VOLCANOES

Elisa Turiello Hernández

2º Bachillerato Bilingüe

Introduction

Volcanoes (word that comes from the ancient Roman god Vulcano) are ruptures in the planet’s surface. From this ruptures magma, ash and gases are or had been expelled. Volcanoes communicate directly the superficial solid Earth’s crust with the lower one.

Definitions

MAGMA: magma is the igneous mass made by molten rock inside the Earth. Saying it in a easier way, magma is a mixture made generally by molten rock, located inside the Earth.

LAVA: lava is the molten material that floods out of a volcano when it erupts, forming fire rivers.

Even easier: the difference between magma and lava is that the magma is inside the Earth and the lava has been already expelled.

Volcanoes structures

A volcano is formed by different parts. We have the magma chamber, a compartment communicated to the surface by a kind of pipe called vent. The magma chamber is the place underground where we can find the magma that will be expelled from the crater, the volcano’s “mouth”. The crater the higher place of the volcano and it’s where the volcano as we know it (the “mountain” that we see) expels the lava, that floods by the mountainside.

Types of magma

The type of magma usually is what makes volcanoes erupt in a way or in another. Generally it depends on the magma’s viscosity (we must understand “viscosity” as the capacity of the magma to flow). If the magma is very viscous, the eruption will be very hard. That is because viscous magma offers resistance to exit and when it finally is expelled, the eruption in harder. The viscosity of magma depends on the silica content of the magma and its temperature. If there is a lot of silica, magma won’t be fluid at all, and so with temperature (if the temperature is high, magma will be more fluid).

Types of lavaThere are three kind of lava, but number three is not very important.

• Pāhoehoe LavaIt has a more or less smooth and plain surface. It’s very fluid and it moves quickly.

• Aʻā LavaIt is characterize by a very irregular surface. It’s very viscous and sticky, and it moves very slowly.

• Pillow LavaIt solidifies under the water, and because of that the lava acquires a characteristic oval shape. It’s because of that because it’s called “pillow lava”, because (with a lot of imagination) it looks like a rock pillow.

Pahoehoe lava

Aʻā lava

Pillow lava

Differences between an extinct volcano and an actives one

Well, obviously an active volcano expels lava from his crater and an extinct one doesn’t do anything, is just like a mountain with a hole. But it’s more complicated than that, and it is not clear at all. All I can say is that someone says that it depends on the time (for example if a volcano has erupt 25.000 years ago it is not active, but if it has erupt 23.000 years ago, it is). Other ones say that it depends if the volcano will in a future erupt again or not. This part is not very clear, solo what can I say being sure is…

This is an active volcano

This is NOT an activ volcano

Types of volcanic eruptions

The main ones are:

• Hawaiian: lava is accumulate in the volcano vent and then it overfloods by the crater. The lava is very liquid, and it falls very quickly by the mountainside forming lava rivers.

• Strombolian: it takes place when air bubbles are formed in the magma. When this bubbles become bigger, they pull the lava out of the crater and it falls down the mountainside. The lava is not very viscous, but it isn’t as liquid as Hawaiian one.

• Vulcanian: tha magma that we see in these eruptions is very viscous. Because of that it moves very slowly (tha lava is ʻAʻā type).The explosions are very hard and they cause a high quantity of ash and gas.

• Peléan: they are characterize by the high quantity of gases, ash, dust and lava that is expelled. The lava of this kind of eruptions is usually very liquid and for this reason it moves very quickly. This type is one of the worst.

• Plinian or Vesuvian: the eruption of this kind is started too in the magma chamber, where gases are stored and then released, pulling lava out of the volcano. This lava floods easily by the mountainside because it’s not very viscous and it reaches a very high speed. A lot of gas is expelled, and it may forms an ash cloud, that can cause ash and rocks rain. This occurred on 79 a.C. in Pompei, with Vesuvius’ eruption.

Vesuvio, Italia (Napoli)

That’s the double crater of the Vesuvio.

Photo of an eruption of the Vesuvio, which took place on the Second War World.

A drawing of the Vesuvio inspirate on the eruption that took place on 79 a.C. on Pompei, destroying the city.

Etna, Italia (Sicilia)

Of course in perpetual activity.

Laghi di Monticchio

They are two lakes in a extinct volcano crater. This water is a natural source of sparkling water.

And now, watch the video. I hope you like it.

THE END