What are volcanoes and earthquakes?
Volcanoes and earthquakes cause rapid and sometimes dangerous changes in the landscape.
How Do Volcanoes Form?
Volcanoes begin deep within the mantle where magma forms. Magma is hot, pasty rock that moves within the mantle. Magma close to the surface melts and flows easily because the pressure is less. Magma can gush out of weak spots in the crust, aided by the pressure of gases it contains. A volcano is an opening out of which this hot material erupts.
An eruption is like opening a can of shaken soda. Bubbles of gas seperate from the liquid and force the liquid out. The material that erupts from a volcano is called lava. As lava cools and hardens, it becomes igneous rock. That's brand-new crust! If the rock builds to great heights, a moutain or island forms.
Magma collects in large pockets called magma chambers. As magma leaves the chamber, it moves up a tunnel or central vent. Sometimes, magma escapes from the central vent and errupts from side vents. Most magma, however, erupts at the top of the volanco through a bowl-shaped crater.