Is the composition of the lava the same? Lava metamorphoses
Scientists have been interested in lava for a long time. Its composition, temperature, flow speed, shape of hot and cooled surfaces are all subjects for serious research. After all, both erupting and frozen streams are the only sources of information about the state of the interior of our planet, and they constantly remind us of how hot and restless these interiors are. As for the ancient lavas, which turned into characteristic rocks, then the eyes of specialists are aimed at them with special interest: perhaps, behind the bizarre relief, the secrets of catastrophes on a planetary scale are hidden.
What is lava? According to modern ideas, it comes from a center of molten material, which is located in the upper part of the mantle (geosphere surrounding the Earth's core) at a depth of 50-150 km. While the melt remains in the depths under high pressure, its composition is homogeneous. Approaching the surface, it begins to “boil”, releasing gas bubbles that tend upward and, accordingly, move the substance along cracks in the earth’s crust. Not every melt, otherwise known as magma, is destined to see the light. The same one that finds its way to the surface, pouring out into the most incredible forms, is called lava. Why? Not quite clear. In essence, magma and lava are the same thing. In the “lava” itself one hears both “avalanche” and “collapse”, which, in general, corresponds to the observed facts: the leading edge of flowing lava often really resembles a mountain collapse. Only it’s not cold cobblestones that roll down from the volcano, but hot fragments that fly off the crust of the lava tongue.Over the course of a year, 4 km 3 of lava pours out of the depths, which is quite a bit, considering the size of our planet. If this number were significantly larger, the processes would begin global change climate, which has happened more than once in the past. IN last years scientists are actively discussing the next scenario of the end catastrophe Cretaceous period, approximately 65 million years ago. Then, due to the final collapse of Gondwana, in some places the hot magma came too close to the surface and erupted in huge masses. Its outcrops were especially abundant on the Indian platform, which was covered with numerous faults up to 100 kilometers long. Almost a million cubic meters of lava spread over an area of 1.5 million km 2. In some places the covers reached a thickness of two kilometers, which is clearly visible from the geological sections of the Deccan Plateau. Experts estimate that the lava filled the area for 30,000 years - fast enough for large portions of carbon dioxide and sulfur-containing gases to separate from the cooling melt, reach the stratosphere and cause a decrease in the ozone layer. What followed sudden change climate led to the mass extinction of animals at the border of the Mesozoic and Cenozoic eras. More than 45% of the genera of various organisms have disappeared from the Earth.
Not everyone accepts the hypothesis about the influence of lava flow on climate, but the facts are clear: global extinctions of fauna coincide in time with the formation of extensive lava fields. So, 250 million years ago, when a mass extinction of all living things occurred, powerful eruptions occurred in the territory Eastern Siberia. The area of lava covers was 2.5 million km 2, and their total thickness in the Norilsk region reached three kilometers.
Black blood of the planetThe 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. Basaltic lavas are half made of silicon dioxide (quartz), half of aluminum oxide, iron, magnesium and other metals. It is the metals that provide the high temperature of the melt - more than 1,200 ° C and mobility - the basalt flow usually flows at a speed of about 2 m/s, which, however, should not be surprising: this is the average speed of a running person. In 1950, during the eruption of the Mauna Loa volcano in Hawaii, the fastest lava flow was measured: its leading edge moved through sparse forest at a speed of 2.8 m/s. When the path is paved, the following streams flow, so to speak, in hot pursuit much faster. Merging, lava tongues form rivers, in the middle reaches of which the melt moves at high speed - 10–18 m/s.
Basaltic lava flows are characterized by a small thickness (a few meters) and a large extent (tens of kilometers). The surface of flowing basalt most often resembles a bunch of ropes stretched along the movement of lava. It is called the Hawaiian word "pahoehoe", which, according to local geologists, does not mean anything other than a specific type of lava. More viscous basaltic flows form fields of sharp-angled, spike-like lava fragments, also called "aa lavas" in Hawaiian fashion.
