How does volcano formed ?
"Volcanoes are formed when magma from within the Earth's upper mantle works its way to the surface" (http://www.weatherwizkids.com/weather-volcano.htm). The magma, once it reaches the surface, cools and deposits as a solid. Over time, the magma's solid deposits build up, and eventually, a volcano is formed.
I hope that helps!
There are different kinds of volcanoes, classified according to what kind of magma they have, and the shape and size of the cones they make.
Here's a summary - as brief as I can make it:
The two kinds of magma are felsic, and mafic.
Mafic lava is made of basalt and it flows.
Felsic lava is thicker and is explosive.
(1) Shield Volcanoes have mafic magma that oozes out of their craters, forming volcanoes like Kilauwea and other Hawai'ian volcanoes.
These volcanoes are the largest.
This photo was taken from far away because this volcano is so big:
Mauna Kea, Hawaiʻi, a shield volcano on the Big Island of Hawaii
(2) A Lava Dome volcano has thick felsic magma that forms an uneven cone, and domes of lava that block the crater, so that it has to clear the dome when it erupts - they're explosive, but don't erupt often.
Puy de Dôme volcano in France
(3) Cinder Cone Volcanoes have a cone made of pyroclastic material or tephra - lava that is hurled into the air, hardening in pieces, building up the sides of the cone.
These are the smallest volcanoes, and they usually erupt just once.
SP Crater, an extinct cinder cone in Arizona
(4) Stratovolcanoes are also called Composite volcanoes.
Popocatepetl in Mexico:
Augustine Island volcano in Alaska - a stratovolcano that also forms lava domes in its craters:
Mt. Etna in Sicily, Italy has numerous craters AND fissures in its sides that ooze lava.
Hope this isn't TOO long.