WHAT CAUSES VOLCANOES?

Mrs. Johanna Fabre Science9th gradeLogos Academy

To understand what causes volcanoes, you need to understand how the earth is made up

Made up of solid rock.60km thick under mountain chains, but just 5km under the oceans

a thick layer of molten rock (called magma)

made up of an outer

liquid layer

solid centre.

The Earth

Temperatures inside the earth are very high. The planet is like a huge fiery ball of hot molten rock, surrounded by a few kilometers of relatively cool, hard rock – the crust.

Because heat rises, the magma in the earth’s mantle has to find a way to rise upwards through the crust above it.

A lot of energy is released with it. This is why many eruptions also produce huge quantities of gases and dust.

Magma sometimes rises under enormous pressure, so it not only finds cracks in the earth’s crust, it can also create them.

Tectonic plates and volcanoes The earth’s crust is its thinnest layer.

It is broken up into large pieces, called tectonic plates.

Each plate contains some continental crust (land) and some oceanic crust (sea-bed). Huge currents of molten rock circulate deep in the mantle, causing the plates to move about very slowly on the earth’s surface.

The subducting plate contains iron and other compounds, when it melts releases carbon dioxide, which mixes with magma and causes gases…

and this is when magma starts to go upward…. Just like our volcanoes in lab!!!

FACTS Cocos and Nazca Plates meet in the vicinity and spread or

move away from each another at a rate of a few centimeters each year, thus creating the spaces for those mantle plumes to form.

Isabela and Fernandina islands are the most recent ones with less than a million years of existence. The southeasternmost island of Española boasts of the oldest rocks ( some 3 million years old ) and this coincides with the direction of the movements of the plates.

The islands each year move 2 to 7 cm closer to the South American continent riding on the Nazca Plate which subducts the American Plate.

THEORY The islands were never connected to any continent but it

is believed that an eroded underwater ridge called the Carnegie Ridge was once above water and is part of the same geological event. This ridge is halfway between the current islands and the South American mainland and would explain more satisfactorily, how some of the animals and plants could have arrived to Galapagos.

Classwork

Write a 150 words essay on your notebook:

How did the Galapagos form? Discuss both plate movement and volcanic activity. Be specific in your answer!

Thanks for you participation!