almost all of South India
The Deccan Plateau is a large trap province located in Hindustan and makes up the Deccan Plateau. The total thickness of basalts in the center of the province is more than 2,000 meters; they are developed over an area of 1.5 million km². The volume of basalts is estimated at 512,000 km3. The Deccan Traps began to flow at the Cretaceous-Paleogene boundary, and are also associated with the Cretaceous-Paleogene extinction event, which wiped out dinosaurs and many other species.
Scientists knew that the series of eruptions that created the Deccan Trap Province occurred near the Cretaceous-Paleogene boundary, which is when the mass extinction occurred. Now, after studying rocks in India and marine sediments from this era, they claim that they have for the first time been able to clearly link volcanism on the Deccan Plateau and the death of the dinosaurs.
The most powerful phase of the period of volcanism in the Deccan ended when the mass extinction had already begun. At the same time, climate-changing carbon dioxide and sulfur dioxide were released from these volcanoes (the lava from which spread over many hundreds of kilometers, forming layers of basalt two kilometers thick) was emitted 10 times more than when the asteroid hit Yucatan.
Scientists also managed to explain the delay in the sharp rise in the development of marine creatures (which is clearly visible in marine fossils after the Cretaceous-Paleogene boundary). The fact is that the last surge of volcanism in the Deccan occurred 280 thousand years after the extinction. This delayed the restoration of the number of microorganisms in the seas.
Currently, fissure volcanism is widespread in Iceland (Laki volcano), Kamchatka (Tolbachinsky volcano), and on one of the islands of New Zealand. The largest lava eruption on the island of Iceland along the giant Laki fissure, 30 km long, occurred in 1783, when lava reached the surface for two months. During this time, 12 km 3 of basaltic lava poured out, which flooded almost 915 km 2 of the adjacent lowland with a layer 170 m thick. A similar eruption was observed in 1886. on one of the islands of New Zealand. For two hours, 12 small craters with a diameter of several hundred meters were active over a 30 km segment. The eruption was accompanied by explosions and the release of ash, which covered an area of 10 thousand km2, near the fissure the thickness of the cover reached 75 m. The explosive effect was enhanced by the powerful release of vapors from the lake basins adjacent to the crack. Such explosions, caused by the presence of water, are called phreatic. After the eruption, a graben-shaped depression 5 km long and 1.5-3 km wide formed in place of the lakes.
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The total volume of erupted pyroclastics was 1 km3, lava - 1.2 km3, total - 2.2 km3. It was the largest basaltic eruption in the Kuril-Kamchatka volcanic belt in historical times, one of fifteen eruptions of the 20th century, the volume of products of which exceeded 1 million cubic meters. km., one of the six large fissure eruptions observed in the world in historical times. Thanks to intensified systematic research, the Great Fissure Tolbachik Eruption is currently one of the three most studied large volcanic eruptions.
The lavas that caused such large-scale events in the past are represented by the most common type on Earth - basalt. Their name indicates that they subsequently turned into a black and heavy rock - basalt.
Vast basalt fields (traps) hundreds of millions of years old hide still very unusual forms. Where ancient traps come to the surface, as, for example, in the cliffs of Siberian rivers, you can find rows of vertical 5- and 6-sided prisms. This is a columnar separation that is formed during the slow cooling of a large mass of homogeneous melt. Basalt gradually decreases in volume and cracks along strictly defined planes. Sounds familiar, doesn't it?
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Israel. Zawitan River. Prism pools. (and this is already mine)
The Golan Heights (Ramat HaGolan) are part of a basalt plateau of volcanic origin, with a total area of 35,000 sq. km. Geologists believe that the age of the Golan is about one and a half million years.
Bordering the Jordan Basin in the west, the Golan Plateau in the east reaches the Nahal Rakkad canyon (a tributary of the Yarmouk River) and a chain of high hills (Hermon spurs), descending from north to south from 1000 m to 350 m above sea level. Several dozen extinct volcanoes (including Avital, Varda and Hermonit, over 1200 m above sea level), some with intact and deformed craters, covered the plateau and adjacent areas with lava in recent geological times, giving rise to a characteristic landscape of black basaltic rocks and brown tuff (volcanic emissions) lying on top of sedimentary chalk and limestone rocks. Running mainly to the west and densely covered with bushes along the banks, the streams washed deep gorges into the soil, often with waterfalls on the ledges.
And the basalt plateau spilled over other rocks, and ledges, and waterfalls. and prisms in rivers - well, they are very suitable for fissure volcanism. P.S. All photographs illustrating the text were found on the Internet. Where she knew, she indicated the exact authorship.
The most typical representation of a volcano is a cone-shaped mountain with spewing lava and poisonous gases erupting from the crater at the top. But this is only one of many types of volcano, and the characteristics of other volcanoes can be much more complex. The structure and behavior of a volcano depends on many factors. Many volcanic peaks are formed by lava cones rather than craters. Thus, volcanic materials (lava, or magma and ash that escaped from the depths) and gases (mainly steam and magma gases) can burst out anywhere on the surface.
Other types of volcanoes include cryovolcanoes, which can be found on the surface of the moons of Jupiter, Saturn and Neptune, and mud volcanoes, which form very frequently without any magma activity in the region. The temperature of active mud volcanoes is much lower than that of volcanoes formed as a result of tectonic activity, except when a mud volcano is a vent crack formed by an ordinary volcano.
vent crack
This is a type of volcano with a flat fault at the top in the form of a line through which lava erupts.
Figure 1. Vent crack
