VOLCANOES DESTROY AND

VOLCANOES CREATE

What is a Volcano? • Opening in the Earth’s surface where magma

escapes

• The word volcano is derived from the name of Vulcano island off Sicily, which was named after Vulcan the Roman God of Fire

What is Volcanism?

Volcanism describes all the processes associated with the discharge of magma,

hot fluids and gases

Magma or Lava• Molten rock below the surface of the

Earth that rises in volcanic vents is known as magma

• After it erupts from a volcano it is called lava

MagmaCommonly contains some crystals, fragments of

surrounding (un-melted) rocks, and dissolved gases, but it is primarily a liquid composed

principally of oxygen, silicon, aluminum, iron, magnesium, calcium, sodium, potassium,

titanium, and manganese

LAVA Red hot when it pours or blasts out of a vent

but soon changes to dark red, gray, black, or some other color as it cools and solidifies.

Very hot, gas-rich lava containing abundant iron and magnesium is fluid and flows like hot tar, whereas cooler, gas-poor lava high in silicon, sodium, and potassium flows sluggishly, like thick honey in some cases or in others like

pasty, blocky masses

List any contributions made by Volcanoes

1. Played a key role in forming and modifying the planet

2. More than 80 percent of the Earth's surface--above and below sea level--is of volcanic origin

Contributions 3. Gaseous emissions from volcanic vents over

hundreds of millions of years formed the Earth's earliest oceans and atmosphere

4. Volcanic eruptions have produced mountains, plateaus, and plains, which subsequent erosion and weathering have sculpted into majestic landscapes and formed fertile soils

Where do most volcanoes form?

PLATE BOUNDRIES

MAP LEGEND

World map• plate boundaries (blue lines), • the distribution of recent earthquakes (yellow dots)• active volcanoes (red triangles)

Courtesy of NASA

Review

• Tectonic plates are composed of huge pieces of the lithosphere, (earth’s crust) that are driven by convection currents in the mantle.

• 3 types of plate boundaries; Convergent, Divergent and Transform

Divergent Volcanism • Occurs at mid-oceanic

ridges• As the plates are

pulled apart pillows of lava form new ocean floor

• Non explosive with large amounts of lava

• About 2/3 of volcanism occurs underwater @ divergent boundries

Convergent Volcanism

• Oceanic-oceanic subduction zone • Produce a line of volcanoes parallel to the oceanic

trench, • The chain of volcanoes is called an island arc• For Example the Aleutian Island chain

Convergent Volcanism

• Oceanic-continental subduction zone • Belt of volcanoes will be generated on continental

crust• The belt is then called a volcanic arc• Characterized by explosive eruptions • For Example the U.S. Pacific northwest, and the

Andes of South America and the most volcanically active belt on Earth is known as the Ring of Fire

452 active and dormant volcanoes

Hot Spots

Hot spots: Regions inside a plate with active volcanism

• Unlike other volcanoes, not created at plate boundaries, created within the plate interiors• For Example The Hawaiian Islands

ANY QUESTIONS?