Hugh Richardson, age 14, of Nashua, N.H., for his question:
WHERE IS THE LARGEST VOLCANO?
A volcano is an opening in the crust of the earth which allows hot gases and molten rock to flow or blow out. The world's largest volcano is named Mauna Loa and it is found in Hawaii. This volcano, and another one called Kilauea, are the only active volcanoes in Hawaii where all of the islands themselves are tops of great volcanic mountains built up from the ocean floor.
Mauna Loa rises about 30,000 feet from the ocean floor and is more than 60 miles wide at its underwater base. The top of the volcano is 13,677 feet above sea level.
The gigantic volcano is located on the western end of the large island of Hawaii, in Hawaii Volcanoes National Park. About 50 percent of the entire island is made of lava from Mauna Loa.
Since the first part of the 19th century, Mauna Loa has sent out flows of lava once every four years or so.
The word volcano comes from "Vulcan," the ancient Roman god of fire.
There are three types of volcanoes: explosive, quiet and intermediate. The volcanoes of Hawaii are of the quiet type, which produce basaltic lava.
Mount Vesuvius in Italy is an example of the intermediate type volcano. Until A.D. 70 it was thought to be extinct, but then it erupted and destroyed the city of Pompeii at its base. The volcano has also erupted occasionally since then, including a large explosion in 1944.
Perhaps the most spectacular example of the explosive volcano can be found in Krakatoa, located in Indonesia between Sumatra and Java. It had been inactive for 200 years until 1883. That year there was a great eruption. More than four and a half cubic miles of ash was blown out at one time, leaving a hole five miles wide. The whole top of the mountain disintegrated. It had been 2,600 feet high and ended up as a hole 1,000 feet deep.
Krakatoa created a 120 foot tidal wave that killed about 35,000 people in Java. The eruption sound was heard as far away as Australia.
Many of the earth's active volcanoes are found around the border of the Pacific Ocean. There is also much earthquake activity in this region.
Rock that is produced from a volcano's eruption can come in a variety of forms. It may be in the form of lava, which is molten rock. This material may be thick and slow moving or it may be thin and rapidly flowing.
Rock may erupt in the form of cinders that resemble clinkers from a coal fire or it may erupt in the form of black smoke, which is really ash.
Pumice may also be produced from a volcano. This is rock that is so full of tiny bubbles that at times it is light enough to float.
The way in which a volcano erupts depends on the pressure of the gases and the kind of lava.
During the past 400 years there have been more than 400 volcaniceruptions on earth.