Start rocks with the volcano
The snow-covered Kilimanjaro can be admired from a great distance. As a single mountain range, it towers far beyond the African steppe - very different from the typical folded mountains such as the Alps or the Himalayas. Because Kilimanjaro was not created when tectonic plates collided. About one and a half million years ago, several volcanoes erupted in close proximity in the region. The mighty Kilimanjaro massif rose up into the sky from the lava masses. Today its highest peak is the Kibo at 5895 meters above sea level.
There are also volcanic mountains in Germany, for example the Siebengebirge near Bonn. Several volcanoes became active here 25 million years ago and hurled their hot rock masses to the surface of the earth. Today they are long gone, but as mountains and heights of the low mountain range they are still clearly recognizable.
Incidentally, the longest mountain range on earth is of volcanic origin - it is sunk in the sea: the mid-Atlantic ridge extends over a full 20,000 kilometers through the middle of the Atlantic Ocean. The mid-Atlantic ridge is one of the mid-ocean ridges. These lie where two oceanic plates move away from each other. A gap forms on the sea floor between the two plates, from which hot magma gushes. Long and high mountain ranges form under water at such plate boundaries. In some places their peaks protrude above sea level. This is where Iceland, the Galapagos Islands and the Azores see the light of day.
30 kilometers south of Iceland, an island was born out of the sea. A young volcano has been spewing fire and ashes here since November 14th. Its lava masses have already given rise to an island 40 meters high and 500 meters long.
White-gray ash clouds hang in the sky and darken it. Fine volcanic rock patters the area, every lava discharge is accompanied by the rumble of thunder. The smoke column caused by the volcanic eruption rises 10 kilometers. And an island off Iceland's south coast continues to grow.
The eruption of the underwater volcano came unexpectedly, but not without its harbingers. Seismologists had already measured smaller earthquakes a week earlier in the capital Reykjavik - signs that a lot is happening at the plate boundary of the Mid-Atlantic Ridge. In addition, a research ship had found that the sea was warmer than usual. And residents of the nearby coastal region believed they smelled hydrogen sulfide. When the volcano erupted on the seabed at a depth of 130 meters, it initially went unnoticed. Its explosions were weakened by the water pressure. But as it grew, it approached sea level and finally broke through it, spitting wildly. That was the birth of an island in Iceland.
The new island off the south coast already has a name: it is called "Surtsey" after Surt, the giant of fire. A Nordic legend tells of him that he hurls fire and destroys all life with his glowing sword.
How Iceland came into being
Iceland is actually nothing more than the peak of a huge mountain range in the Atlantic: The mid-Atlantic ridge, which stretches from north to south through the entire Atlantic, is almost 20,000 kilometers long. At the height of Iceland, the North American and Eurasian plates drift apart, by about two centimeters every year. Where they spread, hot magma penetrates from the interior of the earth to the surface. These volcanic eruptions have been piling up mountains underwater for millions of years and caused Iceland to appear above sea level 17 to 20 million years ago. These volcanoes are still active today. And now they have born another island: Surtsey.
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 sea level.
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.
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.
The Laacher See glitters quietly in the sunlight. But the idyllic tranquility is deceptive: Hell on earth raged here 13,000 years ago - this landscape is the result of a volcanic eruption. And scientists expect the Eifel volcanoes to erupt again. It is only unclear when ...
The first volcanic eruptions occurred in the Eifel 600,000 years ago. The series began with the volcanoes in the West Eifel: ash volcanoes, craters and maars formed here. Later the volcanic area of the Eifel expanded to the southeast. Then the volcanoes came to rest.
However, this calm ended with a bang, almost 13,000 years ago: A huge explosion in the interior of the earth tore a large hole in the landscape. Meter-high streams of mud rolled down into the valley. The Rhinelander were completely surprised by this catastrophe - as shown by skeletons that have been found in the strata of the earth. The Laacher See was created at the site of the volcanic explosion. The last volcanic eruption in the Eifel took place 11,000 years ago, when the Ulmen Maar was formed.