Basaltic lavas are not only common on land; they are even more common in the oceans. The ocean floors are large slabs of basalt 5–10 kilometers thick. According to American geologist Joy Crisp, three-quarters of all lavas erupting on Earth each year come from underwater eruptions. Basalts constantly flow from the cyclopean ridges that cut through the ocean floors and mark the boundaries of lithospheric plates. No matter how slow the plate movement, it is accompanied by strong seismic and volcanic activity on the ocean floor. Large masses of melt coming from ocean faults do not allow the plates to become thinner, they are constantly growing.
Underwater basalt eruptions show us another type of lava surface. As soon as the next portion of lava splashes out to the bottom and comes into contact with water, its surface cools down and takes the form of a drop - a “pillow”. Hence the name - pillow lava, or pillow lava. Pillow lava forms whenever molten material enters a cold environment. Often during a subglacial eruption, when the flow rolls into a river or other body of water, the lava solidifies in the form of glass, which immediately bursts and crumbles into plate-like fragments.
Vast basalt fields (traps) hundreds of millions of years old hide even more unusual shapes. 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. If the trap field, on the contrary, is exposed from above, then instead of pillars, surfaces appear as if paved with giant paving stones - “pavements of giants”. They are found on many lava plateaus, but the most famous are in the UK.
Neither the high temperature nor the hardness of solidified lava serves as an obstacle to the penetration of life into it. In the early 90s of the last century, scientists found microorganisms that settle in basalt lava that erupted at the bottom of the ocean. As soon as the melt cools down a little, the microbes “gnaw” passages in it and establish colonies. They were discovered by the presence in basalts of certain isotopes of carbon, nitrogen and phosphorus - typical products released by living beings.
The more silica in lava, the more viscous it is. The so-called medium lavas, with a silicon dioxide content of 53–62%, no longer flow as fast and are not as hot as basaltic lavas. Their temperature ranges from 800 to 900°C and their flow speed is several meters per day. The increased viscosity of lava, or rather magma, since the melt acquires all its basic properties at depth, radically changes the behavior of the volcano. From viscous magma, it is more difficult to release the gas bubbles accumulated in it. On approaching the surface, the pressure inside the bubbles in the melt exceeds the pressure on them outside and the gases are released with an explosion.
Typically, a crust forms at the leading edge of the more viscous lava tongue, which cracks and crumbles. The fragments are immediately crushed by the hot mass pressing behind them, but do not have time to dissolve in it, but harden like bricks in concrete, forming rock characteristic structure- lava breccia. Even after tens of millions of years, lava breccia retains its structure and indicates that a volcanic eruption once occurred in this place.In the center of Oregon, USA, there is the Newberry volcano, which is interesting because of its lavas of intermediate composition. Last time it became active more than a thousand years ago, and at the final stage of the eruption, before falling asleep, a lava tongue 1,800 meters long and about two meters thick flowed out of the volcano, frozen in the form of pure obsidian - black volcanic glass. Such glass is obtained when the melt cools quickly without having time to crystallize. Additionally, obsidian is often found on the periphery of a lava flow, which cools faster. Over time, crystals begin to grow in the glass and it turns into one of the acidic or intermediate rocks. That is why obsidian is found only among relatively young eruption products; it is no longer found in ancient volcanics.
From damn fingers to fiamme
If the amount of silica occupies more than 63% of the composition, the melt becomes completely viscous and clumsy. Most often, such lava, called acidic, is not able to flow at all and solidifies in the supply channel or is squeezed out of the vent in the form of obelisks, “devil’s fingers,” towers and columns. If the acidic magma still manages to reach the surface and pour out, its flows move extremely slowly, several centimeters, sometimes meters per hour.
Unusual rocks are associated with acidic melts. For example, ignimbrites. When the acidic melt in the near-surface chamber is saturated with gases, it becomes extremely mobile and is quickly ejected from the vent, and then, together with tuffs and ash, flows back into the depression formed after the ejection - the caldera. Over time, this mixture hardens and crystallizes, and large lenses of dark glass clearly stand out against the gray background of the rock in the form of irregular shreds, sparks or flames, which is why they are called “fiamme”. These are traces of the stratification of the acidic melt when it was still underground.
