Download Volcano Intro

Volcanoes
Objective: Identify how magma
forms as a result of plate motion
Explain why plate boundaries have
volcanic activity
Volcano

The opening in earths
crust where molten
rock, gases and ash
erupt.
Magma Formation

Magma: molten rock from deep within the earth
that rises to the surface.
Magma Formation: 3 conditions



Diverging boundary: Convection current,
creates new crust
Hot Spot: Magma from asthenosphere
rises through crust, can create island
chains
Subduction: converging plates, strong
volcanic activity, mountains and island arcs
Types of Magma


Magma is mostly made of Silica
Silica determines a magmas viscosity


High silica = resistant to flow = Basaltic
Low silica = flow easily = Andesitic
Types of Magma and Locations



Basaltic Magma usually at hot spots and
divergent boundaries.
Andesitic magmas tend to form at
subduction zones.
Rhyolitic generally form where hot spots
underlie continental plates.
Lava Flows


Magma that reaches earth’s surface is
called LAVA.
Basaltic lava types:


Pahoehoe: smooth, ropelike, fast moving flow
AA: cooler basaltic flow, slow, rough, and
jagged.
Types of Magma
Underwater Lava


When lava cools
underwater it forms a
distinctive round
shape.
This is called Pillow
Lava
Local Volcanoes



Basalt Mountain: Shield Volcano formed
8.8 mya
Triangle Mountain: Sill created from a
fissure eruption 1.5 mya
Lincoln Creek: Grizzly Caldera 35 mya

Grizzly Andesite