Pumice forms from the violent separation of gas from lava to produce light colored frothy rock fragments. Three Cinder cones are the simplest types of volcanoes in the shape of a circular or oval cone. With the naked eye, a cinder cone resembles a large hill or mound. The only distinction is the bowl-shaped top called a crater that the cinder cone contains. The cones develop from the violent explosion of volcanoes.
Cinder cones are quite numerous in Western North America.
Composite volcanoes are the most violent and dangerous volcanoes with steep slopes closely resembling that of a mountain. In fact, some well known mountains are actually volcanoes. For example, Mount Fuji, Mount Rainier, and Mount St. Helens. Composite volcanoes are the most explosive because they hold reservoirs of magma deep within the earth's crust. Eventually, these reservoirs erupt and produce lava, ash, bombs, and various other materials known as pyroclastics.