VOLCANOES

A volcano is mountain surrounding an opening the earth's crust.Steam,gases ,lava,ashes and other materials are forced out almost continuosly from an active volcano.A dormant volcano,on the other hand,erupts at long intervals.In an extinct volcano,the crater has long been closed up with cold,solid lava.
Our earth was a sphere of gases which slowly cooled off from the outside,forming a thin crust of cold,solid materials,containing hot liquid,magma,and gases.It was the very high pressure of the gases forcing themagma through weak parts in the earth's crust that formed volcanoes.
There are some 500 volcanoes in our country,of which about 180 are still active.They are found in three rows.The first row stretches over distance of 7,000 km from North Sumatra,Java,the northern row of islands of Nusa Tenggara ending upon the of Saparua near Ambon.
The second row runs from Sulawesi trough Sangihe as far as the Philipine Islands,while the third runs from Irian to Halmahera.Kalimantan and the southern islands of NusaTenggara,lying outside those rows,are not volcanic.
Most of our vulcanoes are in Java.The most active one is Mount Merapi at the north of Jogja.The northern part of the crater has a high wall,so in eruptions the lava flows in every direction.The hot lava slowly cools off into what is "lahar".
In the rainyseason,when the cool "lahar" on Merapi's slopes is hit by rain it flows down the slopes with great force,destroying everyting in its path.The flow of "lahar" mixed with rocks fills up the rivers,while sand covers the fields.
The eruptions of sea vulcanoes cause high waves, flooding regions on the coasts.This happened when Krakatau erupted in 1833.The sound of the eruption was heard from places as far away as India and Australia,distances of 3,600 to 4,800 km from Krakatau.Around 18 cubic km of solid materials were thrown up.The skies above place as far away as the southern Pasific.Africa and South Amerika were darkened.30 metre high waves flooded the coast of Java and Lampung,sweeping away villages and 35,000 people.
However,vulcanoes are also a great blessing.Vulcanoes and mountains force the clouds to rise,and cool them off,causing them a drop the water they contain in the form of rain.
The materials thrown up by vulcanoes contain minerals needed by plants.The higher regions,being cool, are good for coffee,tea and other plantations.The woods on the slopes protect the soil againts erosion,while the soil acts as a water reservoir giving water to the rivers.