Geopix UK - Igneous Processes

Extrusions

Extrusions allow magma to escape at the surface of the crust producing lava and volcanoes.
Central volcanoes erupt lava and pyroclastics from one vent forming the conical hill that we normally think of as the typical volcanic shape. Ash and other erupted pyroclastics add to the hill. Lava and ash travel in any direction and the volcano will be conical, whatever its height.
However, a volcano is any opening in the crust (including underwater) through which lava escapes. If that opening is a linear fissure, the lava may may spread outwards on either side to form a level plateau.

Geopix Study Topic "Extrusions"

gives full images of the examples shown below, and others, to illustrate the main types of extrusions
summarises the classification of lavas
classifies and describes volcanic landforms
illustrates different varieties of lava flows
suggests how to answer exam questions on this topic

(Volcanoes and volcanic features are more fully described in the "Volcanoes" Study Guide, and also in "Volcanoes: illustrated by Tenerife" and "Volcanoes:illustrated by Iceland")

Central volcano
Central