Volcanos and Plate Tectonics

Chapter 7.1

Introduction1.Introduction

a.While scientists cannot directly measure earth’s interior temperatures, they can estimate them using seismic wave analysis, heat flow near the surface of the earth, and computer modeling.

Introductionb. Most of the rocks in the lower part

of the mantel are kept below their melting point due to the temperature and pressure in that zone.i.Due to this high pressure, most of the

rock in the asthenosphere is also kept solid.

Introductionii. However, sometimes this rock will

melt and form magma.1.Magma is liquid rock produced

inside of the earth, and is formed when mantle material flows to areas of lower pressure faster than it can lower its temperature by heat flow, or when liquids such as water are added to the mantle material.

Volcanism

2.Volcanisma.Volcanism is any activity that

results in the movement of magma toward or onto the earth’s surface.

Volcanismb. When rock melts in the earth,

pockets of magma are formed and continue to melt rock around it. As this rock melts, it also expands and becomes less dense which causes it to move through the more dense crustal rock toward the surface of the earth.

Volcanism

c. Most magma forms at plate boundaries, usually oceanic – continental. i.When the mantle material subducts, it allows water to come in contact with the asthenosphere which causes the rock to melt.

Volcanismd. Lava is magma that breaks through

to the earth’s surface.i.A vent is the opening through which the

molten rock flows.ii.A volcano is the structure formed by

the vent and the volcanic material that builds up on the earth’s surface around the vent.

Major Volcanic Zones

1.Major Volcanic Zonesa.Most active volcanos and

earthquakes occur in zones near both convergent and divergent boundaries of the lithospheric plates.

b.One of the three major earthquake zones is the Pacific Ring of Fire.

Major Volcanic Zonesi.This zone includes areas in North America, South America, Asia, and the islands of the western Pacific Ocean.

ii.This increased volcanic and earthquake activity is caused by subducting plates encircling the Pacific Ocean.

Major Volcanic Zonesiii. Many island arcs are also

formed in this area. 1.Island arcs are formed by magma

breaking through the earth’s surface and cooling to form solid rock. As this is occurring, the plate continues to move and create a new volcanic island and island arcs.

Major Volcanic Zones

4. A mid-ocean ridge is a place where a large amount of magma surfaces due to plate moving apart from each other. The surfacing magma hardens and forms new lithosphere and underwater volcanos.

Major Volcanic Zonesa.Iceland is an example of the Mid-Atlantic

Ridge that is above sea-level. i.One half of Iceland is on the North American

plate and is moving westward while the other half is on the Eurasian plate and is moving Eastward.

ii.The middle of Iceland is cut by large fissures.

1.Fissures are cracks through which lava flows.

Major Volcanic Zones1.Hot spots are areas of volcanism within

the lithospheric platea.Hot spots occur where magma makes its

way to the earth’s surface within the interiors of lithospheric plates.

b.At a hot spot, the lithospheric plate continues to move while the hot spot stays in place. Hot spots create volcanic chains of islands such as the Hawaiian Islands.