Volcanic Activity Chapter 18 https://www.youtube.com/watch?v=s2i4XS0Esks

Magma Formation Forms deep beneath the Earth’s surface Temperature must be high enough to melt rocks What factors, other than temperature, affect the formation of magma? Magma Formation

Factors Affecting Magma Formation Rocks in Earth’s lower crust and upper mantle do not melt to form magma, even though temperatures are high enough. Pressure Increases with depth As pressure increases, melting point increases Factors Affecting Magma Formation

Factors Affecting Magma Formation 2. Water: Water lowers the melting point of rocks Factors Affecting Magma Formation

Classifying Magma Magma is classified based on the composition Composition of magma impacts magma’s viscosity Types of Magma: Basaltic Andesitic Rhyolitic Classifying Magma

Types of Magma Basaltic Magma Forms in upper mantle Low viscosity Small amounts of dissolved gas and silica Quiet eruptions Types of Magma

Types of Magma 2. Andesitic Magma Found in subduction zones ~60% Silica Intermediate viscosity Source material Ocean crust Ocean Sediments Types of Magma

Types of Magma 3. Rhyolitic Magma Forms from mixing of molten material with silica and water-rich continental crust High Viscosity Large volume of trapped gas Explosive volcanoes Types of Magma

Viscosity Higher temperatures = lower viscosity More silica = higher viscosity Viscosity

Plutons Form when magma cools beneath the Earth’s surface Intrusive igneous rock bodies Can be exposed at Earth’s surface Classified by: Size Shape Relationship to surrounding rock Plutons

Types of Plutons Batholiths Stocks Irregular shape Largest Common in mountain chains Mainly composed of granite Gabbro and diorite also California Stocks Irregular shape Smaller than batholiths Types of Plutons

Batholiths in Real Life

Types of Plutons 3. Laccoliths Rounded side and flat side Mushroom shaped Up to 16 km wide Utah, South Dakota, Montana How did this laccolith become exposed at Earth’s surface? Types of Plutons

Types of Plutons 4. Sills 5. Dikes Intrudes parallel layers of rocks Few cm to hundreds of meters Svalbard 5. Dikes Cuts across preexisting rocks Arizona Types of Plutons

Sills and Dikes in Real Life

Label

Anatomy of a Volcano Vent: hole where lava comes out Crater: depression around vent Less than 1 km Calderas: larger depressions Crater Lake Anatomy of a Volcano

Types of Volcanoes Shield Volcanoes: Broad, gently sloping sides Circular base Largest type Layered basaltic lava Hawaiian Islands Types of Volcanoes

Types of Volcanoes 2. Cinder-Cone Volcanoes: Material ejected piles up around vent Steep sides Usually small <500m high More water and silica than shield Hawaii Types of Volcanoes

Types of Volcanoes 3. Composite Volcanoes Layered volcanic fragments with lava Magma has large amounts of silica, water, and gases Mount St. Helens Types of Volcanoes

Tephra: rock fragments thrown in the air during a volcanic eruptions Classified by size Ranges from ash to the size of a car or house Volcanic blocks: angular fragments Volcanic bombs: rounded tephra Volcanic Material

Clouds of gas, ash, and other tephra moving at incredible speeds Nearly 200 km/hr Can contain poisonous gases Temperatures can exceed 700°C https://www.youtube.com/watch?v=yvG_N7eqMWk https://www.youtube.com/watch?v=Cvjwt9nnwXY Pyroclastic Flows

Where Do Volcanoes Occur? Convergent Volcanism Magma is forced upwards through the plate and forms volcanoes Pacific Ring of Fire – Does the affect our country? Where Do Volcanoes Occur?

Where Do Volcanoes Occur? Divergent Volcanism Magma is forced upward into fractures and faults Rift volcanism occurs along ocean ridges This is how new seafloor is formed Iceland Divergent volcanism above water Where Do Volcanoes Occur?

Where Do Volcanoes Occur? Hot Spots Regions of the mantle where high temperature material moves to the surface Moves vertically, not laterally Hawaiian Islands Oldest island = Kauai Where Do Volcanoes Occur?