EXTINCT VOLCANOES by Amy and Gemma A volcano is an opening in the Earth's crust from which ash or hot molten rock called lava, explodes. Dormant volcanoes are volcanoes that no longer erupt, which basically means they are dead.  Dormant volcanoes leave behind all sorts of landforms that have been created when the volcano was active. Volcanic landforms can take thousands of years to form.  When magma squeezes in between a crack in the crust it sometimes hardens there.  This is called intrusive rock.  When the rock around the intrusion is softer than the volcanic rock, it gradually wears away over time and the lava rock formation is left sticking up.  There are many rock formations in the Warrumbungle National Park in NSW that were formed this way. This picture shows our teacher's brother standing at the bottom of the Breadknife - once a volcanic dyke that has had the rest of the land around it eroded away over millions of years.   Sometimes when a volcano erupts, a crater forms.  When a crater is plugged with hardened lava or other rubble, it forms a big bowl shape at the top of the volcanic mountain.  Over many years this crater can fill with water from rain or snow which forms a crater lake.  The Blue Lake at Mt Gambier in South Australia is an example of a crater lake. When a volcano erupts lava sometimes flows in a hot stream from the crater. When the lava on the outside of the stream cools and hardens, it can form a sort of a rock roof over the hot lava inside which is still flowing. When the pressure pushing the lava through the tube has eased, the tunnel of lava empties which leaves a formation called a lava tube.  This is like a tunnel you can walk through.  There are lava tubes found on some of the Hawaiin Islands which have lots of active volcanoes as well as extinct ones. Click HERE to see our model of an Extinct Volcano.