Buddy Grazioli, age 11, of the Presidio of San Francisco, California, for his question:
What caused the explosion of Krakatoa?
The explosion of Krakatoa was the biggest bang of recorded history. Its thunderous roar was heard 3,000 miles away and its dust hung in the atmosphere over the world for several years. The stupendous upheaval started a titanic tidal wave that swept on its way from ocean to ocean around the globe.
The earth's most restless region of earthquakes and volcanoes surrounds.the Pacific Ocean. It is called the Ring of Fire. At one point, the ring detours in a sharp loop northwestward through Indonesia, paralleling a necklace of volcanic islands. Sumatra and Java form the western curve of the loop. These two long, thin islands are separated by a narrow finger of the Indian Ocean called the Sunda Strait. But this was not always so. In the remote past, this narrow strait was occupied by an immense volcano.
Long before recorded history, this giant mountain exploded with an earth shaking blast. Most of the mountain above and below the water was blown to dust and the sea rushed in and created the Sunda Strait. The massive cone shattered and later reformed into several cones high enough to form small volcanic isles. Later, four of these cones were joined together by other titanic eruptions. The isles of Rakata and Danon, Perboewatan and Verlatan merged to form the island of Krakatoa.
The peak of Krakatoa stood 1400 feet above the sea and in time its steep cindery sides grew vivid green cloaks of tropical foliage. But the deep zone in the earth's crust still was restless. In 1680, Krakatoa erupted and then for 200 years it seemed to sleep once more. But fiery pressures were building.up far below the ocean floor. In the spring of 1883, steamy smoke plumed up from Krakatoa's peak. There were rumblings and hisses and the ground of the whole island became warm.
On August 27, Krakatoa exploded. In two disastrous days, a series of blasts blew most of the island into eight cubic miles of dusty ashes. The roar reached China and Malaya, Australia and points 3,000 miles away. The lofty peak was reduced to a cavity 1,000 feet below the waves and only part of the old Rakata peak was left above water. White hot lava and falling fire bombs made the sea a steaming cauldron and the upheaval started a tsunami or tidal wave 100 feet high. This merciless wave drowned thousands of people on nearby shores and swept on, disturbing the oceans clear around the globe.
Volcanic activity is expected in this region of deep crustal unrest. For ages, the pressures beneath Krakatoa were building up, though they did not erupt to the surface. Perhaps the vents and cracks from the cone to the deep trouble zone were plugged with ancient volcanic debris. At last, the buried fury became so intense that it burst its tomb with history's greatest explosion. There were, however, many such explosions in the geological past. Ages ago, Krakatoa had known one and perhaps two explosions greater than the one that shocked the world in 1883.
An active volcano has open or partly open vents down to the trouble zone below. When the deep pressures become intense, lava and volcanic materials erupt through these shafts to the surface. But if the vents are sealed, the pressure cannot escape. The fury below continues to mount until at last it blows up in a shattering explosion. Until 79 A.D., Mount Vesuvius had no record of eruptions. Then the old volcano exploded, burying whole cities in cinders and turning the Bay of Naples into a seething turmoil. However, volcanic explosions like this one and the one on Krakatoa are very, very rare events.