VOLCANOES
BY EMILY M.
What are volcanoes ?
Volcanoes are a type of hill or mountain that contain a crater or vent , in which rock fragments , hot vapor , lava , and gas erupt from the earth's crust.
FACTS
- The danger area around a volcano covers a 20 mile radius.
- Volcanic lightning occurs mainly inside the cloud of ash during an eruption, and originates from the friction of the ash that rushes toward the surface.
- There are over 500 active volcanoes in the world.
- Over half of the world's volcanoes arise in a belt called the Ring of Fire, located around the Pacific Ocean.
Types of volcanic eruptions.
The most common type of volcanic eruption happens when magma is released from a volcanic vent. Here are the different types of volcanic eruptions :
- In a Hawaiian eruption , fluid lava is thrown into the air in jets from a vent.
- Plinian eruptions are the largest and most violent eruptions.
- Strombolian eruptions are bursts of fluid lava from the mouth of a magma-filled summit conduit.
- A Vulcanian eruption is a short, violent, relatively small explosion of viscous magma.
- Surtseyan eruptions are a kind of hydromagmatic eruption, where magma or lava interacts explosively with water. In most cases, Surtseyan eruptions occur when an undersea volcano has finally grown big enough to break the water's surface.
- Lava domes form when very viscous lava is squeezed out of a vent without exploding.
Types of Volcanoes
There are three main types of volcanoes.
- Shield Volcano - Very gentle slopes; convex upward.
- Cinder Cone Volcano - Steep hill with straight sides. ( Small, less 300 m high )
- Composite Volcano - They are also called 'stratovolcanoes' or simply 'composite volcanoes' .They are cone-shaped volcanoes composed of layers of lava, ash and rock debris. ( Over heights of 8,000 ft )