Volcanoes Unit: Earth and Space Science

An opening in the Earth’s Crust where molten rock (magma), gas, and ash escape.

Volcano

What is magma called once it reaches the surface?

Lava

Where are volcanoes found?

Convergent Boundaries, divergent boundaries, and hot spots

Where are volcanoes found on convergent boundaries?

Subduction zones

Where are volcanoes found on divergent boundaries?

mid-ocean ridges

What is the non-boundary location where volcanoes can be found?

hot spots

What are the 3 types of volcanoes

Shield, Composite/Strato, and Cinder Cone

A broad, gently sloping volcano that has quiet eruptions when active

Shield

A steep volcano with very explosive eruptions when active.

Composite/Strato

Small and steep volcanoes made of ash and cinders

Cinder Cone

Eruption Description: Low viscosity magma (basaltic)

Quiet Eruptions

Eruption Description: thick, viscous magma

Explosive eruption

Factors of eruptions

Gas content, magma temperature, and viscosity

Volcanic Landforms: Large craters (> 1 km) after major eruptions (due to the collapse of the volcanic mouth)

Caldera

Volcanic Landforms: hardened magma left after erosion

Volcanic Neck

Volcanic Landforms: Created when extensive lava flow is spread out over a large area, building up flat, elevated land.

Lava Plateau

Volcanic Landforms: When lava erupts from long cracks in the Earth’s surface instead of a conduit and vent, forming elongated lava fields.

Lava Fissure

Volcanic Landforms: Forms when the batholith are pushed up, or when the rock above the batholith erodes.

Dome Mountain

Volcanic Landforms: Masses of rocks that are formed when a large body of magma cools inside the crust

Batholithe

Volcanic landforms: Cooled rock mound (often including the volcano) and its rock perimeter which can sustain life. It’s occurs when volcanoes appear above the water.

Island

Anatomy of a Volcano: The main opening through which magma and gases escape during an eruption

Vent (Mouth)

Anatomy of a Volcano: The bowl-shaped opening at the top of the volcano

Crater

Anatomy of a Volcano: The structure that magma travel through from the magma chamber to the surface

Conduit (Pipe)

Anatomy of a Volcano: The large underground reservoir of molten rock beneath the volcano

Magma Chamber 

Anatomy of a Volcano: The molten rock that flows out on Earth’s surface

Lava Flow

Anatomy of a Volcano: The small opening forms on the side of a volcano where lava may also erupt

Side Vent

Anatomy of a Volcano: The alternating layers that build up the volcanic cone over time.

Layers of Ash and Lava

Anatomy of a Volcano: The small cloud of gases and tiny rock fragments that escapes the volcano.

Ash Cloud

What is the difference between the vent and the crater?

the vent is the specific point where magma escapes while the crater is a result of the mouth collapsing and leftover magma buildup.

What is the shape of a shield volcano?

Broad, gently sloping sides

What is the shape of a stratovolcano?

Narrow and Steep sides

What is the shape of a Cinder Cone volcano?

small and steep

What type of rocks form in quiet eruptions?

Basalt

What types of rocks form in alternating and explosive eruptions

Andesite and Rhyolite

What type of rocks form in gentle explosive eruptions?

Andesite

A deposit of magma that fills vertical cavities of rock.

Dike

A deposit of magma that fills horizontal cavities of rock.

Sill

What is the rough silicate percentage in quiet, non explosive eruptions?

low, ~50%

What is the rough silicate percentage in gentle explosive eruptions?

moderate, ~60%

What is the rough silicate percentage in highly explosive eruptions?

high, ~>/=70%

What magma is present in quiet volcanoes?

Mafic (Basaltic) Magma

What magma is present in explosive or gentle volcanoes?

Intermediate (andesitic) magma

What magma is present in highly explosive volcanoes?

Felsic (rhyolitic) magma

What determines the expected eruptive explosiveness

chemical composition