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 Hazardsassociated 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?