CLIL/The world's main volcanoes
Mount Vesuvius[edit | edit source]
Vesuvius is located on Italy's south-west coast in the province of Naples. It formed in the crater of the ancient Somma volcano, that exploded in 79 AD causing the destruction of the Roman cities of Herculaneum and Pompeii.
Though the volcano's last eruption was in 1944, it still represents a great danger to the cities that surround it, especially the busy metropolis of Naples.
The African and Eurasian tectonic plates
Mount Vesuvius is located above the subduction of the African plate that slowly moves northward beneath Italy. This subduction also forms other volcanoes like Mount Etna (Sicily) and Stromboli (Eolie islands). The melting of the African plate creates the high-viscosity magma that accumulates in Vesuvius’ caldera.
Type of eruption and magma
Vesuvius is characterized by explosive eruptions. This kind of eruption is determined by the high gas pressure in the magma chamber, caused by the interaction between hot magma and under-ground water. Its lava is a viscous lava with a high concentration of silica that resists flowing.
Its most famous eruption was in 79 AD, which buried the cities of Herculaneum and Pompeii killing about 16.000 people. Ash , mud and rocks in the air dropped and covered the two villages. We remember this catastrophe because it has preserved amazing details such as Roman clothes, human faces, buildings and paintings. In its history we know of about eight destructive eruptions. Nowadays Vesuvius is in a state of quiescence, because its last eruption was in 1944 during the Second World War.
Kilauea[edit | edit source]
- WHAT IS KILAUEA?
Kilauea is the youngest volcano on the island of Hawaii but also the most active one in all the world.
It’s a shield volcano and its name comes from the Hawaiian language and means “spewing”or “spreading” because it has the peculiarity of being subjected to frequent and uninterrupted eruptions of lava: scientists believe that the cause of this phenomenon could be its position above a hot spot in the middle of the Pacific plate, from which magma rises through the mantle creating a great chain of volcanoes. This is also the way Hawaiian islands are formed.
- KILAUEA'S LOCATION
It’s situated on the southwestern flank of Mauna Loa on the Big Island of Hawaii, meaning that it was formed by layers of lava from continual, effusive and non explosive eruptions.
- VOLCANIC ACTIVITY AND LAVA
For many years Kilauea was considered to be nothing compared to the giant Mauna Loa, but recent research has proved that it has its own magma-plumbing system, extending to the surface from more than 60 km deep in the earth.
During the eruptions Kilauea spreads giant amounts of lava that can reach approximately 1000 C°: it can create sudden lava fountains and lakes, causing the ashes to fall out and solidify; also it can form new volcanic cones or destroy the old ones.
Although its eruptions are effusive, when the lava reaches the cold ocean water it explodes, creating enormous steam clouds.
Both pāhoehoe and ʻaʻā lava erupt from the volcano; because of its high activity this zone has a high risk of seismic phenomenon.
- HISTORY AND CURRENT SITUATION OF KILAUEA
It's 1247 meters high. The current eruption, which is the longest happened in the last two centuries, began on January 3 in 1983.
It should be said that this uninterrupted spreading of lava has frightened the Hawaiian people because it is gradually reaching the villages, of which the first houses have been burned and destroyed. Also, the steam explosions created in contact with the water have caused a great number of deaths.
Because of the constant activity of the Kilauea Volcano, there are semi-frequent acid rains. However, Kilauea has caused the development of its own special ecosystem which is constituted by particularly colorful bird species that live in the wet forest, and endangered sea turtle species.
Mount St. Helens[edit | edit source]
- WHAT IS MOUNT ST. HELENS?
Mount St. Helens is an active stratovolcano (or composite volcano) 2.549m high, that is built up of many layers of hardened lava (or simply called basalt), volcanic ash and tephra (which are the pyroclasts that are blown out of the volcano during an eruption).
- WHERE IS IT?
Mount St. Helens is located in the state of Washington (North-West of the USA) and it is part of the Cascade Volcanic Arc; a segment of the Pacific Ring of Fire. The meeting of two tectonic plates, causes a process called 'subduction' during which the oceanic plate goes under the continental plate. In fact the Ring of Fire was born by the collision between the Pacific plate and the continental plate.
- WHAT ABOUT ITS BIRTH?
Mount St. Helens began its growth (in the Pleistocene age about 40.000 years ago), when the little Juan de Fuca (oceanic plate) slid under the North American plate (continental plate) along the subduction boundary. As the oceanic plate descended, the rock melted because of the high temperatures and made magma. As a result, in the magma chamber, pressure rose and the liquid magma searched for a fissure in the Earth’s crust through which it could flow. St. Helens’ magmatic system has evolved from a relatively simple to more complex one, as the volcano grew: it was born as a “shield volcano”, that erupted mafic lava1, but 500 years ago Mount St. Helens began to erupt felsic lava2 and it became a stratovolcano. As a consequence of this change, nowadays it presents layers of basalt and andesite3, on which several domes of dacite4 have dropped off.
1 A kind of lava rich in iron and magnesium that has got low viscosity
2 A type of lava which is rich in silica and has got high viscosity
3Hardened mafic lava
4Hardened felsic lava
- WHAT KIND OF ERUPTION?
Mount St. Helens is the most active volcano in the Pacific Northwest and is well known for its ash explosions and pyroclastic flows : it has had four extended periods of volcanic activity. It has produced both explosive eruptions of volcanic tephra and relatively quiet outpourings of lava.
