Lesson 8

Volcanology. Types of volcanoes.

The volcanoVesuvius erupting in 1872. Mount St. Helens erupting on May 18, 1980

Volcanology

Volcanology (also spelled vulcanology) is the study of volcanoes, lava, magma and other related geology. The term volcanology comes from the Latin word Vulcan, the Roman god of fire.

Volcanologists look at volcanic eruptions; collect material from the eruptions, such as ash or pumice, rock and lava samples.

A volcano is a mountain where lava (hot, liquid rock) comes from a magma chamber under the ground. Most volcanoes have a volcanic crater at the top. When they are active, materials pour out of it. This includes lava, steam, gaseous compounds of sulphur, ash and broken rock pieces. Volcanoes erupt when magma and pressure come together, and the pressure blows off the top of the solid rock, and the magma pours out. Volcanoes are also found on planets other than Earth, like the Olympus Mons on Mars.

Types of volcanoes

The lava and pyroclastic material that comes out from volcanoes can make many different kinds of land shapes. There are three basic kinds of volcanoes.

1. Shield volcano

Shield volcanoes are built out of layers of lava from continual eruptions (without explosions). Because the lava is so fluid, it spreads out, often over a wide area. Shield volcanoes do not grow to a great height, and the layers of lava give the volcano gently sloping sides. Shield volcanoes can produce huge areas of basalt, which is usually what lava is when cooled.

Even though their sides are not very steep, shield volcanoes can be huge. Mauna Kea in Hawaii is the biggest mountain on Earth. If it is measured from its base on the floor of the sea, Mauna Kea is even taller than Mount Everest, the tallest mountain on land.

2. Caldera volcano Caldera is a large volcanic crater, typically one formed by a major eruption leading to the collapse of the mouth of the volcano.

Caldera volcanoes are small volcanic cones that are made by pyroclastic material (the pieces of rock that come out because of an explosion) after fairly explosive eruptions. The pyroclastic material makes rather steeper slopes and a narrower base than shield volcanoes. Caldera volcanoes usually erupt for only a short time and often are gathered together, usually on the sides of shield and composite volcanoes. They erode quickly because the pyroclastic particles are not stuck together firmly by lava.

3. Composite volcano

Composite volcanoes, sometimes called 'stratovolcanoes', are one of the most well-known types of volcanoes. They are made by explosive eruptions of pyroclastic material, after which lava quietly pours out. Both types of eruptions make layers both of pyroclastic material and lava. Composite volcanoes, like Japan's Mount Fuji, have big bases and steep sides that get steeper and steeper as it goes near the top.

Memorize the words:

eruption – виверження pumice – пемза chamber – камера steam – пара compound – сполука pyroclastic – пірокластичний shield – щит fluid – рідкий, рідина steep – крутий, стрімкий caldera– кальдера cone – конус composite – змішаний

Answer the questions:

1. Where does the term volcanology come from?

2. What is a volcano?

3. What materials come out of volcano?

4. What are the three basic kinds of volcanoes?

5. What is a shield volcano?

6. Why is caldera volcano quickly eroded?

7. How are stratovolcanoes formed?