Earthquakes and Volcanoes — Plate Boundaries, the Ring of Fire and Which Scale Measures What

One Cause, Two Headlines

Earthquakes and volcanoes look like two separate disasters. They are two symptoms of one cause: the earth's rigid outer shell is broken into plates, and those plates are moving — a few centimetres a year, endlessly, in different directions.

Wherever two plates meet, stress builds along the join. Released suddenly, it is an earthquake. Where one plate is dragged down and melts, the molten rock finds a way up and it is a volcano. That is why a world map of earthquakes and a world map of volcanoes are almost the same map.

Examiners like the chapter because it is dense with named, checkable facts: three types of boundary, three types of seismic wave, three seismic belts, two rival measuring scales. Almost every wrong answer in this chapter is a real fact filed in the wrong slot — so learn the slots, not just the facts.

1. Which type of seismic wave cannot travel through liquids?

2. Which of the following is India's only active volcano?

3. The point on the earth's surface lying directly above the origin of an earthquake is called the

4. The San Andreas Fault in California is an example of which kind of plate boundary?

5. Stromboli, known as the "Lighthouse of the Mediterranean", is located in which country?

6. Which scale measures the intensity of an earthquake — that is, the shaking and damage actually observed — rather than the energy released?

7. The Mohorovicic discontinuity separates which two layers of the earth?

8. Roughly what share of the world's active volcanoes lies within the Circum-Pacific belt, the Ring of Fire?