Smaller earthquakes between Laacher See and Koblenz indicate today that the earth has not yet finally come to rest. The quiet bubbling in the Laacher See also testifies to volcanic activity. The carbon dioxide bubbles that rise from the water here come from the hot volcanic subsoil. The Eifel is on the move - will it surprise us soon with a new volcanic eruption? A question that science cannot answer either.
Volcano researchers have observed the behavior of ants and want to use it to develop an alarm system for volcanic eruptions. They believe ants will notice an impending volcanic eruption early on and leave their nests. The reason they suspect is that ants are fleeing the poisonous gases that escape during volcanic activity. However, biologists don't really believe in this idea: They have noticed that ants move several times a year, too.
But the volcano experts continue to research and observe more than 2000 anthills in the Eifel. Because, although the Eifel is volcanic, there are only a few fixed measuring stations that could warn of a volcanic eruption. And the volcanoes in the Eifel, the researchers suspect, will not sleep forever!
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 primarily 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. Often water 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.
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. An ash cloud 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. However, none of this happens overnight, 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 rim of the crater 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.
Consequences of volcanic eruptions
Volcanic eruptions can have dire consequences. Hail of rock, ash rain, poisonous gases and glowing lava flows have already killed hundreds of thousands of people. During the eruption of Vesuvius in 79 AD alone, during which the cities of Pompeii and Herculaneum were buried, around 5000 people died. An entire city was also wiped out in Colombia: the eruption of the icy Nevado del Ruiz volcano in 1985 triggered several mudslides. The avalanches buried the city of Armero, 47 kilometers away, and 25,000 residents.
Tsunamis can also arise from volcanic eruptions: The explosion on the volcanic island of Krakatau in 1883 caused a tidal wave that flooded regions thousands of kilometers away. Even earthquakes sometimes follow such an explosive volcanic eruption. During these quakes, built-up tensions in the earth discharge.
In Iceland, the eruption of over a hundred volcanoes in the Laki Fissure in 1783 triggered a famine. The outbreak released toxic gases into the air. The poison settled and contaminated the sheep pastures. The animals died from the poisoned food, an estimated ten thousand people because of the famine that followed.
The “laki fires” on Iceland were followed by a cooling that could still be felt far away. The rising ash cloud darkened the sky, strong winds came up and the temperature dropped. The whole of Northern Europe then experienced an unusually cold winter. In fact, volcanic eruptions change the climate. This is mainly due to the sulfur gases emitted, which form fine sulfuric acid droplets in the air that float in the atmosphere for a long time. The sunlight is scattered by the droplets and partly reflected back. This can lower the average temperature all over the world.
Where on earth are there volcanoes?
There are not volcanoes everywhere on earth, they are very unevenly distributed. Most of them lie along the plate boundaries - where tectonic plates rub against one another, where one plate dips under the other or where they drift apart. At these fractures, hot magma can swell from the earth's interior to the surface.
A particularly large number of active volcanoes can be found around the Pacific Ocean, for example Mount St. Helens in the USA, the Popocatepetl in Mexico and the Bezymianny in Russia. They are all part of an approximately 40,000-kilometer-long chain of volcanoes, the Pacific Ring of Fire. Because all around the Pacific, the Pacific plate is pushed under other plates. When the Pacific plate descends, the earth's crust is melted. Magma collects in these places and volcanoes form above them.
Volcanoes are not just above, but also below sea level - and most of them are still completely unknown to us. These underwater volcanoes are called “seamounts”. They include the volcanoes of the Mid-Atlantic Ridge, a huge underwater mountain range in the Atlantic. There plates drift apart and therefore magma rises constantly to the top. Sometimes the volcanoes also reach the surface of the sea: in 1963, a new volcanic island - Surtsey - grew out of the sea within a few months to the south of Iceland. Iceland itself was also formed by volcanism on the Mid-Atlantic Ridge.
