Because of the large number and types of volcanoes scientists had to look for the similarities and they came up with two categories of classifying them. First one is based on their shape which is very important on account of what kind of landform the volcano is. Volcanologists consider six types of volcanoes:

Fissure eruption: This type represents two plates moving away making a large crack in the surface, called a fissure, through which lava can be ejected. Basaltic material flows over a certain distance on the gentle slope forming a large plateaux filling large hollows ( that is why it doesn’t have a cone). Remains of such a fissure eruption made when Eurasian and North American Plates moved apart still can be seen in Iceland, Greenland and North Ireland.

Basic or shield volcanoes: It is a type of volcano with a vent in the center with wide, gentle slopes allowing lava to spread over large areas before solidifying. The closest volcano resembling this description is Mauna Loa on Hawaii where sides are not steep made of many layers from slow,repeated flows of lava.

Acid or dome volcanoes: Due to high viscosity of acidic lava (when exposed to the air it quickly solidifies) slopes are very steep and convex. In most extreme cases lava crystallizes before it even reaches the top of the vent. Then it actually pushes up basalt spine instead of lava.

Ash and cinder cones: Small eruptions consisting mainly of pyroclastic material and ash result in making a small cone with slightly concaved sides. Of course developing of this type of volcano takes a long period of time.

Composite cones: Scientists say it is a mixture of cider cones and acid volcanoes mainly because the cone of this type is made by alternating layers of ash (violent eruptions) and acidic lava. Mt. Etna is a result of such a process.

Calderas: Sometimes the build up of gasses inside the volcano is so big that explosions which occur clear out all magma and remove the peak of the cone. Sides are moving apart reaching up to several kilometers in radius. If volcano was located below see level it creates a lagoon ,if not fills with water creating a lake.