What can lava melt and not melt

What is the difference between lava and magma?

Magma and lava actually refer to the same thing, just in different places: Magma is inside the earth, lava is on the surface of the earth.

Magma arises where the heat and pressure in the earth's interior are very high. There the rock melts and a viscous rock slurry is created, the magma. The magma collects in underground cavities and flows up to the surface of the earth when the pressure rises. As soon as the magma swells out of the earth during a volcanic eruption, it is called lava. Gases that were trapped in the magma can then escape into the air. Therefore, lava and magma differ in their chemical composition.

As long as the lava is hot, it is soft and malleable. On the surface of the earth, the lava slowly cools down and solidifies. Then it can look very different, depending on where and how it flowed out of the earth: For example, if a volcano erupts underwater, the lava cools down very quickly. It forms into structures that look like lumps or pillows. This is why one speaks of pillow lava. Other lava flows look like long balls of wool and are therefore called knitted lava.

Over time, various rocks are formed from lava. Particularly thin lava turns into dark gray basalt after cooling. This rock is often used as a paving stone for roads and paths. When lava is thrown into the air during a volcanic eruption and puffs up like foam, it creates pumice stone. The trapped air makes pumice stone so light that a piece of it can float on the water. Volcanic ash and volcanic dust that solidify turn into tufa. Many houses in the Vulkaneifel, for example, are made of tuff.

17.6.2014

It is the most active volcano on earth: Kilauea in Hawaii. It has been spraying lava out of craters and crevices since 1983, making for a great natural spectacle. The Kilauea measures 1,247 meters, its older siblings Mauna Loa and Mauna Kea tower more than 4,000 meters above the sea.

It was around 200,000 years ago that Kilauea broke through the earth's crust, 50,000 years ago it emerged from the sea. Due to its constantly swelling lava flows, it continues to grow. At the same time, it keeps losing mass due to landslides.

Kilauea owes its creation - like the entire chain of islands in Hawaii - to a hotspot. This hot spot in the earth's mantle melts the rock and forms a magma chamber. From here a volcano erupts from time to time. Because the hotspot always remains in the same place, but the tectonic plate slides over it, entire chains of volcanoes or volcanic islands are created over a period of millions of years.

Since the lava of Kilauea flows relatively slowly and steadily at a maximum of 10 km / h, it is not particularly dangerous for humans. Nevertheless, several villages have fallen victim to it in the past few decades, and more than 100 houses have been destroyed.

Pele's tears

Wreaths of flowers, gin and cigarettes lie on the edge of Kilauea's crater. They are offerings to the goddess Pele, who is very venerated by the Hawaiians. The name Pele means "molten lava". She is the goddess of fire and volcanoes. And sometimes the Hawaiians dance the hula for them on the edge of the volcano.

According to legend, the quick-tempered Pele is said to have created volcanoes with a magic wand; she found her residence in the crater of Kilauea. When the volcano breathes fire, Pele sometimes shows itself in the glowing lava.

Volcano researchers also seem to be impressed by Pele and named lava rock after the goddess: “Pele's hair” is what they refer to as elongated, hair-shaped volcanic glass. It forms when the volcano hurls out fountains of lava that the wind pulls apart before they get cold. “Tears of Pele”, on the other hand, arise when lava drips down and solidifies into tiny, shiny black spheres.

24.8.1979

At noon on August 24, 79 AD. the summit of the volcano Vesuvius explodes. The terrible volcanic eruption claimed thousands of lives. Hail of rock, lava flows and ash rain bury the inhabitants of Pompeii. The two cities on the Gulf of Naples are completely destroyed.

Until August 24th, Pompeii is a thriving trading city. The day starts sunny, the streets are crowded and there is noise, and merchant ships dock at the port. The residents have no idea of ​​the approaching disaster. They know nothing about the lava stopper that has been blocking the outlet of Vesuvius like a cork has blocked a champagne bottle for centuries. A violent earthquake 17 years earlier caused this plug to loosen dangerously. When it loosens around noon on August 24th, it shoots into the air along with the tip of the volcano with a huge bang - the beginning of the fall of Pompeii.

Soon there will be a hail of stones and a layer several centimeters thick will form on the roofs of the city. The rocks get bigger and with them the horror of the inhabitants. Fist-sized and red-hot pumice stones fall from the sky, smashing windows and roofs. There are the first fatalities. Violent tremors shake houses and streets. Many of the 20,000 Pompeians try to flee, others save themselves in the cellars. But their houses become a trap: the following night, Vesuvius emits deadly gases that settle on the city. Whoever breathes it in suffocates painfully. Over the course of the following day, three streams of lava burn and bury whatever is left of the city. Finally, Vesuvius spreads a thick layer of ash over the already completely devastated city.

The neighboring town of Herculaneum with 4,000 inhabitants is also razed to the ground by the eruption.

Witness to the downfall

From Misenum, a port city 30 kilometers from Pompeii, the 17-year-old Pliny followed the volcanic eruption and the fall of Pompeii. In a letter he describes the course of the catastrophe and the death of his uncle. He was a Roman fleet commander and set off with the ship to save people from Pompeii ...