The situation is completely different with the volcanoes in Hawaii: They are located far away from plate boundaries, in the middle of the Pacific plate. But below Hawaii the earth's mantle is particularly hot; this is called a "hotspot", a hot spot in the earth's mantle. Hot magma rises here and can easily break through the crust - this creates a volcano. Whenever a plate of the earth's crust slides over a fixed hotspot, a new volcano continues to dig its way through the crust. This creates a whole chain of volcanoes, such as the chain of islands in Hawaii. The Kilauea volcano is currently active there because it is currently above the hotspot.
Where plates diverge
A long, deep crack gapes in the earth and is getting wider and wider. Huge forces are tearing the earth's surface to pieces: the East African Rift runs along this break through the continent. Africa began to break up here 20 million years ago. Hot magma from the interior of the earth pushed upwards and tore the earth's crust apart. Since then, the pieces of crust have drifted apart, by about an inch every year. The fact that the earth is very active here can also be seen from the many volcanoes that rise along the rift. Should seawater ever penetrate, the East African Rift will become an ocean. Something similar happened in the Red Sea. The African and Asian continental plates have been separating there for 25 million years. The resulting crack was flooded by sea water.
There where continental Crust breaks apart, one arises Rift valley. Where against it oceanic When pieces of crust move away from each other, mountains grow on the sea floor: the Mid-ocean ridges. They consist of magma that seeps up from the Earth's mantle through the oceanic crust. New sheet material is formed here. It presses itself, so to speak, between two oceanic plates and solidifies to form basalt rock that piles up further and further.
In some places the mid-ocean ridges protrude as islands above sea level. Iceland, for example, and the still young Icelandic island of Surtsey are nothing more than parts of the Mid-Atlantic Ridge. The oceanic crust is constantly growing here due to the replenishment of solidified rock. It not only grows in height, but also to the sides. The two oceanic plates are pushed outwards. Because they spread apart in the process, one also speaks of one Divergence zone.
In this way, new seabed is created and the ocean is slowly getting wider - but only a few centimeters a year. But modern satellites can measure the continents with millimeter precision. From the movement one can calculate that the Atlantic has been 25 meters wider since Columbus' crossing in 1492.
But because the earth as a whole is not getting any bigger, the increase in the seabed has to be compensated for elsewhere. This happens where the oceanic crust is submerged under the continental crust: While the Atlantic continues to grow, the Pacific slowly sinks under the plate margins of America and East Asia.
High and low mountain ranges
The Feldberg in the Black Forest is particularly popular with winter sports enthusiasts. Because of its height of 1493 meters, it is easy to ski here. But the Black Forest, although it has high mountains, is one of the German low mountain ranges. The Alps, on the other hand, are high mountains. But what is the difference between low and high mountains?
The simplest answer is obvious: they differ in their height. High mountains start at 1500 - some say 2000 - meters above sea level. So there are mountains whose peaks protrude far above the tree line. Another typical feature of high mountains is that they are formed by glaciers and have steep mountain walls.
Low mountain ranges, on the other hand, have neither glaciers nor steep slopes. Your landscape is rather hilly and rounded. This is due to the fact that it was created much further back than that of the Alps. Originally, they too were piled high in the mountains - more than 300 million years ago. But unlike in the Alps, there has been no uplift in the low mountain ranges for a long time. They are only removed and their shapes are rounded. Some of them are already so badly weathered and worn that only the trunk remains of the former high mountains: the trunk mountains. These include, for example, the Ore Mountains and the Fichtel Mountains.
During their long history, the low mountain ranges have been constantly redesigned. Even the unfolding of the Alps did not leave them without a trace. The forces of the clashing plates put the old hulls of the low mountain range under a lot of pressure. Because of its old age, however, the rock had become so firm and rigid that it could not be folded any further. Instead, like a gigantic sheet of ice, it shattered into huge clods. Some sank, others began to rise. Sinking clods became deep trenches, rising clods developed into high plateaus. The landscape that emerged from it are broken clod mountains like the Harz. Its highest mountain, the Brocken, is 1141 meters high. That is not enough for the high mountains, so that the Harz clearly belongs to the low mountain ranges.
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