Volcanoes & Volcanism

Anatomy of a Volcano– Primary Features

Anatomy of a Volcano—Secondary Features

Anatomy of a Volcano—Tertiary Features Produced by the collapse of a volcano into its emptied magma chamber

Parts of An Eruption

Geologic Hazards associated with Volcanoes

1. Lava Molten rock released during a volcanic eruption. Can be mafic (thin, and very fluid), felsic (thick and chunky), or intermediate (a mix of mafic and felsic)

1. Lava Pahoehoe – hot mafic lava with a smooth, ropy surface

1. Lava Aa – cooler mafic lava with a sharp, angular texture; also called “clinker”

2. Gases Form from the mixture of ground water with magma and solid rock below the surface– often acidic

3. Pyroclastics (Tephra) Solid rock produced during an eruption Sources – neck, cone, lava cooled in the atmosphere Size ash—small (looks like smoke) blocks—angular up to 6 meters bombs-rounded up to 6 meters

Lahar—mixture of ash and water

Types of Volcanoes…

1. Shield Volcanoes Form from oceanic crust; mafic lava Slope of cone is <5o Example: Hawaii Eruption: mostly lava; have few gases or pyroclastics; eruptions can last for months or years

2. Composite (or Strato) Volcano Form on continental margins with intermediate lava Moderate slope 15-30o is typical Example: Mt. St. Helens, Washington Eruptions– a mixture of lava, gases, and pyroclastics; a delay of 50-350 years is possible between eruptions

3. Cinder Volcanoes Form from continental crust; felsic Steep slope >30o Example: Crater Lake, Oregon Eruptions: mostly gases and pyroclastics; very little lava (if any); very violent eruptions (often destroy the cone)

Where in the world?