Chapter 7 VOLCANOES

Sect. 1 & 2

Volcanism• Mov’t of magma toward or onto the

Earth’s surface magma rises cuz its less dense pushing its way to the surface

• Magma on earth’s surface = Lava• Vent = opening in earth’s surface where

magma flows through• Volcano = structure formed from vent &

material builds around it

Major Volcanic zones

• On divergent & convergent boundaries

1. Subduction Zones

2. Mid-Ocean Ridges

3. Hot Spots

Subduction Zones• A subducted plate is subjected to heat & friction & is forced

downward causing it to remelt & become magma• This magma will be forced to surface and forming volcanic

mountains along continental plate

Subduction Zones• Ring of Fire is a result of plates being subducted

• There can also be collision of 2 oceanic plates forming Island Arcs or volcanic islands (ex. Japan)

Mid-Ocean Ridges• Divergent boundary• Magma rises up through rift• Emerging lava forms new ocean floor

• Iceland is exposed part of ridge & is covered with fissures (cracks)

Hot Spots• Magma comes to the surface from within a plate• Hot spot stays put but plate is in constant

motion forming volcanic islands

Hawaiian Islands

Galapagos Islands

Volcanic Eruptions

Windows to Earth’s Interior

Ability to see firsthand materials from mantle

3 General Types of Lava

1. Mafic (basaltic) low silica content and low in water vapor & CO2 dark color

2. Felsic (granitic) high silica & high in water vapor & CO2

light in color

3. Faults between mafic & felsicrange in composition

Kinds of Eruptions• Type of lava (mafic/felsic) determine

how explosive eruption will bedemo

• Oceanic Volcanoes: produce mafic lava very thin

flow easilylow gas erupt quietly

Kinds of Eruptions• Felsic lava (continental

volcanoes) thick lavalarge amt gases

w/lava boil out of vent explosively solid particles fly out w/ magma

Volcanic Rock Fragments• Pyroclastics: large fragments blown

from the cone of felsic volcanoes.

< 2 mm = volcanic ash

< .25 mm = volcanic dust

< 64 mm = lapilli (lil’ stones)

Three types of Volcanoes• Shield Volcano

covers wide areaquiet eruptionsslow build up around vent

Three types of Volcanoes• Cinder cone

made up of solid fragmentsSteep slopesrarely highvery explosive

Three types of Volcanoes• Composite Cone

Three types of Volcanoes• Composite Cone

formed by alternating explosive & quiet eruptionsdevelop high volcanic mountains

Crater vs. Caldera

• Crater = funnel shaped pit at top of vent; formed when material is blown from vent during explosions

• Caldera = large basin shaped depressions formed either by explosions or cones collapsing

Predicting Volcanoes

• seismographs• study past history of volcanoes• bulging of volcanic slopes• changes in gases given off

Extraterrestrial Volcanism

Many planets & moons in the solar system were and are volcanically

active

Extraterrestrial Volcanism

The MoonCovered by Basaltic flows; no longer active; however, no evidence of plate tectonic activity

Extraterrestrial Volcanism

MarsNumrous volcanoes & features; biggest one is shield volcano called Olympus Mons

Extraterrestrial Volcanism

IOMoon on Jupiter; shows 9 active volcanoes erupting on Io