By Laura Wickenhauser Grade 4

Volcanoes are mountains, but they are not formed the same way Mountains are formed from folds and uplifts on the Earth’s surface Volcanoes are built on top of their own lava and ash from past eruptions. A volcano is an opening or vent where molten rock and gases are released.

What is an Eruption? An eruption occurs when magma rises and reaches the Earth’s surface. Magma is melted rock that flows under the Earth’s surface. Once the magma has pushed through the vents in the Earth’s surface, it is called Lava Lava

Layers of the Earth’s Surface

Some eruptions are explosive and others are not. This depends if the magma is runny or sticky If magma is thin and runny, gases can escape easily from it. This type just flows out of the volcano If magma is thick and sticky, gases can’t escape easily and it causes an explosion.

There are 2 types of Lava:Lava 1) Pahoehoe 2) A’a

Pahoehoe Flows at a slow speed The very top of the lava is cooled by the air, while the lava underneath continues to flow It stops flowing after a few minutes and becomes inflated with lava and a new section starts to flow This lava is smooth and unbroken

Pahoehoe Lava

A’a Flows at a fast speed and is usually results from fountains of lava erupting This lava has very rough top and bottom layers with a dense interior Formed by pasty lava that is pulled apart by twisting and shearing during flow

A’a

How much of the Earth is Volcanic? About 80% of the Earth’s surface (above and below sea level) is volcanic. Gases from the volcanoes hundreds of millions of years ago formed the Earth’s oceans and atmosphere. Eruptions have also produced mountains, plateaus and plains

There are about 500 active volcanoes on Earth today This does not include those that lie beneath the sea

You can simulate your own volcanic eruptionvolcanic eruption To check your knowledge on volcanoes, try to complete this crossword puzzlecrossword puzzle