Volcanoes are one of the most interesting subjects to read and learn about. They also give people an idea of what is going on inside the earth. Some of the facts about volcanoes tend to make a person want to learn even more about them.
Somewhere on Earth, at any given moment, there is an average of 11-13 volcanoes erupting. Most people don't know about most of them for two reasons. The first is that the world is a vast place. The second is that a large number of these are under the ocean, where they aren't normally seen until they break the surface. At times, the under water volcanoes can still cause wide spread devastation, though.
One such occurrence was an eruption of Krakatoa. This mountain rose out of the sea in Indonesia, but it is notable partly because when the mountain blew itself apart, it shifted a huge amount of ocean water. This created an enormous wave, called a tsunami, that swept over islands in the area, carrying whole villages away.
When Krakatoa erupted, it created another wave, too. The other wave was a wave of sound. This wasn't as destructive, but it gives a notion of the power of a volcano. The eruption was heard 3,000 miles away. Some scientists believe that the sound wave traveled around the world over a half dozen times.
While they can destroy, volcanoes can also create. The Hawaiian Islands are an example of the latter. These islands have raised up out of the sea because of volcanic action. The action still continues, and a new island will break the surface within a few decades. The islands are the tops of volcanoes that rose from the ocean floor. From the base to the top of the highest point in Hawaii, the mountain is actually taller than Mount Everest.
A volcano usually follows a particular lifetime, as well. It is often measured in hundreds or thousands of years, but volcanoes are normally classified as active, inactive, dormant, and extinct. Active volcanoes are like those found in Volcanoes National Park, which are erupting frequently. Inactive means that there is no current eruptions going on, but it could happen easily. Lassen National Park is an example. Dormant is a volcano that is "sleeping", but could reawaken. For instance, Crater Lake National Park in Oregon is thought by many to be dormant. An extinct volcano is one that is dead. Many of these have already eroded away.
The eruptions are also of two kinds. One is explosive, as in Krakatoa and Mount St. Helens in Washington, and the other is passive, as in the volcanoes of Hawaii. One of the main differences is the amount of silicon, the main ingredient in sand and glass, that the magma contains. (It isn't lava until it reaches the surface.) The thicker it is, the harder it is for the gases to escape. If the lava is very thick, the result is like shaking a bottle of pop and uncapping it. This is an explosive eruption.
The two kinds of lava also behave differently. Thin lava flows easily and can quickly cover many miles. Thick lava flows slower, and may start to harden within a couple miles.
Volcanoes tend to happen near where two plates in the earth's crust collide. One is forced under the other, melting the rock as this happens, and the result is eruptions. This is how the Cascade Mountains in Washington, Oregon, and California formed. However, there can be volcanoes that are far from where the plate boundaries are. These places are called hot spots, and examples are the Hawaiian Islands and what is now Yellowstone National Park.
Yellowstone is actually a super volcano. The magma pocket under it is estimated to be between 5 and 250 cubic miles in size. If it was to fully erupt, the devastation in the US would be extreme. Still, as the tectonic plate moves, the hot spot appears to very slowly move. The hot spot isn't actually what is moving, but from our perspective on the surface, it looks that way.
Volcanoes are fascinating, and only a few interesting facts have been covered. It is worthwhile to spend more time learning about our world and how important volcanoes are in its continuing formation.
Volcanoes National Park
Crater Lake National Park
Lassen National Park
Yellowstone National Park
United States Geological Survey