Sometimes acidic lava becomes so saturated with gases that it literally boils and becomes pumice. Pumice is a very light material, with a density lower than that of water, so it happens that after underwater eruptions, sailors observe entire fields of floating pumice in the ocean.
Many questions related to lavas remain unanswered. For example, why lavas of different compositions can flow from the same volcano, as, for example, in Kamchatka. But if in this case there are at least convincing assumptions, then the appearance of carbonate lava remains a complete mystery. It, half consisting of sodium and potassium carbonates, is currently erupted by the only volcano on Earth - Oldoinyo Lengai in Northern Tanzania. The melt temperature is 510°C. This is the coldest and most liquid lava in the world, it flows along the ground like water. The color of hot lava is black or dark brown, but after just a few hours of exposure to air, the carbonate melt becomes lighter, and after a few months it becomes almost white. Frozen carbonate lavas are soft and brittle and easily dissolve in water, which is probably why geologists do not find traces of similar eruptions in ancient times.Lava plays a key role in one of the the most pressing problems geology - what heats up the bowels of the Earth. Why do pockets of molten material appear in the mantle, which rise upward, melt through the earth's crust and give rise to volcanoes? Lava is only a small part of a powerful planetary process, the springs of which are hidden deep underground.
by ART-STUDIO MJ LAVA(LAVA)Lava
Depending on the composition, when solidified, it forms various effusive rocks
Types of lava
Lava varies from volcano to volcano.
It differs in composition, color, temperature, impurities, etc.
Carbonate lava
Half consists of sodium and potassium carbonates. This is the coldest and most liquid lava on earth; it flows along the ground like water. The temperature of carbonate lava is only 510-600 °C. The color of hot lava is black or dark brown, but as it cools it becomes lighter, and after a few months it becomes almost white. Solidified carbonate lavas are soft and brittle and easily dissolve in water. Carbonate lava flows only from the Oldoinyo Lengai volcano in Tanzania.
Silicon lava
Silicon lava is most typical for the volcanoes of the Pacific Ring of Fire; such lava is usually very viscous and sometimes solidifies in the crater of the volcano even before the end of the eruption, thereby stopping it. A plugged volcano may swell a little, and then the eruption resumes, usually with a powerful explosion. Lava contains 53-62% silicon dioxide. It has average speed flow (several meters per day), temperature 800-900 °C. If the silica content reaches 65%, then the lava becomes very viscous and clumsy. The color of hot lava is dark or black-red. Solidified silicon lavas can form black volcanic glass. Such glass is obtained when the melt cools quickly without having time to crystallize.
Basalt lava
The main type of lava erupted from the mantle is characteristic of oceanic shield volcanoes. Half consists of silicon dioxide (quartz), half - from aluminum oxide, iron, magnesium and other metals. This lava is very mobile and can flow at a speed of 2 m/s (the speed of a fast walking person). It has a high temperature of 1200-1300 °C. Basaltic lava flows are characterized by a small thickness (a few meters) and a large length (tens of kilometers). The color of hot lava is yellow or yellow-red.
Origin of lava
Lava is formed when a volcano erupts magma onto the Earth's surface. Due to cooling and interaction with gases included in the atmosphere, magma changes its properties, forming lava. Many volcanic island arcs are associated with deep fault systems. The centers of earthquakes are located approximately at a depth of up to 700 km from the earth's surface, that is, the volcanic material comes from the upper mantle. On island arcs it often has an andesitic composition, and since andesites are similar in composition to the continental crust, many geologists believe that the continental crust in these areas builds up due to the influx of mantle material.
Lava- a hot liquid (effusion) or very viscous (extrusion) melt of rocks, predominantly of silicate composition (SiO2 from about 40 to 95%), pouring onto the surface of the Earth during volcanic eruptions. When lava hardens, effusive (outpoured) rocks are formed, and a lava plateau can form. The lava temperature ranges from 500 to 1200 °C.