He hurried to where others fled and headed straight for the danger [...] Ashes were falling on the ships, getting hotter and thicker the closer they got, soon pumice stone and black, half-charred, fire-cracked stones as well. The sea suddenly receded and a landslide made the shore impassable. For a moment he was undecided whether to turn back, then he called to the helmsman who had advised him to do so: "Fortune helps the brave, go to Pomponianus!"

Pomponianus is a friend of his uncle who lives in Stabiae. There is also panic there and people want to flee. Pliny 's uncle tries to calm her down.

In the meantime, wide flames and high columns of fire glowed from Vesuvius in several places, the radiant brightness of which was intensified by the dark night. [...] Together they discussed whether they should stay indoors or go outside, because as a result of frequent, strong tremors, the buildings swayed and seemed to sway back and forth as if they had been released from their foundations. In the open air, on the other hand, the raining down of annealed, but only light pieces of pumice stone was alarming [...] They put pillows over their heads and tied them with towels; that offered protection against falling rocks.

It was already day elsewhere, but there it was night, blacker and thicker than any other night, […] It was decided to go to the beach and see whether the sea would allow one to leave. But it still remained harsh and hostile. There my uncle lay down on a spread out blanket, asked for a sip of cold water every now and then, and took it to himself. Then flames and the scent of sulfur as a harbinger chased the others to flight and startled him. Leaning on two slaves, he got up and immediately collapsed dead, presumably because the thicker smoke took his breath away and closed his throat [...]

Translation from Latin: G / history, Bayard-Media

What happens in the event of a volcanic eruption?

It steams and bubbles, it smokes and hisses. Glowing hot rock shoots up from inside the earth. A cloud of ash rises, lava gushes out of the volcano and flows over the surface of the earth. When a volcanic eruption occurs, enormous forces are at work. But how does a volcano actually erupt?

In the earth's mantle, the rock layer under the earth's crust, temperatures of over a thousand degrees Celsius and very high pressure prevail. If the heat and pressure are high enough, the rock melts and becomes a viscous mass called magma. This magma expands and rises to the top. There it first collects in cavities, the magma chambers. None of this happens overnight, however, but takes tens of thousands or hundreds of thousands of years.

When the magma chamber is full and cannot hold any more material, the hot magma makes its way out. It penetrates through channels and crevices to the surface and emerges there as glowing hot lava - the volcano erupts. The channel through which the magma swells up is called a chimney, and its exit is called a crater.

Some volcanoes regularly spit lava, for example the Stromboli in southern Italy. One can observe its eruptions every day. Other volcanoes remain quiet for centuries but are not actually extinct. Often their craters are clogged with lava and debris. That makes them very dangerous because if they break out there can be huge explosions; well-known for this are, for example, Vesuvius near Naples or Krakatau in Indonesia. Such explosive eruptions blow up millions of tons of rock. The ash cloud that rises from the eruption can stay in the air for a long time and be widely dispersed by the wind. This cloud then only slowly settles on the earth as a fine layer of ash.

Lava that is not thrown into the air flows down from the crater rim as a scorching stream of molten rock. When this lava flow cools, it solidifies into lava rock. Little by little, lava flows, ash and debris build a mountain around the crater - the volcanic cone.

Why is the earth warm inside?

The liquid interior of the earth bubbles under our feet. Volcanic eruptions and geysers show the heat there - over 6000 degrees Celsius in the earth's core. But why is it so hot in the earth?

Much of the heat comes from the Earth's childhood days when dust and rocks condensed into a planet. The word “condense” sounds a little too harmless, however: In reality, you have to imagine how many large meteorite impacts - each impact a gigantic explosion that heated up the young planet and melted the material.

Since then it has become a little quieter and the earth is cooling down again. However, it does this extremely slowly, the heat in the interior of the earth can only very slowly escape into space. Hot magma flows in the tough earth mantle transport the heat upwards. There it remains enclosed under the rigid earth's crust as if under a lid. The crustal rock only slowly releases its heat into space.

In addition, heat is still being produced inside the earth. This is because the core of the earth contains a lot of radioactive substances such as uranium. Since the formation of our planet, they have been disintegrating and giving off heat over a very long period of time. This “fuel” will last for billions of years.

Igneous rocks

Biting granite means that something is hopeless. Because of its great hardness, granite can not only be used as a phrase, but also as a paving stone or for building walls. Granite is a rock that lies over two kilometers below the earth's surface and is common in the earth's crust.

Granite is formed when glowing magma solidifies when it cools. The dark spotted gabbro or the monzonite are also formed from slowly cooling magma. If this process takes place deep inside the earth, geologists speak of Deep rock, also Plutonite called.

