Big encyclopedia of oil and gas. Lava movement

When volcanoes erupt, hot melt pours out rocks– magma. In air, the pressure drops sharply, and the magma boils - gases leave it.

The melt begins to cool. In fact, only these two properties – temperature and “carbonation” – distinguish lava from magma. Over the course of a year, 4 km³ of lava spills across our planet, mainly at the bottom of the oceans. Not so much, on land there were regions filled with a lava layer 2 km thick.

The initial temperature of the lava is 700–1200°C and higher. Dozens of minerals and rocks are melted in it. They include almost all known chemical elements, but most of all silicon, oxygen, magnesium, iron, aluminum.

Depending on the temperature and composition, lava can be different colors, viscosity and fluidity. Hot, it's shiny bright yellow and orange; cooling down, it turns red and then black. It happens that blue lights of burning sulfur run above the lava flow. And one of the volcanoes in Tanzania erupts black lava, which, when frozen, becomes like chalk - whitish, soft and brittle.

The flow of viscous lava is slow and flows barely (a few centimeters or meters per hour). Along the way, hardening blocks are formed in it. They slow down traffic even more. This kind of lava solidifies in mounds. But the absence of silicon dioxide (quartz) in lava makes it very liquid. It quickly covers vast fields, forms lava lakes, rivers with a flat surface, and even “lava falls” on cliffs. There are few pores in such lava, since gas bubbles easily leave it.

What happens when lava cools?

As the lava cools, the molten minerals begin to form crystals. The result is a mass of compressed grains of quartz, mica and others. They can be large (granite) or small (basalt). If cooling proceeds very quickly, a homogeneous mass is obtained, similar to black or dark greenish glass (obsidian).

Gas bubbles often leave many small cavities in viscous lava; This is how pumice is formed. Different layers of cooling lava flow down the slopes with at different speeds. Therefore, long, wide voids are formed inside the flow. The length of such tunnels sometimes reaches 15 km.

Slowly cooling lava forms a hard crust on the surface. It immediately slows down the cooling of the mass lying below, and the lava continues to move. In general, cooling depends on the massiveness of the lava, initial heating and composition. There are known cases when, even after several years (!), lava still continued to crawl and ignited branches stuck into it. Two massive lava flows in Iceland remained warm centuries after the eruption.

Lava from underwater volcanoes usually hardens in the form of massive “pillows”. Due to rapid cooling, a strong crust forms on their surface very quickly, and sometimes gases rupture them from the inside. The fragments scatter over a distance of several meters.

Why is lava dangerous for people?

The main danger of lava is its high temperature. It literally burns living beings and buildings along the way. Living things die without even coming into contact with it, from the heat with which it radiates. True, high viscosity inhibits the flow rate, allowing people to escape and preserve valuables.

But liquid lava... It moves quickly and can cut off the path to salvation. In 1977, during the night eruption of Mount Nyiragongo in Central Africa. The explosion split the crater wall, and lava gushed out in a wide stream. Very fluid, it rushed at a speed of 17 meters per second (!) and destroyed several sleeping villages with hundreds of inhabitants.

The damaging effect of lava is aggravated by the fact that it often carries clouds of toxic gases released from it, a thick layer of ash and stones. It was this kind of flow that destroyed the ancient Roman cities of Pompeii and Herculaneum. A meeting of hot lava with a body of water can result in a disaster - the instantaneous evaporation of a mass of water causes an explosion.

Deep cracks and gaps form in the flows, so you need to walk on cold lava carefully. Especially if it is glassy - sharp edges and debris hurt painfully. Fragments of cooling underwater “pillows” described above can also injure overly curious divers.

The name “volcano” goes back to the name of the ancient Roman deity Vulcan, the patron of fire and blacksmithing. According to legend, it was on Mount Etna, which is still active and periodically erupts, that his workshop was located. Another interesting legend explains the awakening of the volcano by a giant who is trying to get free from captivity under the mountain, which leads to an eruption. In reality, everything is not so bizarre, but no less interesting and, perhaps, as creepy as the idea that a warlike giant could live under a volcano.

