For months after an eruption, dark skies, heavy rain and strong winds can be prevalent90. Geysers rely on volcanic heat to warm trapped groundwater, which they then expel into the air91. Only 20 to 30 volcanoes erupt each year92. The Hawaiian goddess of fire and volcanoes, Pele, was said to have a terrible temper and would throw lava at anyone who made her angry. She was thought to live in the crater of the Kilauea volcano93. Stratovolcanoes are the most common type of volcanoes. Mount Fuji in Japan and Mount Rainer in Washington state are examples of stratovolcanoes. About 20% of all existing volcanoes are located underwater95. Black beaches, like those in Hawaii and Iceland, have sand made from basalt; formed when lava cools and is broken into sand particles96. Geothermal energy uses the thermal energy of magma to operate power plants and heat water in some volcanic areas97. 10% of active volcanoes in the world are located in Japan98. The newest land mass on Earth, Sutsey Island, was created in 1963 from an underwater volcano99. In Japan, it is believed that illnesses can be cured by bathing in hot volcanic sand100. In 1865, the term "magma" was first used in geology to describe molten water.