2. Acid lavas:
These lavas are highly viscous with a high melting point. They are light colored with low
density and have a high percentage of silica. They flow slowly and seldom travel far before
solidifying. The resultant cone is therefore steep sided. Sometimes the lavas are so viscous
that they form a spine or plug at the crater.
Types of Volcanoes
There are three types of volcanoes: active, dormant and extinct. Volcanoes are said to be
active when they frequently erupt or when they have erupted within recent time. Those
that known to be erupted and shows signs of possible eruption in the future are described
as dormant. Volcanoes that have not erupted at all in historic times but retain the features
of volcanoes are termed extinct.
Extrusive landforms
Extrusive landforms are determined by the nature and composition of the lava and other
ejected materials that reach the surface of the earth. The fluid basic lava flowing for
distances produces lava plains and basalt plateau. Volcanic cones are most typical of the
extrusive features. The highly fluid lavas build up lava domes or shield volcanoes.
The highest and most common volcanoes have composite cones. They are
often called strato volcanoes. Mt Stromboli is a composite volcano whose frequent
eruptions make the summit glow and thus it is called as ‘Lighthouse of the Mediterraneam’.
Other well known composite volcanoes include Mt. Vesuvius, Mt. Fuji, Mt. Popacatapetl and
Mt. Chimborazo.
During an eruption material from the top of the conies blown off or collapses
into the vent widening the orifice into large crater. Some volcanoes may have greatly
enlarged depressions called calderas, which may be several miles across. Water may collect
in the crater or the caldera forming crater of caldera lakes, eg. Lake Toba in Sumatra.
SOME VOLCANIC ERUPTIONS
In the history of mankind perhaps the most disastrous eruptions were those of Mt.
Vesuvius, Mt. Krakatau and Mt. Pelee.
Mt. Vesuvius:
Mt. Vesuvius, standing 4000 feet above Bay of Naples, erupted violently
on 24 Aug A.D 79 taking the people who lived around by complete surprise. Then came the
catastrophic eruption of December 1631 when an avalanche comprising red hot volcanic
debris
These lavas are highly viscous with a high melting point. They are light colored with low
density and have a high percentage of silica. They flow slowly and seldom travel far before
solidifying. The resultant cone is therefore steep sided. Sometimes the lavas are so viscous
that they form a spine or plug at the crater.
Types of Volcanoes
There are three types of volcanoes: active, dormant and extinct. Volcanoes are said to be
active when they frequently erupt or when they have erupted within recent time. Those
that known to be erupted and shows signs of possible eruption in the future are described
as dormant. Volcanoes that have not erupted at all in historic times but retain the features
of volcanoes are termed extinct.
Extrusive landforms
Extrusive landforms are determined by the nature and composition of the lava and other
ejected materials that reach the surface of the earth. The fluid basic lava flowing for
distances produces lava plains and basalt plateau. Volcanic cones are most typical of the
extrusive features. The highly fluid lavas build up lava domes or shield volcanoes.
The highest and most common volcanoes have composite cones. They are
often called strato volcanoes. Mt Stromboli is a composite volcano whose frequent
eruptions make the summit glow and thus it is called as ‘Lighthouse of the Mediterraneam’.
Other well known composite volcanoes include Mt. Vesuvius, Mt. Fuji, Mt. Popacatapetl and
Mt. Chimborazo.
During an eruption material from the top of the conies blown off or collapses
into the vent widening the orifice into large crater. Some volcanoes may have greatly
enlarged depressions called calderas, which may be several miles across. Water may collect
in the crater or the caldera forming crater of caldera lakes, eg. Lake Toba in Sumatra.
SOME VOLCANIC ERUPTIONS
In the history of mankind perhaps the most disastrous eruptions were those of Mt.
Vesuvius, Mt. Krakatau and Mt. Pelee.
Mt. Vesuvius:
Mt. Vesuvius, standing 4000 feet above Bay of Naples, erupted violently
on 24 Aug A.D 79 taking the people who lived around by complete surprise. Then came the
catastrophic eruption of December 1631 when an avalanche comprising red hot volcanic
debris
