Question 6
- Name three mountains that have composite volcanic cones.
- With the aid of a diagram, describe the characteristics and formation of composite
volcanic cones.
Observation
This question was attempted by few candidates and their performance was poor. Examples of composite volcanoes are:
- Mt Chimborazo in Ecuador
- Mt Krakatoa in Jakata
- Mt Kilimanjaro in Tanzania
- Mt Cameroun in Cameroun
- Mt Fujiyama in Japan
- Mt Elba in Italy
- Mt Versuvius in Italy
- Mt Popocatepetl in Mexico
- Mt Mayon in Phillipines
- My Cotopaxi in Ecuador
- Mt Etna in Sicily
- Mt Stomboli in Italy
The characteristics of composite volcanoes include:
- feature of extrusive volcanic activity
- found in areas of volcanic activity
- mainly made up of layers of ash, lava and cinder
- has a crater at the top
- makes the highest mountains in the world
- has dykes at the flanks
- broad at the base and tappers at the top/conical in shape
- have very steep slopes or concave slopes
- angle of slope is between 30⁰ to 40⁰
- have parasitic cones or conlets
- have subsidiary vents or dykes
The mode of formation of composite volcanic cones goes thus:
- formed in areas of volcanic activities
- built by alternating eruptions of pyroclastic materials and lava
- violent eruption of pyroclastic materials settle around the vent initially
- lava pours quietly to cover the pyroclastic ash materials
- eruption is mainly through a central vent
- processes are repeated to build a volcanic cone (ash and cinder cone)
- viscous lava blocks the vent and pipe
- subsequent violent eruption causes cracks to appear along the flanks
- volcanic materials are forced out through the flanks
- the materials cool and solidify to form parasitic cones
- many subsidiary cones /parasitic cones may develop at the flanks of the main volcano
- this forms a composite volcanic cone