A cinder cone is a conical hill of mostly cinder-sized pyroclastics containing large amounts of gases.
The profile of the cone is determined by the steepest angle at which debris remains stable and does not slide downhill.
Larger cinder fragments, which fall near the summit, can form slopes exceeding 30 degrees. Finer particles are carried farther from the vent and form gentle slopes of about 10 degrees at the base of the cone.
These volcanoes tend to be explosive but may also extrude some lava.
Cinder cones are numerous, occur in all sizes, and tend to rise steeply above the surrounding area. Those occurring on the flanks of larger volcanoes are called parasitic (or secondary) cones.
A n example of a cinder cone is Paricutín in Mexico. It was born on February 20, 1943 in a corn field and grew to 300 feet in 5 days. It is now 3000 metres. It reached almost 1500 metres in its first year. It has been dormant since 1952.
Hot gas and ash that are pushed out of a volcanic vent form a jet. The force with which the gas is pushed out diminishes quickly away from the vent, but where the ash and gas are hot they rise through the atmosphere as a plume.
As the plume rises it mixes with, and heats, cold air to become more buoyant and rise still further.
Under certain conditions the ash cloud may become unstable and collapse down the side of the volcano to form a pyroclastic flow, with temperatures typically at 1,000C and speeds of up to 700k/hr (450mls/hr). These pyroclastic flows are very dense and do the most damage and cause the most loss of life. They can knock down houses and uproot massive trees.
The large quantities of gas (including water vapour) and fine ash particles that are emitted often result in violent rainstorms. The deluges of rain upon the volcano slopes, which may be augmented by melting ice, help to mobilise ash and debris flows to form lahars or mudflows.
Nearly 1,900 volcanoes are active today or known to have been active in historical times.
Of these, almost 90 percent are situated in the Pacific Ring of Fire . This belt partly coincides with the mountain ranges of western North and South America, and the volcanic island arcs fringing the north and western sides of the Pacific basin.
Look at the map page 15 to get a better idea of the ditribution of volcanoes around the world.