Volcanoes Chapter 13 Volcanoes Plate Tectonics Volcanic eruptions

Volcanoes Chapter 13

Volcanoes & Plate Tectonics • Volcanic eruptions can be caused by the movement of tectonic plates • Plates are moved by the internal heat of the Earth • A volcanic eruption can be more powerful than an atomic bomb

Formation of Magma • Magma – liquid rock that forms under Earth’s surface • Comes from melted crust and mantle

Volcanism • Magma naturally rises to the surface because it is less dense • The amount of magma increases because it melts rock along the way

Volcanism • Volcanism – any activity that includes the movement of magma onto Earth’s surface • Lava – magma that has reached the surface • Volcano – the vent in Earth’s surface where magma reaches the surface

Major Volcanic Zones • Like earthquakes, volcanoes tend to occur near convergent or divergent plate boundaries

Subduction Zones • Where one plate goes beneath another • Oceanic crust + oceanic crust = island arc chain • Oceanic crust + continental crust = mountain range

Mid-Ocean Ridges • The largest amount of magma comes to the surface at mid-ocean ridges • Forms under water volcanoes • Water quickly cools the lava creating pillow lava

Hot Spots • Volcanically active areas in the interior of a tectonic plate • The plate moves over the hot spot, causing a volcano to form • That volcano eventually moves away and a new one forms

Intrusive Activity • Magma that cools and solidifies under the ground (intrusion) • Forms plutons – Dikes (thin areas) – Batholiths (large areas >100 km 2) Devil’s Tower Wyoming

Exit Ticket 1. What is the difference between lava and magma? 2. Which of the following is the most accurate definition of volcano: • A. Any activity that includes the movement of magma toward or onto Earth’s surface. • B. Magma that flows onto Earth’s surface; the rock that forms when lava cools and solidifies • C. A mountain of rock that spews hot lava onto Earth’s surface • D. A vent or fissure in Earth’s surface through which magma and gases are expelled.

Do Now • Create a hypothesis that answers the question: • Which liquid will be able to trap the most bubbles when I blow into the liquid through a straw: water, cooking oil or honey? (Use I think… because… form) !

Viscosity • A fluids resistance to flow. • Magma can have different viscosities, which affect the force with which a particular volcano will erupt.

Volcanic Eruptions • 2 types of magma – Mafic – magma or rock rich in magnesium and iron; dark colored – Felsic - magma or rock rich in silicates; light colored

Types of Eruptions • Quiet Eruptions – Usually oceanic volcanoes (ex. Hawaii) – Lava has a low viscosity (runny) – Gases easily escape from the lava – Formed from mafic magma

Types of Eruptions • Lava Flows – Crust may form on top of the lava – If the lava keeps flowing, it forms wrinkles called pahoehoe Aa lava – surface breaks into jagged chunks Blocky lava – lava is more viscous (thicker)

Types of Eruptions • Explosive Eruptions – Usually continental volcanoes (ex. Mt. St. Helens) – Lava has a high viscosity (thick & sticky) formed from felsic magma – Gases trapped inside lava – Pyroclastic material – fragments of rock that form during a volcanic eruption • Thrown into the air during an explosive eruption

Pyroclastic Material • Volcanic ash – <2 mm in diameter • Lapilli – <64 mm in diameter – “little stones” • Volcanic bombs – Form when red hot lava is thrown and cools in the air • Volcanic blocks – Largest material – Pieces of rock blasted from the vent

Quick Check • Using the term viscosity, explain why a milkshake is harder to drink with a straw then a can of pop.

Calderas • Can form when the magma chamber empties and the cone collapses • Lakes can form in the caldera basin Crater Lake (Mount Mazama) Oregon

Predicting Volcanic Eruptions • Increase in strength and frequency of earthquakes may be a sign of an eruption • Before an eruption, the surface of a volcano may bulge outward from the magma • Scientists compare a volcano’s previous behavior to current measurements

Types of Volcanoes • The shape of a volcano is related to the composition of its matter. • http: //www. youtube. com/watch? feature=pla yer_embedded&v=u. Zp 1 d. Nybgfc

Types of Volcanoes • Shield volcano – Broad base; gently sloping sides – Covers wide area – Quiet eruption – Layers of mafic lava build up cone – Ex: Hawaiian Islands

Types of Volcanoes • Cinder cones – Very steep slopes – Rarely less than a few hundred meters high – Explosive eruptions – Cone made of pyroclastic material – Ex: Parícutin, Mexico

Types of Volcanoes • Composite volcano – Cone made of alternating layers of… • lava flows (quiet eruptions) • pyroclastic material (explosive eruptions) – Form large volcanic mountains – Ex: Mt. Hood, Mt. St. Helens, Mt. Rainier, Mt. Fuji

Exit Ticket The depression that results when a volcanic cone collapses over an emptying magma chamber is a: • A. Crater • B. Caldera • C. Vent • D. Fissure • Compare three main types of volcanic cones: Shield, Composite, and Cinder-Cone.