Volcanoes VOLCANIC LANDFORMS What Landforms Do Lava and

Volcanoes VOLCANIC LANDFORMS

What Landforms Do Lava and Ash Create? • Volcanic eruptions create landforms made of lava, ash, and other materials. • These landforms include shield volcanoes, cinder cone volcanoes, composite volcanoes, and lava plateaus. • Other landforms include calderas, which are the huge holes left by the collapse of volcanoes.

Calderas • Large eruptions can empty the main vent and magma chamber beneath a volcano. • With nothing to support it, the mountain top may collapse inward. • A caldera is the hole left when a volcano collapses.

• A lake can form, filling the hole. • If the volcano erupts again, a steep-walled cone may form in the middle.

Cinder Cone Volcanoes • If a volcano’s magma has high silica content, it will be thick and sticky. • So the volcano can erupt explosively, producing ash, cinders, and bombs. • These materials can build up around the vent in a steep, cone-shaped hill or small mountain that is called a cinder cone.

• For example, Paricutin in Mexico erupted in 1943 in a farmer’s cornfield. • The volcano built up a cinder cone that was about 400 meters high.

Composite Volcanoes • Sometimes, the silica content of magma can vary. • So eruptions of lava flows alternate with explosive eruptions of ash, cinder, and bombs. • The result is a composite volcano.

• Composite volcanoes are tall, cone-shaped mountains in which layers of lava alternate with layers of ash. • Mount Fuji in Japan and Mount St. Helens in Washington State are composite volcanoes. • Composite volcanoes can be more than 4, 800 meters tall.

Shield Volcanoes • At some spots on Earth’s surface, thin layers of lava pour out of a vent and harden on top of previous layers. • Such lava flows slowly build a wide, gently sloping mountain called a shield volcano. • Hot spot volcanoes that form on the ocean floor are usually shield volcanoes. • For example, in Hawaii, Mauna Loa rises 9, 000 meters from the ocean floor!

Lava Plateaus • Lava can flow out of several long cracks in an area. • The thin, runny lava floods the area and travels far before cooling and solidifying. • After millions of years, repeated floods of lava can form high, level plateaus. • The Columbia Plateau is a lava plateau that covers parts of Washington State, Oregon, and Idaho.

• Homework is pages 168 & 169

What Landforms Does Magma Create? • Sometimes magma cools and hardens into rock before reaching the surface. • Over time, forces such as flowing water, iced, or wind may strip away the layers above the hardened magma and expose it. • Features formed by magma include volcanic necks, dikes, and sills, as well as dome mountains and batholiths.

Volcanic Necks • A volcanic neck forms when magma hardens in a volcano’s pipe and the surrounding rock later wears away.

Dikes and Sills • Magma that forces itself across rock layers hardens into a dike. • Magma that squeezes between horizontal rock layers hardens to form a sill.

Dome Mountains • Bodies of hardened magma can create dome mountains. • A dome mountain forms when uplift pushes a large body of hardened magma toward the surface. • The hardened magma forces the layers of rock to bend upward into a dome shape.

• Eventually, the rock above the dome mountain wears away, leaving it exposed. • This process formed the Black Hills in South Dakota.

Batholiths • A batholith is a mass of rock formed when a large body of magma cools inside the crust. • Batholiths form the core of many mountain ranges. • Over millions of years, the overlying rock wears away, allowing the batholith to move upward. • Flowing water and grinding ice slowly carve the batholith into mountains.

• Volcanoes and Volcanic Landforms Interactive Art • Homework is pages 170 -173