Lava (Italian lava, from Latin labes - collapse, fall) is a fiery liquid, predominantly silicate melt, pouring out during volcanic eruptions to the earth's surface. The difference from magma is that there are no gases that escape during an eruption.
Depending on the composition, when solidified, it forms various effusive rocks
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» Lava movement
The speed of lava movement varies depending on its density and the slope of the terrain where it makes its way. Relatively small lava flows flowing down steep slopes move forward extremely quickly; a stream ejected by Vesuvius on August 12, 1805, rushed along the steep slopes of the cone with amazing speed and in the first four minutes made 5 ½ km, and in 1631 another stream of the same volcano reached the sea within one hour, i.e. walked 8 km at this time. Particularly liquid lavas are produced by open basaltic volcanoes on the island of Hawaii; they are so mobile that they form real lava falls on the cliffs and can move with the slightest slope of the soil, even in the mountains. It has been repeatedly observed how these lavas passed 10-20 and even 30 km per hour. But such speed of movement belongs, in any case, to the number of exceptions; even the lava that Scrope observed in 1822 and which managed to descend from the edge of the crater of Vesuvius to the foot of the cone within 15 minutes is far from ordinary. On Etna, lava movement is considered fast if it occurs at a speed of 1 km in 2-3 hours. Usually lava moves even more slowly and in some cases only moves 1 m per hour.
The lava flowing out of the volcano in a molten state has a white-hot sheen and inside the crater retains it for a long time: this can be clearly seen where, thanks to cracks, the deep parts of the flow are exposed. Outside the crater, the lava quickly cools, and the flow is soon covered with a hard crust consisting of a dark cinder mass; within a short time it becomes so strong that a person can calmly walk on it; sometimes along such a crust covering a still moving flow, you can climb to the place where the lava flows out. The solid slag crust forms something like a pipe, inside which the liquid mass moves. The front end of the lava flow is also covered with black, hard crust; with further movement, the lava presses this crust to the ground and flows along it further, becoming covered in front with a new slag shell. This phenomenon does not occur only when the lava moves very quickly; in other cases, by dumping and moving slag, a layer of solidified lava is formed, along which the flow moves. The latter presents a rare sight: the front part of it is compared by Pulet Scroop to a huge pile of coals, which, under the influence of some pressure from behind, are piled on top of each other. Its movement is accompanied by a noise similar to the ringing of spilling metal; this noise occurs due to the friction of individual lumps of lava, their fragmentation and contraction.
The hard crust of a lava flow usually does not have a flat surface; it is covered with many cracks through which liquid lava sometimes flows; blocks formed as a result of fragmentation of the original cover collide with each other, like ice floes during ice drift. It is difficult to imagine a wilder and more gloomy picture than that presented to us by the outer surface of a blocky lava flow. Even more peculiar are the forms of the so-called wavy lava, which is observed less frequently, but is well known to every visitor to Vesuvius. The road from Rezina to the observatory was laid over such lava for a considerable distance; the latter was thrown out by Vesuvius in 1855. The cover of such flows is not broken into pieces, but represents a continuous mass, the uneven surface of which, in its peculiar appearance, resembles intestinal plexuses.
Ecology
Volcanoes on our planet are geological formations on the earth's crust.
From here magma comes to the surface of the earth , which forms lava, as well as volcanic gases, rocks and mixtures of gas, volcanic ash and rocks. Such mixtures are called pyroclastic flows.
It is worth noting that the word “volcano” itself came to us from Ancient Rome, where Vulcan was the name of the god of fire.
There is a lot of interesting information about volcanoes, and below you can find some facts about them.
25. Strongest volcanic eruption (Indonesia)
Of all the documented volcanic eruptions, the largest was recorded at the Tambora stratovolcano on the island of Sumbawa, Indonesia, in 1815.
According to the indicator of volcanic explosiveness, the force of the eruption reached 7 points (out of 8).
This eruption reduced average temperature on Earth by 2.5 °C during next year, which was called "the year without summer."
