Mt Kilimanjaro in Tanzania is a dormant volcano It is the tallest mountain in Africa and is 19,341 feet 5,895 meters tall Volcanoes that have produced lava or eruptions in the past 10,000 years or since the Ice Age are active volcanoes Eruptions happen when molten rock gases and ash from below the Earth’s surface are forced up and out through cracks Hot Fact Alaska contains three-fourths of the volcanoes that have erupted in the past 200 years 6 Dormant volcanoes are active volcanoes that are not erupting but are expected to erupt again Extinct volcanoes have not erupted in at least 10,000 years and are not expected to erupt again Still some extinct volcanoes have surprised people and erupted in the past
Types of Volcanoes Volcanoes are often classified by shape and how they were formed However not every kind of eruption falls into a single group The speed of the flowing lava builds the shape Slow-moving lava forms a gently sloping cone called shield volcanoes They are not normally explosive Shield volcanoes are most often basalt a type of lava that is very liquid and flows easily This view of Mauna Loa from Mauna Kea in the late evening shows the distinctive shape of shield volcanoes Mauna Loa one of five volcanoes that form the island of Hawaii is one of the largest active volcanoes today The mountain it forms is 60 miles 97 kilometers long and 30 miles 48 kilometers wide Mauna Loa is the Hawaiian term for long mountain It is a shield volcano Its eruptions have averaged one every six years for the past 300 years 7
Cinder cones are the simplest type of volcanoes Lava flows out of a central vent and down the sides forming a cone The lava in a cinder cone volcano cools quickly It builds up rock to form the typical steep-sided cone The cinder cone can be part of another volcano system such as one growing on a shield volcano Paricutin in Mexico is a cinder cone volcano Strato volcanoes produce two types of lavas These lavas are thicker and cooler than basalt The thick lavas often plug the opening Different gases build up below the plug They make a more explosive eruption when they blow The tall sides may trigger mud or landslides and earthquakes during an eruption 8
The lava pours down the volcano’s sides Cooled layers of rock form the sides Strato volcanoes are also called composite volcanoes Over half of the world’s volcanoes are strato volcanoes Mt St Helens Mt Rainier and Mt Fuji are strato volcanoes eruption of lava pyroclastic material volcanic crater solidified ash layer side vents smoke and ash solidified lava layer steam crust mantle central conduit channel magma chamber Magma comes from the upper fluid part of the mantle and moves upward and out through a variety of vents Mt St Helens in Washington Hot Fact Mt St Helens lost a large section of its north side when it erupted because it was so explosive Mt Rainier in Washington Mt Fuji in Japan 9