From geography lessons at school, everyone remembers that under the surface earth's surface, called the crust, is a layer of molten, incredibly hot rock - the mantle. When in earth's crust cracks appear, igneous rocks from the upper layers of the mantle, which were under enormous pressure, rush outward, like a mythical giant, making their way through the resulting fault. Already on the surface, magma is divided into:

lava - the temperature of which varies from 500 to 1200 degrees Celsius
ash

Since the main reason for igneous rocks reaching the surface is the formation of cracks in top layer lithosphere due to the shift of tectonic plates, it is not surprising that majority active volcanoes is located in the so-called Pacific Ring of Fire zone, which is a kind of “poorly stitched seam” between continental plates. The remaining active volcanoes around the world are at the moment There are about 500, in the vast majority of cases they are confined to other fault zones of the earth's crust.

Eruption process

The structure of the volcano is quite simple, and its eruption is devoid of any mysticism, being only a consequence of the internal processes of our planet. The channel through which hot magma escapes from the center of the earth is called volcano crater. It is connected to a magma chamber - an underground reservoir that, as the name suggests, is filled with magma. During the eruption process, a kind of volcanic “body” begins to form around the vent, most often in the shape of a cone. It consists of lava, ash and stones. At the top, where the magma finally finds its way out, there is a crater, in most cases shaped like a funnel or just a depression. Sometimes cracks and side craters appear on the slopes of volcanoes, through which magma can also escape.

A volcanic eruption occurs when the pressure in the magma chamber becomes too great, and the gases saturating the magma begin to rapidly rise to the top, literally pushing it out. This process is somewhat reminiscent of shaking a bottle of soda - if the cork in the neck does not hold well, then gases under high pressure knock out the cork, “pulling” water out of the bottle.

Classification of volcanoes

Classification by activity

Volcanoes themselves are classified according to several criteria, the most important of which is the degree of their volcanic activity, because this determines whether a volcano is potentially dangerous or not. So, according to the degree of activity, they are divided into only three types - active, dormant and extinct.

Active those volcanoes are considered whose eruptions there is human evidence. These eruptions could have occurred ten, one hundred, a thousand or five thousand years ago, but since the period of activity of the volcano is quite long (in some cases it can reach several million years), they are usually classified as active.

Sleeping These are volcanoes that have not erupted for a long time and may never erupt again, but there is always such a chance for them.

The possibility of an extinct volcano erupting tends to zero. But at the same time, there are cases when a volcano, previously considered extinct, woke up and brought a lot of troubles.

However, among scientists there is no consensus on this classification, just as there is no way to 100% reliably determine the degree of activity of the volcano.

Classification by type

The following method of classifying volcanoes divides them into two main types - linear and central.

Linear volcanoes are long fissures from which liquid flows. basalt magma that forms real lava fields around the volcano. For example, the relief of Iceland was formed in this way.

Central volcanoes are, most often, exactly those same cone-shaped elevations that our imagination pictures for us when we hear the word “volcano.”

Regardless of whether volcanoes are linear or central, they are usually classified according to their shape, which mainly depends on the composition of the magma they erupt.

Shield volcanoes appear as a result of multiple eruptions of liquid basaltic magma, which spreads in all directions for many kilometers, forming a kind of shield, which gives them their name.
Stratovolcanoes consist of alternating layers of thick, quickly hardening lava and pyroclastic material (a mixture of hot gas, rocks and ash). These are the most high volcanoes and, perhaps, the most dangerous, since the high viscosity of the magma causes the crater to clog, resulting in powerful and destructive explosions.
Cinder cones are the most common type of volcano on land. They are formed as a result of the accumulation of porous slag rocks around the crater of a volcano. Most often their height does not exceed several hundred meters.

Of course, it happens that some volcano cannot be classified as one a certain type. In this case, it is called complex (composite).

All these classifications make it possible to understand what, in fact, such a phenomenon as volcanism is, what people can expect from these fiery giants and how they can learn to coexist with them. Due to extreme danger volcanic eruptions such a field of science as volcanology is very significant for the safety of humanity. At the same time, volcanoes are studied not only in order to predict their eruptions, but also in order to learn more about our planet, its origin, internal processes, mysteries of the emergence and development of life. It is assumed that once upon a time it was volcanic activity that made it possible for life to arise on Earth. And if this is really the case, then who knows what other secrets volcanoes hide.