If, on the other hand, the hot rock slurry penetrates outwards during a volcanic eruption and pours over the surface of the earth, it is Effluent rock or Volcanite the speech. The volcanites include the light pumice stone, the porous tuff or the rhyolite, which was formed from the same material as granite, but has a different structure and is less hard because it cools faster on the surface of the earth than the granite in the depths. Basalt is also a volcanite. Sometimes it freezes into hexagonal, closely spaced columns that look as if they have been cast into shape. Basalt forms on the surface of the earth from the same mass as the gabbro in the depths.

Vulcanites weather immediately after their formation, plutonites only when the overlying rock layers have been eroded. Because both volcanites and plutonites became rock from cooled magma, both are classified as igneous rocks.

Cycle of rocks

No rock on earth is made to last. It weathers on the surface, is removed and redeposited. When two plates collide, layers of sediment are compressed and unfolded to form high mountains. The rock of submerged plates melts in the earth's interior and forms the source of volcanoes. Lava that spits out from a volcanic crater cools down and solidifies again into rock.

It is an eternal cycle that ensures that even the hardest rock is constantly changing and new things are created from it. The transformation does not happen overnight, of course, but over millions of years. "Players" in this cycle are three groups of rocks, each of which is formed under different conditions:

When magma cools, the hot mass solidifies igneous rock. This can happen both on the surface of the earth and inside the earth. On the other hand, where layers of excavated rock pile up, the sediments are compressed under the weight of their own weight. This pressure causes them to solidify Sedimentary rock. In turn, high pressure and great heat in the earth's interior ensure that rock is transformed and another is created. Then geologists speak of transformation or of metamorphic rock.

These three types of rock are closely related: each type can transform into any other. This rock cycle will continue as long as the earth exists.

What do volcanoes look like?

A steep mountain, flames shoot into the sky, above it a dark ash cloud: this is what a volcano looks like in a picture book. But there are also completely different volcanoes. What shape they have depends above all on the lava that penetrates from the interior of the earth.

Thin lava flows smoothly and evenly out of the crater. It cools down slowly and spreads widely. This creates extensive areas or flat mountains that look like large shields. Hence these volcanoes have their name: Shield volcanoes. Typical examples are the Hawaii volcanoes with their glowing lava lakes and diameters of up to 400 kilometers.

Viscous lava, on the other hand, does not get very far - it partially sticks to the inside of the volcano and clogs it. Below that, magma continues to push upwards. The pressure rises until the lava plug is blasted out of the volcano in a big explosion like a cork from a champagne bottle. Lava fragments and rocks fly into the air and fall on the volcano. A layer of ash settles on the area. In the course of time, a pointed mountain of ash and rock debris piles up, increasing layer by layer with each eruption. Well-known examples of this Stratovolcanoes are Mount Etna in Sicily or Mount St. Helens in the USA. Stratovolcanoes are particularly dangerous because of their explosive eruptions.

There are also volcanic explosions that take place underground. When hot magma meets groundwater in the depths, the water suddenly evaporates. The resulting pressure is so high that the soil above is blown up. What remains is a hole in the surface of the earth, shaped like a bowl or funnel Maar. Water often collects in this crater, then a maar lake is created, such as the Laacher See in the Eifel.

If the magma chamber is empty after a volcanic eruption, the volcano can collapse over it. There is a deepening in the landscape, a Caldera. The dimensions of the collapsed magma chamber can be guessed at from the size of the caldera. Some are huge, like the caldera of Ngorongoro in Tanzania with a diameter of around 20 kilometers. When magma rises again from the depths and emerges as lava, a new volcano forms in the caldera; one then speaks of a daughter volcano. Vesuvius, for example, is such a daughter volcano: It originated in the caldera of Monte Somma.

From inside the earth: ores and solid metals

Copper was the first metal that humans discovered in the earth's crust. It could be shaped into simple tools or weapons and was so important that an entire epoch was named after it: the Copper Age. The tools got better when man mixed the copper with tin and thus invented the bronze.And when he learned to smelt iron, the triumph of metal tools finally began.

Unlike the core of the earth, the earth's crust consists largely of non-metals. Nevertheless, metals such as iron, aluminum, manganese and potassium can be found in their rock. Experts (geochemists) can determine exactly how often they occur. They found out that around seven percent of the earth's crust consists of iron.

Like most metals, iron occurs as a chemical compound with other elements, so-called ore. In order to extract iron from the ore rock, the ore rock is ground, mixed with coal and heated. Then a chemical reaction takes place that removes the other elements from the ore, leaving the pure, elemental iron.

On the other hand, some metals hardly combine with other elements. They therefore do not weather and occur in pure form in the earth's crust. These “solid metals” include gold, silver and platinum. Platinum and gold are also extremely rare: gold is only contained in an average of 0.001 grams per ton of rock. A place is only referred to as a deposit if it contains a thousand times the amount of gold - i.e. one gram of gold per ton of rock.

The "rare earth metals" are more common than gold or platinum. What sounds strange has a simple reason: These metals are considered rare because they do not form their own deposits, i.e. they do not occur in concentrated form, but only in scattered areas. We are therefore also talking about spice metals. Their importance has increased significantly in recent years because they are required for the manufacture of electronic devices such as cell phones or computers.