Volcanoes: Mountains with a Difference
1. Introduction
Volcanoes are mountains, but they are different from other mountains because they have a hole at the top from which hot molten rock, ash and gas can escape. Over 700 million people live within reach of an active volcano, making them one of the most dangerous natural hazards. The main task of scientists is to determine the time and place of an eruption to minimize its danger and damage.
2. Plate boundaries
Most volcanoes occur near plate boundaries. Plate boundaries are areas where Earth’s crust is being created, destroyed or moved. There are three types of plate boundaries:
– Divergent boundaries: Also known as constructive boundaries, these are areas where new crust is being created as the plates move apart. The classic example is the Mid-Atlantic Ridge where the North American and Eurasian plates are moving apart.
– Convergent boundaries: Also known as destructive boundaries, these are areas where crust is being destroyed as the plates collide. The classic example is the Andes mountain range, where the South American plate is colliding with the Nazca plate.
– Transform fault boundaries: These are areas where plates are sliding past each other. The classic example is the San Andreas fault in California, USA.
3. The lithosphere
The lithosphere is the outer solid layer of Earth that includes the crust and the upper part of the mantle. It is broken into pieces called plates that move around on the underlying molten mantle. The Earth’s mantle is made of hot rock that slowly flows like plastic. The lithosphere sits on top of this mantle and moves around on it like ice floats on water.
4. Earthquakes
Earthquakes happen when plates move and grind against each other. The force creates stress in rocks that can build up for a long time until they finally break, causing an earthquake. Earthquakes can also be caused by volcanic eruptions, landslides and human activity such as mining or dam construction.
– Measuring earthquakes
Earthquakes are measured using seismometers. Seismometers work by detecting ground shaking and measuring its strength and duration. The strength of an earthquake is measured using the Richter magnitude scale, while its duration is measured using the Modified Mercalli Intensity Scale.
– The Richter magnitude scale
The Richter magnitude scale was developed in 1935 by Charles Francis Richter to measure the strength of earthquakes. It is based on the amplitude (height) of waves recorded on a seismogram (a graph that shows ground shaking over time).Richter magnitudes range from 0 to 10, with larger numbers indicating stronger earthquakes. An earthquake with a Richter magnitude of 7 or more is considered a major earthquake, while an earthquake with a Richter magnitude of 8 or more is considered a great earthquake.
– The Modified Mercalli Intensity Scale The Modified Mercalli Intensity Scale (MMIS) was developed in 1931 by Giuseppe Mercalli to measure the duration and intensity of ground shaking during an earthquake. It ranges from I (not felt) to XII (total destruction), with larger numbers indicating greater intensity. Most people can only feel earthquakes with intensities of V or greater.
5. Shear waves
Shear waves are a type of seismic wave that can travel through solid rock. They are created by earthquakes and can be used to map the inside of the Earth. Shear waves are important because they can help scientists understand how the inside of the Earth is structured, and they can be used to study plate boundaries.
6. Conclusion
Volcanoes are mountains, but they are different from other mountains because they have a hole at the top from which hot molten rock, ash and gas can escape. Over 700 million people live within reach of an active volcano, making them one of the most dangerous natural hazards. The main task of scientists is to determine the time and place of an eruption to minimize its danger and damage.