Krakatau volcano   is in a small island in Indonesia. It had been peaceful for about 200 years before it erupted  in 1883. The first signs of the activity of the volcano appeared in May 1883, when fire and smoke could be seen at the top of the mountain. Great noise could be heard even in Jakarta a hundred miles away. Later the activity grew much greater. The peak  was covered with smoke and fire; the smoke at one time was seventeen miles high in the air. The lava--soft and hot rock--shot up into the air and rolled down the sides of the mountain. The mouth of the volcano was not at the peak of the mountain but on its side, close to the sea. As it grew bigger and bigger with the eruption, the sea water got into it. When the sea water reached the lava inside the volcano, it made the upper part of the lava colder and harder. And this sealed off   the rest of the lava below. As the inside of the lava could not break through the seal, the pressure   built up until the mountain blew up. The eruption of the volcano was followed by several earthquakes which brought about bad result. About 36000 people were killed and many towns and villages near the sea were completely destroyed by the great waves which the earthquake caused. What makes volcanoes erupt?
The sea water which goes into the volcano The lava. The pressure which is bigger and bigger. All the above.