Lesson 9 How volcanoes are formed. Volcanic activity.

Parts of a volcano: 1. Large magma chamber 9. Layers of lava emitted by the volcano 2. Bedrock 10. Throat 3. Conduit (pipe) 11. Parasitic cone 4. Base 12. Lava flow 5. Sill 13. Vent 6. Branch pipe 14. Crater 7. Layers of ash emitted by the volcano 15. Ash cloud 8. Flank

There are two main processes.

1. Volcanoes are made when two tectonic plates come together. When these two plates meet, one of them (usually the oceanic plate) goes under the continental plate. Afterwards, it melts and makes magma (inside the magma chamber), and the pressure builds up until the magma bursts through the Earth’s crust.

2. The second way is when a tectonic plate moves over a hot spot in the Earth's crust. The hot spot works its way through the crust until it breaks through. The places known as hot spots in geology are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere.

Volcanic activity

A traditional way to classify or identify volcanoes is by pattern of their eruptions. Those volcanoes which may erupt again at any time are called active. An active volcano is currently erupting, or it has erupted in the last 10,000 years. Those that are now quiet called dormant (inactive). A dormant volcano is "sleeping," but it could awaken in the future. Those volcanoes which have not erupted in historical times are called extinct. An extinct volcano has not erupted in the past 10,000 years.

Edinburgh Castle on the site of an extinct volcano, c. 1581

Memorize the words: bedrock – корінна, підстильна порода conduit – підвідний канал sill – пластова інтрузія to emit – випускати, випромінювати flank – бік, сторона throat – горло lava flow – лавовий потік vent – вхідний (вихідний) отвір to burst – прориватися, вибухати to feed (fed, fed) – забезпечувати, постачати, to identify – ототожнювати(ся) pattern – зразок currently – зараз, у цей час dormant – бездіяльний, що спить extinct – згаслий

Answer the questions:

1. By what two main processes are volcanoes formed?

2. When two tectonic plates meet, which of them usually goes under the other?

3. What makes magma within the magma chamber?

4. What are hot spots thought to be?

5. What are the three types of volcanoes according to the pattern of eruption?

6. Which volcanoes are called active?

7. Why do we say that a dormant volcano “is sleeping”?

8. Which volcanoes do we call extinct?