Sunday, December 26, 2010

PROJECT natural disasters --- Volcanic eruptions

volcanic eruptions

During a volcanic eruption, lava, tephra and various gases are expelled from a volcanic vent or fissure. Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series.

Different Type of Volcanoes and Eruptions

Shield volcanoes- these are broad shielded volcanoes formed by eruptions of lava having low viscosity. Lava of these volcanoes usually don’t get explode out but it can travel a large distance with very low velocities.
Lava domes- these are the volcanoes which came into origin by eruptions of lava with high viscosity. These volcanoes produce very violent and explosive eruptions. Their lava don’t travel large distances from the vent.
Stratovolcanoes- These are also called as composite volcanoes. These are tall mountains of conical shapes; these volcanoes are composed of flowing lava and ejecta in layers, called strata. Most common example is the Mt. Fuji of Japan. These volcanoes claim most hazardous eruptions of history.

Super volcanoes- It is simply a term used for large sized volcanoes. These volcanoes usually produce lava on very large scales. Supervolcanoes eruptions cause extreme cooling of the surrounding global temperatures, because they produce a large amount of sulfur and ash clouds. This decrease in temperature lasts for many years. So they can be classified as the most dangerous volcanoes, for example- Lake Taupo of New Zealand.

Submarine volcanoes- These are the volcanoes which are located at the floors of oceans. They can be at lower or extreme depths. Those volcanoes which are present at lower depths produce bubbles of steam and gases, which can be observed above the sea surface. But other volcanoes which are present at extreme depths are almost invisible about their existence. But even these deep volcanoes can also be marked by observing discoloring of water at a particular portion of ocean. This discoloration is because of release of volcanic gases in the sea.
Other less common types of volcanoes are sub glacial volcanoes, Antarctica volcanoes, mud volcanoes etc.






Thursday, December 23, 2010

PROJECT natural disasters --- Flood

Flood
A flood is an overflow of an expanse of water that submerges land.Flooding may result from the volume of water within a body of water, such as a river or lake, which overflows or breaks levees, with the result that some of the water escapes its usual boundaries.it is not a significant flood unless such escapes of water endanger land areas used by man like a village, city or other inhabited area.Floods can also occur in rivers, when flow exceeds the capacity of the river channel, particularly at bends or meanders. Floods often cause damage to homes and businesses if they are placed in natural flood plains of rivers. While flood damage can be virtually eliminated by moving away from rivers and other bodies of water, since time out of mind, people have lived and worked by the water to seek sustenance and capitalize on the gains of cheap and easy travel and commerce by being near water.