Mount. St. Helens is an active volcano located in Skamania county, Washington. It's known for its deadly explosion on May 18, 1980 that killed 52 people.

Mount Vesuvius is a stratovolcano located in the gulf of Naples, Italy. It is regarded to be the most dangerous volcanoe to ever erupt. Though it has erupted many times in the past 1,000 years 300,000 people still live right below it.

Volcanoes are caused by tectonic plates coming together or moving apart. The stress of their movement causes magma to come close to the surface of the Earth, and volcanoes form where that magma is able to break through the Earth's crust (this can happen anywhere that the surface is thin--not just where two or more plates are interacting).

Magma is the molten material beneath Earth's crust. This material consists of rock, gases, and mineral crystals. The temperature of the magma can be as high as 5000 degrees Fahrenheit. The pressure is also very high since the magma supports the weight of Earth's crust.

Lava is the molten rock that comes out of a volcano or from a fissure in Earth's surface. A fissure is a crack. The molten rock comes from the underground magma. Lava is thus magma that has broken through Earth's surface.

An active volcano is a volcano that has had at least one eruption during the past 10,000 years. An active volcano might be erupting or dormant.

An erupting volcano is an active volcano that is having an eruption...

A dormant volcano is an active volcano that is not erupting, but supposed to erupt again.

An extinct volcano has not had an eruption for at least 10,000 years and is not expected to erupt again in a comparable time scale of the future.

ENVIRONMENTAL EFFECTS

• Burial by ash lava and mud.
• Gas emitted by eruption.
• They ruin entire landscapes.