Section 1: Volcanoes and Plate Tectonics What Is a Volcano? Volcano – a weak spot in the earth’s crust where molten material (magma), comes to the surface Magma – molten mixture of rock-forming substances, gases, and water from the mantle Lava – when magma reaches the surface it is called Lava Volcanic activity is a constructive force that adds new rock to existing land and forms new islands

Where Are Volcanoes Located? There are about 600 active volcanoes on land and more beneath the sea Ring of fire – one major volcanic belt where volcanoes rim the pacific ocean Three major locations: Diverging plate boundaries Converging plate boundaries Hot spots

How Do Volcanoes Form at Diverging Plate Boundaries? 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 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 Convergent Plate Boundaries? At subduction zones: Slabs of oceanic crust sink though a deep ocean trench into the mantle The crust melts forming magma Magma rises back towards surface and erupts as lava Many volcanoes occur on islands but can occur on land where a continental plate collides with a oceanic plate Island arc – string of islands arcing in the shape of the deep ocean trench Major island arcs: Japan Indonesia

Section 2: Properties of Magma 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

What is magma made up of? Elements and Compounds Each substance has a particular set of physical and chemical properties that can be used to identify a substance or to predict how it will behave Elements – substances that cannot be broken down in other substances Compound - a substance made of two or more elements that have been chemically combined

What are physical and chemical properties? Physical Property – any characteristic of a substance that can be observed or measured without changing the composition of the substance Ex. Boiling point Chemical Properties – any property that produces a change in the composition of matter. Ex. Silver jewelry darkening when exposed to air

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

Why do liquids differ in viscosity? In some liquids, there is a greater degree of friction among the liquid’s particles – these liquids have higher viscosity

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

Section 3: Volcanic Eruptions What happens as a volcano erupts? As magma rises toward the surface, the pressure decreases allowing the dissolved gases to separate out forming bubbles During a volcanic eruption, the gases dissolved in magma rush out, carrying the magma with them

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

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

What types of volcanic eruptions are there? Quiet eruptions – magma appears to flow out easily producing pahoehoe and aa lava Explosive eruptions – pressure inside the volcano builds possibly resulting in a pyroclastic flow

Shield Volcanoes Cinder Cone Volcanoes Composite Volcanoes Calderas Section 4: Volcanic Landforms 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

Mount St. Helens Mount st helens before it erupted in 1980-smoke coming out but trees and snow still there-sides are turning black-trees blown down by gas like toothpicks