Remember Karl Bryullov’s painting “The Last Day of Pompeii”? A giant cloud of volcanic dust and ash covers the city. The lava is rapidly creeping in, consuming house after house. People are in panic trying to leave the dying city. They cry for help, but the gods do not hear them. The wrath of the Almighty fell on sinners, and Pompeii, a prosperous, rich city, disappeared from the face of the Earth.

The volcano suddenly woke up; before that it was absolutely calm. Its slopes have long been overgrown with dense forests. People and animals lived well near this giant. Legends warned about the wrath of the volcano. But who believes the myths? Those first people who built the city at the foot of Vesuvius were no exception.

The volcano warned them of the impending disaster, shaking the walls of their homes from time to time. But people are careless and always hope for something. After a small earthquake, the tremors of which continued for a week, there was a powerful explosion. An eruption began, boiling magma rushed out. First, the city was covered with a thick layer of ash, and then lava flowed through its streets.

What is lava? This is magma from which gases escaped during an eruption. That is, lava is magma that has changed its properties. This word in Latin means collapse or fall. Yes, in fact, lava is the fall of the contents of a volcano from a height. Volcanological scientists chemical composition define three types of lava.

The most common type is basaltic lava. Oceanic shield volcanoes erupt from the mantle a “hellish mixture”, half of which consists of silicon dioxide. And the second half is oxide of aluminum, iron, magnesium and other metals. A real chemical laboratory, hidden in the mantle, prepares this mixture to splash it onto the surface of the earth. Basaltic lava is always light in color. Sometimes yellow, sometimes yellow-red. It is liquid, so it always flows quickly. Average speed movement - 2 meters per second. In addition, the temperature is extremely high – at least 1200 degrees. You can’t run away from this and you can’t be saved!

Silicon lava is primarily found in the Pacific Ring of Fire. It is so thick and viscous that sometimes during an eruption it clogs the mouth of the volcano and does not pour out. To be fair, it should be said that sometimes it accumulates so much that the volcano, taking a deep breath, throws it out of itself. Usually there is a powerful explosion, and the lava, slowly and reluctantly, slides down the slope of the volcano. The speed is ridiculous - from 2 to 5 meters per day.

This type of lava is called siliceous lava because it usually contains silicon dioxide or silica. Moreover, in such an unimaginable amount - from 55 to 65%. It is this type that forms black volcanic glass when hardened. And the lava itself is usually black and red. From a distance she is very beautiful, but up close she is, of course, dangerous. Why? Experts joke when they say that this type of lava is “cold.” This almost “ice” heats up to only 500 (!) degrees.

And scientists classify another type as cold. This is carbonate lava, which also has a temperature of 500 - 600 degrees. It contains equal amounts of sodium and potassium carbonates. It is very liquid, so it also rushes down the slopes at great speed. By the way, it threatens only one place on Earth, because it pours out from the Oldoinyo volcano - Lengai in Tanzania.

The carbonate lava flowing along the slopes has dark color, but when it hardens, it brightens, becomes soft and even brittle. It dissolves easily in water. Local healers prepare various potions based on it. And they say that they are quite successful in healing those who suffer.

After an eruption, all types of lava radically change the appearance of the volcano and its surroundings. Huge mountain plateaus appear. Sometimes the lava hardens, forming a bizarre, almost cosmic landscape. All vegetation burns. But very soon life returns to the ashes. First, the wind brings plant seeds. And a year later the first green shoots begin to emerge.

After 5 - 10 years, nothing reminds of the eruption; on the contrary, the slopes turn into a paradise. Here lush greenery trees, plenty of game and water. People, deceived by a quietly sleeping volcano, build houses and raise children. And this peaceful picture pleases the heart. But one day everything will happen again, and the next Pompeii will fall victim to lava.

» 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.

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 cools quickly, 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 a liquid mass moves. Front end lava flow also covered with black hard bark; 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 Scrope 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 peculiar appearance resembles intestinal plexuses.

» » 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.