3rd Session: Volcanoes. Video: What is a volcano?

Lesson 2: Internal forces of the Earth: earthquakes and volcanoes

3rd session: Volcanoes.

3. Watching the video: “What is a volcano?”

Watch this video paying atention to the explanation. You have enough time to watch the video two times if you want.

You have 15 minutes.

What is a volcano?

Hi! I'm Emerald Robinson in this “what is” video we're going to take a closer look at volcanoes.

A volcano is a vent in the Earth's crust where molten rock, gas and steam are wrapped. On to the planet's surface volcanoes are most common in areas of seismic activity such as where the Earth's continental plates pull apart or collide. Volcanoes also occur far from plate lines in hot spots where the Earth's crust melts. Hawaii's volcanoes are examples of such hotspots volcanoes exist on all continents except Australia and also form in ocean trenches.

The molten rock beneath the Earth's surface is called magma. Lava refers to the magma ejected from a volcano. Magma’s mineral composition determines how its lava behaves. Mafic Magma contains high concentrations of iron-rich minerals in magnesium. Mafic Magma flows freely producing lava capable of traveling some distance before cooling and solidifying. Felsic Lava contains silica and produces thicker lava.

Thick lava can't travel as far. Because felsic lava solidifies quickly, it produces the classic cone like volcanoes which are called composite volcanoes. Felsic magma can also solidify beneath your surface creating magma chambers where hot gases and magma build up. This causes composite volcanoes to explode violently. Mafic lava produces a broad low-profile volcano called a shield volcano. Instead of explosive eruptions, shield volcano eruptions calls lava to flow in all directions. Mount Aloha as shield volcano, on the Big Island of Hawaii, is the world's largest volcano rising 13 thousand six hundred and eighty feet above sea level.

Seismologists classify volcanoes as active, dormant, and extinct. Active volcanoes are either erupting or likely to erupt in the future. Dormant volcanoes have not erupted in recent history. Extinct volcanoes have exhibited no activity for long periods and are unlikely to erupt in the future. And that's the hot news on volcanoes.

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