1980: THE MOST IMPORTANT ERUPTION
This eruption is the deadliest and most economically destructive volcanic event in the history of the US. It was preceded by a two-month series of earthquakes and steam-venting episodes, caused by an injection of magma at shallow depth below the volcano (as the image below shows). When it erupted, it released the equivalent of 1,600 times the size of the atomic bomb dropped on Hiroshima. It ejected more or less 3km radius of material and killed 57 people. At the end of the eruption, the volcano appeared destroyed: 2,5 km cubical of the north flank had disappeared.
|Most famous/catastrophic eruption
|Mount St. Helens
|Shield volcano (then), Stratovolcano (now)
Mount Etna[edit | edit source]
Location: Sicily, Italy
Elevation: 3.329 m
Kind of volcano: both shield and stratovolcano
Craters: there are five craters and the new south-east one is currently the most active.
Welcome to Mount Etna
Mount Etna is one of the most famous volcanoes in Italy. It is collocated on the east coast of Sicily, in the hinterland of Catania's Province. Some years ago, in June 2013 it was added to the list of UNESCO World Heritage Sites.
Mount Etna has a very heterogeneous vegetation depending on the climatic changes due to altitude (citrus and oak trees, birches,vineyards, olive trees and pistachio). Obviously, near the craters at a high attitude there is no vegetation.
Damages caused by the eruptions
The fall of lava and ash after a violent eruption of the volcano usually causes serious environmental damage with consequent inconveniences for the native population. Due to this, airports close, roads are impracticable and the agriculture is compromised. Moreover, ash and other substances released by the eruption, may also damage people's health in various ways (skin rashes, respiratory tract).
Mount Etna was born as a shield volcano because of the subduction of the African plate under the Eurasian plate but in time it turned into a stratovolcano. A shield volcano in fact is not supposed to erupt with explosions (it should have "effusive" eruptions) so when it started a persistent activity of explosive eruptions in 1966 its classification changed. Mafic lava is less viscous(runnier) than felsic lava due to a lower silica content, this causes non-violent eruptions while Felsic lava is mainly found at convergent zones (areas of colliding plates) and has a high silica and water content which causes the lava to be highly viscous and causes very violent eruptions. So in mount Etna we can see both these types of lava according to the type of eruption.
The explosive activity is produced by acid magmas (distinguished by the high presence of gasses and silica), while the effusive activity is produced by basic magmas (characterized by gasses and less concentration of silica). In the effusive eruptions we are supposed to see only lava, but in the last years, the explosive eruptions have been becoming more common. This kind of eruption can produce "bombs" or lapillus and ashes which go very high in the sky up to a hundred meters. The formation of the pyroclastic materials is caused by the gasses that create air bubbles in the magma of different sizes. The most famous activity of mount Etna is the “Strombolian activity” (from the name of the namesake volcano) where we can see the spectacular expulsion of magmatic bodies in the sky. When this activity increases, “lava fountains” are created where lava is thrown up continuously.
Active volcano: a volcano that is currently erupting or just about to erupt.
Effusive eruption: a relatively gentle, non-explosive volcanic eruption.
Eruption: the release of magma onto the Earth's surface. Usually an eruption is accompanied by the release of gases as well.
Explosive eruption: a volcanic eruption that releases large amounts of gas, so that mama is violently thrown up into the air.
Lava: molten rock that has been erupted onto the Earth's surface. Magma becomes lava once it emerges on the surface.
Magma: molten rock found under the Earth's surface.
- Where is Mount Etna?
- Why is it so famous?
- What kind of volcano is Mount Etna?
- What kind of eruption does it have?
- And what about lava and magma?
- How does it behave?
- What about its vegetation?
Erta Ale[edit | edit source]
- WHERE IT IS
Erta Ale is the most famous volcano situated in the Erta Ale volcanic range in Ethiopa. Its name means "smoking mountain" in the local language.
- WHAT TYPE OF VOLCANO IT IS
It is a shield volcano, so it is not very high, only 613m high, but it has gently sloping sides with a large base of 40 km.
- HOW ERTA ALE WAS FORMED
It was formed by the Arabian plate and the African plate that pulled away from each other. In fact, there is a divergent boundary between them.
- VOLCANIC ACTIVITY
It is an active volcano and the last eruption was in 2009. It erupts mafic lava, which contains iron and magnesium. This kind of lava is characterised by low-viscosity. That means that the lava flows down slowly and calmly. For this reason, Erta Ale is an effusive volcano and it does not explode when it erupts.
- ERTA ALE IS A PARTICULAR VOLCANO
Erta Ale is one of the few volcanoes on the Earth that has a lava lake. There are pieces of basaltic rock that float in it like icebergs in the ocean.
- AN UNKNOWN VOLCANO
Scientists do not know much more about Erta Ale, because it is situated in one of the most inhospitable places on Earth and the native people are not friendly towards foreigners.
Review questions[edit | edit source]
- Describe the structure of a volcano
- Describe the main types of volcanoes: shield, stratovolcanoes (cone shaped), caldera.
- Explain how volcanoes are formed
- What's the difference between magma and lava?
- Where do the majority of volcanoes occur and why?
- What is the Pacific Ring of Fire?
- Explain the volcanic hot spot.
- Explain the difference between an explosive volcano and an effusive volcano
- Can you explain the three names of the non-explosive lava?
- Describe the main characteristics of the following volcanos: Etna, Vesuvius, Kilauea, St. Helens, Erta Ale.