shaped mountains which are flatter than strato volcanoes and built of lava flows. They may start on the sea floor and become so large that islands can rise far above sea level. The Hawaiian mountains were formed this way. The islands, which rise about 10,000 meters above the ocean floor, are the worlds most massive volcanoes.
Volcanoes also create holes, called craters and calderas. Calderas are larger than craters and are formed when parts of the volcano collapse. Sometimes these holes are filled with water and form a lake.
Volcanic activity
Some volcanoes are active. They erupt very often, like Italys Mount Etna, which erupts every few years. Inactive volcanoes have not erupted for a long time, but scientists warn that they may become active some day. Extinct volcanoes, like Mount Kenya in Africa, will probably never erupt any more.
Volcano experts do their best to warn the population when a volcano may erupt. Sometimes smaller earthquakes or clouds of gas from vents tell observers that a volcano could erupt soon. Most of the time, however, there are no signs at all.
Effects and benefits of volcanoes
Although volcanoes may cause a lot of damage and big eruptions can kill many people, there are also advantages of volcanic activity.
Volcanic lava and ash spreads over the slopes of mountains and creates good farmland. Volcanic rock is used to build roads, make special tools and ornaments.
The heat that is formed underneath a volcano is called geothermal energy. Hot water that lies below the surface is used to heat homes and greenhouses. Countries with many volcanoes like Japan, Iceland or Italy use this kind of energy to produce electric power.
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