19.4: Volcanoes

Objectives

Describe different types of volcanoes Explain how and where volcanoes occur

Active and Extinct Volcanoes

Magma vs. Lava Underground liquid

rock

Once magma has broken the earth’s surface, it becomes lava

Types of Volcanoes

Shield Volcanoes Composite Volcanoes Cinder Cones

Shield Volcanoes

Magma rich in iron and magnesium is very fluid and flows easily

Eruptions are mild Builds a gently sloping

mountain Hawaii

Shield Volcanoes

Composite Volcanoes

Alternating layers of ash, cinders, and lava

Magma rich in silica is thicker and traps gases

Gases in magma cause more explosive eruptions

Mt Fuji, Mt St Helens, Mt Hood, Mt Shasta, Mt Rainier

Composite Volcanoes

Cinder Cones

Smallest and most abundant type Violent eruptions from lots of

trapped gas Short lifespan Mt Paricutin in Mexico

First erupted in 1943 In 2 years was 450 meters tallStopped erupting in 1952

Cinder Cones

Supervolcanoes

If you haven’t been to Yellowstone – you need to go

My favorite – the mudpots

Yellowstone’s Debris Zones

Colossal sized eruptions Earth Changing Currently 7 known, 3 in US We are finding more

Now total 8 The Discovery Channel has documented seven known

supervolcanoes Yellowstone (Wyoming), Long Valley (Mammoth, California), and Valles Calderas (New Mexico) in the US;

Lake Toba, North Sumatra, Indonesia; Taupo Volcano, North Island, New Zealand; Aira Caldera, Kagoshima Prefecture, Kyūshū, Japan; and the Siberian Traps, Russia

The newest: Sesia Valley Caldera in Northern Italy

Valle Caldera, New Mexico

Volcanoes form along plate boundaries and above hot spots

Openings in the earth’s crust are called vents

Volcanoes at Convergent Plate Boundaries

75% of all active volcanoes on Earth are located on Convergent Plate Boundaries

The Pacific “Ring of Fire” The sinking ocean plate melts and

magma rises to the surface The lava is cooler, sticky and gaseous Forms Composite volcanoes

Volcanoes on Divergent Plate Boundaries Magma rises to fill the gap, forming

ridges around a central valley San Luis Valley is formed this way Mid-Atlantic Ridge and Iceland

Volcanoes on Hot Spots

Some volcanoes form in the middle of plates

The form above mantle plumes Hawaiian Islands Yellowstone