A volcano is a hill or mountain constructed by the extrusion (center) of lava, or solidified magma. In volcanoes pillow lava or rocks form in a pillow shape mass, fitting closely together. This is caused by underwater lava flow. A a cooling agent, lava produces pumice. In a volcano the gas cannot escape easily and the lava is turned into a froth. This forms pumice, or a frothy glass with void space that floats in water. A volcano produces obsidian, which is a volcanic gas not composed of minerals.
 
 

WHAT HAPPENS IN VOLCANOES?

In a volcano lava is solidified quickly as it is blasted by gases into the air, producing pyroclasts or rock fragments. Pyroclastic debris also goes by the name tephra. In some parts of the world lava flows out of fissures into the ground as a flowing agent. The tephra and rock formed by the solidifying of lava are regarded as extrusive rock, or the surface of rock resulting from volcanic activity.
 
 

WHAT ARE THE TYPES OF VOLCANOES?

*Shield volcanoes are gently sloping cones constructed of solidified lava flows. During eruption the lava spreads wide and thin due to low vicousity. The slope it forms are 2 and 10 from the horizontal, more less forming a volcano shaped like a flattened dome or shield.

*Cinder Cone is a volcano constructed of pyroclast ejected from a control vent. Cinder cones have a slope of about 30. Most of the material ejected during this volcano lands near the vent, building up the cone to a peak. They are smaller than shield volcanoes.
 
 

*Composite volcano is constructed of alternating layers of pyroclastic and rock solidified from lava flows. The slopes are intermediate in steepness, compared to cinder cones and shield volcanoes. The lava flow flattens the profile of the cone as the downward flow builds up the height. The solidified lava acts as a protective cover over the pyroclastic layer, allowing the volcano to be less vulnerable to erosion. They build over a long span of time.
 
 

PROPERTIES OF VOLCANOES

1. Gentle running with low viscousity

2. Steep and thick with a high viscosity

*both are effected by the temperature, texture, physical and gastric properties.
 
 

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