What is lava? Types of lava. Types of volcanic eruptions What is lava
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, 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 (the 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 very incredible shapes, which is exactly what 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 of global climate change would begin, 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. The subsequent dramatic climate change led to 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 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 average speed running man. 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, such as in cliffs 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 a rock with a 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, “ damn 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. Because of what, pockets of molten material appear in the mantle, which rise upward and melt through 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.
» » Cooling of lava
The time required for lava to cool cannot be determined precisely: depending on the power of the flow, the structure of the lava and the degree of initial heat, it varies greatly. In some cases, lava hardens extremely quickly; for example, one of the flows of Vesuvius froze in 1832 in two months. In other cases, lavas are in motion for up to two years; often, after several years, the temperature of the lava remains extremely high: a piece of wood stuck into it instantly catches fire. This was, for example, the lava of Vesuvius in 1876, four years after the eruption; in 1878 it had already cooled down.
Some streams form fumaroles over many years. At Jorullo, in Mexico, in the springs passing through the lava that poured out 46 years ago, Humboldt observed a temperature of 54°. Flows of significant power freeze even longer. Skaptar-jokul in Iceland in 1783 identified two lava flows, the volume of which exceeded that of Motzblanc; It is not surprising that such a powerful mass solidified gradually over the course of about a century.
We have seen that lava flows quickly solidify from the surface and are covered with a hard crust, in which the liquid mass moves, as if in a pipe. If after this the amount of lava released decreases, then such a pipe will not be completely filled with it: the upper cover will gradually sink, stronger in the middle and less at the edges; Instead of the usual convex surface, which is represented by any thick fluid mass, you get a concave surface in the form of a trench. However, the hard crust covering the stream does not always sink: if it is powerful and strong enough, it will withstand its own weight; in such cases, voids form inside the frozen flow; no doubt this is how the famous grottoes of Iceland arose. The most famous among them is Surtshellir (“Black Cave”) near Kalmanstung, located among a huge lava field; its length is 1600 m, width 16-18 m and height 11 - 12 m. It consists of a main hall with a number of side chambers. The walls of the grotto are covered with glassy shiny formations, magnificent lava stalactites descend from the ceiling; Long stripes are visible on the sides - traces of a moving fiery liquid mass. Many lava flows on the island of Hawaii are cut through by long grottoes, like tunnels: in some places these grottoes are very narrow, sometimes they widen up to 20 m and form vast high halls decorated with stalactites; they sometimes stretch for many kilometers and twist, following all directions of the lava flow. Similar tunnels have also been described on the volcanic islands of Bourbon (Reunion) and Amsterdam.
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 over the next year, which has been 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
The largest explosion of 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 for a very 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 rarest phenomenon 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.
LAVA (Italian lava, from Latin labes - collapse * a. lava; n. Lava; f. lave, сulee; i. lava) - hot (temperature 690-1200 ° C) liquid or very viscous mass of partially or completely molten rocks, poured out or squeezed out onto earth's surface during a volcanic eruption. It differs from magma in the absence of a number of components (primarily water and other volatiles), and in certain geological and physicochemical properties. When lava hardens, it forms a corresponding chemical composition erupted (effusive) or squeezed (extrusive) rock, also called lava. The most common are basaltic, andesite, dacite and rhyolite lavas of varying alkalinity (see), less commonly trachyte, phonolite, pantellerite, comendite, and ongonite. Exotic lavas in chemistry: soda (Ol-Doinyo-Lengai in Central), native sulfur (Siretoko and Tokachi volcanoes in Japan, Ebeko in the Kuril Islands, Mauna Loa in Hawaii, etc.), magnetite (Chilean Andes), etc.
In general, with an increase in the SiO 2 content and a decrease in the content of volatile components (especially water) and alkalis, the viscosity of lava increases. The viscosity of lava determines the shape of the geological bodies it composes. During the eruption of low-viscosity mobile basaltic, andesitic and other lavas, nappes are often formed (Laki volcano, Iceland, etc.), flows of varying thickness (Kamchatka, Khorgo volcano in Mongolia, etc.). Acidic, usually dacite, trachyte and rhyolite lavas form domes (Auvergne, France, etc.), peaks, needles, obelisks (Montagne-Pelée on the island of Martinique, etc.). Lava cascades in flows and cones are common. Depending on the conditions and composition of the eruption, several morphological types of lavas are distinguished.
Lavas erupting onto the dry earth's surface: ; lava-pahoehoe (pehuhu) - a flow with a wavy glassy surface, often twisted into folds, sometimes finger-shaped, divided into separate streams, often with tunnels. Its variety is rope lava, when the wrinkled surface of the flow looks like ropes. Block or block lavas are also common - a flow more viscous than aa-lava, with a surface consisting of polyhedral blocks formed during the rapid cooling of a thick crust of the flow, which breaks up into blocks under the influence of lava moving under the crust.
Lava that erupts underwater (for example, at the bottom of the sea) is called pillow, spherical, ellipsoidal, pillow lava. It is a cluster of rounded “pillows” or “balls” pressed into each other or extended one after another and connected by tubes and necks. The "balls" have a bubbly, often glassy crust and a concentric structure in cross section. Often found in geological deposits of different ages(see) together with siliceous or terrigenous sediments. Modern pillow lavas are especially typical of mid-ocean ridges.
Lava lakes are known in some volcanic craters. When lava droplets eject from such a lake during an explosion, they usually pull filaments of melt with them, which, when tempered in the air, form tangled thread-like fibers of natural glass from golden brown to dark brown in color ("Pele's hair"), capable of being carried by the wind.
» 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.
