A volcano is an opening in Earth’s crust. When a volcano erupts, hot gases and melted rock from deep within Earth find their way up to the surface. This material may flow slowly out of a fissure, or , in the ground, or it may explode suddenly into the air. Volcanic eruptions may be very destructive. But they also create new landforms. There are more than 1,500 potentially active volcanoes in the world today.

During a volcanic eruption, hot melted rock called magma escapes from a vent, or opening, in Earth’s surface, or crust. Magma released from a volcano is known as lava. Fresh lava ranges from 1,300 to 2,200 °F (700 to 1,200 ° C) in temperature. It glows red as it flows out of the volcano’s opening. As it cools, it hardens into rock.

Strong volcanic eruptions throw bits of magma into the air.

Earth’s crust is made up of huge, rocky pieces called plates. The plates move slowly over the crust. Most volcanoes lie along the boundaries between these plates.

Some of the most violent eruptions take place where the edge of one plate is forced beneath the edge of another. This forces magma to rise to the surface. Hot gases in the magma make these volcanoes very explosive.

Volcanic eruptions create new landforms that are also called volcanoes. The two most common types are stratovolcanoes and shield volcanoes.

Stratovolcanoes, also called composite volcanoes, are mountains shaped like cones. They have a narrow top with steep sides and a wide bottom. A crater, or bowl-shaped pit, usually lies at the top. Stratovolcanoes are made up of layers of hardened lava and ash. Thousands of eruptions left these layers over millions of years. 

Hot springs, geysers, and fumaroles are other types of volcanic activity. They happen in places where magma heats underground water. A hot spring is a place where warm water comes up through the ground. A geyser is a kind of hot spring that shoots water and steam into the air. Fumaroles are vents that release gas and steam.

Volcanology is the branch of geology that focuses on volcanoes. Many volcanologists work in observatories, from which they keep track of earth tremors and other signs of volcanic activity. Others venture forth to the slopes and craters for an even closer look. On the basis of what they measure and see, they try to predict when an eruption might take place, how severe it will be, and which places will be in the danger zone.

The effects of volcanoes are not entirely harmful. Volcanic ash soil—called andisol—is good for growing crops. In addition, the volcanic glass called obsidian has been used by many of the world’s peoples for weapons, tools, and ornaments. People also use the volcanic stone called pumice for cleaning wood, metal, and other surfaces and in producing building materials.

The heat within Earth that is released in volcanoes is an enormous potential source of energy.

The word volcano comes from the name of Vulcan, the ancient Roman god of fire and metalworking. The Romans believed that volcanic eruptions resulted when Vulcan made thunderbolts and weapons for the gods. Other cultures explained volcanoes as outbursts of anger from a god or goddess. Pele was the name of the volcano goddess of the native Hawaiians.

Volcanoes have a long history of destruction.

did you know about the explosio of 79ad of mount vesuvious?

Mount Vesuvius, a volcano near the Bay of Naples in Italy, is hundreds of thousands of years old and has erupted more than 50 times. Its most famous eruption took place in the year 79 A.D., when the volcano buried the ancient Roman city of Pompeii under a thick carpet of volcanic ash. The dust “poured across the land” like a flood, one witness wrote, and shrouded the city in “a darkness…like the black of closed and unlighted rooms.” Two thousand people died, and the city was abandoned for almost as many years. When a group of explorers rediscovered the site in 1748, they were surprised to find that–underneath a thick layer of dust and debris–Pompeii was mostly intact. The buildings, artifacts and skeletons left behind in the buried city have taught us a great deal about everyday life in the ancient world.

Life in Pompeii
Ever since the ancient Greeks settled in the area in the 8th century B.C., the region around Mount Vesuvius and the Bay of Naples attracted wealthy vacationers who wanted to soak up the sun and the scenery. By the turn of the first century A.D., the town of Pompeii, located about five miles from the mountain, was a flourishing resort for Rome’s most distinguished citizens. Elegant houses and elaborate villas lined the paved streets. Tourists, townspeople and slaves bustled in and out of small factories and artisans’ shops, taverns and cafes, and brothels and bathhouses. People gathered in the 20,000-seat arena and lounged in the open-air squares and marketplaces. On the eve of that fateful eruption in 79 A.D., scholars estimate that there were about 20,000 people living in Pompeii and the surrounding region.

