Volcanoes 11

Montse PARERAS Mariona DALMAU 6è PRIMÀRIA

A volcano is like a chimney in the Earth’s crust where magma flows out.

Magma is solid rock that melts to form hot liquid rock. The hole is called a vent. When magma leaves the vent, it becomes lava. Plate tectonics theory explains how volcanoes form. Some volcanoes form above a hot spot, which is a very hot place in the mantle.

hard

Magma

Contents: gas, dust, water vapour, lava, ash. Scientists put volcanoes into three groups: Active volcano: is one that is erupting or will soon erupt. Dormant volcano: is one that has not erupted for a long time. Extinct volcano: is one that has not erupted for more than 10.000 years.

Are in many places in the world. Types of volcano: Fisure volcano, Shield volcano, Dome volcano, Ash-cinder volcano, Composite volcano, Caldera volcano

Magma forms igneous rocks. These fragments are called Tephra. Types of tephra: bomb, lapilli, ash, dust. Liquid lava flows fast and forms smooth folds that look life rope. This is called pahoehoe. When slow sticky lava gets hard it forms rocks with sharp edges. This is called AA. Sometimes lava forms long, thin strings like human hair. It’s called Pele’s hair.

PAHOEHOE AA

PELE’S HAIR

The floor of the ocean is similar to dry land. There are flat plains, mountain ridges, canyons and trenches in the ocean floor. There are more volcanoes under the ocean than on land.

The minerals and chemicals in the lava and ash make soil fertile so it is good for farming. Volcanoes also help to produce electricity. They heat rocks that are near the Earth’s crust. When these rocks heat underwater, it turns to steam. People use this steam to make electricity. This is called geothermal energy.

Special scientists are called volcanologists. They study volcanoes in different ways. This helps to learn about the volcano’s history and to know what it is going to do. Because of this, people who live near volcanoes can plan what to do. Volcanologists wear special suits while they collect lava.