What is a Volcano A volcano is a weak spot in the crust where molten material, or magma, comes to the surface. Magma is a molten mixture of rock –forming substances, gases, and water vapor from the mantle.

What is a Volcano When magma reaches the surface, its called lava. When lava cools, it forms solid rock. Volcanic activity is a constructive force that adds new rock to existing land and forms new islands.

What does the inside of a volcano look like? Magma chamber – the pocket beneath a volcano where magma collects Pipe – a long tube through which magma moves from the magma chamber to the Earth’s surface Vent – an opening where magma and gas leave the volcano Lava flow – area covered by lava as it pours out of a vent Crater – a bowl-shaped area that may form as the top of a volcano around the vent

Location of Volcanoes One major volcanic belt is the Ring of Fire, formed by the many volcanoes that rim the Pacific Ocean. Volcanoes can also form at “hot spots” far from the plate boundaries. Hot spots = Thermal Anomaly

Location of Volcanoes Volcanic belts form along the boundaries of Earth’s plates. Most volcanoes occur along diverging plate boundaries, such as the mid-ocean ridge, or in subduction zones (convergent boundaries) around the edges of oceans.

How Do Volcanoes Form at Hot Spots? Hot spot – an area where magma from deep within the mantle melts through the crust like a blow torch These are often in the middle of a plate Locations: Hawaii, Yellowstone national park in Wyoming

How Do Volcanoes Form at Diverging Plate Boundaries? sea-floor spreading: The plates move away from each other and Lava pours out of cracks in the ocean floor Ex. mid-ocean ridge In Iceland and the Azores Islands the volcanoes of the mid-ocean ridge rise above the ocean’s surface

How Do Volcanoes Form at Convergent Plate Boundaries? At subduction zones: Slabs of oceanic crust sink though a deep ocean trench into the mantle The crust melts due to increased pressure, temperature, and friction forming magma Less dense magma rises back towards surface and erupts as lava The denser oceanic crust dives under the continental crust. Examples include the volcanoes of the Andes Mountains in South America.

Volcanoes at Converging Boundaries Many volcanoes occur on islands, near boundaries where two oceanic plates collide called subduction zones. The volcanoes will usually create a string of islands called an island arc.

Volcanoes at Converging Boundaries Island arc – string of islands arcing in the shape of the deep ocean trench Major island arcs: Japan Indonesia

Where does Magma come from? Lava begins as liquid magma in the mantle Liquid magma is less dense than the surrounding solid material, this causes magma to flow upward into any cracks in the rock above Magma will continue to travel upward until it reaches the surface or is trapped beneath layers of rocks and then forms igneous rock.

Volcanic Activity Magma forms in the asthenosphere where it is under extreme pressure. Because liquid magma is less dense than the surrounding solid material, magma flows upward into any cracks in the rock above.

Volcanic Activity Just like the carbon dioxide in a can of Coke, magma contains dissolved gases under tremendous pressure. During a volcanic eruption, the gases dissolved in magma rush out, carrying the magma with them. A pyroclastic flow happens when an explosive eruption hurls out ash, cinders, and bombs as well as gases.

Characteristics of Magma The force of a volcanic eruption depends on the amount of gas dissolved in magma, how thick or thin the magma is, its temperature, and its silica content. Silica is a material that is formed from oxygen and silicon, and is one of the most abundant materials in the Earth’s crust and mantle. The more silica, the thicker the magma.

What causes some liquids to flow more easily than others? Viscosity – the resistance of a liquid to flowing The greater the viscosity of a liquid, the slower it flows. Ex. Honey The lower the viscosity of a liquid, the more easily a liquid flows. Ex. water

What factors determine the viscosity of magma? Silica content Silica – made up of particles of the elements oxygen and silicon; most abundant materials in Earth’s crust Silica content of magma ranges from about 50% to 70% The more silica magma contains the higher its viscosity; ex. Rhyolite The less silica magma contains the lower its viscosity; ex. Basalt Temperature Viscosity increases as temperature decreases; ex. Cold honey versus warm honey Pahoehoe – fast-moving hot lava that has a low viscosity Aa – slow-moving cooler lava that has a higher viscosity

Is all magma the same? No, some types of magma are thick and flow very slowly. Other types are fluid and flow almost as easily as water. Temperature and the amount of silica account for the differences Silica – material that is formed from the elements oxygen and silicon Obsidian – lava cools fast Pumice – gas bubbles get trapped leaving spaces

Types of Volcanic Eruptions The silica content of magma helps to determine whether the volcanic eruption is quiet or explosive. In quiet eruptions, magma flows out easily an the gas dissolved bubbles out gently.

Quiet Eruptions Quiet eruptions produce two different types of lava: pahoehoe and aa. Pahoehoe is fast moving, hot lava, that forms a wrinkled rock. Aa is a cooler and slower moving lava that when hardens forms rough jagged chunks.

Explosive Eruptions If its magma is thick and sticky, a volcano erupts explosively. It slowly builds up pressure in the volcanoes pipe, plugging it like a cork. Dissolved gasses cannot escape and build up so much pressure the EXPLODE VIOLENTLY! Pyroclastic flow

Stages of a Volcano An active, or live, volcano is one that is erupting or has shown signs it may erupt in the near future. A dormant, or sleeping, volcano is one that scientists expect to awaken in the future and become active. An extinct, or dead, volcano is unlikely to erupt again.

What type of landforms are created from lava? Shield Volcanoes Cinder Cone Volcanoes Composite Volcanoes Lava Plateaus Calderas

What is a shield volcano? A wide, gently-sloping mountain made of layers of lava and formed by quiet eruptions Shield volcanoes created the Hawaiian Islands

What is a cinder cone volcano? A steep, cone-shaped hill or mountain made of volcanic ash, cinders, and bombs piled up around a volcano’s opening.

What is a composite volcano? A tall, cone shaped mountain in which layers of lava alternate with layers of ash and other volcanic materials.

What is a caldera? The large hole at the top of a volcano formed when the roof of a volcano’s magma chamber collapses

Volcanic neck- Forms when magma hardens in a volcano’s pipe and the surrounding rock layer wears away. Dike- Magma that forces itself across layers of rock Sill- magma that squeezes between horizontal layers and hardens Dome mountains- When lava pushes rock layers upward in the shape of a dome. Batholiths- forms when a large body of rock cools inside of the crust.