Shirley Duke - Volcanoes

VOLCANOES

Shirley Duke

Volcanoes begin deep within the Earth. Hot, collects far underground. Forces below it crack the underground rock. Pressure pushes melted rock upward through these openings. The molten rock explodes from the opening or flows out.

The molten rock is now lava. Once cooled, the lava solidifies and becomes igneous rock. Over time, a cone shape builds up.

Hot Fact

Igneous rock is one of three main types of rocks. The other types are sedimentary and metamorphic.

Magma chambers underground hold different amounts of magma. Cracks and allow the hot magma to move upward and collect in chambers in volcanoes. Certain conditions force the magma above ground, where it cools as lava.

Did You Know?

The word volcano came from the name of the Roman god Vulcan. People once thought the lava and gas clouds erupting from the island of Vulcano was Vulcan forging thunderbolts for Jupiter, king of their gods, and for Mars, their god of war.

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 Earths 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.

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 , 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.

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.

The lava pours down the volcanos sides. Cooled layers of rock form the sides. Strato volcanoes are also called composite volcanoes. Over half of the worlds volcanoes are strato volcanoes. Mt. St. Helens, Mt. Rainier, and Mt. Fuji are strato volcanoes.