Did you know? Mount Vesuvius has not erupted since 1944, but it is still one of the most dangerous volcanoes in the world. Experts believe that another Plinean eruption is due any day–an almost unfathomable catastrophe, since almost 3 million people live within 20 miles of the volcano’s crater.

Mount Vesuvius
The Vesuvius volcano did not form overnight, of course. In fact, scholars say that the mountain is hundreds of thousands of years old and had been erupting for generations. In about 1780 B.C., for example, an unusually violent eruption (known today as the “Avellino eruption”) shot millions of tons of superheated lava, ash and rocks about 22 miles into the sky. That prehistoric catastrophe destroyed almost every village, house and farm within 15 miles of the mountain.

But it was easy to overlook the mountain’s bad temper in such a pleasant, sunny spot. Even after a massive earthquake struck the Campania region in 63 A.D.–a quake that, scientists now understand, offered a warning rumble of the disaster to come–people still flocked to the shores of the Bay of Naples. Pompeii grew more crowded every year.

79 A.D.

Sixteen years after that telltale earthquake, in August 79 A.D., Mount Vesuvius erupted again. The blast sent a plume of ashes, pumice and other rocks, and scorching-hot volcanic gases so high into the sky that people could see it for hundreds of miles around. (The writer Pliny the Younger, who watched the eruption from across the bay, compared this “cloud of unusual size and appearance” to a pine tree that “rose to a great height on a sort of trunk and then split off into branches”; today, geologists refer to this type of volcano as a “Plinean eruption.”)

As it cooled, this tower of debris drifted to earth: first the fine-grained ash, then the lightweight chunks of pumice and other rocks. It was terrifying–“I believed I was perishing with the world,” Pliny wrote, “and the world with me”–but not yet lethal: Most Pompeiians had plenty of time to flee.

For those who stayed behind, however, conditions soon grew worse. As more and more ash fell, it clogged the air, making it difficult to breathe. Buildings collapsed. Then, a “pyroclastic surge”–a 100-miles-per-hour surge of superheated poison gas and pulverized rock–poured down the side of the mountain and swallowed everything and everyone in its path.

By the time the Vesuvius eruption sputtered to an end the next day, Pompeii was buried under millions of tons of volcanic ash. About 2,000 people were dead. Some people drifted back to town in search of lost relatives or belongings, but there was not much left to find. Pompeii, along with the smaller neighboring towns of Stabiae and Herculaneum, was abandoned for centuries.


Word help 

Lava is hot, liquefied rock that flows from a volcano or other opening in the surface of Earth. When the liquid rock is still underground it is known as magma. Igneous rock is formed when lava cools and hardens.

A mountain is a landform that rises high above its surroundings. Taller than a hill, it usually has steep slopes and a rounded or sharp peak. Mountains are rarely found alone. Groups of mountains are called ranges. Lines of ranges form mountain belts.

Geology is the study of the physical features and history of Earth. Scientists who work in geology are called geologists.

Geology is an important science for many reasons. It answers questions about how Earth came to have its present shape and form. It is useful for finding important materials in Earth’s crust, such as oil. Geology is also helpful for predicting earthquakes and other natural hazards.

In an earthquake, huge masses of rock move beneath the Earth’s surface and cause the ground to shake. Earthquakes occur constantly around the world. Often they are too small for people to feel at all. Sometimes, however, earthquakes cause great losses of life and property.

Energy is another word for power. Energy makes things move. It makes machines work. Energy also makes living things grow.

Mount Vesuvius is an active volcano in southern Italy. It is famous for an eruption that happened in ad 79. Thousands of people died when lava, ashes, and mud buried the cities of Pompeii, Herculaneum, and Stabiae. The cities were forgotten until archaeologists began digging up their ruins in the 1700s.

Mount Vesuvius stands about 4,200 feet (1,280 meters) high, but its height changes after each major eruption.

Mount Vesuvius stands about 4,200 feet (1,280 meters) high, but its height changes after each major eruption.

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