20180420 【 Volcanoes 】

Volcanoes
They're beautiful and dangerous

Volcanoes inspire fear and curiosity, fables and legends.

Millions of people visit them ever year.

But what are they, and why do they capture the imagination?

You can trace the word volcano to the name of a small island near Italy.

In Italian, volcano means "burning mountain," and ancient Romans believed it was a chimney for an underground forge.

Today we call any crack or vent in a planet's crust a volcano.

When you picture a volcano, you might think of the classic steep symmetrical cone that sweeps up to a sharp peak , like Mount Fuji in Japan or Arenal in Costa Rica.

But volcanoes take many different forms on land and underwater!

Between the molten core of the earth and the relatively thin crust to the planet is a thick layer of solid rock, or mantle.

Extremely high temperatures and pressure can melt the rock in the mantle,which becomes magma.

When magma rises to the surface through the Earth's crust, it's called lava.

As lava flows, cools and mixes with other materials, it forms the shape of volcanoes.

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forge
Some of the country's finest knives are made in this forge.
These hammers were forged by the hands of a skilful toolmaker.
The smuggler used a forged passport to try and get into the country.

asymmetric
symmetry
asymmetry

trial by fire
I'm going through trial by fire.

molten
Molten glass can be formed into different shapes when it's still soft.

magma
From above the volcano, you can see the magma being squeezed upward toward the crust.

lava
The whole village was covered by molten lava in the matter of seconds.