Did you know that according to the Smithsonian Institute book, “Volcanoes of the World” that there are over 1500 active volcanoes right here on Earth? That’s quite a lot of mountains all ready to blow their tops, isn’t it?

While some of these are on the ocean bottom, many are land based. In fact it is estimated that 15 to 20 volcanoes are erupting right now as you read this plus some at the ocean’s bottom we know nothing about.

So what causes these eruptions?

Volcanoes are actually a natural phenomenon which is very important to the life cycle of our planet. The Earth uses volcanoes to cool off its mantle. The massive heat generated there escapes and the heat rushes towards the surface. On the way rocks are melted from the extreme temperatures and these melted rocks, called magma, along with gasses break through the Earth’s crust which is what we call an eruption.

Just as earthquakes are measured on what is called the Richter Scale, volcanoes also have their own system to categorize the size of an eruption. This scale is called the Volcanic Explosivity Index (VEI), and it was developed by Steve Self and Chris Newhall.

The dynamics and types of volcanic eruptions are much more complex than an earthquake so a scale was hard to devise and although this system is not perfect it is generally considered the most useful and best conceived scale that anyone else has developed.

The VEI scale goes like this:

0 Gentle
1 Effusive
2-3 Explosive
4-5 Cataclysmic
6 Pyroxysmal
7 Colossal
8 Un-named

The reason level 8 is un-named is that in recorded history we have never had an explosion of that magnitude. The majority of eruptions over the last 10,000 years have been VEI 3 or less. During that time there have been eighty-four VEI 5 eruptions, thirty-nine VEI 6, and only four VEI 7 eruptions.

The buildup of ash and flows of lava around the eruption hole (or in the case of underwater cases, a ‘vent’) is what we actually call a volcano. Some of these after one eruption which can last as short as a few days to a couple weeks never erupt again while other times a large volcano will erupt thousands of times and will be active for hundreds, thousands, and even millions of years.

The largest volcano on Earth is Mauna Loa in Hawaii. Its volume is about 40,000 cubic kilometers and covers an area of 5125 square kilometers, this is half the size of the island of Hawaii on which it rests! This ancient volcano is over a million years old however this volcano pales in size to the king volcano named Olympus Mons. This volcano is estimated to be 27 km tall (17 miles). Imagine that! Mt Everest is only about 10 km (6 miles) tall. But don’t worry as this volcano is located on Mars so an eruption won’t affect you that much.