Volcanoes often act up just when they're not expected to. Mt. St. Helens, which rises almost 10,000 high in Washington State, got feisty a few weeks ago.
It began spewing smoke and cinders, but not lava, when everybody thought the volcano was no longer active.
The last time Mt. St. Helens erupted was 123 years ago, so everybody thought it had gone to sleep.
Volcanoes have existed for three billion years. The word "volcano" comes from the name of an ancient island off the cost of Sicily that was thought to be the island of Vulcano. The early Romans believed this smoking mountain or volcano was the home of Vulcan. Vulcan was the Roman god of fire. He was also thought to be the blacksmith of the gods.
Volcanoes can be so powerful they can change the shape of the land by throwing up new mountains. Sometimes volcanoes have buried whole cities.
This happened with one of the most famous volcanoes, Mt. Vesuvius on the Bay of Naples in Italy. It erupted about 1,900 years ago in AD 79. The Volcano threw up smoke, volcanic ash, and molten rocks that came cascading down on the town of Pompeii where about 20,000 people lived. After three days of volcanic activity the city was buried under 15 to 25 feet of volcanic debris.
It was not until about 1,700 years later that Pompeii was dug up.When Pompeii was uncovered, everything was found to be perfectly preserved. Volcanoes are found in many different parts of the world. Today there are about 430 active volcanoes.More than 330 of them are in or around the Pacific Ocean.
Active volcanoes are those that have erupted in recent times. Dormant volcanoes are those that have showed signs of being active, but not for a long time. Extinct volcanoes are those that have not erupted since records of history began thousands of years ago.
Volcanoes form along lines of weakness in the earth's crust. They are called fault lines.
Scientists do not know the precise reason why volcanoes become active. When they do become active, hot, liquid rock called magma is forced upward by the pressure of gases. When the magma is blown out of volcanoes, it is known as lava.
The lava, which is red or white hot when it pours out, is like hot tar. As it cools it is more like a thick syrup and slowlybecomes darker in color.
Volcanoes can do terrible damage, burying cities like Pompeii and causing tidal waves. There are also good things about volcanoes. They throw up wonderful new land forms. The mighty Sierra Nevada range, for instance, was caused by volcanic activity. So were the chain of Hawaiian Islands.
Steam is a major force behind volcanic explosions. Italy first used volcanic steam to make electricity in 1904.
Basalt, which is a volcanic rock, is used in some places for stone for building and crushed for making roadbeds. Pumice, which is one of the materials thrown out by a volcano, is an important substance in cleaning powders.
The most positive thing about volcanic rocks is that they break down quite quickly to form very rich soil. This is because the rocks are full of minerals. The fertile soil brings many people to live in volcanic areas so that they can grow crops.