What do Jejudo, Sicily, and Hawaii have in common? They are islands, of course. In fact, they are all islands made from volcanic eruptions. Volcanoes are very powerful, so they are named after Vulcan, the Roman god of fire. They can make big islands appear or destroy entire cities like Pompeii. Therefore, they should be studied and understood. Nobody knows for sure how many volcanoes there are in the world. According to scientists, there are about 1,500 active volcanoes above sea level. Many more are underwater, and they are hard to locate. Still, scientists have discovered a large number of them so far.

Many of the volcanoes on Earth are located along the Ring of Fire that circles the Pacific Ocean. The ring is about 40,000 kilometers long, and it is home to around 75% of the world's active volcanoes. Indonesia alone has over 120 active volcanoes since the country lies on the Ring of Fire. This ring is also the area where most of the world's earthquakes occur. 《A Sudden Volcano》 Working on a cornfield one day in 1943, farmers in Mexico found something surprising. A volcano appeared overnight on a flat cornfield. Residents watched the volcano grow over 100 meters tall within a week. The volcano, called Paricutin, kept growing, and it finally stopped growing at 424 meters in 1952. You may think volcanoes can be found only on Earth. However, they have been discovered on other planets, too, such as Mars and Jupiter. In fact, Olympus Mons on Mars is the largest known volcano in the solar system. Its volume is about 100 times greater than that of Mauna Loa, the largest volcano on Earth.

Being very powerful and dangerous, volcanoes do harm to people in many ways. Sometimes people get hurt, or they may lose their houses. Crops may be destroyed, and air traffic can be threatened. Volcanoes can also have serious effects on world weather. A volcanic eruption shoots lots of ash and dust into the air, preventing some of the sunlight from reaching Earth and thus disturbing usual weather patterns. 《A Deadly Volcano》 Mt. Tambora, an active volcano on the island of Sumbawa, Indonesia, erupted in 1815. The eruption killed more than 10,000 residents. It also caused an unusually cold summer around the world the following year. What volcanoes do is not always bad for humans, however. The soil near a volcano is good for farming. Volcanoes are also a great tourist attraction. Looking for fantastic scenery, millions of tourists visit Mt. Halla in Jejudo, Mt. Etna in Sicily, or Diamond Head in Hawaii every year. Volcanoes can be used to produce electricity, too. Iceland, for example, actively turns its volcanoes' heat energy into electricity. Today people around the world are studying ways to live in greater harmony with volcanoes, and they are hopeful that more ways will be found soon.