Earthquakes & Volcanoes

Keywords

Volcano, earthquake, plate tectonics, crust, mantle, tsunami, topography, shield, cone, composite, eruption.

Introduction

Possibly the most notable earthquake known in history is that of Pompeii. Mount Vesuvius blew up in anger in 79CE and destroyed the city of Pompeii, killing all the people that lived there as well. They had previously suffered in 62CE from another earthquake. So, what's the deal with earthquakes and volcanoes?

Earthquakes

An earthquake is where two tectonic plates are moving in different directions for long periods of time. This then results in a lot of energy being built up. When it reaches a certain point, it erupts as a mass of shock waves.

If an earthquake is under the ocean, it can cause enough shock waves to create a tsunami, a large wave of water.

Interesting fact: there are thousands of earthquakes every year. Some we don't even notice, others register high on the Richter scale.

Dangers of Earthquakes

When we have an earthquake, we use a scale to base the severity of it on. This is called the Richter scale (named after the American seismologist, Charles Francis Richter), and it measures the magnitude of the quake.

Dangers of an earthquake include:

• minor damage to buildings
• shaking of indoor objects
• items knocked over
• major damage or collapse of buildings
• loss of life
• permanent changes to ground topography

Volcanoes

A volcano is an opening in the Earth's crust that spits out molten lava, hot ash, gases and rocks. They look just like a mountain or a hill.

There are two types of volcano:

Composite volcano: the most common type, they have violent eruptions and grow bigger as layers of thick lava and ash harden on top of each other. Mount Vesuvius in Italy is a composite volcano

Shield volcano: these volcanoes have gentle slopes and have runnier lava spreads, which harden over a larger area. Their eruptions are not as violent as a composite volcano. Mauna Loa in Hawaii is an example of a shield volcano.

Dangers of Volcano Eruptions

When a volcano erupts, it can deposit all sorts of magmatic components from under the crust of the Earth onto the surface. This includes:

• pyroclastic flows - gas, rock and hot ash
• volcanic bombs - large pieces of rock blown from the volcano, shot out almost like a cannon
• ash clouds - recent events such as the Grimsvotn volcano in Iceland, which released a giant ash cloud and stopped commercial flights for most of Europe