Volcanoes

Target #16- I can summarize the conditions needed for magma to form Despite the high temperature in the mantle, most of the layer remains solid due to extreme pressure Magma: liquid rock produced under Earth’s surface

Melting Point: the temperature at which a substance will change from a solid to a liquid Magma can form in three ways Temperature rises above the melting point of rock Pressure decreases lowering the melting point of rock Addition of fluids, like water, can decrease the melting point Target 16- cont.

Target 17- I can define volcanism Target #18- I can differentiate between magma and lava Volcanism: any activity that includes the movement of magma and gases toward or onto Earth’s surface Magma rises because it is less dense than the surrounding rock magma that flows onto Earth’s surface is called lava Flows from an opening, or vent

Target #19- I can differentiate between mafic and felsic magma When magma erupts from a volcano and then cools & hardens, it forms an igneous rock Mafic: magma that is rich in magnesium and iron Dark in color Makes up oceanic and continental crust Felsic: magma that is rich in feldspar and silica Light in color Makes up continental crust only

Target #20- I can describe viscosity Viscosity: resistance to flow Affects the force with which a particular volcano will erupt Target #20- I can describe viscosity

Target #21- I can describe quiet eruptions Form from mafic magma Low viscosity Occur with oceanic volcanoes Magma “oozes” out of the vent

When mafic lava cools rapidly, a crust forms on the surface of the flow If the lava continues to flow after the crust forms, the crust wrinkles Pahoehoe: a volcanic rock that forms from hot fluid lava As it cools it forms a smooth, ropy texture Means “ropy” in Hawaiian Target #22- I can describe the lava rocks produced from quiet eruptions

Target #22- cont. If the crust deforms rapidly, or grows too thick to form wrinkles, the surface breaks into jagged chucks Aa: a jagged volcanic rock that forms from lava that has the same composition as pahoehoe Blocky Lava: a volcanic lava that has a high silica content, and is highly viscous

Target #23- I can describe explosive eruptions The felsic lavas of continental volcanoes tend to be cooler and stickier than the fluid lavas produced by oceanic volcanoes Pyroclastic material: fragments of rock that form during a volcanic eruption

Bellwork What are the differences between an explosive eruption and a quiet eruption?

Types of Volcanoes

Target #24- I can identify where volcanoes are located Volcanoes are usually located at the edge of plate boundaries Ex: A major zone of active volcanoes encircles the Pacific Ocean Known as the Pacific Ring of fire Subduction zones Continental-oceanic convergent boundaries Oceanic-Oceanic convergent boundaries Target #24- I can identify where volcanoes are located

Target #24 cont. The largest amount of magma is found at divergent boundaries along mid-ocean ridges The magma erupts to form underwater volcanoes These volcanoes produce pillow lava

Target #25- I can differentiate between shield, cinder, and composite volcanoes Shield Volcanoes: volcanic cones that are broad at the base and have gently sloping sides Covers a wide area Generally forms from quiet eruptions Layers of hot, mafic lava flow out around the vent, harden, and slowly build up to form the cone Ex: Hawaiian Islands

Target #25- cont. Cinder Cones: a volcano that has a very steep slope Not usually tall- max height is not more than a few hundred meters Form from explosive eruptions and are made of pyroclastic material

Composite Volcanoes: made of alternating layers of hardened lava and pyroclastic material Quiet eruptions deposits lava and an explosive eruption follows depositing ash Also known as stratovolcanoes Develop to form large volcanic mountains Target #25- cont.

Target #26- I can describe a caldera Caldera: a large, circular depression that forms when the magma chamber below a volcano partially empties and causes the ground above to sink Calderas may fill with water to form lakes Ex: Mount Mazama in Oregon (known as Crater Lake) Target #26- I can describe a caldera

Target #27- I can describe how a hot spot forms an island chain Hot Spot: an area of volcanic activity within the interior of a tectonic plate Magma rises from the mantle in the middle of a plate, and not at a plate boundary The rising magma creates a volcano, producing an island As the plate shifts over the magma, a new volcano and new island is formed Continues creating a chain of islands Ex: Hawaiian Islands Target #27- I can describe how a hot spot forms an island chain