It is worth noting that the volume of emissions into the atmosphere was approximately 150-180 cubic meters. km.
24. Long-lasting effects of a volcanic eruption
Gas and other particles released into the atmosphere during the 1991 eruption of Mount Pinatubo on the island of Luzon, Philippines, lowered global temperatures by about 0.5 degrees Celsius over the next year.
23. Lots of volcanic ash
The 1991 eruption of Mount Pinatubo sent 5 cubic kilometers of volcanic material into the air, creating an ash column 35 km high.
22. Big volcano explosion
Most big Bang The 20th century occurred in 1912 during the eruption of Novarupt, one of the chain of Alaska volcanoes - part of the Pacific volcanic Ring of Fire. The force of the eruption reached 6 points.
21. Kilauea's long eruption
One of the most active volcanoes on Earth, Hawaii's Kilauea has been erupting continuously since January 1983.
20. Deadly volcanic eruption
The colossal magma chamber that was located inside the Taupo volcano continued to fill very for a long time, and finally the volcano exploded.
After the eruption in April 1815, the strength of which reached 7 points, from 150 to 180 cubic meters were thrown into the air. km of volcanic material.
Volcanic ash also filled the remote islands, leading to a huge number of deaths. Their number was approximately 71,000. About 12,000 people died directly from the eruption, while the rest died as a result of starvation and disease that resulted from the eruptive fallout.
19. Big mountains
18. Active volcanoes today
Hawaii's Mauna Loa volcano is the largest active volcano in the world, rising 4,1769 meters above sea level. Its relative height ( from the ocean floor) - 10,168 meters. Its volume is about 75,000 cubic kilometers.
17. The surface of the earth covered with volcanoes
More than 80 percent of the Earth's surface above and below sea level is of volcanic origin.
16. Ashes Everywhere (Volcano St. Helens)
During the eruption of Mount St. Helens in 1980, approximately 540 million tons of ash covered an area exceeding 57,000 square meters. km.
15. Volcano disaster - landslides
The St. Helens eruptions resulted in the largest landslides on Earth. As a result of this eruption, the height of the volcano was reduced by 400 meters.
14. Underwater volcano eruptions
The deepest recorded volcanic eruption occurred in 2008 at a depth of 1,200 meters.
The cause was the West Mata volcano, located in the Lau Basin near the Fiji Islands.
13. Lava lakes of a volcano in Antarctica
The southernmost active volcano is Erebus, located in Antarctica. It is worth noting that the lava lake of this volcano is the most a rare occurrence on our planet.
Only 3 volcanoes on Earth can boast of “non-healing” lava lakes - Erebus, Kilauea in Hawaii and Nyiragongo in Africa. And yet, a lake of fire in the middle of eternal snow is a truly impressive phenomenon.
12. High temperature (what comes out during a volcanic eruption)
Temperatures inside a pyroclastic flow - a mixture of high-temperature volcanic gases, ash and rocks that form during a volcanic eruption - can exceed 500 degrees Celsius. This is enough to burn and carbonize the wood.
11. First in history (Nabro volcano)
On June 12, 2011, the active Nabro volcano, which is located in the southern Red Sea, near the borders of Eritrea and Ethiopia, awoke for the first time. According to NASA, this was its first recorded eruption.
10. Volcanoes of the Earth
There are about 1,500 volcanoes on Earth, not counting the long volcanic belt on the ocean floor.
9. Pele's tears and hair (parts of a volcano)
Kilauea is where Pele, the Hawaiian volcano goddess, is said to live.
Pele's Tears
Several lava formations were named after her, including Pele's tears (small drops of lava cooled by air) and Pele's hair (splashes of lava cooled by wind).
Pele's hair
8. Supervolcano
Modern man could not witness the eruption of a supervolcano (8 points), which could change the climate on Earth.
The last eruption occurred approximately 74,000 years ago in Indonesia. In total, there are approximately 20 supervolcanoes known to scientists on our planet. It is worth noting that on average, such a volcano erupts once every 100,000 years.
