What are Volcanoes Volcanoes are holes in the Earth’s surface where hot magma and gas from deep underground are released Over time volcanoes grow into tall mountains made from hardened lava and ash There are currently around 1,900 active volcanoes on Earth Mount St Helens page 9 ASIA FOCUS ON Mount Fuji page 20 FOCUS ON Mauna Loa page 21 Mount Pinatubo page 8 FOCUS ON Krakatoa page 24 Location Volcanoes are often found along the boundaries of tectonic plates where sections of the Earth’s crust meet Some volcanoes form at hot spots places where magma inside the Earth is particularly hot There are volcanoes on every continent on Earth 4 PACIFIC OCEAN INDIAN OCEAN AUSTRALIA Plate boundaries
Eruption Active dormant extinct Volcanoes sometimes erupt Lava flows down the sides of the volcano Gas and ash are released into the air When the lava hardens it forms rock Active volcanoes still erupt frequently or are expected to erupt soon Dormant volcanoes are unlikely to erupt again Extinct volcanoes will never erupt again Scientists can measure the amount of magma inside a volcano to determine if it will erupt again soon NORTH AMERICA ATLANTIC OCEAN SOUTH AMERICA EUROPE AFRICA FOCUS ON Eyjafjallajökull page 23 FOCUS ON Mount Vesuvius page 14 Mount Teide page 7 Soufrière Hills page 29 Popocatépetl page 9 In space There are also volcanoes on other bodies in space Io one of Jupiter’s moons has hundreds of volcanoes some of which shoot lava hundreds of miles into the air 5
Earth’s Layers The structure of Earth is made up of several layers During a volcanic eruption material from inside Earth comes to the surface Structure The structure of Earth can be divided into four parts At the center are the inner and outer cores which are made from solid and liquid iron and nickel Then there is the mantle which contains magma During a volcanic eruption magma comes to the surface as lava The outer layer of Earth is the crust which is made of solid rock Tectonic plates Earth’s crust is divided into large pieces called tectonic plates which fit together like puzzle pieces Continental plates have land on top of them They make up most of the land on Earth Oceanic plates are found under most of the oceans on Earth Oceanic plates are more dense than continental plates 6 crust mantle outer core inner core Movement The plates that make up Earth’s surface are always moving They move one or two inches every year This movement is caused by convection currents in the mantle Hotter magma which has been heated by the core rises to the top and then falls again as it cools Plates can move toward each other away from each other or slide past each other
Meeting plates Volcanoes often form at plate boundaries between continental and oceanic plates When the plates meet the oceanic plate is pushed under the continental plate and down into the mantle The solid crust melts in the heat of the mantle and turns into magma continental plate oceanic plate magma chamber Magma chambers Magma gathers in huge pools beneath the surface of Earth known as magma chambers Over time more magma rises into the chamber as more of the oceanic plate is destroyed Pressure inside the magma chamber builds until it can’t hold any more magma At this point the magma rises causing a volcanic eruption Hot spots In hot spots the magma in the mantle is much hotter than in the surrounding areas This hot magma rises to the surface and erupts creating a volcano Some hot spots are near plate boundaries while others are hundreds of miles away Scientists have not yet been able to prove why hotspots exist Mount Teide in the Canary Islands Spain is a hotspot volcano Scientists predict that it will probably erupt violently in the future 7
