Volcanoes start to form at the mantle when rocks melt.                       This happens because of extreme heat and pressure.  When the magma gets large enough it rises to the surface.  Then it is called lava.  Different types of lava form, depending on the composition of the rocks mantle.
            Volcanic rock comes in three composition, which are called: basalt, andesite, and hydilite. Basaltic, is the most common and has the least silica content whereas tyolitic has high silica content, but rare.  Andesite contains more gases.  But lava flows are not a serious threat since they are so slow.  Falling ash creates a bigger threat.  The tephra is the ash that cause a threat and are most common.
            Volcanoes form on plate boundaries. There are three types called; convergent which come together, also there is divergent, which are the exact opposite, and split apart.  The transform fault slides against each other.  Tilt meters and geometer can monitor volcanoes. These instruments help predict volcanoes.  So forecasting volcanoes can save people.
 

                                                 Nyiragongo
            The Nyiragongo volcano in Zaire is 11,365 feet tall.  It is part of the Virunga Volcanic chain in Africa.  It is Africa's most active volcanoes, with the most current activity beginning in June 1994.  It is a statovolcano, which contains both lava flows and pyroclastic material.  It is in a National park called Virunga.
            From 1894 to 1977 it had a lava lake from a crater.  Then on January 10,1977, the lake drained in about an hour.  It erupted, killing 70 people. The volcano erupted in fissures, which have liquid flows also pyroclastics, which were traveling at 40 miles. In 1994 the lake filled up again, with 130 feet diameter and 500 ft. deep.
 
 

                                                                         Spurr
            The Spurr Alaska volcano is 11,066 feet high.  It is also a stratovolacano, which is mostly composed of andestie which also contains  silicon, iron and magnesium.  It was actually made on top of another volcano. It is about 12 miles around.
            The base is surrounded by ash flows and apyroclastic.  Snow covers the north side, and the upper part being mostly lava flows. A second brach grew off the older volcano. It is 4 miles wide, which is mostly covered with ice.  The year 1992 the volcano erupted 3 times, the 3rd time being the most recent eruption.

                                          What Causes an Eruption?
            Eruptions happen on plate boundaries. An eruption happens when magma builds up and rise to the surface. Some are more dangerous then others. If you can predict when a eruptions are going to occur,more people will be saved. For more information click here.
 

                                                Hazards of Volcanoes
            A volcano's eruption can either be explosive or lava flows. Lava flows can be spatter cones, lava fountains, and flood basalts.  They are not as hazardous, but have global consequences.  Explosive volcanoes eruptions cause ash fall, pycoclastic flows, alvolcanoe and landslides.  But both can kill and damage property and nature. For more information click here.