By Alexia LouvierisBy Alexia Louvieris

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Mount St Helens is a composite volcano in the Cascade mountains, 153 km south of Seattle, Washington, USA.

Its major eruption happened on the 18th of May 1980. 57 people died and it caused millions of dollars worth of damage to the surrounding area. Hot ash and rocks started forest fires and melted the snow on caps of the mountains. The resulting floods and mudslides washed away buildings, roads and houses. The eruptions also spread a thick layer of volcanic ash over a wide area, destroying crops, wildlife and blanketing cities.

This is the eruption in 1980. The pillar of ash moved eastward, growing into a vast dark cloud that plunged towns 85 miles away into darkness. Most of northern Idaho, western Montana, and eastern Washington came to a halt because of the ash fall.

In 1980 it was the first time it was possible for volcanologists to use modern technology to monitor Mount St. Helens as it built up to its eruption. They gathered lots of information and data, but it was still impossible to say the exact time it would erupt.

It had been dormant for 123 years. On 20th of March a series of small earthquakes shook the region. The following few days the magnitude and frequency shock waves began to increase and then the small gas eruptions began, they observed these as erupting volcanoes give off large amounts of sulphur dioxide gas beforehand. Volcanologists regarded the volcano as a hazard. Warnings were issued to citizens in the area and mountain roads were closed.Thousands evacuated the area and their lives were saved.

Volcanologists installed highly sophisticated equipment on the mountain. They constantly monitored the chemical composition of groundwater and escaping gasses, they used laser surveying techniques to look for any expansion of the ground, and recorded the constant seismic activity. The side of the mountain was clearly beginning to expand as pressure began to increase. By late April there was a bulge 1000m wide and over 2000m long. It was rising at a steady rate of about 1.5m every day as the mountain began to fill with magma being forced up from below.

This is the lava dome in Mount St. Helens before it erupted.

The eruption started with an earthquake which had a magnitude of 5 on the Richter scale. The pressured magma exploded and flattened forests. The speed of moving air and debris overtook cars and people as they tried to escape. Superheated steam and ash caused mudflows and ashclouds were formed, burning everything in their paths.

If the 1980 eruption follows the patterns of the previous eruptions, it will be active for the next ten to twenty years, before it quietens down.

This is what Mount St. Helens looked like before the eruption. It reduced its height from 2,950 metres to...

...2,569 metres. This is what Mount St. Helens and its surroundings looked like after the eruption.

Mount Vesuvius is a complex volcano in southern Italy, about 11km south-east of the city of Naples. It is a cone within the rim of Mount Somma, a large crater formed when the top of the mountain collapsed in the eruption in 79AD.

It is the only active volcano on the mainland of Europe. It has been studied more than any other volcano because it erupts frequently and is easy to reach. The top of the active cone is a cup-shaped crater, ranging from 15 to 120 metres across.

Mt. Vesuvius's most famous eruption was in 79 A.D. when it

destroyed the cities of Herculaneum and Pompeii. When Vesuvius erupted it

covered the cities of Herculaneum and Pompeii with

20 feet of volcanic debris. During this eruption about

2000 people were killed. That eruption was called a plinian explosion. This means that extremely gas-rich, viscous

magma explodes deep inside a volcano and a blast shoots

straight up at twice the speed of sound, creating a vertical

column of ash as much as 20-miles high. Since then it has erupted over 50 times and is

still active.

Bird’s eye view of Mt. Vesuvius.

The height of Vesuvius changes with each eruption. In 1900 it was 1,303 metres high but after several eruptions, its height dropped to 1,227. Vesuvius spouts columns of steam, cinders, and sometimes small amounts of lava into the air.

Many people live on the lower slopes of the mountain and on the plains at its foot, in spite of Vesuvius' history of disastrous eruptions. The volcanic soil is extremely fertile and the area is famous for its vineyards of wine grapes.

Mt. Vesuvius is still active today. Its last recent eruption was in 1944. About 2 million people live near Mt. Vesuvius and they could be in danger.

However, a plug indicates that the once-threatening magma deep below Vesuvius has cooled and hardened into a dormant, harmless mass.

But the plug’s presence also means that the next eruption is likely to be explosive producing, deadly, avalanche-like pyroclastic flow of gas, rocks, and hot ash, rather than an eruption of hot but slow-moving lava, which is less dangerous.

The crater of Vesuvius.

No volcanologist knows when exactly Mt. Vesuvius will erupt, but they know it might erupt any time soon as it is active. It has erupted many times before, so there is no saying that it won’t.

Volcanologists are using seismographs, which are very accurate when for-telling eruptions. They monitor the force and direction of earthquakes, as most eruptions start off with one or even many earthquakes. The history of eruptions also helps.

The people of Pompeii were wiped out by this eruption. The volcano blew on the 24th of August at 1pm. The day darkened and soon it was raining pumice stones on the city. The roofs on buildings collapsed, killing people and doorways were blocked. A man called Plinny the Younger recorded these events. He noticed a cloud of molten rock and ash-which today is known as a pyroclastic surge. It’s so hot it burns people instantly. Bodies lay under 25m metres of debris.

The ruins of Pompeii.

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It is in the form of a mountain as they are on the edge of the earth’s tectonic plates.

A volcano is an opening in the earth’s surface.

When they erupt, gases, rock fragments and lava burst out.

WHAT IS A VOLCANO????WHAT IS A VOLCANO????

HOW DOES A VOLCANO WORK????HOW DOES A VOLCANO WORK????

•MOUNT ST HELENS IS A VOLCANO IN WASHINGTON, USA.

•IT’S MAJOR ERUPTION HAPPENED IN MAY 1980.

•57 PEOPLE DIED IN THE ERUPTION AND NEARBY TOWNS WERE SERIOUSLY DAMAGED.

• MOUNT VESUVIUS IS A VOLCANO, NEAR NAPLES IN ITALY.

• ITS MOST FAMOUS ERUPTION HAPPENED IN 79AD.

• IN THAT ERUPTION, ALL THE CITIZENS OF POMPEII WERE BURNT OR KILLED.

Tectonic plates - the earth’s crust is broken up into pieces. These pieces are called plates. Imagine the earth as an apple. The earth’s crust would be the apple’s skin.

Erupt - burst out suddenly or dramatically

Magma - lava when it is underground

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